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1.

What is ovality of auxiliary engine crank pin?

Combined effect of reduced effectiveness of L.O and directional thrust of the con rod. This is maximum at around 45 degree ATDC Uneven loading of units and overloading Max Allowed: 1/4th of the bearing clearance Removed By: Insitu Grinding and polishing Reference: Fillet of crank web Max. Allowed Grinding: 2mm, because after grinding 2mm or more surface hardness reduces drastically. Due to this maximum allowable grinding is 2mm. Bottom bearing damage reason is the ovality, bearing clearance and condition of L.O supply 2.

Why are concentric springs fitted for A/E cylinder head valve s?

If the frequency of the natural vibration of air or exhaust valve springs is a harmonic of the camshaft speed, then the spring may vibrate axially and are said to surge. Surge can be avoided by modifying the sizes of springs by arranging the springs in pairs and fitting one inside the other. If one spring fails the valve is held up and is not damaged by striking the piston. The thickness of individual springs can be reduced as against srcinal thickness. Normally two springs of different vibration characteristics are chosen. Moreover, the stiffness requirements and the space congestion at this place warrants a concentric springs arrange ment. The net stiffness is e qual to th e sum of individual stiffness.

3.

What isSQUAT Phe nomenon?

It is a venturi effect while vessel is moving on shallow water. A vacuum is created due to which the draught of the vessel is increased there by increasing the engine load. Steering ability of the ship is reduced as a result. 4.

What is a thermostatic ex pansion valve?

This is a regulator t hrough which t he refrigerant is metered from the high pressure side to the low pressure side of the system. The pressure drop causes the evaporating temperature (saturation temp.) of the refrigerant to fall below that of the evaporator. a. Avoids liquid refrigerant return to the c ompressor suction. b. Automatic expansion control and maintain 6 ~ 7 degree sup erheat. 5.

What is the function of an L.P controller ?

The LP controller stops the compressor at low suction pressure caused by the closure of all compartmental solenoids. When the pressure in the compressor suction rises due to solenoid opening, the LP controller restarts the compressor. 6.

What is the function of an L.P cutout?

This is use d to protect the com pressor against the low suction pressure due to loss o f refrigerant o r blockage. If the a /c compressor suction press ure is allowe d to fall below atmospheric pressure then there exists a risk of moisture and air ingress into the system.


7.

What is a Coalescer?

A device consisting of a material whose surface provokes coalescence. The process of combining of larger droplets of a liquid like oil into larger droplets is called coalescing.

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MEOClass4OralQuestionsWithAnswers

8.

Why is there a st arting air overlap provided in a diesel engine?

a. To give a pos itive starti ng in correct direction. b. Starting ability from any position. c. If any one of the valve is malfunctioning. Engine can still be started. 9.

What is the significance of firing order?

a. Balancing of primary and second ary inertia forces. b. To assist the ex haust grouping. c. For distribution of stress over the length of c rankshaft and optimum bearing loading. d. A firing interval for even tur ning moment. 10.

What are the reasons for foaming in refrigeration compressor crankcase?

Due to rapid boiling out of the refrigerant dissolved in the oil when the pressure is suddenly reduced. When the compressor starts operating, if a large quantity of refrigerant has been dissolved, larger quantity of refrigerant boils out and can be carried through the refrigeration lines. Reasons: a. Liquid in the suction line (viz. TEV stuck open, in correct super heat setting, sensi ng bulb not closing, overcharge etc.,) b. Crankcase heater not working. c. Compressor capacity too high at the start. d. Expansion valve giving too small superheat e. Oil charge is less. 11.

Explain the functions of lube oil in refrigeration system

a. Lubricati on b. Seal the clearance spaces between the discharg e and suct ion sides of the compressor. c. Act as a coolant. d. Actua te cap acity co ntrol. e. Dampen the noise generated by the compressor. 12.

What are the va rious windlass safeties?

ELECTRIC: a. Electromagnetic brake. b. Motor overload protection . c. Short circuit protection. d. Restart delay timer. e. A Restart sto p. MANUAL: a. Manual brake / mech. Brake. b. Cable stop per. c. Slipping clutc h (t orque limiter).


d. Relief va lve. 13.

What are the steering gear motor safeties?

a. Overload alarm. b. 200% insulation in motor. c. High temperature alarm. d. Self-starti ng after power failure. e. Short circuit trip. f. Phase fa ilure alarm. g. One of the steerin g motor is fed from the emergency bus. Hydraulic side there is two trips a. Low level cuto ut b. High lube oil temperature cutout. 14.

What are the overhead crane safeties?

Current to motor‟s field c oils passes t hrough solenoid coil of a brake which is magnetized and holds a brake against spring and releases the rotor. Incase of power failure the solenoid is demagnetized and brake is applied. SAFETY: a. Limit switch on t he f‟wd, aft, port, s‟tbd, hoistin g and lowering prevents movements more than the allowed limits. b. Overload trip. c. Dead man‟s handle. d. Guards over the pulley. e. Locking device on the lif ting hook. f. Mechanical locking (to avoid crane movement during heavy weather) http://class4exam.com/MEO_oral_question_answers.html

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15.

What is a critical pressure?

It is the pressure at which gas will just liquefy at its critical temperature. 16.

What is a critical temperature?

It is the temperature above which the gas cannot be liquefied under isothermal compression. 17.

What are the air bottle safeties?

a. Relief valve b. Fusible plug c. Drain d. Low pressure alarm 18.

What happens if fuel pump leaks?

a. Fuel quantity is reduced – loss of power, cylin der liner lubricat ion is affec ted. b. Loss of cylinder power. c. Late injection. d. After burning. e. High exhaust temperatures, smoky exhaust. f. Power imbalance among units.


19.

What are the c onstant tension winches?

It is a variation of the constant pressure and constant horsepower control for variable capacity pumps. It is used to achieve constant tension winch system. In this case the pump control is automatically operative across the neutral such that constant system pressure and hence a constant motor torque is maintained whilst both drawing in and paying out. 20.

What are the c auses of turbocharger surging?

a. Rapid variation (reduction) in load. b. Chocked exhaust and air passage like scavenge ports, valve or air cooler etc., c. Abnormal fuel system like a unit misfiring. d. Chocked air suction filter, fouling of the t urbocharger, unbalanced output from the engine, damaged exhaust valve, scavenge fire. 21.

What are the causes of cylinder head cracking?

a. Scale deposits b. Inefficient cooling water c. Uneven tightening of bolts and fuel valves d. Fluctuating cooli ng water temperature (excessive temperature gradient) e. Overloading or racing of engine f. Faulty relief valve g. Mechanical failure due to gas corrosion, ac idic corrosion due to leaky exhaust valves h. Water side corrosion 22.

What is the normal relief valve setting of cylinder head in a diesel engine?

10 ~ 14.5% more than the working pressure about 120 bar (some what higher than maximum pressure) 23.

State the a dvantages of uniflow scav enging

a. Simple liner construction b. Long skirt (for piston) not required c. Stroke length can be increased d. High scaveng ing efficiency e. High thermal efficiency f. Low grade of fuel can be burnt g. Uniform wear of piston rings and liner h. Less ther mal stresses i. Less intermixing of scavenging air with the exhaust gas j. Exhaust valve can be made to open late – more work, close early – sc avenge air is more utilized. 24.

Why cylinder liner wear is more a t the top?

a. High temperature exposure due to t he combustion gases b. Loss of liner lubrication in low speed diesels c. Corrosion, predominantly ac idic due to combustion product s d. Fuel impingement, deposits e. Change of direct ion of the piston, wh ich causes to a st ep like formation at the rever sal point http://class4exam.com/MEO_oral_question_answers.html

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25.

What actions do you ta ke incase of ste rn tube of the ship starts leaking?

a. Maintain low head. b. Use higher viscous oil. c. Replenish periodically to count er for the oil loss. d. Drain off the water per iodically. e. Try to remove foreign particles by changing direction of shaft. 26.

How do you tes t a fresh water generator plant for leaks?

a. Close the outlet of the distillate pump, vacuum breaker valve, bottom blow off valve and feed water valve b. Inject air into the evapo rator shell c. Keep the shell pressed up to about 1.0bar gauge d. Sprinkle soap solution on to the join tings, packings, and suspected areas of t he shell 27.

What are the reasons for a piston crown to crack?

a. Casting defect b. Thermal stresses due to cold starti ng air and scavenging air c. Scavenge fire d. Overheated piston(cool ing failure, cooling side deposits due to oxidation of the c ooling oil) e. After burning f. Faulty fuel injection system (more penetration or loss of atomization) 28.

What are the reasons for black smoke from a diese l engine?

a. Poor combustion due to faulty injection system b. Low compression c. Insufficient scavenging air d. Fouled exhaust syste m e. Broken piston rings f. Ineffectiv e lube oil seal g. After burning, bad fuel and other fuel assisted faults h. Faulty cylinder lubrication i. During starting, it is inevitable as the engine maker sets t he starting fuel index to a fixed value. At this index there is insufficient air, low piston speed, cold combustion chamber, low fuel injection pressure etc., each compounding the cause for black smoke 29.

What are the critical speed e ffects?

Resonance, torsional vibration, fatigue failure of components Can be remedied by: a. Detuners b. Vibration dampers c. Electric vibration compensator unit


30. What are the types of vibration in a diesel engine and which is the most damaging?

Types of vibration: a. Linear vibration b. Torsional vibration c. Resonant vibrations involving any two of the above or may be combinational Most damaging form of vibration is the torsional vibration mode, af fec ting c rankshaft and propeller shafting. 31.

What is a node?

A node is found where the deflection is zero and the amplitude changes its sign in a vibrating medium. T he more t he nodes in a given length the higher the c orresponding natural frequency. 32.

What is a forcing frequency?

W.r.t the crank shafts, the forcing frequencies are caused by the firing impulses in the cylinders. http://class4exam.com/MEO_oral_question_answers.html

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Firing impulses superimpose on one another and appear as a complex waveform represented by harmonics – 1x cycle frequency: first order harmonics of firing 2x cycle frequency: second order harmonics 3x cycle frequency: third order harmonics and so on… 33.

How can the frequency of resonance, the forcing impulses and the resultant stresses adjusted?

a. By adjusting shaft sizes b. Number of propeller blades c. Firing order d. Using viscous or other dampers e. Using balancing weights f. Detuning coupling 34.

What is balancing?

Balancing is a way of controlling vibrations by arranging that th

e overall summation of the out o f

balance forces and couples cancels out, or is reduced to a more acceptable amount.

35.

Explain the vibration characteristics of low speed 2- S engines

a. External unbalanced moments b. Guide force moments c. Axial vibrations in the shafting system d. Torsional vibrations in the shafting system 36.

What is 1st order moment?

These moments acts in both vertical and ho rizontal directions. For engines w ith 5 cylinders or more, the 1st order moments a re of rare signific ance to th e ship bu t it could be of a


disturbing magnitude in with the 4two cylinder Resonance withcompensator a 1st order moment occur for hull vibrations and/orengines. three nodes. 1st order can be may introduced in the chain tightener wheel. It comprises of two counter rotating masses rotating at the same speed as the crankshaft. 37.

What is a second order moment?

The second order moment acts only in the vertical direction and precaution needs only be considered for 4, 5 and 6 c ylinder engines. Resonance with t he 2nd order moment may only occ ur at hull vibrations with more than 3 nodes. A 2nd order moment c ompensator comprises two counter rotating masses running at twice the engine speed. 38.

What are the methods to cope up with the second order moments?

a. A c ompensator mounted on the aft end of t he engine driven by the main engine chain drive mechanism. b. A c ompensator mounted on the fore end dr iven from the c rankshaft thus a separate chain drive. c. A compensator on both aft and fore end completely eliminating the external 2nd order moment. 39.

What is an electric compensator?

It is electrically driven compensator preferably located in the steering gear compartment, where deflections are t he maximum and the effec t of t he c ompensator is maximum. Suc h a compensator is synchronized to the correct phase relative to the external force or moment and can neutralize the excitation. The compensator requires an extra seating to be fitted. 40.

What are guide force mom ents and their types?

The srcin of the guide force moment is the angularity of the connecting rod. It is the vibration of the engine about the foundation bolts. Guide force moments are caused by the transverse reaction forces acting on the cross head due to the con rod crankshaft mechanism. Guide force moments may excite engine vibrations moving the engine top arthwartships causing a rocking (excited by the H moment) or twisting (excited by X moment) movement of the engine. Guide force moments are harmless except when the resonance occurs in the engine double bottom system. As a precaution, top bracing is installed between the engine‟s upper platform brackets and the casing side for all its 2S models. 41.

What are different types of the top bracing for a diesel engine?

a. It comprises of the stiff c onnections (links) either with frict ion plates which allows adjustment to the loading conditions of the ship http://class4exam.com/MEO_oral_question_answers.html

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b. A hydraulic top bracing – by using the top br acing natural frequency will increase to a level where resonance will occur above the normal engine speed.


42. How are the axial v ibrations caused in the crankshaft? How are they remedied?

When the crank throw is loaded by the gas pressure through the conrod mechanism, the arms of the crank throw deflect in the axial direction of the crankshaft, exciting axial vibrations. These vibrations may be transferred to the ship‟s hull through the thrust bearing. Its remedy is t o axially dampen the c rankshaft vibrations. 43.

How is torsional vibrations generated?

The varying gas pressure in the cylinders during the working cycle and the crankshaft / conrod mechanism create a varying torque in the crankshaft. It is these variations that cause the excitation of torsional vibration of the shafting system. The torsional excitation also comes from the propeller through its interaction with the non-uniform wake field. Remedy: modify c rankshaft natural frequency by adjusting the diameter. Use a torsional damper. 44.

What is under critical running?

The natural frequency of the one node vibration is so adjusted that the resonance with the main critical order occurs about 35~45% above the engine speed at specified maximum continuous rating (MCR). The characteristics of an under critical system: a. Relatively short shafting system b. c. d. e. 45.

Probablywheel no turning wheel Turning with low inertia Large diameter of the sh afting Without barred speed range What is overcritical running?

The natural frequency of the one node vibration is so adjusted that the resonance with the main critical order occurs about 30~70% below the engine speed at the specified MCR. The characteristics of the system are: a. Turning wheel may be necessary on the crankshaft b. Turning wheel with a relatively high inertia c. Shaft with relatively small diameter (shaft material has to be of high UTS) d. With a barred speed range of about +/- 10% w.r.t t he critical eng ine speed 46.

If resonance occurs, what is the solution?

The following modification(s) have to be carried: a. Lanchester balancers, either o n the engine or electrically driven units usually located in the steering flat, compensated for ships vibration caused by the 2nd order vertical moment b. Counter balancing weights on the c rankshaft t o be adjusted for compensating the first order vibrations c. Combined primary and secondary balancers

d. Adjusting the side stays 47.

How to prepare a DB fuel oil tank for a survey/inspection?

a. Empty the oil, strip with portable pumps if required


b. Clean the tank with sea water and p ump it through the oily water separator c. Ventilate the tank(s) with a blower specially provided for the purpose, always cross ventilate i.e. there should be at least two openings, each for entry and exit for the air

d. Check the space for explosive gases at various points suitably, more sampling should be carried out at the corners at the bottom most part of the tank e. Obtain the necess ary certi ficates and ge t the checkl ist completed http://class4exam.com/MEO_oral_question_answers.html

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48.

Why are the CO2 bottl es provided with dip tubes?

It is t o ensure that only liquid is drawn during release. The liquid expands af ter t he nozzles and assumes the gaseous state. This will prevent co2 freezing and blocking the nozzle Also it achieves the 85% discharge in 2 Minutes as liquid part represents a large volume of gas The materials used in its construction are copper, stainless steel 49.

Why a crankcase relief door is not fitted in the refrigeration compressor crankcase?

a. Possibility of t he contamination of the refr igeration system by air by leaks b. Oxygen is not available in the compressor crankcase c. The incoming refrigerant temperature is low and chances of hot spots is low d. Crankcase forms the suct ion chamber of the compressor and chances exist that the compressor may draw in air and moisture 50.

Why heaters are provided in the crankcase of a refrigeration compressor?

a. To avoid carry over of the lube oil because at low tem perature, the separ ation of the refrigerant and the oil is difficult b. To c ondition the lube oil, by maintaining the viscosity so t hat the lubrication is effect ively c arried out. c. This prevents the lube oil achieving its floc point which may cause narrowing or chocking of the passages (flocculation) 51.

What are the causes of a ce ntrifugal pump reduced output?

a. Frict ion and leakage losses, loss of suction h ead, chocked suction fi lter, worn out wear ring, air ingress in t he suc tion side b. Low voltage is applied to the pump motor c. Cavitat ions on the impeller d. Bad maintenance, incorrect fixing up of the parts after overh aul 52.

What are the c auses of vibration in the vertical c entrifugal pump?

Misalignment of the shaft, worn out bearing, foundation bolts loose, hydraulic clearances not proper on the impeller, c oupling bolts / seating damaged, bottom bush worn out, heavy objects/debris deposits, and corrosion/erosion on the rotating parts 53.

What is volumetric efficiency of air compressors?

Actual volume of air drawn in / swept volume


54.

What is compression ratio?

(Swept volume + clearanc e volume)/c learance volume 55.

What is brake thermal e fficiency?

Ratio of the energy developed at the brake to the energy supplied. Amount of heat liberated during the combustion to the heat equivalent at the brake 56.

What is the function of a Solenoid valve in the refrigeration syste m?

There is an electric si gnal actuate d valve in the liquid li ne of the refrigeration s ystem just before the thermostatic expansion valve. This is being actuated by the thermostat in the refer compartment. The so lenoid shu ts off the refrigerant s upply if the compartm ent is s ufficiently cooled to the lower set point of the thermostat. Also it connects the supply when the temperature of the compartment goes high i.e. above the thermostat higher set point

57.

What is the function of the back pressure valve in the refrigeration system?

Back pressure valve is fitted just at the exit of the refrigerant from the evaporator coil in a multi temperature rooms system. This being fitted at the exit of the compartments whose temperature is set higher (usually at about 4~5 degrees centigrade). The function of the valve is to maintain equilibrium of the system as the pressure of the gas at the exit of each compartment differs. More over the back pressure valve creates a back pressure on the evaporator coil and ensures that most of the liquid refrigerant is made available to the lesser temperature requirement compartments as their demand for the refrigerant is higher than the compartments being maintained at a higher temperature. It is spring loaded non return valve 58.

What is the function of a H.P cut out in a refrigeration syste m?


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This is a safety device (trip) provided in the discharge of the compressor. It functions to trip the c ompressor if the pressure in the HP side goes high above the working level 59.

What is the function of the driers in the refrigeration system?

The filter/drier is installed in the main liquid line of the system to absorb any moisture present in the refrigerant. It consists of activated alumina or silica gel in a renewable cartridge. It also accommodates the charging connection 60.

What are the usual stern tube bearing clearances?

a. Water c ooled stern bearing clearance: 8.0mm (8~12mm) b. Oil cooled stern tube bearing: 1.87~2.0mm 61.

What is a usual volumetric efficiency of a diesel e ngine?

a. Naturally aspirated engine: 0.85~0.95 b. Supercharged engine: up to 4. 0 c. For 2S engine: 0.85~2.5


62.

What is a usual propeller drop usual value?

1mm/160mm of the shaft diameter 63.

What are the adva ntages of a thin shell bearing?

a. Increased fatig ue resistant properties b. High load carrying capaciti es c. Embed ability d. Conformability e. f. g. h. 64.

Bedding not required Easy storage, easy fitting, light in weight Increased (enhanced) mechanical properties Better heat tran sfer due to reduced thickness an d uniformity of the contac t with the bearing housing What are the t ypical bearing failures?

a. Fatigue failure (crack s) b. Tin oxide encrustati on (black SnO 2 ) c. Wiping damage of the bearing surfac e d. Tearing of th e overlay e. Acidic corrosion f. Cavitations, erosion g. Dross inclusion h. Spark erosion i. Bacterial attac k damage (honey colored deposits on the bearing surface) 65.

What are the advantages and disadvantages of the sy nthetic lube oils?

Advantages: a. Better low temperature fluidity and pump ability, due to nil wax content b. Better oil retention at high temperatures c. Lower friction losses

d. Reduced thickening of the oil in service due to oxidation e. Lower deposits at higher temperature due to resi stance to oxidation properties and thermal stability Disadvantages: a. b. Uses: a. b.

Increased cost of the lube oil (about 6~12 times) Poor ava ilability Air compressors Purifiers

c. Hydraulic units

66.

What is the purpose of the lube oil analysis?

a. To determine any deterioration in lube oil properties or additives levels and assess its suitability for further service b. To determine the type and l evel of the contami nants held within the oil which indicat e the rate of contamination and effectiveness of the purification process c. To predict the internal wear rate on the machinery components d. To lengthen the time between overhauls or surveys http://class4exam.com/MEO_oral_question_answers.html

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67.

When is the lube oil said have deteriorated?

a. TBN reduces b. Visco sity red uces c. Flash point reduces d. Oxidation increases e. Water content high f. Insolubles increase g. Dispersancy increases 68.

What are the problems in cast iron welding?

a. Brittleness (cracks easily) b. High carbon content in the form of graphite c. Close grain structure d. Poor thermal conduct ivity and differential cooling e. Possibility of stress es and distortion 69.

How is a propeller drop measured?

a. Turn the engine to c oincide with the mark on the liner and the stern tube or n ormal reference is taken to be that the engine‟s unit 1 will be in TDC prior measuring the propeller drop This could be also arranged as with a designated blade of the propeller up wards while measuring this drop. Blades are assigned alphabets A, B, C, D and so on. b. Take the poker g auge reading and the c ompare with t he previous reading c. Bearing clearance : 2mm (oil sealed) : 8mm (sea wat er lubricat ed) Bearing length is about 2xdia of the shaft for oil cooled stern tube bearing 4xdia of the shaft for sea water lubricated stern tube bearing 70.

Compare a n engine flywheel and its governor

a. A governor maintains the speed of the engine b. A flywheel controls the cyc lic fluctuations of the engine RPM c. Flywheel works on the virtue of the inertia alone and the governor uses the inertia principle to actuate the fuel linkages to counter the changes in the engine RPM 71.

Why are tie rods provided?

Tie rods are provided to keep the whole engine structure in compression which: a. Increases the fatigue strength of the engine struct ure as it is the tensile stress which causes fat igue b. Maintain running gear alignment to avoid fretting The firing forces that press down the bearing saddle also attempt to push up the cylinder covers, the net effect being to put the whole engine structure into tensile loading. So the tie rods are tightened such that the engine structure is maintained in compression even during the peak firing conditions and that the engine is not subjected to the tensile loading.

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72.

Register Yourself In Our Forums Why tie rods are placed c lose to the centerline of the c rankshaft?

During firing, the transverse girders are subject ed to a bending moment as t he saddle is pushed down by the crankshaft acting on the cylinder head. To limit this bending effect and consequent distortion of the bearing housing the tie rods are positioned as close as possible to t he centerline of the c rankshaft. 73.

Where is a thrust bearing installed in an auxiliary engine? And why?

Axial location of the crankshaft may be required if the coupling does not incorporate a thrust housing. T his is achieved by forming white metal rings on t he sides of one main bearing shell that allows the shaft to run with a small clearance between running faces on the two adjacent webs. In some engines a small collar may be provided at one side of the b earing. It is important to appreciate that only one such locating bearing should be fitted to any one shaft, otherwise the differential thermal expansions of frame and the crankshaft may cause prob lems.

74.

What are the environmental problems with the use of C FCs?

a. CFC released into the at mosphere are broken down by pyrolysis to release c hlorine atoms which catalytically destroy ozone layer.(this layer in the stratosphere acts http://class4exam.com/MEO_oral_question_answers.html

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as a filter to the UV radiation from the sun) b. Furthermore CFCs along with other greenhouse gases inhibit radiation from the earth‟s surface thereby contributing to the global warming. 75.

What is a pH value?

It is the logarithm of the reciprocal of the hydrogen ion concentration expressed in gram ion per liter. Pure water at 25 degree centigrade consists of equal concentration of the hydrogen and the -14 hydroxyl ions and equal to 10 gram ion per liter. If the hydroxyl ion concentration ex ceeds the hydrogen ion concentration then the solution is basic and vice versa is acidic in nature. pH value = log [1/H+] If the water temperature is increased, the concentration of the hydrogen ion increases and hence ac idity. 76.

Why is a man hole door elliptical in shape?

Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the direction in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as t he stress in this direct ion is maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a c onsiderable material and weight saving is ac hieved as minor is along the direction of maximum stress.


77.

Why is the fridge compressor belt driven?

a. A slight misalignment is a problem or vibration of the elect ric motor may lead to shaft seal leakage, leading to loss of the refrigerant. So minimize these the fridge compressor is belt driven. b. In case of the liquid entry into the refrigeration compressor, the belt dri ve gives a limitation of the damage owing to the slip in the belt and flexibility of the belt material. 78.

Why intercooling is provided in an air compressor? And why is the compression distributed into stages?

a. By employing the interstage coolin g we are trying to achieve an isother mal compression cycle. So least work is expended in the process. b. The air outlet t emperature after c ompression is lowered by intercooling. So oxidation of the lube oil is prevented. Also good lubrication is achieved. c. Lesser deposits in the air system. d. Intercooling increases the air den sity and hence reduced volu me of the HP compression chambers is possible. e. It facilitates removal of moisture by condensati on at the intercoolers. f. To fac ilitate intercool ing the compression is distributed into stages. Also even load distribution is achieved over the cycle. 79.

What if the compressor moto r connections are reve rsed after ov erhauling?

a. The lube oil pressure will not be sufficient for lubricat ion so the c ompressor may trip on low lube oil pressure. T he moving parts may get damaged due t o the failure of the lubrication. b. The c ooling water pump which is also shafted driven usually does not build up enough flow/pressure hence the compressor may trip of the cool water non flow or high air temperature. 80.

If viscotherm is absent or damaged how do you maintain the fuel oil viscosity?

The required viscosity prior injection and the viscosity of the fuel oil at 50°C are provided by the fuel oil analysis report. Basing on the visc osity nomogram the required fuel oil heating is determined. The steam inlet to the fuel oil heater is manually adjusted to maintain the temperature and a close observation has to be maintained on the steam pressure and temperature of the fuel oil at the outlet of the heater. 81. What are the reasons for the e rror between the helm order and the angle shown locally on the steering gear unit?


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a. Air in the hydraulic telemotor system b. Buffer spring too weak or stiff, faulty hu nting gear c. Instrument error/defec tive d. Worn out linkages


82.

Why are the accumulators used in the hydraulic syste ms?

a. To absorb shock due to load var iation or sudden change in the direct ion of flow, impact loading b. To maintain the c ircuit pressure by c ompensating for the loss due to leaks or pr essure increase due to rising temperature c. To supplement t he pump delivery where multiple c ircuit operations have wide flow variations with a short term peak demand in excess of the pump capacity. Accumulator c harge can take place during low demand periods to meet maximum demand later 83.

Explain the cross head slipper lubrication

a. The lubricating oil is fed to the guide sho es by a pipe from the main lube oil system b. The lubricating oil may also be fed from the drilled passages in the pin to the slipper faces 84.

What is th e material of the CO 2

bottl e and its accessori es?

CO2 bottle: solid drawn seamless manganese st eel Cable: phosphor bronze Seal/bursting disc: thickness 0.3mm, phosphor bronze Pipeline: solid drawn MS galvanized Siphon copper 19mm tube Cutter: tube: 120° /travel 85. How will you decide for reentry into the engine room after flooding it with CO2

Re-entry is determined by a. Heat build up due to the scale of t he fire and the elapse d time after release b. Has the fire been extinguished or chances of a smol dering fire exists c. Ship‟s position, condition and the prevailing weather (ship may be listing to the angle of progressive flooding etc.,) d. The location of the entry point e. Risk analysis outcome 86.

What is the quality of the vapor coming back to the compressor suction in the refer system? In addition, how will you ensure that the vapor has adequate degree of superheat?

a. The c ondition of the vapor com ing to the compressor suction line should have adequate degree of superheat b. The c ondition is chec ked by reading the pressure of the returning vapor and its corresponding temperature from the P-T chart provided for the specific refrigerant. This temperature is compared with that of the evaporator outlet and the degree of super heat is expressed as the difference in the temperature. 87.

What is the length of the crank web?

Length of the crank web = stroke length/2


88.

What is lignum vita?

In the traditional sea water lubricated stern tubes the bearing material consisted of the staves of the wood called lignum vitae. This has a property of lubrication in the presence of sea water. They are fitted with the grains in the axial direction for economy and are shaped with V or U grooves between them at the surface to allow for access to water. They also http://class4exam.com/MEO_oral_question_answers.html

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act as a debris collector points. The staves are held in place in the bronze boss by bronze keys attached to the bush by counter sunk screws. Bearing length is equal to 4times the shaft diameter. 89.

What are the safeties in the fridge sys tem?

a. HP cut out b. Differential lube oil pressure cutout c. LP cutout d. Relief valve in the con denser e. Belt driven f. Cylinder head relief valve g. Cooling water low flow/high temperature alarm h. Motor o verload i. Oil separator j. Drier k. Mech. Seal l. Unloaders /capacity controllers m. Non return shut off valves n. Sensors – temperature, pressure 90.

How will you know the presence of air in the refrigeration system? Explain the procedure for purging air

a. High condenser pressure b. Small bubbles in the sight glass c. Compressor discharge pressure high/running hot d. More superheat e. Pressure fluctuati ons f. Inefficient working PROCEDURE FOR PURGING AIR a. In the normal operation of the syst em, measure the liquid refrigerant pressure, temperature at the outlet of the condenser/reservoir b. Check the c orresponding saturation temperature for the recorded p ressure of the liquid refrigerant from the P- T chart for the same refrigerant c. Compare the measured temperature with the determined sat uration temperature for any sub-cooling and adjust the flow of the cooling water through the condenser to achieve near saturation condition inside the condenser, Then, d. With the condenser liquid refrigerant outlet valve closed, circul ate c ooling water, start the compressor and pump down the liquid to the condenser/reservoir, checking the pressure in the suction line. If this pressure is allowed to drop down below the atmospheric pressure then there could be chances of air ingress into the system e. Circulate the c ooling water till the cooling water outlet and the inl et t emperatures equal, a check to ensure complete pump down operation f. Check the conden ser sea water out let temperature, check the r efrigerant pressure corresponding to its temperature from the P-T chart of same refrigerant


g. Due to the pr esence of air the y don‟t agree h. Release air from the condenser, through the vent c ock until the pressure of the refrigerant in the condenser corresponds to the saturation pressure at the sea water outlet temperature 91.

What is the material of the boiler gauge glass?

The material used in the gauge glass is a special toughened glass containing a. Silicon oxide or magnesium oxide b. Borosilicat e or lime soda glass 92.

What is the material of a boiler tube?

Low c arbon alloy st eels c ontaining chromium, nic kel, molybdenum 93.

What is the material of the ship side valv e?

BODY: Nickel-Aluminium bronze / cast steel Stem/Seat/Disc: Monel metal (c upro nickels of varying proportions are used popular being a Cu:Ni = 2:1) The cupronickels are known for their great resistance to the sea water corrosion, erosion by the particles in the sea water, and strength. 94.

What is the ma terial of the propeller material?

a. Nickel aluminium bronze (nickalium) Copper: 55~62%, Aluminium: 0.5~2.2%, Nickel: 0.5%, Manganese: 0.5~1.0%, Iron: 0.4~1.5%, balance is Zinc b. Manganese bronze Copper: 58%, Iron: 1%, Aluminium: 1%, Manganese: 1%, Nickel: 0.5%, http://class4exam.com/MEO_oral_question_answers.html

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Zinc: 38%, Tin: 0.5% 95.

What is the general composition of the stainless ste els?

Chromium: 18%, Nickel: 8%, Carbon: 0.12% 96. What is the ma terial of the 4S e ngine co nrod? a. Forged steel: Open hearth plain carbon steel UTS: 432~494 MN/m2 % Elongation: 25~30% Fatigue limit: 208 MN/m2 (push pull) b. Nickel stee l, 3%Ni UTS: 695 MN/m2 %Elongation: 20% Fatigue limit: 309 MN/m2 (push pull) METHODS OF TIGHTENING: a. Measuring the extension of the b olts b. Use of the cali brated tor que wrenches c. Hydraulic tensioning d. Angle tightening


97.

What is the ma terial of the foundation bolts?

High tensile steel 98.

What is the material of the tie rod?

High tensile steel 99.

What is the material of the double bottom plug?

Silicon steels 100.

What is the material of the crankshaft?

Forged low carbon alloy st eel. Carbon: 0.12% and less 101. What are the materials used for the diesel engine’s liner and piston rings? State their principle differences

Generally the materials used for the piston rings are harder than the liner material. This is due to the fact that the rings are subjected to wear always during their operation but only the portion of the liner in contact with the rings wears. Material used for the liner is generally the nodular cast iron, which is tailored to have expansion along the length and negligible expansion circumferentially. Alloying materials are added to improve certain charact eristics like vanadium and titanium. Piston rings are cast and machined from graphite grey cast iron. T his ring may include chromium, nickel & copper as alloying substances. The prime property which distinguishes it from the liner material is t hat it has to flex c ircumferentially. This is of primary concern for running in and to match the contour of the wearing liner surface. Also they have to form an effective sealing of the combustion gases. 102.

What are the liner wear rates? And how is it ac hieved?

Old engines: 0.1mm/1000hrs Modern engines(2S): 0.03mm/1000hrs Modern engines(4S): 0.12mm/1000hrs This is achieved by: a. Highly alkaline lube oil b. Load dependant jacket cooli ng water temperature control c. Good quality of cast iron with a hard face d. Careful design of the piston ring profile e. Improvement in lube oil f. Multilevel cylinder lubrication g. Condensate separation from the scavenging air h. By use of the anti-polish ing ring or the piston cleani ng 103.

Explain why sta inless steel is resistant to corrosion?

Stainless steel depends on the formation of a protective oxide film, tenacious chromium oxide for resisting corrosion. This film is formed spontaneously on exposure to air or well aerated water. http://class4exam.com/MEO_oral_question_answers.html

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Without this oxide film, their corrosion resistance is only slightly better than other engineering steels. 104.

What is the material of the fuel valve needle and body?

Needle: hi gh speed steel Body: case hardened stee l

105.

What is the ma terial of the chain and its tightener arrangement?

High tensile st eels 106.

Quote some important clearances in the rudder system

Jumping clearance: 6mm Clearance at raphson slide mechanism: 16~19mm Propeller drop: 1mm/160mm diameter of the tail shaft Pintle c learance: 1.1mm~3.3mm 107.

What are the usual pressures to which the boilers are t ested?

New boilers, if > 6.9bar working pressure, 1.5xdesign pressure If < 6.9bar working pressure, 2.0xdesign pressure After major repair, 1.25~1.5x working pressure, duration of the test ing: 30Min. 108.

Explain the purpose of the hunting gear

a. To put the pump on stroke gradually b. To stop the pump at the end of the stroke gradually c. To lock the rudder at desired position till further movement is given at helm d. To t ransmit movement of telemotor to pump e. Spring in the hunting g ear store extra c ontrol movement to ensure t hat the pump operates at the maximum capacit y for major part of the turning operation 109.

Differentiate between the terms priming and foaming with reference to their occurrence in a steam boiler

Both refer to the carry over of water into the steam outlet. Priming is due to the mechanical/physical aspects and the foaming refers to certain insouble/solubles in the boiler water, which by the principle of increased surface tension cause priming. The various reasons for priming: a. High water level in the bo iler b. Rapid changes in the steam demand c. Safety valve lifting frequently due to its malfunction d. Rough weather causing heavy rolling/pitc hing e. Rapidly raising steam f. High salinity of the b oiler water Foaming is the formation of unbroken chain of bubbles on t he surface of boiler water. A common cause of the same is the oil contamination. 110. Mention some important mechanical properties of metals a.

Elasticity:


b. Hardness: Resistance to abras ion c. Plasticity: d. Toughness: Ability to absorb maximum energy before fracture e. Duct ility: Ability of t he metals to deform plastically under tensile force f. Stiffness: Ability to withstand d eformation g. Malleability: Ability of the materials to deform plastically under compressive force as in forging or rolling h. Resilience: Resist shock and impact i. Brittleness: Tenden cy of t he material towards brittle fracture. B rittle fracture is the failure of the material without plastic deformation j. Creep: Plastic flow under constant load applicat ion or heat k. Weld ability: l. Endurance: Abi lity t o withstand alternating stresses m. Cast ability: n. Strength: Ability t o withstand rupture 111. What is a tie rod bolt pinch screw? And what is its purpose? Pinch screw is normally provided at the foot of the engine cylinder jacket to stop the tie rod from vibrating during the normal service of the engine. http://class4exam.com/MEO_oral_question_answers.html

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The pinch screw is fitted at the antinodal point of the tie rod to limit its transverse vibration amplitude, thereby preventing its fracture due to vibrations. These can be arranged as a group of three screws positioned equilaterally at the antinodal point. Each screw consists of a stud, which is hand tightened by screwing the outer sleeve and held in place by a lock nut which is tightened to a torque specified by the manufacturer. 112.

What is the course of action after finding that a bottom end bolt is slackened?

a. Check the length of the bolt b. Check whether it is within the limits c. Check for cracks / surface finish. Check the threads d. The tie rod can be rolled over a flat surface c oated with Prussian blue. Any twists i n the rod are revealed by the Prussian blue lines on the tie rod which get adhered along the twisted plane e. If found alright, tighten the bolt and check the rem aining bolts 113.

Define higher calorific value and the lower calorific value

[H2O formed by the hydrogen in the fuel oil cannot exist as water at the high temperatures in an internal combustion engines. T he wat er formed by t he c ombination of hydrogen and oxygen absorb the heat from the combustion and forms st eam. Therefore, some amount of available energy is lost in converting water into steam. This energy is not available to the engine. Therefore, the calorific value of the fuel reduced by this amount presents the actual calorific value available to the engine.] - Æ This definition is given by reeds and I feel this has to be altered after looking into the MANBW manual, which provides a graph to calculate the Lower calorific v alue based on the Specific Gravity and Sulfur content.

Therefore, the amount of heat loss due to the inclusion of sulfur, which cannot be separated by normal fuel oil treat ment and its subsequent oxidation to SOx warrants the entire calorific value to include correction for corresponding fuel content in a specific mass of fuel sample


and the energy loss due to sulfur oxidation. Corrections should also include for ash & water content. Therefore, t o get the practical sc enario two specific calorific values are mentioned Lower calorific value and the higher calorific value. Lower calorific value = higher calorific value – the energy loss in converting the mass of the [water into steam ] + sulfur to sulfur oxides + Loss of specific enthalpy due to ash content present in unit mass of f uel. 114.

Explain gear pumps w.r.t the materials used and the clearances

Rotors and shafts are integrally forged of Nitraalloy steel. Gears are c ase hardened, medium carbon steel. They are hardened all over and ground finished after hardening Casing and bearing housing are close grained grey c ast iron Shafts are supported by white metal bearing or roller bearings or bronze bushes on the free ends Liquid being pumped is forced out after being carried around the gear teeth between the gear teeth and the c asing. Backflow is limited by: a. Minimizing the radial clearances between the teet h of the gears and the housing b. Increasing the number of teeth c. Optimizing the side t olerances /play Gear pump suitable for operating up t o 25bar and can ac hieve displacement volume of 0.35~1.0 liters/revolution Clearances between the gear teeth and the housing are of the order 0.02~0.03mm

115.

What are the advantages and disadvantages of resin chocks?

ADVANTAGES: a. 100% contact on uneven surfaces b. Cheaper to install as no hand fitting is required c. Don‟t corrode and are resistant to most of the chemicals d. As they achieve good contac t, there is little chance of fretting , thus cheaper, shorter, non resilient bolts can be used. These permit a reduction in the bolt tension by a factor of 4 e. Avoid vibrations DISADVANTAGES: a. Overstressing of the bolts causes the r esin to shatter and break b. Maximum temperature is limited to about 80°C 116.

Explain the cav itation in the bearings


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Vaporization due to oil pressure falling locally below vapor pressure causes bubbles in the oil, which when goes to higher pressure region, collapses and shock wave is generated causing heavy impingement. The causes: a. High oil temperature b. Low oil pressure c. Vibration d. Oil conta mination


117.

What are the Nimonic and Stellite coatings?

These are considered to be the hardened materials by the process of metallic cementation Nimonic: carbon, chromium, Titanium, Aluminium, Cobalt, Molybdenum, Iron, Nickel There could be other constituents such as Manganese, copper, silicon Stellite: T hey are alloys of Cobalt, and Chromium, with the addition of varying amounts of tungsten and other elements They are very resistant to corrosion and abrasion. Retain their hardness at a red heat Since they cannot be forged, they must be cast direct to shape or deposited by welding 118.

Why is an equalizing line provided in the refrigeration system?

It is used in the installations where a large drop in pressure occurs in the evaporator. In the expansion valve, the pressure acting outside (top) of the bellow corresponds to the saturation pressure plus the degree of superheat of the refrigerant leaving the evaporator. This pressure is trying to open the valve against the spring force from below the diaphragm. The external equalizer connection has a saturation pressure of the refrigerant leaving evaporator, to act below the diaphragm. Therefore the saturation pressure from the external equalizer connection balances the saturation pressure of the sensing bulb leaving only the pressure due to degree of super heat only to oppose the spring force. Therefore, this degree of superheat is supposed to open the expansion valve. By this method, wethe areevaporator getting a control over only the degree of superheat of the of the refrigerant leaving coil. This is important to ensure proper utilization refrigerant and that no liquid refrigerant reaches the suction of the compressor. 119.

What are the reas ons for short cyc ling of a refrigerant compressor?

a. Refrigerant char ge is too lo w b. Frosting or clogging of the evaporator c. Dirty suction strainer d. Low pressure control differential too small e. Wrongly adjusted capaci ty regulator f. Refrigerant vapor in the liquid line g. Too much coo ling water h. TEV faulty i. Too high compressor cap acity 120.

What is viscosity? Differentiate between the kinematic viscosity and the dynamic viscosity

Defined as the resistance of fluids to change of shape, being due to the internal molecular friction of molecule with molecule of the fluid producing the frictional drag effect. Absolute (Dynamic) viscosity is numeri cally equal to the force to shea r a plane of fluid

surface of area of a unit square meter, over another plane surface at the rate of one meter viscosity per sec, when between viscosity the surfaces is one meter. Kinematic is the the ratiodistance of the absolute to the density at the temperature of viscosit y measurement. Viscosity index is a numerical value which measures the ability of the oil to resist the change in viscosity with the change in temperature. A high viscosity index shows a good resistance to the change in viscosity with change in temperature.


121.

What is an Otto cycle or the constant volume cycle?

This is the constant volume cycle. Although no actual engine cycle operates strictly following this ideal cycle, the analysis of this cycle provides a tool for comparison of performances of actual engines under different operating conditions. http://class4exam.com/MEO_oral_question_answers.html

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The most important noted difference between this ideal cycle and the normal cycle is that this is a non-flow cycle involving an ideal gas whereas the actual cycle is a flow process and the gases are real. This cycle is explained as follows: At the beginning of the process the cylinder is assumed to be full with a charge of fresh air. γ The air is compressed isentropically following the law PV = constant. Heat is then added to the same mass of air at constant volume. This point represents the maximum pressure and temperature in the cycle. From here the air is expanded isentropically to the initial volume and then the heat is rejected at the c onstant volume. 122.

What is a Diesel cy cle?

This t hermodynamic c ycle is first analyzed by Rudolph Diesel. T his is a slight variation of the above c onstant volume c ycle, t he difference being that the heat addition in the cyc le takes place at constant pressure. The other processes during compression, expansion, and heat rejection remain same as with the constant volume cycle. 123.

What actions do you ta ke incase of an EGB Soot fire?

The oxygen levels in the EG Boiler/Economizer is about 14~16%, so this can support combustion. The nature of combustible deposits include soot from the combustion of fuel in the plant as well as some amount of unburnt oil (fuel and lube oil), partic ularly at low loads. Ignition of soot may arise at sufficient high temperature of the layer of the soot whose surface temperature may go up to 300~400˚C, but presence of unburnt oil may lower this temperature to about 150˚C and under favorable conditions to about 120˚C. SMALL SOOT FIRES: Mainly occ urs during maneuvering with the engine being operated at prolonged low loads. The situation may arise even at short low load running if the fuel is bad. Indications: a. High economizer exhaust gas outlet temp erature b. Sparks from the funnel c. Engine running parameters showing deviations due to increased exhaust back pressure d. High steam pressure or outlet temperature from the super heater section if fitted How to deal with this situation: a. Stop the main engine so that t he oxygen levels can be brought well below the fire sustenance levels b. Carry out the bou ndary cooling c. Fire to be kept on deck due to the risk of the funnel sparks, fire hoses to be keptwatch charged

d. e. f. g.

Continue running the circulatin g water pump Never use the soot blowers for fire fighting Stop the auxiliary blowers Ensure that all the exhau st valves are positi vely closed (check the sprin g air pressure)


If the soot fire has now turned into metal fire (identified immediately by the loss of the circulating water of the economizer), stop the circulating water pump. Carry out the boundary c ooling. If means are provided, deluging the ec onomizer fires with c opious amounts of water should be carried out to the seat of the fire. This is essential because, if lesser amount of water used the fire is additionally supported by the production of steam sourcing hydrogen for the situation to get worse. Hydrogen fire: Occurs because of dissociation of water (steam) into hydrogen and oxygen or carbon in connect ion with c arbon monoxide and hydrogen This occurs only above 1000˚C Iron fire: Oxidation of the iron at high temperature occurs at a rate sufficiently high to make the amount of hest release from the reactions sustain the process. These reactions may take place at a temperature in excess of 1100˚C 124. How do you identify the s ymptoms of a crank case explosion? What action would you take to minimize the hazard?

a. Engine noise b. Oil mist detector a larm c. High bearing temperature (alarm if fitted) d. In case of minor explosions the c rank case relief door releases the pressu re ACTION: a. Slow down the engine, inform the bridge b. Take permission from the bridge for stopping the engine c. Continue running the engine lube oil pumps d. In severe cases, it is prudent t o open the engine room skylights and other vents and http://class4exam.com/MEO_oral_question_answers.html

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abandoning the engine room. T he doors from the engine room to t he ac commodation should be kept shut. Return to the engine room only after carrying out risk assessment e. Turn the engine by turning gear with the indicat or cock opened to prevent seizu re of the hot spots f. Stay clear of the crank case specially in the region of the relief door to the turbocharger suction g. Don‟t open the crank case door until sufficient time has elapsed 125.

What are the various IG plant alarms and trips?

ALARMS: a. O2 content high b. Scrubber tower water level low c. Deck seal water level high d. Deck seal water level low e. IG pressure low f. IG pressure high g. IG temperature high h. Boiler uptake soot level hig h (Ringlemann) TRIPS: a. Scrubber tower water level high b. Venturi water pressure low c. Low IG cool sea water pressure


Scrubber cool sea water pump abnormal stop Power failure Incorrect mode of the boiler (mode set to NAV, GF.. etc) IG temperature high high (more than alarm level) IG blower abnormal stop Deck seal water low flow IG deck main extreme high pressure 126. out? Reciprocating pump is getting ov er heated, what checks should be ca rried a. Inlet and outlet valves are to be examined b. Inspect the seat and lap ping should be done if required c. Valve lift should be checked d. Inspect piston and piston rings e. Spring (valves should be checked for tensi on and springing action) f. Liner wear down should be checke d g. Driving belt should be checked for wear d own or damage 127.

Explain the va rious rudder inspections and testing in the dry dock

a. Visual examination of the rudder plating for cracks and distorti on b. Air plugs and drain plugs are to be opened in the presence of t he class surveyor, repair superintendent and chief officer. Water draining out indicates a breached rudder and the breach to be located by air pressure testing and applying soap solution, repairs t o be planned c. Check t he rudder drop in the st eering gear compartment (t rammel gauge) d. Check the pintle clearan ces, jumping bar clearance and the palm coupling bolts tightness to be checked e. Check the rudder stock for corrosion, erosion and any damage f. The inspect ion plates in the way of the u pper, the lower pintle to be cut open, an d the pintle nuts checked for proper securing. Later the plates to be welded and tested. g. Hydraulic t est the rudder for a static head of about 2.45 m of sea water h. After draining and re oiling the internals, plug the drain and check the effec tiveness by a vacuum check and cement the plug i. The rudder stock gland packing has to be chec ked and renewed 128. What is caustic cracking or embrittlement? What is its cause ? Suggest remedy

This is a form of intercrystalline/intergrannular cracking and occurs when a specific corrodent and sufficient tensile stress exists. Iron consists of ferritic granules bonded by iron carbide so this gives a scope of the intergrannular corrosion. This can be found in water tubes, super heater, reheat tubes, and in stressed components of the water drum. The stress may be due to thermal, bending or residual stress (due to welding). This usually occurs as a localized attack in the combination of NaOH, some soluble silica and a tensile stress. The mechanism begins with the accumulation of the corrodent NaOH due to – 143. DNB (departure from nucleate boiling) 144. Deposition 145. Evaporation at the water line 146. Small leakage 147. High heat flux (rapid evaporation) 148. High pressure http://class4exam.com/MEO_oral_question_answers.html

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This corrosion below 149˚C or with NaOH concentration below 5% is rare. Increased susceptibility occurs at about 20~40%. This corrosion is difficult to identify in the beginning and ND testing has to be carried out at the suspected areas. At some time after the initial start of the corrosion, this manifests as a whitish highly alkaline deposits or sparkling magnetite. COUNTER MEASURES: a. Applying heat t reatment process to reli eve stresses after fabrication/ repairs (welding etc) b. Correct and accur ate boiler water tr eatment c. Avoid DNB d. Avoid accumulation of the dep osits e. Prevent leakage of corrodents f. Prevent carryover g. Use of rifling in the water tubes A shell & tube type cooler tubes are leaking, what is the procedure to rectify the leaks?

129.

Before jumping to any conclusions it is prudent to check where the leaks are from. It could be from the breach on the tube (a hole etc) or from the srcination of small gaps between the tube plate and the expanded portion of the tube. The procedure should to be based on the findings. A holed tube should be plugged from both the sides; the plugs can be of cork, wood, rubber, brass, or copper as supplied by the manufacturer. Care should be taken when plugging with the metal plugs, not to damage the tube plate. If the leaks are from the gaps between the tube plate and the tubes, slight flaring of the tube may help preventing the leaks however this flaring, if excessive will damage the tube plate and also the tube itself. Alternative methods are available by carrying out surface preparation and applying metal repair putty, like Devc on‟s brush able c eramic repair putty. In the above process, if the plugging of the tubes is about 10% the tubes have to be renewed. 130. Explain a tube renewal process To remove the tube, first remove the flare on the tube by chiseling off the flare flush with the tube plate and then split the tube taking care not to damage the tube plate. The tube can then be cut by a tube cutter to drop the tube inside the shell. Fitting of a new tube is carried out by first positioning the tube in place between the end tube plates and flaring to the correct amount by a flaring tool after fixing the other end by a brass wedge. It could by either hand operated, pneumatic or motor operated. The tube should have a protruding part about 1/4”~1/8” and the flaring should be to about 1/8” + tube diameter at the tip. 131.

What is a phosphate reserve? Why is it important in high-pressure boilers?

A reserve of phosphate should be present in the boiler water to neutralize any hardness salts, which may enter. These salts would deposit as a scale on the heating surface if reserve were too low while, too high a reserve leads to foaming and possible excess production of sludge. It also gives alkalinity.


3CaCO3 + 2Na 3PO 4 ----Æ Ca3 (PO4 )2 + Na 2CO 3 3CaSO4 + 2Na 3PO 4 ----Æ Ca3 (PO4 )2 + Na 2SO 4 3CaCl2 + 2Na 3PO 4

----Æ Ca3 (PO4 )2 +6NaCl

MgSO4 + 2Na 3PO 4

----Æ Mg (PO 4) 2 +3Na2 SO4

Precipitates as Sludge At high pressure and temperature, reac tion from left to right will be more. T herefore, it is very important in high pressure boilers to keep the reserve level up to required concentration to avoid excessive caustic alkalinity and thus caustic cracking. Na2CO3 + H 2O Å---

Æ

2NaOH + CO 2


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In high pressure boilers where there is a risk of caustic concentration and subsequent caustic attack it is common to apply a coordinated or congruent phosphate control programme. T hese c ontrol methods are based on t he hydrolysis of tri-sodium phosphate (TSP) and disodium Phosphate (DSP) in the boiler water. Na3PO4 + H 2O Å--- -Na2HPO4 + NaOH

Æ

Na 2HPO 4 + NaOH

Å - -- - Æ

Na 3PO 4 + H O 2

The objective is to maintain a desirable pH without the presence of free OH alkalinity. The desired conditions are obtained by maintaining the relationship of the pH to phosphate concentration in the boiler water at less than that of the equivalent stochiometric solution of Na3PO4 (<3:1). This is achieved by the equi librium reaction above. The congr uent phosphate approach utilizes mixtures of TSP and DSP to further ensure the absence of free OH alkalinity and usually run with a Na:PO4 ratio of <2.8. 132.

What is the routine anchor windlass maintenance?

a. Brake drum should be free of oil, grease and other deposits. The brake drum should be cleaned periodically with a solvent prescribed by the maker b. The brake drum and the disk should be chec ked for wearing out or damage c. Gear oil should be checked for contaminants and level d. The direct ion of tensioning should correspond to the correct operation o f the brake. As the reverse direction for tensioning would render the brake ineffective, check should be carried out to ensure the same e. Brake test of the windl ass is to be carri ed out to t he pressure mentioned by the maker on the jack tool. If necessary, the spring tension adjusted. It should be done in guidance of the instructions and in the tensioning direction. The number of turns on the drum should also be checked and should be same as to the makers quote f. The sec uring device of t he tension spring adjust should be checked periodically for any tamper


g. Anchor windlass testingshould shouldraise be carried out check the from efficiency windlass. The windlass the anc hortowith c hain 82.5moftothe 27.5m at a mean speed of 9m/min h. The foundation of the windlass should be checked i. Other routines of t he prime mover should also be c arried out like for the windlass electric motor or the hydraulic motor as the case may be 133.

What are the cylinder lube oil properties?

a. SAE 50 or higher range oils b. TBN about 70 for heavy oi l burning engines with sulfur content of about 3% c. Ability to burn completely and leave no deposits d. Good detergency e. Good load bearing property f. Good spread ability g. Incompressibility for acc urate metering and timing the injection h. High flash point 134.

What is a pressure-vacuum valve and why can’t it be used to vent the cargo vapors during loading?

PV valve is designed to compensate for the variations in the tank pressure conditions due to variation of temperatures and the vapor quantity. A drop towards vacuum condition because of condensation of steam will also be handled by this valve. Usual set point of the valve is about +700mmHg and -350mmHg on the vacuum side. This valve cannot cope up with the requirements of cargo loading, as its capacity of pressure venting is small. Moreover it is not designed for this purpose. The valves displace a weight that vents the tank in case of an overpressure or vacuum condition. The valves are fitted with velocity vents that make sure that the inert gas is ejected out of the tank with such a velocity that it clears the deck sufficiently rendering the deck surface safe. 135.

What is a high velocity v ent?

Tank vapors can be sent clear of the deck in case of excess pressure or during cargo loading operation by a high velocity vent. The usual construction of such a valve is incorporated in a mast riser, which is a long tower for safely venting the excess pressure of the inert gas in the tanks to the atmosphere. The control is affected through a valve. The height of the mast riser is arranged to vent outside the hazardous zone, generally 9m or more. The valve consists of a variable moving orifice held by a counter weight to seal around the batten of a fixed cone. Pressure build up in the tank causes the moving orifice to lift. The small gap between the orifice lip and the fixed cone gives high velocity. The escaping gases are made to pass through a flame arrestor and a flame screen. The valve has a cover that is normally closed during sailing. http://class4exam.com/MEO_oral_question_answers.html

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136.

Air bottle maintenance and inspection

a. Regularly drain the bottle of water and oil b. Regular inspection to ensur e that the internal condition of the bottle is goo d c. Check for c orrosion both externally and internally d. Inside coating, COP AL varnish condition to be chec ked to ensure that it is unb roken and no peeling is taking place e. Welding seam to be checked, carry out dye-penetran t test at suspect ed areas


f. g. h. i. j. k. l. m. 137.

The tell tale hole between the lap wel ding seams of the doubler plate / ring to be checked for leaks in service to ensure that the internal welding is intact Face of the man hole is to be checked for pitting marks Drain should be clear All points of high stress and corrosion are to be thoroughly checked viz. wel ds, supports braces, the bottom of the bottle where water/oil is collected. Pay attent ion to the zone of water line. Check for leaks at the mounted valve glands/flanges, carry out inspect ion of the valve face and seat for wire drawing effect A timing check with the air bottle comp letely charged an d isolated will give a good idea of the intac tness of t he pressure vessel The safety/relief valve setting to be inspected as per the class requirement Regularly c heck t he alarms and monitoring equipment for proper functioning Explain the air bottle e ntry procedure

a. Inspect ion is to be carried out when the receiver capacity is not r equired for maneuvering b. Receiver properly isolated, depressurized and notice pasted c. The internal pressure is to be checked by the pressure gauge and by opening the drain valve d. Open the manhole door carefully and ventilate the air b ottle e. Obtain an enclosed space permit and comply with it f. Ventilation is to be maintained during the entire time of enclosed space entry 138.

What action should be taken in case of corrosion/wasting observed on air bottle?

MINOR: clean the site of corrosion, observe the varnish manufacturer instructions for surface finishing prior applying the coat. Apply new coat of the varnish. MAJOR: The site has to be cleaned and revarnished as above. The air bottle has to be derated. Incase of excessive the entire bottle has to be replaced. The derating procedure should be carried out as follows:

a. The extent of the derati ng is determined by the class sur veyor to a value which ensures the safe limit of the hoop stress at this reduced thickness of the shell plating b. The derating should not violate the starting air requirements for consecut ive starts of the main propulsion engine c. The setting of the safety/relief valve, should be set not exceeding 10% of the maximum working pressure after derating d. The c ut in and cut out pressu re switc hes for compressor automation should be readjusted For these reasons the air pressure vessels on board ship are fabric ated to allow for derating in future still complying with the consecutive sta rt requirements o f the propulsion e ngine

139.

What is a PV breaker? Why is it fitted?

This is a U tube manometer f illed with an ethylene glycol solution (as a measure against freezing). The height of the manometer is manipulated such that the pressure on either side may displace the solution, into tanks incase of vacuum inside cargo tanks and outside on to the deck incase of over pressurization inside cargo tanks. Usual set values of PV breaker are +1800mmHg on high pressure and -700mmHg on vacuum side.


Pressure-Vacuum breaker is fitted to the IG main line on the deck to protect cargo tanks from the following: a. Abnormal rise of pressure in the cargo tanks whi ch oc curs when cargo i s loaded with specified rate and that all gas outlets are closed b. Abnormal drop of pressure in cargo tanks which occurs when cargo is unloaded with the rated capacity of the cargo pumps and the inert gas blower fails http://class4exam.com/MEO_oral_question_answers.html

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c. Abnormal rise or drop of pressure in cargo tanks which occurs, when the breather

valves fails to operate properly for the fluctuation of the pressure in cargo tanks, due to variation in atmospheric and sea water temperatures, altering the vapor pressure inside tanks 140.

What is the routine maintenance, c hecks on the PV breaker?

CHECKS: a. Check the seal liq uid periodically and replenish the liquid in c ase • Liquid levels of inner and outer pipes do not coincide • “0” points of inner and outer pipes do not coincide when t he pressure inside the cargo tanks is atmospheric pressure b. Clean the flame screen in the cover at t he top when the ships makes a dockin CHECKING PROCEDUR E: a. Checking the liquid level of the inner pipe (open the vent coc k locat ed at most top of the gauge, close the upper gauge cock and open the lower gauge cock) this is also termed as “bigger range” b. Checking the liquid level of the outer pip e (close the vent coc k, open the upper gauge cock also open lower gauge is also “smaller Two distinct scales are the provided for the cock) liquid this gauge one termed “higher”asand other range” “lower” the respect ive readings (as in „a‟ and „b‟) should matc h numerically MAINTENANCE & INSPECTION IN DRYDOCK: Disconnect and remove top cover with attached internal stand pipe. Disconnect and remove Flame Arrestor Assembly. Remove flame screen. Thoroughly clean internal of flame arrestor. Renew flame screen with shipyard supplied equivalent type mesh. Drain breaker liquid, thoroughly clean internal breaker body, and stand pipe. Apply two coats of shipyard supplied tar epoxy by hand brushing to all internal surfaces. Level gauges, cocks and protective housing to be removed and transported t o workshop for c leaning and overhaul. Dismantle sight glass tubes and cocks for overhauling and cleaning. Upon completion, re- assemble and re-install onboard with new shipyard supplied approved type jointings, studs, and nuts. Prove filling and level coc ks clear and f ree. Disconnect and remove PV Breaker valve. Dismantle and clean surfaces. Lap valve and disc. Set valve to +0.21kg/cm2 and 0.07kg/cm2 in the presence of the attending superintendent. Record and submit calibration of valve settings. Close on c ompletion with new shipyard supplied approved t ype jointings and sealing compound and bolts and nuts. 141.

Explain the mounting arrangement of boiler feet

The alignment of boiler should incorporate provisions for t hermal expansion at the boiler feet (saddles) when the boiler is in hot operating condition. Expansion may be in the order of 10mm. Assuming a four-point support; one foot will be bolted down hard to the foundation, while the other three feet will be bolted down so as to permit the feet to slide. Holes for the fixed bolts will be reamed in place. The foundation bolts in way of the sliding feet must be accurately located with respect to the elongated holes in the boiler feet to enable the feet to slide clear of the bolts. The pipe sleeves prevent the bolts from tightening down on the sliding feet. A brass liner or a lubricant such a s molybdenum disulfi de is


normally used to facilitate the sliding action. In some cases, the pipe sleeves are not used. Instead, the bolts are tightened only slightly so that the boiler foot can slide. FIXED F OO T BOLT

ELONGATED HOLE IN BOILER FEET

SLIDING FEET OUTLINE OF BOILER

Lock Nut


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MEOClass4OralQuestionsWithAnswers Boiler Feet

Steel Liner

Foundation Bolt

Interference body bolt or fitted bolt FIXED FOOT


142.

What is a fitted bolt?

The answer lies above. This is a closely fitted bolt. The holes are initially drilled to undersize and are reamed in the assembling place before the bolts are tightened in place. Accuracy is required in the machining. These bolts could be of two types one having a slight taper of about 1:100 on diameter and the other having a large taper of about 1:15 on diameter. However, the holes in either case are reamed in final place. Some times an oversized bolt is stretched hydraulically reducing the bolt diameter. When tightened down and the hydraulic pressure is released the final exact fit in the bolt hole is achieved, like a pilgrim nut on coupling shafts. These bolts find place in engine / boiler mountings, coupling shafts etc. and form a rigid fixture. On main engine mounting these are situated aft of the engine in the way of thrust block. The foundation bolts towards the fore end (either side of the engine „P‟ „S‟) are generally simple foundation bolts which are not fitted bolts. This system of foundation bolts offers the rigid seating with provision for thermal expansion towards fore end. 149.

What is the ma terial of main stea m piping and explain how it is supported?

Main steam piping is usually made of seamless low alloy steel. Where t emperatures are above 455˚C, the most widely used alloy contains 0.5% molybdenum, 1.25% chromium. Gaskets between the flanges are made of thin stainless steel strips spiral wound with insulating filler between successive layers. There are three types of supporting to carry the weight of main steam piping. a. Rod hangers b. Variable spring hangers c. Constant force spring hangers Horizontal sway braces are often used to resist dynamic forces applied to the piping due to rolling and pitching or due to vibrations transmitted to pipe anchor points. Sway braces could be of the turnbuckle-rod type, the preloaded spring type or the hydraulically damped type. At fixed anchor points, the pipe anchor brackets are separated from the anchor foundation by insulating material to reduce the heat transfer from the steam piping to the hull structure. 144. Soon after complete overhauling a generator engine, its lube oil consumption increases . What checks do y ou carry out in this regard?

a. Check that the lub e oil system valves are set back to normal, and that the c oncerned valves are correctly holding b. Verify dip stick bottom for any blockage which c an give erroneous results http://class4exam.com/MEO_oral_question_answers.html

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c. Check for normal operation of the purifier

d. Ensure that t he piston sc raper ring is set correctly, if this ri ng is boxed back upside down, the oil scraping action of the ring is lost and uncontrolled lube oil enters the combustion chamber. This presents a significant oil loss e. Ensure that the c ylinder head valves are c orrect ly boxed back. Misalignment of the valve spindle with their guide also causes lube oil to enter the combustion chamber causing oil loss 145.

Generator lube oil sump level increases, what are the checks you would carry out?

a. Check that the gener ator lube oil systems valves are correctly posi tioned and that the sump filling valve is holding b. Ask the personnel for if they have c arried out any t ransfers just before, related to the sump oil of the generator c. Check the purifier for correct operation and that no water is being discharged with the purified oil d. Change over the generator concerned, isolate it and check the sump for any contamination like water. Basing on the findings further inspections can be carried out, like checking the cylinder liner jacket cooling wa ter se aling O-ring etc.,

146.

How do you prepare a boiler for survey?

Before a survey, the boiler must be prepared. The preparation process involves: I. Water side preparation prior entry into the steam drum for internal inspectio n II. Gas side preparation for external tubes inspection a lso the refractory cond ition can be inspect ed III. Elect rical isolation Electrical side isolation: The power supply to the boiler control panel should be isolated. The power supply breakers for the FD fan; burner pilot fuel oil pump should be switched off and caution tags put. Gas side/Exhaust side: a. If the boiler is an exhaust gas boiler, then the main engine should be isolated from starting positively. The composite boiler should be isolated on the fuel side in addition by manual isolation of the fuel line by a shut off valve and isolating the power of the boiler control panel. b. Oil fired boiler should be isolated on the fuel side by a manual shut off valve and isolating the power of the boiler control panel Waterside isolation: a. The boiler should be taken out of servi ce. With t he boiler shut, isolate t he boiler on fuel/exhaust side electrical side and water side by isolating valves, power supply breakers as the case may be b. Empty the boiler of water by blowing down, after allowing sufficient time for the boiler to cool gradually to prevent excessive thermal shock c. When blowing down to sea, open the overboard valve first then the boiler valve to be opened gradually. The nearing completion of the blowing down operation can be felt by falling noise, pressure. At this point, care must be taken not to let the cold seawater into the boiler. Start closing the boiler blow down valve when the boiler pressure is low enough, and when it is down to the desired value, the valve must be closed down tightly and the ships side cock closed. This is to be done to keep out the seawater ingress positively even though the valves are usually of non-return type.


d. Allow the boiler to cool down fur ther and loose all its pressure, and when the boiler pressure is at atmospheric pressure open the air cock and gauge glass drains t o ensure the pressure is atmospheric inside t he boiler e. Either the top door or the bottom door can be opened at t his stage but not both, while removing bottom door care must be taken against any hot water if present can cause injury to the personnel near it

After the boiler has sufficiently cooled the access points can be opened, the spaces well ventilated, enclosed space entry/steam drum entry procedures should be followed. The fire/exhaust side should be cleaned after initial examination a. Open access doors i n way of the uptake an d front and rear walls and the burner register and all hand holes b. Hydro-jet all soot deposits on tubes. All ow for collect ion and disposal of fresh water c. Mop up the fireside to dry. Neutralizing chemical can be added in order to avoid corrosion. Heating lamps can be used to dry out the furnace d. Scrape hard deposits on all generating and water wal l tubes, sweep and r emove all carbon, soot and debris on the furnace floor The waterside requires a similar approach for c leaning a. Remove for acc ess to st eam drum and water drum manholes and headers b. Allow for header blanks for water side survey http://class4exam.com/MEO_oral_question_answers.html

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c. Remove all st eam baffle plates in t he steam drum

d. Hydro-jet cleaning of the internals of drums and tubes may be required to remove mill scale and sediments 147.

What are oxygen scavengers?

Oxygen scavengers are chemical compounds, which are added to the boiler feed water to eliminate oxygen residuals and to assist in the passivation of metal surfaces. There are a number of these chemicals available, and a selection is a function of the amount of oxygen present, risk, feed system design, economics and any particular limitations required by the process using the st eam. Some widely used oxygen sc avengers are: a. Sodium sulfite (Na 2SO 3) Method of dosage: Dose the feed water continuously to maintain a desired concentration. Where corrosion in the feed system is experienced, it is used as a catalyzed form of sodium sulfite. The catalyst (usually a salt of cobalt) is to speed up the following reaction, so that this is complete before the water gets into the boiler. How is O2 Scaven ged ?: 2Na 2SO 3 +O2 --------- Æ 2Na 2SO 4 Limitations: The speed of the reaction is influenced by the pH of the feed water which should be between 8.0~9.5. Sodium sulfite adds some solids to the feed water, so it should not be overdosed or applied to the cold feed water. Otherwise, this may lead to increased blow down requirement. Sodium sulfite can be used in the boilers of pressures up to 62 bars. Above these pressures, decomposition products such as H2S and SO2 can affec t st eam purity b. Hydrazine (N 2H 4) Method of dosage:Liquid hydrazine is injected at the earliest possible point in the feed water system. How is O2 Scaven ged ?: N 2H 4+O 2-------- Æ N 2+2H O2 Limitations:Excess hydrazine should be controlled to avoid an undue rise in the ammonia level in the steam; there is a danger of c opper corrosion in the c ondensing plant. (Ammonia is produced by the decomposition of excess of hydrazine can provide a suitable alkaline condition in the steam and in the condensate system,

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2H4 st 2). Hydrazine 3N -------4NH3 +t Nwith is not permitte d in the systems where eam is in contac the foodstuffs. c. Carbohydrazide (Eliminox) (N 2H3) 2CO) Carbohydrazide is a combined form of hydrazine. It is superior in performance and is designed to minimize exposure to hydrazine vapors during handling. Carbohydrazide reaction products will add no dissolved solids to water. This can be used as an o o oxygen scavenger an d a metal passivator at both high (230 C) and low (60 C) temperatures. Carbohydrazide c an be applied to boilers up to 170 bars. How is O2 Scaven ged ?: (N 2H 3) 2CO + 2O 2-------- Æ 2N 2+ 3H O2 + CO 2 Limitations:in boiler, Carbohydrazide dec omposes t o hydrazine as one of t he products, so it cannot be used in systems where the steam is used for humidification. (FDA rules) d. Tannins Certain alkaline t annin solutions have good oxygen absorbing c apability. A 6ppm of certain tannins extracts can remove 1ppm of oxygen at a pH of 12. The oxygen scavenging efficiency is better than that of sodium sulfite. e. Erythorbic Acid (Sur-Gard) (R1-C(OH)=C(OH)-R 2) This is an effective oxygen scavenger and a metal passivator. This is the only nonvolatile scavenger, which can be used for spray attemperation. This does not add measurable solids to the boiler water; is non-volatile and will not hamper the steam purity. Erythorbic acid can be used in boilers up to 122 bars. This is considered as a safe substance by FDA. Æ 2 1 22 1 2 2 Ho is O Scaven ged ?: Ris-C(OH)=C(OH)-R + ½Oas--a--by-product -- -R -(C=O) H2OwLimitations: Ammonia produced in the boiler . T his is -R not +

recommended for use for boiler lay-up. Good corrosion control requires a high boiler water pH value since the magnetite film is at its most stable condition when the pH is 10.5~11.5. 147.

What are the va rious control actions?

The basic controller actions can be grouped as a. Two position or on-off contro llers b. Proportional controllers: It is also called corresponding control. The corrective act ion of controller, C, bears a constant ratio to the error θ = ± (Measured Value – Desired Value), T hus C = -Kθ (where K= constant of proportionality) c. Integral controllers: It is also called the reset action control. The rate of change of corrective action is proportional to the error. Mathematically, dC/dt = -Kθ or C= -K∫θdt + k (where K= constant of proportionality, k= constant of integration, C= control act ion) d. Derivative controllers: It is also call ed the rate act ion control. The amount of corrective action is proportional to the rate of change of error. It is never used alone and is always used in conjunction with the integral and or proportional controllers. As with a constant error, the control action being derivate becomes zero. C = -K dθ/dt, (K= constant, C= control action) http://class4exam.com/MEO_oral_question_answers.html

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e. Proportional-plus-Integral controllers f. Proportional-plus-Derivative controllers g. Proportional-plus-Integral-pus-Derivative c ontrollers 148. How is the chain drive of a ma in engine inspected? Chain inspection is to be carried out as follows: a. Make a general inspection for loose screws and bolts b. Inspect lube oil pipes for damage, and chec k oil jet nozzles for p ossible stoppages or deformations


c. Examine the rubber track of the guideways for cracks or other damage, replace the

guideway bits if they have started to be plucked out of the rubber stack d. Check the teet h of the c hain wheels. If abnormal wear is found, take a measurement by placing a straight edge over the wear edges and measure the length of the wear along the straight edge and the gap between the straight edge and the wear trough e. Check the chain s for cracks on possibly defect ive rollers and side plates f. Check that for each chain link, chain rollers can run freely and that the c hain links can freely move on the pin and bushing g. Check the c hain wear by measuring the length of 10 chain li nks and compare the result with the value in the data provided by the maker. If the parameter shows abnormality then adjust the chain tightener 149. Explain the procedure of chain tightening [Courtesy MANBW]

a. Loosen the nuts A, B, C and D to free the chain tightener bolt b. Turn the engine so that the sl ack part of the chain is on the same side as the tightener wheel. If balance weights are mounted, turn the engine so that the weights hang vertically downwards c. With the balance weights in this position, tighten the nut B on the chain tightener bolt until there is a clearance of 0.1mm between the shaft and the nut . then tighten the o nut B to a tightening angle of about 720 d. Tighten the nut C har d against the contact fac e of the shaft. Tig hten the n ut D, lock nuts A and B with the tab washer o procedur e e. Measure X, ifnut theB conly haintois aworn (i.e. X>165mm) repeat600 the from „a‟, the butdistance tighten the reduced tightening angle . f. If the distance exceeds t he maximum distance 265mm, find and eliminate t he cause of this abnormal chain elongation, like a defective chain, damaged chain wheels or bearings etc., repeat the procedure from „a‟. g. Repeated tighteni ng of the c hain will gradually alter the c am angle in relation to t he crankshaft. It is therefore necessary to readjust the camshaft to its initial angular

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position after the lead angl e has been increased b y 2 . T he camshaft is adjusted by turning both halves at the coupling joint with the chain wheel 150.

Why is a copper gasket annealed?


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The essential qualities of a copper gasket are softness and toughness (provision for cold working without fracture). In its place the copper gasket is subjected to considerable mechanical stress, resulting from elastic strains internally balanced. These elastic strains are due to jamming of dislocat ions, which occ urred during cold deformation (during service). If this cold worked gasket is heated to a sufficiently high temperature the total energy available to the distorted regions will make possible the movement of atoms into positions of equilibrium so that the elastic strains diminish and the locked-up energy associated with them „escapes‟. T ensile strength and hardness will fall to approximately t heir original values and capacity for cold work will have returned. 151.

What is the difference between a safety valve and a relief valve?

A safety valve is a pressure relief valve actuated by inlet static pressure and characterized by rapid opening or pop action. A relief valve is a pressure-relieving valve actuated by inlet static pressure and opens in proportion to t he increase in pressure over t he opening pressure. The terms „safety‟ and „relief‟ are synonymous; the safety valve is generally applied to valves protecting any vessel, which could explode and endanger life whereas the relief valve is more appropriate t o the valve protec ting syst em containing non-expansible liquid a burst causing no violent explosion. Another notable difference between these valves is that t he vent of a safety valve is led to a „safe‟ place (harmless to the w orking personnel) whereas a relief valve vent s just outside the valve. 152.

What are the parameters of a lube oil analysis?

The parameters of a two stroke, heavy fuel oil engine circulating/system lube oil are a. Specific gravity: Range 0.90~0.98. This is used for i dentificat ion of the oil. Limits: 5% of initial value b. Viscosity: Viscosity increases wi th oxidation, contamination with cylin der oil, heavy fuel or water. Diesel fuel contamination decreases viscosity. Limits: Max 40%, Min 15% of initial value c. Flash point: Gives an indication of possible dilution with diesel oil. Limits: Minimum: 180˚C d. TAN (total acid nu mber): Expresses the tot al content of organi c and inorganic ac ids in the oil. Organic acids are due to oxidation products. TAN = SAN + weak acid number. Limits: TAN 2 e. SAN (strong acid number): This expresses the amount of inorganic acids in the lube oil. Inorganic ac ids are usually sulfuric acid from the c ombustion chamber or hydrochloric acid arising from seawat er. This will be stat ed. SAN makes lube oil corrosive (especially together with water) and should be zero. Limits: SAN = 0 f. Alkalinity/T BN (total base number): Gives the alkalinity levels in the lube oil containing acid neutralizing additives. Limits: High = 100%, Low = -30% of initial value g. Water: Could be fresh water or sea water, wi ll be stat ed. Limits: Fresh water: 0 .2% (0.5% for short period), saline water: Traces h. Conradsen carbon: Residue from incomplete combustion, or crac ked lubricat ing and cylinder oil. Limits: Max 3%


i.

Ash: May be used to indicat e the amount of additives in the lube oil. It c an also consist of wear particles, sand and rust. It should always be evaluated by comparison with the ash content of the unused oil. Limits: Max 2% j. Insolubles: Stated as pentane/hept ane and benzene insolubles. Equal parts of the oil sample are diluted with benzene and normal pentane or heptane. As oxidized oil (lacquer and varnish like constituents) is only soluble in benzene, and not in pentane or heptane, difference in theare amount of insolubles is indicative the degree of oil oxidation.the Benzene insolubles t he solid c ontaminants. Limits: of Pentane insolubles Max 2%, Benzene insolubles Max 1% Apart from the primary parameters as stated above, the insolubles are usually stated as percentage/ppm of individual constituents such as Vanadium, Sodium, Aluminium, Iron, Silicon, Tin etc., which shows the engine wear and tear empirically. 153.

Explain hot gas defrosting in a/c fridge sys tem

Reducing v/v

Evaporator

Re-evaporator

Sensing Line

Suction solenoid v/v Drain

Expansion v/v

D rain

From other Evaporators


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MEOClass4OralQuestionsWithAnswers Hot Gas Solenoid v/v Liquid Solenoid v/v

A/C Com pressor

Electric Motor Condenser Defrosting Circuit

To Other Evaporators

Two kinds of hot gas defrosting systems by pass line are shown here. A by pass line hot gas defrosting system as above. This can be carried out for one evaporator coil when others are in use. Below is another type of hot gas defrosting system which is also called reverse cycle defrosti ng system and is use d w hen all the evaporator coils have to be defrosted.


Evaporator

Defrost circuit

Drain

Check v/v Expansi on v /v

Electric Motor

Four way v/v

A/C Compressor

Reservoir Condenser

Check v/v

Expansion v/v

154.

What is the difference between coagulation and coalesc ing?

A Coalescer filter element of some pre-filter for particulate removal followed by compressed inorganic fiberconsists coalescing unit in which water is collected into larger globules Coalescing action is relatively complex and simply it can be said to be due to the molecular attraction between the water droplets and the inorganic fibers is greater than that between the oil and the fibers. When the water globules are large, enough they will move with the stream out of the coalescing unit. Coagulation is the process of agglomeration of smaller particles into larger particle due t o intermolecular at traction bet ween similar molecules in preferenc e 155.

Why do we carry out boiler water treatment?

The objects of boiler water treatment are: a. Prevention of scale for mation and feed system by i. Using distilled w ater ii. Precipitating all scale forming salts into the form of a non-adherent sludge b. Prevention of corrosion in the boiler and feed system by maintaining the boiler water in an alkaline c ondition and free f rom dissolved gases c. Control of the sludge formation and prevention of carry over with the steam d. Prevention of entry into the boiler of foreign matter such as oil, waste, mill-scale, iron oxides, copper particles, sand, weld spatter, etc., by careful use of oil heating arrangements (close watch on the drains), effective pre-commission cleaning and maintaining the steam and condensate systems in a non-corrosive condition http://class4exam.com/MEO_oral_question_answers.html

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156.

How do you indent a drill bit?

a. Order the drills in consultation with the personnel routinely working with the tools b. Take the inventor y of the drills, estimate t he consumption of eac h drill, analyze to ensure that excess inventory is not kept d. Regarding the t echnical specifications fol low the instruct ions as per the ordering book viz. IMPA/ISSA e. Some aspect s should be looked into before arriving at a c onclusion, these are: a. Material of the tool and the in tended nature of its work, like for light or heavy duties b. Industry specification like DIN, JIS, BIS etc., b. Length of the drill, normal or extra length c. Cutting angle, st andard angles are 118 & 135 degrees d. Nature of twist, right handed, left handed, spiral etc ., e. The shan k shape, tape red, straight or „S‟ cut f. Number of flutes g. Drills and coun ter sinks h. Reputation of the company and cost i. Any previous experience with the com pany‟s tools Most commonly used drills on board are jobber drills (drills without a shank, which are gripped in the vice) for light duty, tapered shank drills for medium to heavy duty 157.

What checks do y ou make if a compressor trips on low lube oil pressure?

Incase of reciprocating compressor a. Direction of rotation, in case the motor is overhauled or some maintenance carried on the motor b. Suction filter should be cleaned c. Check the pressure switch d. Inspect the lube oil pump e. Check if any lube oil pipe is holed f. Check for excessive foaming Incase of rotary compressor, a. Check whether the lube oil pump is rotating with the compressor b. Check the condition of vanes and the elliptical casing for scoring damage c. Check the compressor is free to turn, no seizure of rotor, no wear on the vanes and the casing 158.

What are the reas ons of piston se izure in a reciprocating air compressor?

a. Failure of lubricat ion b. Failure of cooling water c. Valve part broken and fell into the chamber d. Piston ring breakage 159.

What are the instructions you would give to the watchkeepers regarding boiler?

a. Check the water level by gauge glass b. Keep an eye on the steam pressure c. Watc h the flame patt ern d. Check the vicinity of the oil burning equipment for any traces of oil

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Maintain the hot well temperature about 85C Check the hot well level and maintain it Atomizing steam pressure should be monitored Fuel oil pressure, temperature, t he fuel oil pump its suct ion pressure Amperage drawn by the related motors like FD fan

160. What is the procedure of conrod removal from a ma in engine? [Courtesy MANBW]

a. Turn the engine to BDC.

Dismount the nuts from the crosshead bearing studs b. Mount the shackles in the top of t he crankcase in the lifting brackets, in the athwart ship direction, and suspend two tac kles c. Turn the crank to TDC. Dismount the crankpin bearing cap, and remove the bearing cap from the engine http://class4exam.com/MEO_oral_question_answers.html

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d. Mount the four supports for guides shoes on the crosshead guides, turn the crank towards the camshaft side, until the guide shoes rest on the supports. Adjust the supports brackets to the guide so that the weight of the crosshead is evenly distributed on the four supports e. Mount the lifting attachments for securing the connecting rod on the head of the connecting rod . Fast en tac kles to the lifting brackets A and B on the box wall, and attach the tackle hookshments to t he on mentioned liftinging attac the connect rod head. Haul the tackles tight. Also mount a lifting attachment on the lower end of the conrod, on the exhaust side f.

Turn the crankthrow carefully towards BDC while following with the tackles, thus continuously supporting the connecting rod. The crosshead now rests on the


four supports. Turn the crankthrow to 90˚ before BDC g. Shift tac kle B from the lifting attac hment on one side of the connecting rod to the lifting attachment on the other side. Dismount the lifting attachment on the c amshaft side of the c onnecting rod. Attac h a tackle to the lifting bracket C on the frame box wall box and connect the tackle hook to the lifting attac hment on the lower end of the connect ing rod. Mount t he wire guide on the doorframe. T urn the crankthrow towards TDC while following with the tackles thus continuously supporting and guiding the connecting rod towards the doorway h. Attac h a t ackle to t he gallery-mounted lifting bracket E, and hook on to the lifting attachment on the connecting rod. Shift tackle A from the lifting attac hment on the head of t he connecting rod to the lifting attac hment on the head of t he connecting rod to the lifting attachment at the bottom of the connecting rod. Turn the crank upwards while following with tackles A, B, C and E, guiding the head of the connecting rod out of the doorway. Shift the tackles from one lifting attachment to the other as necessary i. Mount a strap around the c onnecting rod and suspend the connecting rod from the engine room crane. Shift tackle B, from the lifting attachment on the head of the connecting rod to the lifting attac hment at the bottom of the c onnect ing rod. Remove t ackles A and E. c ontinue turning upwards till about 30˚ after TDC while following with the tackles and the engine room crane j. Shift t ackle from lifting bracket C t o A. lift t he connecting rod out of the engine, using the tackles and the engine room crane. Remove the tackles by means of the engine room crane. 161. What is the importance of starting air overlap? What should be the minimum number of cylinders for a two-stroke engine for air starting? What is the corresponding number for four-stroke engine?

Some overlap of the timing of starting air valves must be provided so that one c ylinder airstart v/v opens as another closes. It is essential that there is no angular position of the engine crankshaft with insufficient air turning moment to give a positive air start. The usual minimum overlap provided is 15˚. Starting air is admitted in the working stroke of the engine http://class4exam.com/MEO_oral_question_answers.html

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and the period of opening is governed by a. The firing interval of the engi ne = No. of degrees in en gine c ycle/No. of cylin ders b. The valves must close befor e the exhaust c ommences. It is dang erous and a waste blowing air to exhaust manifold. c. The cylinder starting air valve should open after TDC to give a positive turning moment in the correct direction. The minimum number of cylinders for a two stroke engines is FOUR and that for a four stroke engine it is SIX.


This can be concluded as follows: For a two-stroke engine the air starting valve timing is Air on 15˚ATDC, Air off 50˚BBDC (exhaust opens at about 40˚BBDC) therefore a net starting angle of 115˚. At the end of this angle of a unit in power stroke, another unit of the engine should be 15˚ATDC in the power stroke, for continuity of starting. For this to happen, the maximum possible crank angle difference c an be 115˚ between units. A tw o-stroke engine has a c omplete c ycle angle of 360˚, t herefore the minimum number of units ≥ (360˚/115˚) = 3.13…. Minimum possible number of units in a two-stroke engine is therefore FOUR. Similar approach to four-stroke engines gives the following inference.

Air on 15˚ATDC, Air off 40˚BBDC (exhaust valve opens at 30˚BBDC) therefore a net starting angle of 125˚. Therefore, maximum possible crank angle difference between units is 125˚. A four-stroke engine has a complete cycle of 720˚ Therefore, the minimum number of units in a four-stroke engine ≥ (720˚/125˚) = 5.76 Minimum possible number of units in a four-stroke engine is therefore SIX 162. Show how the requirement of carbon dioxide in a ship’s installation is calculated. How is t he number of bottles required calculated?

Regulation stipulates the requirements of CO2 onboard ships as follows a. For cargo space, 30% of gross volume of largest cargo space b. CO2 of sufficient amount to give minimum value of free gas equal to larger of following volumes I. 40% of gross volume of largest machinery space exclu ding casing II. 35% of gross volume of largest machinery space protected including casing Regulation also states that, for machinery space, piping arrangement should be such that 85% of the gas can be discharged into the space protected including the casing with in 2min. The following information about CO2 is important Volume of free CO2 should be taken as 0.56m3/Kg (inverse of density) CO 2 content in a bottle is 45.4Kg (standard) Water capacity of the bottle = 65.1 liters (standard) For example, consider a ship in which

a. Engine room gross volume (to upper deck) = 4658m3 b. Engine room gross volume to top c asing = 5358m3 c. Volume of the largest cargo hold = 6849m3 Calculation of the CO2 cylinder required as per the regulations for the volume of the air reservoir = 375m3 Therefore, f or engine room the CO2 bottle requirement is calculated as F or gross volume exc luding casing, (4658+375)*0.4/ (45.4x0.56) = 80 cylinders For gross volume of engine room including casing, (5358+375)*0.35/ (45.4*0.56) = 79 cylinders For cargo hold, requirement is calculated as (6849*0.30)/(45.4*0.56) = 81 c ylinders The requirement is the largest of the a bove v alues, which is 81 cylinders

163.

What is a compensating ring in a boiler?

If any hole drilled in the boiler shell exceeds the value 2.5t + 75mm, where t = thickness of boiler shell, the vessel should be compensated for the loss of strength (due to lost material) by a stiffening ring around the hole (circumferentially). T his is called a compensating ring.


164.

What is BOD?

In sewage system, the effectiveness of the biological treatment of raw sewage is measured by BOD, biochemical oxygen demand. In a biological sewage treatment plant certain bacteria feeds on the raw sewage aerobically there by rendering the sewage harmless and with reduced suspended solids. After complete http://class4exam.com/MEO_oral_question_answers.html

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treatment the bacteria has no or little action. Therefore, by measuring, t he amount of oxygen c onsumed from a sample of t reated sewage the ac tivity of these aerobic bacteria and hence the c ompleteness of the treatm ent c an be estimated. In actual check, 1Litre of the sample is collected in a measuring container and stored at about 20˚C in water, which is well oxygenated and in a container and the amount of oxygen consumed in a period of five days is measured and is expressed in mg/L or ppm as BOD. 165.

What is the difference between a filter and a strainer?

A filter is a fine mesh insert in the pipeline of a fluid for the prime purpose of f iltration. It is normally positioned in the discharge line before t he utility (equipment) or in the return line in some hydraulic syst ems. T he usual size of the mesh is mentioned in microns, which is the smallest particle that can be filtered by the filter. A strainer is a coarse mesh inserted usually in the pump suction. It is positioned for the prime purpose of safeguarding pumps from ingress of heavy debris. In addition, this strainer helps in preventing choc king of t he pipeline in the upstream especially near sharp bends or narrow passages like coolers. Its objective is not filtration. It is usually mentioned as „mesh‟ and is the size of t he holes of t he mesh. 166.

What is principle of viscotherm?

The principle of viscotherm is that a drop in pressure of a fluid of laminar flow, across a tube is directly proportional to its viscosity. In a viscotherm, a sample of the fuel is pumped at a constant rate through a fine capillary tube. As the flow through the tube is laminar, pressure drop across the tube is proportional to its viscosity. Tapping points are provided to enable the pressure difference to be measured by means of a differential pressure gauge. The gauge is calibrated directly in terms of viscosity. A differential pressure transmitter provides an analogue of viscosity to a pneumatic controller, which regulates the supply of fuel heating. 167.

What is a bore relief in a bearing?

The bearing sliding surface is machined at the mating faces of the upper and the lower shells to create bore reliefs. Their main objective is to compensate for the misalignments, which could result in a protruding edge (step) of the lower shell‟s mating face to that of the upper shell. Such a protruding edge can act as an oil scraper and cause oil starvation


168. What is microbial infestation of lube oil? What are its ca uses, e ffects? Suggest remedies.

Microbial infestation of lube oil is the undesirable growth of bacteria, yeasts and/or moulds in the oil. Infestation of the oil can be due to contaminated seawater, hydrocarbon source already onboard or due to poor housekeeping practices. The problems are like tank washing with c ontaminated seawat er, wat er ingress f rom leaks of seals (as in a stern tube, CPP etc.,), leaking cooling water, microbe infested fuel oil contamination, onboard contamination due badly maintained or stagnant tanks (long lay off), bilge water etc ., The effects of such microbial infestation can be a. Slimy appearance of t he oil; the slime tends to c ling to the c rankcase doors b. Rust films c. Honey-colored films on the journals, later associated with corrosion pitting d. Black stains on white m etal bearings, pins and journals e. Brown or grey/black deposits on metallic parts f. Corrosion of the purifier bowl and newly machined surface g. Sludge acc umulation in crankcase and excessive sludge at the purifier discharge h. Paint stripping in the cran kcase i. Additive de pletion j. Rancid or sulfitic smells k. Increase in oil acidity or sudden loss of alkalinity. (BN) l. Stable water content in the oil, which is not resolved by the purifier m. Filter plugging in heavy weather n. Persistent demulsificat ion problems o. Reduction of h eat trans fer in coolers To counter the problems of the microbial infestation, it is necessary to take steps to prevent such infestation. http://class4exam.com/MEO_oral_question_answers.html

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The microbial infestation is not possible without the presence of water. Some water in the oil in inevitable due to leaks, condensation, etc., so it is necessary to constantly purify the oil. Tanks should be provided with drain cocks at the bottom most part to regularly drain the tank of water. The tanks should be designed to prevent any pockets where the flow is minimal or stagnant. T he oil should be stored outside the 15~35˚C range. T his temperature zone is very conducive for bacterial growth. Preferably, the tank should be kept at a higher temperature t o fac ilitat e st erilization. Lube oils have a maximum risk of infestation in the water-cooled pistons engine. Therefore, care must be taken not to allow any scope for water leakage from the cooling system and the coolers should be kept leak free. Once the oil is infested, it is necessary to kill the bacteria by physical, chemical or other means. PHYSICAL MEANS:

a. Settling: microbes sett le the as they have a high er specific gravity (Sp.gr. 1.05) b. Centrifuges: they can be separated by centrifuging c. Filtration: microbes can be filtered by suitably staging filters d. Heat: This is a functi on of bo th temperature a nd time at that temperatu re. A temperature o f over 70'C for 20 minutes is effective in kil ling the microbes. How ever

this is difficult to achieve at the plate surfaces and it may be necessary to sterilize the tank first say CHEMICAL MEANS:

by the use of steam lances before filling with oil for heat treatment

Killing microbes using microbes is eas y and e ffective, howe ver the s election of chemic als appropriate for the system application and should be done with care. Such things as compatibility and hazards should be taken into account. However, if the infestation is acute,


higher concentration of dosage of the chemical is required. This may render the oil unusable and has to be discharged to shore facilities. Other means of c ombating the microbes are available like a. Irradiation (UV Rays, Gamma Rays or X Rays) b. By ultrasonic treatment of the infested oil c. Using microwaves d. Continuous pasteurization of the infested oil and heat control 169.

What are the properties of gear oil?

Properties required for gear c ase oil: a. High viscosity. T his gives high film strength to prevent metal-to- metal contac t. Also a adhesive of the film to the metal is required to counter the sliding and centrifugal force b. It should prevent c orrosion c. It should have high specific heat to be a good coolant d. High viscosity index e. Antifoaming f. Sound damping with good cushioning property t o prevent pitting on the g ear teeth faces g. Oil should be suitable for elasto-hydrod ynamic lubrication 170.

What is Osmosis? What is Osmotic hea d?

Osmosis describes the process whereby a fluid will pass from a more dense to a less dense solution through a semi-permeable membrane. It is very important to the water absorption processes of plants. Reverse Osmosis is a process, which uses a semi permeable membrane that retains both salt and impurities from seawater while allowing water molecules to pass. Filtration of up to 90% is possible thus making the produced water unsuitable for boiler feed without further conditioning. Improved quality is possible using a two or more pass system.

The fig. shows an experiment to show the effect of Osmosis (Osmotic head). When the jar is immersed in the concentrated solution the liquid inside jar increases due to diffusion of liquid from the concentrated solution to the clean water inside the jar, which is reflected as an increase in the water column. This increment in the water column is the Osmotic head. 171.

What are Detergency a nd Dispersancy properties of lube oil?

Detergency of lube oil is the property of the lubricant to keep engine parts clean. In motor oil formulations, the most commonly used detergents are metallic soaps, usually of c alcium (metalloid-organic c ompounds) with a reserve of basic ity t o neutralize ac ids formed during combustion. Dispersancy of lube oil is the property of the lubricant to keep solid contaminants in a colloidal suspension, preventing sludge and varnish deposits on engine parts. Usually the additives used t o impart this property are nonmetallic ("achless"), and used in combination with detergents.


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172. Why are air compressors and diesel generator engines not provided with crankcase oil mist detectors?

Crankcase oil mist monitoring for engine protec tion are to be provided when: a. When arrangements are provided to override the automatic st op for excessive reduction of lubricat ing oil supply or pressure b. Power rating is 2250 Kw or more c. Having cylinders of more than 300mm bore Air compressors and generator engines in a ship usually do not meet any of the above criteria and hence are not provided with crankcase oil mist detectors. 173.

What is the purpose of stea m traps?

Steam traps are automatic valves that release condensed steam (condensate) from a steam space while preventing the loss of live steam. They also remove air and noncondensable gases from the steam space. Steam traps are designed to maintain steam energy efficiency by performing specific tasks such as maintaining heat for process. Once steam has transferred its energy, it becomes hot water and is removed by the trap from the steam side as condensate and either returned to the boiler via condensate return lines or discharged to atmosphere (a wasteful practice). 174.

What is the importance of ‘Lip clearance’ in a boiler safety v alve?

The boiler safety valves make use of a special shaped valve seat and a lip on the valve which gives increased lift against the increasing downward force of the spring. The ac tion is as shown ab ove. And this lip value is of importance and should be checked during inspection. Damage to this region can lead to malfunctioning of the valve. 175. What are the reasons for a lot of deposits in the scavenge s pace of a m arine engine?

The usual reasons for a lot deposits in the scavenge space of a marine engine are a. Chocking of the scaveng e drains b. Blow-by due to broken or sticking piston rings c. Excessive liner wear d. Faulty inject ion due to altered timing, bad fuel or incorrect at omization e. Blow back of exhaust due to increased exhaust back pressure f. Leaking piston stuffing box g. Excessive cylinder liner lubricat ion

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176.

Register Yourself In Our Forums How does a leaky piston manifests as in an indicator diagram?

As shown above the loss of intactness of the combustion chamber due to leakages, increased volume or f ouling c auses t he c ompression pressure and peak pressure to drop. http://class4exam.com/MEO_oral_question_answers.html

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177.

What is the thermal e fficiency of the main e ngine?

Thermal efficiency of a plant = Heat energy converted to work/Heat input In a main engine heat input = (Fuel consumed x Calorific Value x reference time) Heat energy c onverted t o work = Brake power x Reference t ime 178.

What is composition of thin shell bearings?

Thin shell bearings are broadly of a. Tin based White Metal: Tin-based white metal is an alloy with minimum 88% tin (Sn), the rest of the alloy composition is antimony (Sb), copper (Cu), cadmium (Cd) and small amounts of other elements that are added to improve the fineness of the grain structure and homogeneity during the solidification process. b. Tin-Aluminium (AlSn40): Tin aluminium is a c omposition of aluminium (Al) and tin (Sn) where the tin is trapped in a 3-dimensional mesh of aluminium. AlSn40 is a composition with 40% tin. 179.

How do you operate the main engine after a Turbocharger breakdown?

Some points are to be taken into consideration for engine operation with turbocharger out of operation: a. Air supply for amount of fuel inject ed b. Adequate flow path of the ex haust gas pr oduced c. Cooling of t he turbocharger casing, rotor or bearings d. Isolation of air/gas/lubricating spaces in the event of no sealing ai r available e. Securing damaged parts The method of turbocharger isolation may be done in a number of ways depending on the nature of damage. Bypass arrangem ent: Tur bocharger i s bypassed of exhaust gase s by a suitable bypass pipe. Turbine inlet and outlet are isolated by fitting blanks and by pass pipe is fitted to give a


suitable gas fpath. The the compressor also water requires to prevent loss may of scavenge air due to back low from rec eiver.side Cooling andisolation lubricating oil systems also require isolation if casing and or seal is damaged. Rotor removal: If t he rotor is damaged it should be removed for repairs. The openings of t he casings should be blanked to prevent internal and external leaks of exhaust gas or air. Cooling of the casing should be effected as exhaust gases still pass through the casing. Locking of rotor: If requirement of propulsion is of concern and time is limited, rotor is locked into position by attaching the appropriate fixtures provided by the maker. An orifice plate should be inserted on the compressor side to allow a controlled amount of scavenge air to effect cooling. Cooling water to the casing should also be continued since exhaust gases pass through the casing. Isolation of the lubrication system may be necessary due to lack of sealing air. LIMITATIONS OF OPERATION: The limits of engine load depend on the actual configuration of the system and how many turbochargers remain in operation. A broad consideration of the following points should be made: a. The ac tual operating temperatures should be taken into acc ount and limits should not be exceeded b. Condition of the exhaus t should be monitored to ensure acc eptable combustion inside the cylinder c. Allowance should be given for rate of change of air supply during acceleration of the engine d. Remaining turbochargers should be also monitored for abnormal operation due to altered gas flow e. Auxiliary air supply should be provided where possible, but this may be effec ted by remaining turbochargers in operation Internal water leaks: In the event of a holed water jacket it is possible to operate the turbocharger as an air cooled unit by supplying compressed air as the coolant after isolating the water supply. Attention must be paid to the operating temperatures of the casing, and bearings especially turbine end. Four stroke engines with turbochargers out of service and no alternative air supply may be operated as a naturally aspirated engine with suitable attention being paid to the operating temperatures In any case the engine loa d is to be limited a value s pecified by the engine maker for the conditions of operation and usually for a two-stroke engine its value is about 15%MCR

180.

What is the procedure of plugging boiler of boiler tubes?

Procedure of plugging water tubes a. Clean the face of leaky tube remove all the scales and dirt both in steam and water drum b. Plug with brass plug, hammer tight and weld c. Cover this tube on the furnace side with heat resisting material Procedure of plugging smoke tubes a. Brass plug with stud and tightened by nut at both the ends http://class4exam.com/MEO_oral_question_answers.html

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181.

What is the difference between a purifier and a clarifier? Purifie r

A centr ifuge for separation two liquids of differentdensities Sealing water is added to a purifier to establish a seal

C la rifie r

A centr ifuge for separation of solid particles fromaliquid No sealing water is added

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Gravity d isc n eeds to altered with the changing density of the l iquid to be pu rified

A smallest of t he gravity d iscs provided, called a clarifier disc is fitted and r equires no alteration Interface is to be maintained and depends on Interface is not required but is established if process variables viz. density, flow, viscosity water is present and moves inwards or temperature Water outlet is normally open Water outlet is normally closed by the clarifier ring Provided wate r seal is maintained particle Provided no water, particle separation is separationisalsogood good 182.

How do you detec t a leakage in a bilge pump suction line?

With the main suction of the pump closed, start the pump with discharge open. Monitor the vacuum in the pump suction, if the vacuum is maintained for sometime the pump is in good condition. Proceed for checking the integrity of the suction lines as follows: With the discharge of the pump opened for delivery, a. Set t he pump to draw bilge from each particular wel l closing other suction li nes valves b. Start the pump and note the build up of vacuum c. Repeat the operation for all other suction lines individually, closing other remaining lines Now conclusion can be drawn with above observations. The pump does not achieve good vacuum for any well, in this case The manifold intactness by opening the sea water valve on the suction side and check it for the seawater leaking. Repair the line after identifying the location Identify for the leaks on the suction lines for which the pump does not achieve good vacuum This can be done by pressure testing the line by opening the seawater valve on the pump suction. The non-return valve on the line has to be dismantled and the valve put back after removing the valve disc. The sealings on the strainers have to be checked, like renewing gaskets. 183.

How is an engine lube oil sample collected?

Sampling points for an engine lube oil are clearly mentioned by the maker of the engine. In any case, the following points are to be adhered to a. Sample of lube oil should be drawn from the inlet t o the engine b. Before collecting a sample some amount of oil is to be drained from the sampling point. Later sufficient amount of oil should be collected into a clean container, decanted and collected in a clean sampling bottle c. Engine should be in operation as close as possible to the MCR for some time before collecting a sample d. The sampling container should be unused one specially produced for lube oil sampling e. After collecting a sam ple in the bottle, it shou ld be stored in a cool dry place to let the oil cool down before securing it with cap/seal. This is essential to prevent slight condensation in the bottle f. The sample should be fully identified with the date, vessel name, running hours of t he engine, lube oil running hours, sampling point identification g. Each t ime the sample should be drawn from the same point


185.

Explain onboard testing of lube oil

Some or all of t he testing explained below is done onboard ship. 1. FLASH POINT (Pensky Martin Apparatus) This method determines the flash point of the lube oil sample in a closed cup. This gives the lowest possible ignition point of the oil. A portion of the lube oil sample is slowly heated at a constant rate, whilst http://class4exam.com/MEO_oral_question_answers.html

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cont inual stirring is provided. A small flame is direct ed through an open shut ter at regular t emperature intervals, with simultaneous interruption of stirring. The flash point is the lowest point at which the application of the test flame causes the vapor above the test point to ignite. For a new oil the flash point should be above 220˚C, and any reduction would indicate fuel oil contamination. 2. BASE NUMBER BN tester kits are provided onboard to determine the alkaline properties of t he lube oil. These testers use the chemical reaction of a reagent with the alkaline lube oil additive (calcium) to produce a pressure rise. 10ml of oil is mixed with equal volume of a reagent. 10ml of another reactive reagent is placed in a plastic cup, which is floated on top of the oil and reagent. The testing unit is sealed and thoroughly mixed. The resultant pressure rise is directly read on an c alibrated pressure gauge against base number. 3. KINEMATIC VISCOSITY Onboard testing lube oil for viscosity is by the use of a comparative flow stick. This measures the relative flow between two oils, usually a sample of the in-use lube oil is measured against a fresh unused sample of the same grade of lube oil. The flow stick is filled with 3ml of each oil in each reservoir, once both the oils are at the same temperature, the flow stick is tilted to cause both oil grades to flow down the channels. Once the new oil has reached the reference mark, the position of used oil in the channel is checked. The following inferences can be drawn a. If the used oil has a low viscosity, due to li ght fuel dilution. Then oil will have traveled further down the channel than the new oil. b. If the used oil has a higher viscosity, due to ox idation or heavy fuel oil contamination it would not have traveled as far as the new oil. 4. DENSITY This method uses hydrometer to test the sample oil density. It is important to keep the oil and the hydrometer at the same temperature and maintained throughout the experiment. 5. WATER CONTENT Onboard water content is tested by using a calcium carbide. The tested is carried out by mixing 5ml of oil with 15ml of a petroleum reagent (paraffin, toluene). The two liquors are thoroughly mixed and then a measured amount of reagent (c alcium carbide) is placed on floating on the oil/reagent surface. The test unit is sealed and thoroughly mixed to bring all liquids together. If water is present the carbide will produce acetylene gas, and the resultant pressure rise will indicate the level of water contamination. 185.

What is the material of a boiler valve ?

Valve body: Cast Steel Spindle, valve seat, valve disc and other parts: Monel Metal, Bronze or stainless steel 186.

What will be the effect of water in fuel oil?

The effec ts of water content on fuel oil are a. Loss of calo rific value of the fuel oil b. Corrosion in the lines, fuel pump (plunger/barrel), inject ors


c. Water in oil can lead to vapor lock in the line leading to fluctuating engine RPM,

seizure of fuel pumps d. In case of seawater contami nation, it would lead to hig h temperature corrosion in the exhaust syst em e. Results in increased cylinder liner wear f. Cause increased fouling of the exhaust gas ways an d turbocharger blades 187.

What are actions you would take if a purifier starts overflowing?

Some or all of t he following should be c hecked for in c ase t he purifier overflowing: a. Sealing water low b. Excessive fuel back pressure c. Low pressure, chocked water line (check the water filter) d. Gravity disc oversi zed for the density of the fuel oi l in question e. Oil temperature high f. Excessive sludge deposition inside the purifier bowl g. Excessive feed rate h. Sealing ring damaged (between the Bowl and Hood) i. Check RPM and direction of r otation of bowl j. Leaking three- way valve 188.

How do you calculate the specific fuel oil consumption?

a. Take the fuel oil flow meter readings for a specific t ime interval usually for an hour b. Calculate the volume (difference between the ab ove readings) c. Using the fuel oil sample test results provided by the shore facility, calculate the density of the fuel oil at the temperature near the flow meter d. Calculate t he mass of t he fuel consumed by multiplying the results in b and c e. Calculate t he shaft power o f the engine during this interval of time, take an averag e value f. Specific fuel consumption is calculated b y mass of fuel consumed/Avg.shaft power http://class4exam.com/MEO_oral_question_answers.html

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developed by the engine in the time interval. Express the result in the Units of specific fuel oil consumption: g/Kw-h 189.

How do you calculate the shaft power of main engine? [Procedure for MANBW Engines ] During an interval of time, 1Hour measure engine

a. Fuel index of each unit b. Engine RPM c. Scavenge Air temperature d. Ambient air temperature (Engine Room Temp.) e. Fuel oil preheating temperature f. Obtain the specific gravi ty of the fuel oil at 15˚C, its sulfur content & Lo wer calorific value g. Obtain the cylinder constant (eng ine data) Calculate the average fuel pump index, Pθ = sum of all individual fuel index/total number of cylinders. Corrected fuel index, Pθ‟ = average fuel index x K Where K = Correction factor for fuel pump index


= K1 X K 2 X specific gravity of f uel @ 15˚C

An example of calculation is shown with the following data to calculate K, Hence Pθ‟ Lower calorific value of fuel: 9700Kcal/Kg, Specific Gravity @ 15˚C: 0.947, Preheated Temperature: 104˚C, Engine room temperature: 30˚C, Scavenge air temperature: 32˚C K1 = 0.953, K2 = 0.926 K = K1 x K2 x Sp.Gr. @ 15˚C = 0.836. Hence Pθ‟ = Pθ x K


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Mean Effective Pressure Pe=

Horizontal coordinate in t he above graph

Brake Horse Power (BHP) =

C x Pe x Ne Where C = Cylinder coefficient = 8.811 for 6S60MC MANBW engine Pe = Mean Effective Pressure Ne = Engine RPM OUT PUT OF THE ENGINE (Shaft Power in = Kw) BHP x 0.7355 190.

What is P-Alkalinity and T-Alkalinity?

P-Alkalinity:phenolphthalein

is less alkaline than hydroxides or c arbonates, and when it is added to a sample containing hydroxides and or carbonates it will first neutralize the hydroxides forming salts, it will turn pink in color. The acid used after this c oloration will first neutralize the hydroxides forming salts, it will then react with the carbonate molecules present forming bicarbonate molecules. Bicarbonate molecules are less alkaline than phenolphthalein, hence, the pink coloration disappears once all the hydroxides and carbonates have been dealt with by the acid. One bicarbonate molecule is formed from two carbonate molecules, hence in the test the quantity of acid used is a measure of the alkalinity due to the hydroxides (caustic) present and half the carbonates. T-Alkalinity:Methyl-orange indicator is less alkaline than phenolphthalein and bicarbonates. It can be used initially in place of phenolphthalein or in continuation after the alkalinity to phenolphthalein test. If no yellow coloration results when the methyl-orange is added to the alkalinity to phenolphthalein sample no bicarbonates are present. Hence no carbonates are present. Therefore, the alkalinity as determined in the alkalinity to phenolphthalein test has been due to hydroxides alone. 191. What is the difference between an over speed gov ernor and a constant speed governor?

If within a governor, an over speed detection/actuation mechanism is provided to trip the engine in case of over speeding and or rapid increase of speed then the governor is called an over speed governor. These were the obsolete governors and commonly had fly or bob weights restrained spring. thecutoff. engine exceeds a predetermined speed, the weight moves out to strikeby some formWhen of fuel Governors designed to maintain the engine speed at the set point are called constant speed governors. These are also referred to as isochronous governors like the ones usually installed on COPT and main engine. 192.

What are the properties of steering gear lube oil?

a. Satisfactory flow properties b. High viscosity index c. Low compressibility d. Good lubricat ing properties e. Low vapor pressure f. Compatibility with system materials g. Chemical sta bility h. Protection against corrosion i. Rapid air-release and water separation j. Good thermal conduc tivity k. Fire resistance (desi rable)


193. What is the material of connecting rod bolt? What is the importance of elongation? What is the nature of stresses in this component and why should these bolts be replaced after some time in service?

The connecting rod bolt in service is subjected to: a. A dynamic tension loading due to c entrifugal force of the mass of connecting r od rotating with the crank pin b. A dynamic t ension loading owing to inertial forces of t he reciprocating mass of t he piston which is fluctuating with angular displacement of the crank and having the peak value at an instant of 360˚ after the firing TDC in a cycle of operation c. A dynamic shear stress at the parting of the two halves of the bearing housing Dowel pins with fitted bolts or serrations at the face or both are used to reduce shear loading on bolts and possibility of frett ing. Bolts should be constructed of materials having high resilience and should not be stiffer w.r.t bearing housing. http://class4exam.com/MEO_oral_question_answers.html

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Pretension of the bolts should be regarded as the single most important factor which contributes towards the fatigue life of the material of the bolt. Pretension must be kept high enough, so that the increase in stress owing to dynamic loading remains within the range of stress already given by pretension. Some routine checks on this part are (rejection criteria of the bolt) a. Check for corrosion by acidic lube oi l, discard if any present on shanks b. Check the leng th of t he bolt against a new or bol t t olerances. If longer, yielding of the material should have taken place. Renew the bolt in this circumstance c. Check for mechanical damage, espec ially on shanks d. Check for fractures b y NDT e. Check the landing faces for uneven tightening f. Discard the bolt when either designated life, over speed fai lure or piston seizure has occurred 194. What are the bunker specifications? What changes would you make in the event of a bad bunker?

THE INTERNATIONAL STANDARD In 1982a the working group responsible for the development of t he international standard issued draft proposal which became ISO 8217 Petroleum products – Fuels (Class F) – Specification of marine fuels. Another draft proposal was issued at the same time which became ISO 8216 Petroleum products – Fuels (Class F) – Classification Part 1 – Marine Fuels. In 1987 the first edition of the international standard was published followed by the publication of BS MA 100 in 1989, which was identical to the International Standard. The second edition of ISO 8217 was issued in 1996 and this is denoted as ISO 8217 : 1996. Table 1 from ISO 8217 Limi t

Characteristic Appearance 3 Density at 15°C, kg/m

Category ISO - F DMX DMA Visual

Viscosity at 40 °C, mm /s*

Min Max

1.40 5.50

890. 0 1.50 6.00

Flash point, °C

Min

43

60

2


Max

DM B 900 .0 11. 0

60

DMC 920. 0 14.0

60

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Pour Point (upper, °C) Winter quality Summer quality Cloud Point, °C Sulfur,% (m/m) Cetane Number Carbon residue, (micro method, 10% (v/v) Distillation bottoms), % (m/m) Carbonresidue,(micromethod, 10% (m/m) Ash,%(m/m)

Max Max Max16 Max 1.0 Min 45 Max

-6 0

0 6 -

1.5 40

0.30

0.30

0 6 -

-

2.0 35

2.0 -

-

-

Max

-

-

0.3 0

2.50

Max

0.01

0.01

0.0

0.05 1

Sediment, % (m/m)

Max

-

-

0.0

7

Totalexistentsediment,%(m/m) Max 0.10 Water, % (v/v) Max 0.3 0.3 Vanadium, mg/kg Max 100 Aluminium&silicon,mg/kg Max 25 * mm² / s = cst Distillate Fuels There are four grades of marine distillate fuels – DMX, DMA, DMB AND DMC. The „DM‟ denotes „Distillate Marine‟ and the t hird letter distinguishes the different grades. Grade DMX is a pure distillate used for emergency equipment external to the machinery space. Grade DMA is the equivalent of a gas oil and is also a pure distillate. Grade DMB is equivalent of a clean diesel, although it may contain some residue giving it a black color. This means that an appearance test cannot be used on DMB as it is for grades DMX and DMA. Grade DMC relates to a blended diesel oil which c ontains a residual component, normally up to 10 % Viscosity

Grades DMX and DMA have a specified minimum viscosity t o ensure the fuel has sufficient lubricity. Flash Point

The flash points for marine fuels is det ermined by the closed c up method c orresponding to the opening of a previously c losed vessel. T he minimum flash point is 60°C for all fuels within the machinery space of a merchant ship classed for unrestricted service, as laid down by SOLAS national classification f or emergency equipment external to theand machinery space,regulations. must have Grade a flashDMX, pointused greater than 43°C. It should be noted in some countries gas oil and diesel oil are produced for local land based market to a national spec ification. A minimum flash point is usually included in such a specification, however, this value may be below that required by international legislation for normal marine use. Pour and Cloud Point

The pour point parameter specifies a winter and summer quality temperature. Normally vessels burning DMA, DMB, and DMC do not have t ank heating. Purchasers should ensure the pour point is suitable for the equipment on board, particularly if a vessel is operating in both Northern and Southern hemispheres. The cloud point is the temperature at which wax begins to crystallize from a clear distillate fuel. These wax crystals will cause rapid filter blockage. This parameter is only applicable to


grade DMX and is a technical limitation so that emergency equipment can start and operate at an ambient temperature of –15°C. Ignition Qua lity

The Cetane number is the measure of the ease of ignition of a distillate fuel determined by a special engine test with a variable compression ratio. The higher the number the easier it is for fuel to ignite in the engine. The Cetane index is an empirical measure of ignition quality for distillate grades of fuel. This index is calculated in a number of ways, suc h as from the mid-boiling point and density. Bear in mind, these empirical equations do not take account of any cetane index improver which may have been added in the manufac ture of the fuel. Sediment

The sediment test for the DMB is sediment by extraction which defines the insoluble residues remaining after extraction of the fuel by toluene. For the blended diesel grade DMC, the sediment test specified is the Total Existent Sediment. This is the combination of inorganic and hydrocarbon sediments existing in fuel when delivered. T his test is aimed at limiting the maximum amount of sludge present that could be separated by the filters or centrifuges. Catalyst F ines

In distillate fuels the elements vanadium and aluminium, plus silicon for grade DMC, http://class4exam.com/MEO_oral_question_answers.html

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relate to he residual component of the blend. RESIDUAL FUELS

From table 2, ISO 8217 : 1996, there are fifteen grades of residual fuel which are distinguished by three letters and two numbers. The first two letters are common to all residual grades, „RM‟ denotes „Residual Marine‟, and t he third lett er refers to the characteristic of the fuel. The two numbers are the viscosity of the fuel at 100°C. Grade RMA relates to a residual fuel which normally does not require tank heating because of the def ined low pour point. Other residual grades require tank heating as they may have a considerably higher pour point as defined in the specification. ISO FUEL STANDARD 8217, 1ST REVISION 1996, FOR MARINE RESIDUAL FUELS CHARACT ERISTIC DENSITY @15°C

UNITS

LIMIT

kg/m Max

VISCOSITY@100°C

mm2/SMax APPROX VISC. @ 50°C * mm2/s FLASHPOINT °C Min POURPOINT,WINTER °C MAX

RMA RMB RMC RMD RMERM F RMGRM H RMK RMH RMK RM L RMH RMK RML 10 10 10 15 25 25 35 35 35 45 45 455 5 55 55 975 981 981 9859 91 991 991 991 10 10 10 50 50 50 60 60 60 0 24 24

15 25 25 35 1002 25 225 390 60 60 60 60 30 30 30 30

35 390 60 30

1010

991

35 390 60 30

45 585 60 30

1010

-

45 45 5855 85 60 60 30 30

991 55 810 60 30

1010

-

55 55 8108 10 60 60 30 30

POURPOINT,SUMMER °C Max 6 24 24 30 30 30 30 30 30 30 30 30 30 30 30 MCR %m/mMax 10 10 14 14 15 20 18 22 22 22 22 -- 22 22 -ASH %m/mMax 0.1 0.1 0.1 0.10 .1 0.15 0.15 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 WATER % V/V Max 0.50 .5 0.50 .8 1 1 1 1 1 1 1 1 1 1 1 SULFUR %m/m Max 3.53 .53 .5 4 5 5 5 5 5 5 5 5 5 5 5 VANADIUM mg/kg Max 150 150 300 3502 00 500 300 600 600 600 6006 00 600 6006 00 ALUMINIUM&SILICON mg/kgMax 80 80 80 80 80 80 80 80 80 80 80 80 80 80 80 TOTAL SEDIMENT POT %m/m Max

0.1 0.1

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Density

Grades RMA 10 to R MA 15 have a restricted dens ity so as to give acceptable ignition quality characteristic s w hen empirically dete rmined from either the Calculated Ca rbon Aromatici ty


Index (CCAI) or Calculated Ignition Index (CII). The density limit of 991 kg/m³ at 15°C is the technical limit for the efficient removal of water by a centrifuge set up as a purifier operating with a water seal. Three grades (RMK 35, 45, 55) have a density limit of 1010 kg/m³ which are suitable for vessels with fuel treatment plant capable of receiving such densities. T he tw o grades with no density limit (RML 45, 55) are intended f or machinery installations where the fuel treatment plant does not include centrifuges, namely a steam ship. Viscosity

The below table shows the approximate equivalent viscosities at 50°C to those shown in table 2. The data in the below table. cSt Kinematicviscosity@ 100°C Kinematicviscosity@ 50°C

10 50

15 100

25 225

35 390

45 585

55 810

Carbon residue

The carbon residue of a fuel depends on the refining processes used in the manufacture. Two grades have no def ined carbon residue or density limit (RML 45 and RML 55), a maximum of 22 per cent m / m applies to Rmh, RMK, 35, 45, and 55, while a limit of 18 per cent m / m applies t o RMG 25. The lower limits f or viscosity grades 10, 15 and 25 reflect the use of diluents to cut back heavy residual fuel to produce light intermediate fuel. Ash

In general there is a relationship between the specified ash level in a residual fuel and that for vanadium. T his is bec ause vanadium is the major ash forming component in residual fuel. Water

The specification limit for water in residual fuel is based on t raditional limits. Excessive water represents a loss of energy to the fuel purchaser, potential engine operational problems and possible waste disposable problems. Sulfur

Sulfur limits in residual fuel provides guidance to lubricant suppliers as to the level of alkalinity required to neutralize corrosive compounds srcinating from the combustion of sulfur. Vanadium

The level of vanadium in residual fuel depends on the source of crude oil and the refining process used in manufacture. On a global basis this varies c onsiderably, from 50-100mg / kg to over 500mg / kg, and the specification differentiates between low and high vanadium fuels, such as RME 25 and RMF 25. Catalyst F ines


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The purpose of a control for aluminium and silicon is to limit the amount of catalyst fines delivered with the fuel. Globally, the composition of catalyst fines varies considerably and can be c ontrolled using limits f or aluminium and silicon, c onsidered better t han the historical method of just controlling the level of aluminium. Sediment

Total Sediment Potential (TSP) provides a measure of the stability of a fuel. Following are the points to be looked at when using new bunker a. Start c onsuming the fuel only after t he fuel analysis report from a shore lab with recommendations is available b. Bunkers should be stored in the bunker tanks above the minimum transferable temperature mentioned by t he shore lab


c. A watch should be kept on the line filters/strainers soon after changing over. Clean

the filters and ensure no excessive debris d. Ensure that fuel oil transfer pump is in good operating condition e. Monitor the purifier / clarifier operation and make adjustments if problems arise like considering another gravity disc if the purifier starts overflowing f. Make adjustments like dec reasing purifier throughput, preheating tem peratures or operating the purifiers in parallel / series inline with the analysis report g. Frequently drain the settling and service tanks to asses the am ount of water in the fuel and take further steps in line with the findings like increasing / decreasing desludging intervals h. Monitor the line filters/strainers before pumps viz. purifier feed p/p, booster pump and circulating pump i. Adjust the back flushi ng interval of the automatic fuel oil filter based on the fi ndings j. Adjust t he visc otherm to att ain the rec ommended visc osity prior engine inlet (altered preheating temperature) k. Adjust VIT/FQ S if required l. Cylinder lubrication, sometimes the sc avenge air and JCFW out let temperatures may be required to be altered if the sulfur content warrants the changes m. Low load operation of the engine should be limited incase the fuel report shows high CCAI value n. Exhaust gas ec onomizer soot blowing & cleaning interval may have t o be reduced if the Conradsen number, CCAI, ash, water content is high. Boiler water circulating temperature should be monitored so as to ensure that economizer operates above pinch point o. Fuel injectors/exhaust valve overh aul intervals may also be altered basi ng on high ash, sodium/vanadium, Conradsen number, asphaltenes and CCAI values p. Soon after the engi ne is put t o consume new bunkers take the performance of t he engine with draw cards to ensure good health of the engine. Further changes in fuel injection settings may have to be effected if the indicator card diagrams show deviation 195.

How do you selec t a grav ity disc of a purifier?

Makers nomogram is an aid to select a tentative gravity disc in purification, when the density of the oil at a temperature of 15˚C is known. The hole diameter of the first gravity disc to be tried appears directly from the nomogram. However, in practical operation the best result is obtained by using the gravity disc with the largest hole diameter that will not cause a break of the liquid seal in the bowl or an emulsification in the water outlet. The presence of seawater may demand the use of a gravity disc with larger hole than indicated in the nomogram. (t he nomogram is based on t he properties of fresh water) The nomogram consists of two graphs arranged in series, one consists of density of fuel at 15˚C Vs Separating temperature and the other graph is divided into different zones of disc hole diameters against t hrough put of the purifier. 196. Explain running direction interlock Running direction interlock is provided to withhold the fuel supply during maneuvering if the running direction of the engine is not coincident with the setting of the engine telegraph lever. At the camshaft, forward end the shaft is coupled to the camshaft and carries round with it, due to the key, a flanged bush and spring plates which cause an adjustable friction pressure axially due to the springs and nut. This pressure acts on the coupling disc which


rotates through an angular travel until the stop pin prevents further rotation. This causes angular rotation of a fork lever and the re-positioning of a control valve plug in a new position within the sleeve. Oil pressure from the reversing valve can only pass to the valve http://class4exam.com/MEO_oral_question_answers.html

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block valve (air) and unlock the air start lever and the fuel control if the rotation of the direction interlock is correct. If the stop pin were to break, the fork lever would swing to position M and the fuel supply would be blocked. 197.

Explain capacity c ontrol in a refrigeration syste m

Automation provided to effect refrigerating compressor operation to meet to the varying refrigerating load is called capacity control in a refrigeration system. The nature of automation is dependant on the size, capacity of the refrigeration system. Capacity control in refrigeration can be achieved by any of the following methods a. On/off c ontrol: if the refrigeration load is absent, c apacity c ontrol may be effected by cutting out the compressor motor b. Variable motor speed: during reduced load, capacity c ontrol may be effect ed by reducing the t hroughput of the refrigerant by reduc ing compressor motor speed. c. Cylinder unloading: during reduced load condition in a multi cylinder unit compressor, c apacity c ontrol may be effec ted by suc cessively cutt ing in or out cylinders or c ylinder groups d. Hot gas bypass: involves passing a portion of the dischar ge gas from the compressor directly to the evaporator, bypassing the condenser e. Hot gas injection to evaporator f. Evaporator pressure control 198.

Explain unloader of a refrigerating compressor, reciprocating ty pe

Large reciprocating c ompressors are provided with an unloading syst em which enables the compressor to start easily with no vapor pressure load in the cylinder, permitting the use of electric motors with low starting torques. Unloading is effected by holding the suction valves open, or by opening a by pass valve between the discharge and suction sides during starting. T he unloading mechanism is ac tuated hydraulically, mechanically or by solenoid valve. 199.

What are the reasons for engine running on air but failing to run on fuel?

a. Fuel pump valves are leaking: valve cages leaking, dirt in fuel, governor gear jammed and holding valves off seats, faces require grinding b. Fuel system not properly primed: water in fuel, air left in system, leaky valves, priming connections left open c. Fuel oil supply restricted: suction strainers dirty, gravity tank empty, vacuum in gravity tank, valve in suction line not fully open d. Fuel injection pressure too low: spill valve jammed, priming valves left open e. Rotational speed on ai r too low: starting ai r pressure t oo low, starting ai r restricted, cylinder head valve leaking, tight bearings f. Compression pressure too low: piston rings leaking, indicator c ocks open, cylind er head valve leaking g. Timing of fuel pumps incorrect: f uel pump plungers not funct ioning properly(spring return type), incorrect spill valve timing h. Speed governor jammed: inertial weight jammed, trip pawl not engaging, connec ting mechanism not properly adjusted


200.

What are the lube oil properties of a diesel generator engine?

a. Dispersivity or capacity to the cold par ts of an engine clean b. Detergency or capac ity to keep hot parts of an engine clean c. Thermal strength or capacity to withstand temperature changes d. e. f. g.

Anti-oxidant or capacity to resi st the ac tion of oxygen Anti-wear or capacity to contain wear Anti-scuffing or capac ity to preserve oil film even in the presence of high p ressures Alkalinity reserve or c apacity t o neutralize acids formed during combustion or other sources thereby preventing corrosive wear h. Demulsibility or capacity to separate contam inants i. Resistance to hydr olysis or capaci ty to withstan d the action o f water wh ich can affect additives j. Pump ability k. Centrifugibility and filterab ility or c apacity t o separate insol uble elements l. Anti-rust, c orrosive and anti-foam are just some of the other pro perties required 201.

Explain a torsion meter on a main engine shafting. How is engine power calculated from the torsion meter?

Torsion meter is an instrument provided on t he engine shafting to measure the torque developed by the engine. Torsion meter uses the principle that when a torque is applied to a shaft an angular twist θ is produced which is dependant on the shaft material torsional rigidity. It is given by T/r = Gθ/L where r= radius of the shaft, G= torsional rigidity, L= reference length of the shaft. Where radius, length, and material of the shaft are constant, θ is directly proportional to the angular twist. http://class4exam.com/MEO_oral_question_answers.html

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A modern instrument is a contact less all electric instrument. It is as described below: It based on the magnetic stress sensitivity principle, some ferromagnetic materials reluctance is less along the plane of stress than across it. Magnetic fields are induced in a shaft; the distortion of these fields gives an indication of the torque being transmitted. It consists of three rings fitted on to the shaft each of which carries four electromagnetic poles. The centre ring acts as a transformer primary with two outer rings acting as secondary coils arranged at a phase of 45˚ to the primary but are in line with each other. Poles for inducing currents in the shaft coils are held in a stator frame so that there exists no contact between this stator and the shaft. A gap of about 3mm is usually maintained between this stator and the shaft. An alternating current is fed to the central ring (primary) generating a magnetic field. This causes an induced currents in the outer secondary coils, which are connected in series such that when there exists no twist (no torque condition, rpm=0) in the shaft, the induced currents oppose each other and neutralize. When torque is applied to the shaft stress lines are inclined to the axis. This distortion causes the induced current in the secondary coils to increase on one side and decrease on the other side. Thus a resulting induced voltage is developed in the secondary which is sensed by the secondary poles in the stator. The magnitude of this induced voltage is proportional to the torque applied.


The signal out put from the instrument is directly calibrated in terms of torque developed by the engine and read on the display. Nowfollowing as torque T is known, power developed by the engine can be calculated from the relation, Shaft Power, P = 2 π NT/60 where N= RPM, π= 22/7 (PI) 202.

Explain the procedure of setting a boiler safety v alve

The safety valve is the sole safety device, which relieves the boiler of a dangerous excess pressure. In t he majority of designs the oil fired boiler and the exhaust gas boiler have a common steam circuit, though separate heat input and flue gas paths. The oil fired section of the oil fired boiler has a fuel cut out which is operated by the steam pressure limiting device, whereas the exhaust gas boiler has to depend solely on its safety valve to protect it. In a composite boiler as mentioned above the pair of safety valves can serve to protect the common steam circuit. An additional pair of safety valves is provided in the outlet header of the exhaust gas boiler, which has to be set separately. The setting of the safety valve has to be done when the heat input and the rate of pressure rise is maximum. The setting of the exhaust gas boiler safety valve to comply with the above, shall be carried out as follows: While at sea, with the main engine running at normal service speed and when all systems are steady, the oil-fired section of the boiler can be fired to augment steam production (all precautions such as adequate water level in the boiler, operator standing by the burner quick shut off valve etc. are to be followed). With the safety valve on the steam receiver of the boiler lightly gagged. The safety valve of the exhaust gas boiler section is set at slightly higher flooded pressure.conditions In order to that ittheis economizer the exhaust gas boiler) under at ensure all times, customary (or to adjust the safety valvesoperates of the economizer to a slightly higher pressure than the safety valves of the boiler steam receiver of which t hey are connected. After setting the safety valve as above to satisfaction locking it to make it tamper proof, the oil-fired boiler firing is stopped, the steam receiver safety valves gags removed and all the easing gear properly connected. The exact lifting pressures are recorded in the logbook authenticated by the CEO and a copy of the above is to be forwarded to the classification society upon arrival next port. In the setting of the safety valve of a boiler, three items are of great importance. They are: 1. Setting pressure at which the valve should lift. 2. The ac cumulation of pressure, which will be above the former due to the valve spring characteristics 3. “Blow down” which is a drop in pressure below the sett ing pressure after the valve has lifted and reseated. 4. For example the following values are relevant: a. Boiler working pressure: 7 bar. b. Safety val ve settin g pressure: 9 bar. c. Accumulation of pressure: Maximum of 10% of the setting pressure = 9.9 bar. d. Blow down at 3% of lifting pressure.


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