From KAUSHAL KUMAR, 6280 For orals fn 4,6 AIR COMPRESSOR Bumping clearance- what is bumping clearance, why it is called so, would it increase with time or decrease (may increase or decrease),how to adjust in tandem type, why not adjusted by using metal shims in palm end connection, effects of increased clearance, what was the value of bumping clearance on your ship( 1% of cyl. Bore, 1.8 mm(CYL bore 180mm ) n 1.4 mm(cyl. Bore 140mm))? Does B/E bearing adjustment in a/c affect the bumping clearance? Bumping clearance as the name signifies is a clearance given so that the piston of the marine reciprocating compressor would not bump into its cylinder head How to Check Bumping Clearance 1. In case a suitable opening is available the piston can be barred to the top dead centre and then feeler gauges can be put inside and the clearances checked at two three points. 2. The more convenient method is to take lead wire from the engine store and make a small ball based on the expected clearance and put it between the piston and the head from the valve opening. Then the piston is slowly turned to the top dead centre with the help of a Tommy bar. After that the piston is again turned down and the lead wire ball is extracted and the thickness measured with the help of a micrometer. This measurement would give the bumping clearance. The caution which must be observed in these methods is that the clearances of the main and the crank pin bearing have not been taken into account. The correct method is thus that after turning the piston to top dead centre the piston connecting rod must be jacked up with the help of a crow bar. It is only after this hidden clearance has been accounted for, will the correct bumping clearance be found. How to Adjust the Bumping Clearance 3. The cylinder head gaskets can be changed to a different thickness thus altering the bumping clearance. 4. The shims between the foot of the connecting rod and the bottom end bearing can be changed thus changing the bumping clearance. However after adjusting the bumping clearance the clearance should be checked once again to make sure that there is no error and the clearance is within the range as specified by the manufacturers. Change in bumping clearanceWear at the crankpin bearing. The crankpin bearing wears down due to use and this clearance can travel right up to the piston and an unloaded piston can hit the cylinder head. This type of wear can be recognized when the compressor makes impact sounds running unloaded at the starting and stopping operations. This type of wear would also be accompanied by a slow decrease in oil pressure over a period of time. Opening up of cylinder heads. In certain types of reciprocating compressors the cylinder head have to be removed for the changing of the first stage suction and discharge valves. When the cylinder head is put back the correct thickness of the cylinder head gaskets should be used otherwise it would change the bumping clearance.
Wear on the main bearings. Over all wear on the main bearings would lower the crank shaft and would thus lower the piston and increase the bumping clearances. IMPORTANT….bump clearance or squish is most definitely done with the head gasket installed between head and cylinder. Use 2 pieces of lead. Put one piece of lead directly over each end of the wrist pin out near the edge of the piston but not under a valve. This will give you 2 measurements. 1. piston clearance or squish. 2. Piston/cylinder angle relative to crank. This angle is important as it shows the cylinders relationship to the crankshaft. If the pieces of lead are too different in thickness, the piston can run out of available ring compression and wrist pin end travel and contact the cylinder(scuff) at top and bottom. differential squish is how the Indians measure and determine the sum of machine errors and the need for half gaskets under the cylinder base on engines that have alignment issues. #4 lead shot is perfect for this measurement as it is a uniform size and crushes very consistently. A little dab of grease or drop of oil will hold them where you put them on top of the piston during the measurement.
Q. Relief v/v n fusible plug- setting (10% above stage pressure), Reason for lifting of relief v/v of LP stage and HP stage, where fitted? Why fusible plug is fitted, its material (tin, antimony, bismuth), what temp blows(121*C)?how to test relief v/v( by normal hydraulic p/p)?
Reasons of LP stage relief v/v lifting- HP stage suction v/v or discharge v/v leaking, 2nd stage suction n discharge v/v interchanged after over’hl. Reasons of HP stage relief v/v lifting- delivery v/v shut, setting error of pressure switch, delivery v/v which is SDNR type is fitted inverted. Lubrication- how it takes place in main/brg, crankpin bearing, upper n lower cyl. In case of tandem type, how piston gets cooled? Pressure value n alarm value(2-4 bar, alarm at 2 bar)? Reasons….pressure suddenly drops, pressure drops slowly (increase in clearance of main brg or crankpin brg), increased oil consumption? Why Breather is provided in lub. Oil filling line? Is crankcase pressurized during running condition? For main brg n crankpin brg. Lubrication normally thr is a shaft driven gear p/p. For lower cyl. In tandem type- it’s by splash. For upper cylinder in tandem type thr is a supply line from the gear p/p going to suction side of air which supplies small amount of oil mist with air n that mist lubricates the upper cyl. Sometimes the supply is from drilled hole in con. Rod like we have in A/E. Reasons oil pressure not rising- motor rotation direction reverse, oil line block due to rag, no oil in sump, filter clogged, worn metal so increase of clearance. Increased oil consumption- too much oil in sump( above level H), oil scraper ring wear out, worn piston and liner. Breather- it is used so that pressure or vacuum is not created inside crankcase. It has filter so moisture and dirt don’t go inside and also has metallic plate on the inner side which don’t allow lub. Oil to come out.
Cooling line- pressure( 0.2-2 bar), alarms(90*c), why bursting disc, its material( copper), action if it bursts during maneuvering, at what pressure it bursts, why we prefer bursting disc over relief valve( no chance of getting reset), purpose of intercooler n aftercooler, What if Main air compressor runs without cooling water(may cause explosion)? Auto drain trap working? ANS. If bursting disc bursts during maneuvering- Inform the bridge about the problem and to give lesser kicks,
Start the stand by compressor, Isolate the compressor whose bursting disc is damaged, Change the bursting disc, if available onboard, If Not available, then let the S.W go into the E/room bilges, otherwise Fresh water cooled, then join a flexible hose and put into the expansion tank.
Suction n delivery v/v- how u will come to know they r leaking( temp. increase of air, relief v/v lift), its affects, What would be the consequences of too high valve lift in an air compressor( chances of damage due to impact, decrease in vol. efficiency)? What would be the consequences of a high spring constant of spring plates in an air compressor(open late n sit with higher impact which may cause damage)? Can we interchange spring of suction n delivery v/v( no, delivery v/v spring stiffness is more)? parts of v/v(remember,the suction n delivery v/v for first stage r in single set but for 2nd stage they r different, the v/v parts for both suction n discharge of 2nd stage r same but arranged in opposite order)?
Starting- checks before manual starting, current value of air compressor?(Starting 310Amps,full load 30A) ANS. 1. Lubrication: check the oil level in the sump (b/w H n L)and in the lubricator tank. 2. Unloading: the valves in the unloading lines must be open. 3. Pressure gauge cocks: the cocks must be slightly open to avoid excessive pressure fluctuations which can damage the pressure gauges. 4. Air filter: check that the air intake filter is clean. 5. Cooling: check that the cooling water pressure is correct(0.2-2bar) and in the case of attached pumps a visual check of the pump and all the valves in the line must be open. 6. Relief valves: some relief valves have hand testing levers given for testing, the same can be done. 7. Air line piping: check that all the valves in the discharge piping are open and correctly lined up. 8. Final check: the compressor can be turned a few revolutions with a turning bar to check for the free movement. Why reciprocating type compressor(pr.ratio is higher )?why two stage, pv diag for you comp. clearance volume? each stage pressure(4-6 BAR, 25-30 BAR)? Can they vary from normal during starting? unloader ….purpose, design? What is volumetric efficiency, free air delivery? ANS. Free air delivery- volume of delivered air is measured at 1 atm and 15*C, it’s called free
air. If the valve has too much lift then the valve closes late and reduce volumetric efficiency and also its causes valve to close with greater impact and hence liable to break. Why 2 stage- first, bcoz we can’t give a pressure of 30 bars in single stage as the lub.oil will start burning.
T2/T1=(P2/P1)^n-1/n where n is around 1.35 for air Now for p2/p1=30/1 T2=450*C And at this temp. lub. Oil will start burning. Flash point for lub.oil is 200*C. so we keep the pressure ratio limited to 5:1. Secondly, we want to save work by moving towards isothermal line by providing intercooling b/w stages.
PURIFIER Why we need to heat oil, purifier formula, why we need disc stack, use of gravity disc, position of e-line? ANS. For ans see mcgeorge mar. aux. pg-58-62. Q. what to do if u want to change DO purifier for HFO purifier? ANS. adjust temp.(around 95*C),adjust feed rate(reduce), adjust desludge time(increase desludge time as DO don’t have so much of impurities).NOW FOR GRAVITY DISC,SINCE DENSITY IN DECREASING, so increase size of gravity disc. Q. Purifier ……Starting n disludging ? Small fire in purifier trays...wt's ur action?? pairing disc? (SEE MM,OM2) Back Pressure: The back pressure should be adjusted after the purifier is started. The back pressure varies as the temperature, density, viscosity of feed oil inlet varies. The back pressure ensures that the oil paring disc is immersed in the clean oil on the way of pumping to the clean oil tank. .
Throughput of oil feed: Throughput means the quantity of oil pumped into the purifier/hr. In order to optimize the purification, the throughput must be minimum. Pre-checks before starting a Purifier 1. If the Purifier is started after a overhaul, then check all fittings are fiited in right manner. The bowl frame hood locked with hinges. 2. Check the Oil level in the gear case. Ensure that it is exactly half in the sight glass. Also ensure the sight glass is in vertical position, as there is a common mistake of fixing it in horizontal position. 3. check the direction of rotation of the seperator, by just starting and stopping the purifier motor. 4. Check whether the brake is in released position. •
Starting the Purifier 1. Ensure the lines are set and respective valves are open. Usually the lines are set from settling tank to service tank. 2. Start the purifier feed pump with the 3-way re-circulation valve in a position leading to settling tank.
3. Open the steam to the heater slightly ensuring the drains are open so that the condensate drains. close the drains once steam appears. 4. Start the Purifier. 5. Check for vibrations, check the gear case for noise and abnormal heating. 6. Note the current (amps) during starting. It goes high during starting and then when the purifier bowl picks-up speed and when it reaches the rated speed, the current drawn drops to normal value. 7. Ensure the feed inlet temperature has reached optimum temperature for separation as stated in the Bunker delivery note and nomogram (can get the separation temperature and gravity disc size from the nomogram) 8. Now check whether the bowl has reached the rated speed by looking at the revolution counter. The revolution counter gives the scaled down speed of the bowl. The ratio for calculation can be obtained from the manual. 9. Now, after the bowl reaching the rated RPM, check for the current attaining its normal value. •
De-sludge Procedure 10. Open the bowl closing water/operating water, which closes the bowl. (Ensure sufficient water is present in the operating water tank) 11. Now after 10 seconds, open the sealing water to the bowl. 12. The sealing water should be kept open till the water comes out of the waste water outlet. 13. Once the water overflows through the waste water outlet, stop the sealing water. 14. Now open the bowl opening water. (This is done to ensure the bowl has closed properly). During de-sludge we can hear a characteristic sound at the opening of the bowl. 15. Repeat the steps 10, 11 ,12 & 13. 16. Open the 3-way re-circulation valve such that the dirty oil feed is fed into the purifier. 17. Wait for the back pressure to build up. 18. Check for overflowing of dirty-oil through waste water outlet & sludge port. 19. Now adjust the throughput to a value specified in the manual. Correspondingly adjust the back pressure, too. 20. Now the purifier is put into operation. Change over the clean-oil filling valve to service tank.
Q. purifier rpm not coming, reasons, Explain about purifier drive mechanism….how you will check that ?when you will change it(see MM p4-12,change spiral gear if wear down is more than 3mm,change friction block lining if wear is 3mm,change pulley if wear is 1mm,change brake lining if wear is 5 mm). When d motor attains full speed does d horizontal shaft rotates at d same speed of motor? Q. why frictional clutch in purifier?? ANS. 1.it gives less staring current for motor, also 2.worm and worm wheel arrangement will break due to high starting torque.
REFRIGIRATION SYSTEM TROUBLE HIGH CONDENSING PRESSURE .
POSSIBLE CAUSE
CORRECTIVE MEASURE
INLET WATER WARM.
INCREASE QUANTITY OF CONDENSING WATER.
AIR ON NON-CONDENSABLE GAS IN SYSTEM .
PURGE AIR FROM CONDENSER
INSUFFICIENT WATER FLOWING THROUGH CONDENSER.
INCREASE QUANTITY OF WATER.
CONDENSER TUBES CLOGGED OR SCALED.
CLEAN CONDENSER WATER TUBES.
TOO MUCH LIQUID IN RECEIVER,
DRAW OFF LIQUID INTO SERVICE CYLINDER.
CONDENSER TUBES SUBMERGED IN LIQUID REFRIGERANT.
LOW CONDENSING PRESSURE.
FROSTING OR SWEATING OF A LIQUID LINE .
HIGH SUCTION PRESSURE.
TOO MUCH WATER FLOWING THROUGH CONDENSER.
REDUCE QUANTITY OF WATER .
WATER TOO COLD.
REDUCE QUANTITY OF WATER .
LIQUID REFRIGERANT FLOODING BACK FROM EVAPORATOR.
CHANGE EXPANSION VALVE ADJUSTMENT, EXAMINE FASTENING OF THERMAL BULB.
LEAKY DISCHARGE VALVE.
REMOVE HEAD, EXAMINE VALVES. REPLACE ANY FOUND DEFECTIVE .
REFRIGERANT LINE RESTRICTION.
CHECK FOR PARTIALLY CLOSED STOP VALVE, OR STUCK SOLENOID VALVE .
SYSTEM LOW ON REFRIGERANT.
CHECK FOR LEAKS, ADD REFRIGERANT.
OVERFEEDING OF EXPANSION VALVE.
REGULATE EXPANSION VALVE, CHECK BULB ATTACHMENT.
LEAKY SUCTION VALVE.
REMOVE HEAD, EXAMINE VALVE AND REPLACE IF WORN.
RESTRICTED LIQUID LINE AND EXPANSION VALVE OR SUCTION SCREENS.
RUMP DOWN, REMOVE, EXAMINE AND CLEAN SCREENS,
INSUFFICIENT REFRIGERANT IN SYSTEM.
CHECK FOR REFRIGERANT STORAGE.
TOO MUCH OIL CIRCULATING IN SYSTEM.
CHECK FOR TOO MUCH OIL IN CIRCULATION. R EMOVE OIL .
IMPROPER ADJUSTMENT OF EXPANSION
ADJUST VALVE TO GIVE MORE FLOW.
COMPRESSOR CRANKCASE SWEATING
LOW SUCTION PRESSURE.
VALVES
EXPANSION VALVE POWER ELEMENT
REPLACE EXPANSION VALVE POWER
COMPRESSOR SHORT CYCLES ON LOWPRESSURE CONTROL .
DEAD OR WEAK
ELEMENT.
LOW REFRIGERANT CHARGE.
LOCATE AND REPAIR LEAKS. CHARGE REFRIGERANT.
THERMAL EXPANSION VALVE NOT FEEDING PROPERLY.
ADJUST, REPAIR OR REPLACE THERMAL EXPANSION VALVE .
a. DIRTY STRAINERS.
a. CLEAN STRAINERS.
b. MOISTURE FROZEN IN ORIFICE
b. REMOVE MOISTURE OR DIRT ( USE SYSTEM DEHYDRATOR).
OR ORIFICE PLUGGED WITH DIRT.
c. POWER ELEMENT DEAD OR WEAK
COMPRESSOR RUNS CONTINUOUSLY.
COMPRESSOR SHORT CYCLES ON HIGHPRESSURE CONTROL SWITCH.
COMPRESSOR WILL NOT RUN.
c. REPLACE POWER ELEMENT.
WATER FLOW THROUGH EVAPORATORS RESTRICTED OR STOPPED. EVAPORATOR COILS PLUGGED, DIRTY, OR CLOGGED WITH FROST.
REMOVE RESTRICTION. CHECK WATER FLOW. C LEAN COILS OR TUBES .
DEFECTIVE LOW-PRESSURE CONTROL SWITCH.
REPAIR OR REPLACE LOW-PRESSURE CONTROL SWITCH.
SHORTAGE OF REFRIGERANT.
REPAIR LEAK AND RECHARGE SYSTEM.
LEAKING DISCHARGE VALVES.
REPLACE DISCHARGE VALVES.
INSUFFICIENT WATER FLOWING THROUGH CONDENSER, CLOGGED CONDENSER.
DETERMINE IF WATER HAS BEEN TURNED OFF. C HECK FOR SCALED OR FOULED CONDENSER.
DEFECTIVE HIGH-PRESSURE CONTROL SWITCH.
REPAIR OR REPLACE HIGH-PRESSURE CONTROL SWITCH.
SEIZED COMPRESSOR.
REPAIR OR REPLACE COMPRESSOR.
CUT-IN POINT OF LOW-PRESSURE CONTROL SWITCH TOO HIGH.
SET L. P. CONTROL SWITCH TO CUT-IN AT CORRECT PRESSURE .
HIGH-PRESSURE CONTROL SWITCH DOES NOT CUT-IN.
CHECK DISCHARGE PRESSURE AND RESET P. H. CONTROL SWITCH.
1 .DEFECTIVE SWITCH.
1. REPAIR OR REPLACE SWITCH.
2. ELECTRIC POWER CUT OFF.
2. CHECK POWER SUPPLY.
3. SERVICE OR DISCONNECT SWITCH OPEN.
3.CLOSE SWITCHES.
4. FUSES BLOWN. 5. OVER-LOAD RELAYS TRIPPED.
5. RE-SET RELAYS AND FIND CAUSE OF OVERLOAD.
6. LOW VOLTAGE.
6. CHECK VOLTAGE (SHOULD BE WITHIN 10 PERCENT OF NAMEPLATE RATING ).
4. TEST FUSES AND RENEW IF NECESSARY.
7. REPAIR OR REPLACE MOTOR. 7. ELECTRICAL MOTOR IN TROUBLE. 8. TROUBLE IN STARTING SWITCH OR
8. CLOSE SWITCH MANUALLY TO TEST POWER SUPPLY. I F OK, CHECK CONTROL
CONTROL CIRCUIT.
9. COMPRESSOR MOTOR STOPPED BY OIL PRESSURE DIFFERENTIAL SWITCH.
CIRCUIT INCLUDING TEMPERATURE AND PRESSURE CONTROLS.
9. CHECK OIL LEVEL IN CRANKCASE. CHECK OIL PUMP PRESSURE .
DECREASED CAPACITY OF THE COMPRESSOR.
HIGH VAPOR SUPERHEAT.
ADJUST OR REPLACE EXPANSION VALVE.
SUDDEN LOSS OF OIL FROM CRANKCASE.
LIQUID REFRIGERANT SLUGGING BACK TO COMPRESSOR CRANK CASE .
ADJUST OR REPLACE EXPANSION VALVE.
CAPACITY REDUCTION SYSTEM FALLS TO UNLOAD CYLINDERS.
HAND OPERATING STEM OF CAPACITY CONTROL VALVE NOT TURNED TO AUTOMATIC POSITION.
SET HAND OPERATING STEM TO AUTOMATIC POSITION.
COMPRESSOR CONTINUES TO OPERATE AT FULL OR PARTIAL LOAD.
PRESSURE REGULATING VALVE NOT OPENING .
ADJUST OR REPAIR PRESSURE REGULATING VALVE .
CAPACITY REDUCTION SYSTEM FAILS TO LOAD CYLINDERS.
BROKEN OR LEAKING OIL TUBE BETWEEN PUMP AND POWER ELEMENT.
REPAIR LEAK.
LOW DISCHARGE PRESSURE WITH HIGH SUCTION PRESSURE .
DISCHARGE RELIEF VALVE LEAKING BACK TO THE SUCTION SIDE .
REPLACE RELIEF VALVE.
COMPRESSOR CONTINUES TO OPERATE UNLOADED.
PRESSURE REGULATING VALVE NOT CLOSING .
ADJUST OR REPAIR PRESSURE REGULATING VALVE .
COMPRESSOR OIL BROWNISH IN COLOR
COPPER PLATING CAUSED BY MOISTURE IN THE SYSTEM .
CHANGE FILTER DRIER, OR DEHYDRATOR.
COMPRESSOR OIL GRAY OR METALLIC.
COMPRESSOR BEARING WEAR OR PISTON SCORING .
REPLACE OR OVERHAUL COMPRESSOR.
COMPRESSOR OIL BLACK
CARBONIZATION RESULTING FROM AIR IN THE SYSTEM .
REMOVE AIR FROM SYSTEM.
REFRIGERATION SYSTEM WORKS ON FIRST LAW OF THERMODYNAMICS, REVERSE CARNOT CYCLE . COP= Q/ W
1 TON REFRIGERATION CAPACITY= RATE OF HEAT TRANSFER IN FORMING I TON OF ICE AT 0*C FROM WATER AT 0*C. ADVANTAGE OF UNDERCOOLING = INCREASE REFRIGERATION EFFECT BY REDUCING AMOUNT OF FLASH OFF AT EXP. V/ V. ST
NAMING OF REFRIGERENT- 1 DIGIT FROM LEFT IS ONE LESS THEN NUMBER OF C ATOMS.
2ND IS ONE MORE THEN H ATOM THIRD IS NUMBER OF F ATOMS.
Q.PURPOSE F BACK PRESSURE V/V IN REFER OF REFRIGRENT JUST AFTER EAVPORATER. HOW DIFFERENT ROOM TEMP R MAINTAINED IN REFRERATION SYSTEM ? ANS. BACK PRESSURE V/V- TO KEEP DIFFERENT TEMP OF DIFFERENT ROOMS. WE USE IT IN VEG. ROOM. WE SET BACK PRESSURE, SO IT INCREASE THE BACK PRESSURE IN VEG ROOM LINE. AND SO THE SATURATION TEMP. INCREASE . SITUATED AT VEG ROOM DICHARGE . back pressure valve is fitted at the outlet of veg room. the reason being that the veg room is maintained at a temperature of +4 -5 degress while fish room is at about -12 to -15 degrees and the flow and amount of refrigerant at fish room and meat room is greater as compared to that of veg room. hence if back pressure valve is not fitted then when refrigerants will come at the outlet of all the three rooms then the refrigerant will tend to flow towards veg room. hence to avoid it a back pressure valve is fitted which will allow refrigerant to flow out only if the pressure inside the veg room outlet will be greater than the outlet from the main line. Q: WHAT IS THE DIFFERENCE BETWEEN THE "AUTOMATIC EXPANSION VALVE" AND THE " THERMOSTATIC EXPANSION VALVE"? THE AUTOMATIC EXPANSION VALVE WAS THE FIRST VALVE DEVELOPED TO PREVENT MANUAL ADJUSTMENT OF THE FLUID METER, THEN USED AS EXPANSION VALVE . T HE VALVE IS DESIGNED TO KEEP CONSTANT PRESSURE IN THE EXPANSION VALVE OUTLET. ON KEEPING CONSTANT PRESSURE , IT ALSO INDIRECTLY CONTROLS THE TEMPERATURE , HOWEVER, IT DOES NOT ASSURE OVERHEATING, WHICH WILL PROTECT THE COMPRESSOR.A S THE EVAPORATOR CAPACITY IS REDUCED, THERE IS LESS FLUID EVAPORATION, ON THE OTHER HAND, BECAUSE THE VALVE MAINTAINS THE PRESSURE, IT ALSO MAINTAINS THE VALUE OF THIS FLOW. ON DOING SO , HOWEVER, EXCESS REFRIGERANT STILL IN LIQUID STATE IS FED INTO THE EVAPORATOR, WHICH RESULTS IN ITS RETURN TO THE COMPRESSOR, WITH HUGE MECHANICAL LOSS. A LTERNATIVELY, IF THERE IS INCREASE IN LOAD, THERE WILL BE GREATER FLUID VAPORIZATION AND IF THE VALVE MAINTAINS THE FLOW, IT WILL INCREASE OVERHEATING OF THE GAS AND LITTLE USE OF THE HEAT EXCHANGE SURFACE . UNFORTUNATELY, THIS RESULTS IN OPERATION OF THE EVAPORATOR CONTRARY TO THE PRODUCTION OF COLD, WHEN ITS LOAD IS HIGHER.T HESE COUNTERPARTS RESULTED IN REPLACEMENT OF THE AUTOMATIC EXPANSION VALVE BY THE T HERMOSTATIC EXPANSION VALVE IN MOST APPLICATIONS. T HE T HERMOSTATIC EXPANSION V ALVE CORRESPONDS TO THE OVERHEATING AT THE EVAPORATOR OUTLET AND, AS A RESULT, THIS RESPONDS BETTER TO THE ACTUAL LOAD, RESULTING IN A MORE EFFICIENT SYSTEM . Q.REFER COMPRESSOR CHARGING LIQUID AND GAS ? WHERE U CONNECT THE CHARGING CONNECTION? WHY WE TAKE PURGE AIR IN A SEALED CONTAINER? N HOW U WL COME TO KNOW DAT SYSTEM IS ENOUGH CHARGED WITHOUT WEIGHING BOTTLE ( SEE IN GAUGE GLASS)... ANS. LIQUID CHARGE- CONNECTION IS B/W CONDENSER AND DRIER. BEFORE DRIER BCOZ MOISTURE MAY ENTER DURING CHARGING, SO IT WILL BE ABSORBED . AFTER CONDENSER BCOZ BEFORE CONDENSER ALL IS GAS. FOR CHARGING CONNECT CYL . T O A BOTTLE , PURGE , THEN CONNECT TO CHARGING POINT. WG AS CHARGING - CONNECTION IS IN SUCTION SIDE , JUST LITTLE BEFORE SUCTION LINE .
REMEMBER, REFRIGERANT COMES TO CRANKCASE FIRST THEN IT GOES TO SUCTION SIDE OF 1ST CYL. CHARGING CYL. HAS 2 V/V- ONE RED IS CONNECTED TO DIP TUBE AND IS FOR LIQUID CHARGING. AND A BLUE V/V IS FROM TOP AND DON’ T HAVE DIP TUBE AND IT IS FOR GAS CHARING. IN BOTH CONDITION CYL . WE KEEP CYL. UPRIGHT. IF ONLY ONE V/V THEN WE NORMALLY WE DON’T HAVE DIP TUBE AND IN THIS WHEN LIQUID THEN TURN DOWN BY HEAD.
GAS CHARGING OF REFRIGERATION PLANT : FOR GAS CHARGING, A SPECIAL T PIECE VALVE BLOCK WITH MOUNTED PRESSURE GAUGE IS PROVIDED TO COMBINE THREE CONNECTORS INTER-CONNECTING: FOLLOWING STEPS ARE TO BE TAKEN FOR CHARGING GAS INTO THE REEFER PLANT: 1. CONNECT GAS BOTTLE OR CHARGING CYLINDER, VACUUM PUMP AND CHARGING POINT IN THE REEFER SYSTEM TO THE VALVE BLOCK.
2. THE DISCHARGE OF THE VACUUM PUMP IS TO BE CONNECTED IN THE EMPTY RECOVERY BOTTLE 3. FIRST OPEN THE VALVE BETWEEN VACUUM PUMP AND CHARGING BOTTLE LOCATED IN THE VALVE BLOCK WITHOUT OPENING THE MAIN VALVE OF THE CHARGING CYLINDER. T HIS WILL REMOVE ALL THE AIR INSIDE THE PIPE . ONCE VACUUM IS REACHED, CLOSE THE VALVE OF CHARGE CYLINDER IN THE VALVE BLOCK 4. NOW OPEN THE VALVE OF THE CHARGING POINT PIPE IN THE VALVE BLOCK AND RUN THE VACUUM PUMP UNTIL THE VACUUM IS REACHED. T HIS WILL REMOVE THE TRAPPED AIR FROM THIS PIPE . T HEN SHUT THE VALVE IN THE VALVE BLOCK 5. NOW KEEP THE SYSTEM IDLE FOR 5 MINUTES TO CHECK THERE IS NO PRESSURE DROP. T HIS WILL ENSURE THERE ARE NO LEAKAGES IN THE SYSTEM 6. NOW OPEN CHARGING BOTTLE PIPE VALVE AND THE CHARGING POINT PIPE VALVE LOCATED IN THE VALVE BLOCK. T HIS WILL SET THE LINE FOR CHARGING. E NSURE THAT THE VACUUM PUMP VALVE IS SHUT 7. NOW OPEN THE MAIN VALVES IN THE CHARGING CYLINDER AND CHARGING POINT OF THE REEFER SYSTEM 8. DO NOT OVERFILL THE SYSTEM. MAKE SURE THE RECEIVER HAS 5 % SPACE FOR EXPANSION ENSURE THAT NO REFRIGERANT IS LEAKED OUT IN THE ENVIRONMENT AS THESE EFFECTS THE OZONE LAYER IN THE ATMOSPHERE .
Q.AIR,MOISTURE,OIL,OVERCHARGING,UNDERCHARGING?INDICATION,HARMS,ACTIONS? OIL IN THE REFRIGERATION SYSTEM
INDICATION: • • • • •
TEMPERATURE IS NOT DROPPING IN THE COLD ROOMS AS NORMAL, DUE TO FACT THAT OIL ACT AS INSULATION IN THE EVAPORATOR. IT MAY CAUSE EXCESSIVE FROST ON THE SUCTION LINE. REFRIGERANT COMPRESSOR RUNS FOR THE EXTENDED PERIOD OF TIME. LUBRICATING OIL LEVEL IN THE COMPRESSOR WILL DROP. REFRIGERANT LEVEL WILL FALL IF OIL HAS CAUSED BLOCKAGE.
CAUSES: • • • •
THIS MAY HAPPEN IF THE OIL SEPARATOR IS NOT WORKING PROPERLY. OIL MAY CARRY OVER FROM THE COMPRESSOR AND MAY NOT COME BACK TO THE COMPRESSOR DUE TO BLOCKAGE IN THE SYSTEM . DEFECTIVE PISTON RINGS OR WORN OUT LINER OF THE COMPRESSOR MAY CAUSE THE OIL TO CARRY OVER ALONG WITH THE REFRIGERANT. COMPRESSOR MAY TAKE HIGH CAPACITY CURRENT DURING STARTING.
ACTION : • • • • •
CHECK THE OIL SEPARATOR FOR PROPER FUNCTIONING. CHECK THE DRIER FOR PROPER CLEANING AND IF ITS REQUIRE CLEANING CLEAN IT EVAPORATOR COIL SHOULD BE DRAINED TO REMOVE ANY TRACE OF OIL. IF THERE IS OIL IN THE COOLING COILS, INCREASE THE CONDENSER AND EVAPORATOR TEMPERATURE DIFFERENTIALS AND REMOVE EXCESS FROST ON THE SUCTION PIPE . HEAT PIPES WITH BLOW TORCH.
AIR IN THE SYSTEM
INDICATION: •
THIS MAY CAUSE THE REFRIGERATION COMPRESSOR TO OVERHEAT, WITH A HIGH DISCHARGE PRESSURE AND NORMAL CONDENSING TEMPERATURE .
• • • •
THERE ARE POSSIBILITIES OF SMALL AIR BUBBLES IN THE LIQUID SIGHT GLASS OF THE CONDENSER. CONDENSING PRESSURE OF THE REFRIGERANT IN THE CONDENSER MAY BE HIGH. IF THERE IS EXCESSIVE AIR, IT MAY REDUCE THE COOLING CAPACITY OF THE SYSTEM, MAKING THE COMPRESSOR TO RUN FOR THE EXTENDED PERIOD OF TIME . IT MAY CAUSE THE GAUGE POINTER OF THE CONDENSER TO JUMP INDEFINITELY.
CAUSES: • •
DURING CHARGING, AIR MAY ENTER IN TO THE SYSTEM. IF FREON-12 IS USED AIR MAY LEAKS IN TO THE SUCTION LINE BECAUSE THE WORKING PRESSURE OF THE FREON-12 REFRIGERANT IS LESS THAN THE ATMOSPHERIC PRESSURE.
ACTION : •
• • •
•
AIR IN THE SYSTEM CAN BE REMOVED BY COLLECTING THE SYSTEM GAS IN THE CONDENSER, LEAVING THE CONDENSER COOLING WATER ON AND VENTING OUT THE AIR FROM THE TOP OF THE CONDENSER BECAUSE AIR WILL NOT BE CONDENSED IN THE CONDENSER BUT REMAINS ON TOP OF THE CONDENSER ABOVE THE LIQUID REFRIGERANT. CONNECT THE COLLECTING CYLINDER TO THE PURGING LINE OF THE CONDENSER, OPEN THE VALVE, AND COLLECT AIR IN THE CYLINDER. AFTER PURGING THE AIR FROM THE SYSTEM DON’T FORGET TO SHUT THE PURGING VALVE. PUMPING DOWN, CLOSE CONDENSER INLET VALVE , COOLING WATER AT FULL FLOW, WHEN CW INLET AND OUTLET TEMP BECOME EQUAL , SEE WHAT IS THE CONDENSING PRESSURE AND FROM COMPRESSOR SUCTION GAUGE FIND OUT SATURATION TEMP AT THAT CORRESPONDING CONDENSING PRESSURE , IF IT IS EQUAL TO CW TEMP THEN IT MEANS AIR HAS BEEN REMOVED. R ESTART THE COMPRESSOR WITH ALL SAFETY PRECAUTIONS.
UNDERCHARGING OF REFRIGERATION SYSTEM
INDICATION: • • • • • • •
COMPRESSOR IS RUNNING HOT AND PERFORMANCE OF THE COMPRESSOR FALLS OFF DUE TO HIGH SUPERHEAT TEMPERATURE AT THE SUCTION SIDE OF COMPRESSOR. SUCTION AND DISCHARGE PRESSURE OF THE COMPRESSOR IS LOW. LARGE VAPOR BUBBLES IN THE LIQUID SIGHT GLASS. LOW GAUGE READINGS IN THE CONDENSER. AMMETER READING FOR THE COMPRESSOR MOTOR IS LOWER THAN NORMAL. RISE IN ROOM TEMPERATURE WHICH IS TO BE COOLED. COMPRESSOR IS RUNNING FOR EXTENDED PERIOD OF TIME.
CAUSES: • • •
LEAKAGE OF REFRIGERANT AT THE SHAFT SEAL, FLANGE COUPLINGS, VALVE GLAND ETC. EXPANSION VALVE MAY BE BLOCKED AT THE STRAINER. PARTIAL BLOCKAGE OF REFRIGERANT AT THE FILTER OR DRIER OR EVAPORATOR MAY CAUSE UNDERCHARGING.
ACTION : • • • •
IDENTIFY AND RECTIFY THE LEAKAGE OF REFRIGERANT FROM THE SYSTEM. CLEAN THE FILTER AND DRIER. CHARGE THE SYSTEM WITH FRESH REFRIGERANT AS REQUIRED.
OVERCHARGE OF REFRIGERATION SYSTEM
INDICATION: • • •
THE LIQUID LEVEL IN THE CONDENSER IS TOO HIGH (HIGH CONDENSER GAUGE READING). THIS WILL REDUCE THE AVAILABLE CONDENSING SURFACE , WITH CORRESPONDING INCREASE IN THE SATURATION TEMPERATURE AND PRESSURE . HIGH PRESSURE SWITCH OF THE REFRIGERANT COMPRESSOR ACTIVATES AND STOPS THE COMPRESSOR. THE SUCTION AND THE DISCHARGE PRESSURES ARE HIGH.
CAUSES: • • •
IT MAY BE DUE TO THE REASON THAT EXCESSIVE REFRIGERANT HAS BEEN CHARGED IN THE SYSTEM. AIR IN THE SYSTEM MAY ALSO CAUSE OVER CHARGING INDICATION. IT MAY ALSO BE DUE TO THE FORMATION OFFICE ON THE REGULATOR.
ACTION :
• • • •
REMOVE THE REFRIGERANT FROM THE SYSTEM. THIS IS DONE BY CONNECTING A CYLINDER TO THE LIQUID LINE CHARGING VALVE, STARTING THE COMPRESSOR, AND THEN OPERATING THE CHARGING VALVE . PURGE THE AIR FROM THE SYSTEM AND MAINTAIN EFFECTIVE COOLING. REMOVE ICE FROM THE REGULATOR BY USING ANY OF THE DEFROSTING METHODS.
MOISTURE IN THE SYSTEM
THIS NORMALLY COMES WITH THE INGRESS OF AIR IN THE SYSTEM. MOISTURE MAY FREEZE AT THE EXPANSION VALVE , GIVING SOME OF THE INDICATION OF UNDER CHARGING . IT WILL CONTRIBUTE TO THE CORROSION IN THE SYSTEM . IT MAY CAUSE LUBRICATION PROBLEMS AND BREAKDOWN OF THE LUBRICATING OIL IN THE REFRIGERANT COMPRESSOR. ACTION : • •
RENEW SILICA GEL IN CASE OF MINOR MOISTURE. COLLECT REFRIGENANT AND REMOVE ALL AIR AND MOISTURE BY VACUUM PUMP IF THE AMOUNT IS HUGE .
69. recharging LO in refrigerant compressor. - Collect the refrigerant into the condenser by shutting off the condenser outlet valve. - Stop the compressor and shut off the inlet and outlet valves of compressor. - Open the oil filling plug and start filling the oil slowly. - Start the compressor momentarily(0.5- 0.6 seconds) to facilitate speedy charging. - After charging to the correct level, tightened up the oil plug. - Bleed off air in the compressor casing by slightly opening the suction valve and loosening connecting caps from the high pressure gauge (In case connection fittings for vacuum pump are provided, use the vacuum pump to extract the air from the compressor crankcase). Extracting Oil - i. Pump down the refrigerant into the compressor only. Ensure that refrigerant - pressure is higher than the atmosphere. - ii. Loosen the oil drain plug in the compressor crankcase and extract the amount oil. Precautions: - 1.) Care to be taken when charging oil so that no air will be trapped in the - compressor crankcase. - 2.) Ensure to bleed off air every after charging and extracting refrigeration oil.
Q. bulb in thermostatic exp v/v has come off...what will be the effect??reasons 4 icing on expansion v/v? Q.what is short cycling OF REFRIGIRATION, reasons and what u will do?
Refrigration system LO
properties. recharging LO in refrigerant compressor? 2.what is the function of condenser..what is sub cooling..?what will u check to insure that condenser is working properly...what will happen if temp diff between inlet and outlet of cooling sea water is increasing(cooling water flow is less or chocked) or decreasing(scaling,) and how will u make sure that it is being restored?
Changing of filter drier of ref.
comp? ANS. For changing filter drier. We can do this when plant is running. Open bypass v/v. close inlet outlet of drier. Change drier. open inlet outlet n close bypass. Q. Tev equalising connection. Why? ANS. We use where evaporator is large. So we have different pressure at inlet and outlet. Act as second line of defense. That is if bulb comes out then.
Q. Did refrgrt’n compressor have relief door?(NO) Why not?(crankcase doesn’t have o2,so chances of fire is very less.temp. so less bcoz of cool refrigerant .and. also vol. of crankcase is less so no need as per regulation) Q. refrigeration oil separator working, type complete...why required? ANS. Impingement type- fitted in discharge line. Its a closed container fitted with a series of baffle. As vapour enters the oil separator, there is reduction in velocity due to larger area of separator. Since oil particles have greater momentum, they impinge on the baffles. And later gets drained to crankcase through a float valve. 3. What is suc. Press. of refer and AC plant....is thr any diff ..if yes y? AIR. CONDITIONING WHAT IS SPECIFIC HUMIDITY, RELATIVE HUMIDITY, SENSIBLE HEAT, WET BULB TEMP, PSYCHOMETRIC CHART, HOW TEMP. IS CONTROLLED IN AIR CON. SYSTEM, LIGIONILA BACTERIA,
MAIN ENGINE AND AUX. ENGINE FULL FORM Q. Make and type of a/e and m/e with meanings. Alarms,interlocks, trips on that. ANS. M/E-MAN B&W 6S46MC-C MAN-MASCHINEN FABRIK AUGSBERG NURMBERG (DENMARK), BURMEISTER AND WEIN (GERMANY) 6-NO. OF CYLINDERS , S-SUPERLONG STROKE,APRROX. S/B RATIO-3.8 AND ABOVE(OTHER IS L,LONG STROKE-3.2 AND SHORT STROKE ,K,S/B RATIO-UPTO 2.8) 46-CYLINDER BORE IN cm , M-ENGINE PROGRAMME C-CAMSHAFT CONTROLLED(OTHER USED IS E-ELECTRONICALLY CONTROLLED) C-COMPACT, In 1996 and onward the MC-C versions of the small and medium bore engines were added to the programme. In this case the -C stands for "compact", as the engines were intended to be lighter, cheaper and yet more powerful. They feature an integrated camshaft housing, simplified cross-head and a variety of other smaller changes to facilitate the "compact" concept. In exchange the fuel injection system was simplified and the VIT system was made an option. The small and medium bore MC-C engines are thus best suited to vessels operating for prolonged periods at the power at which the engines are optimised. AUXILLARY ENGINE - 5H 21/32 5-NO. OF CYLINDERS, H-HYUNDAI’s HIMSEN(HIMSEN STANDS FOR-Hitouch and Hitech Medium 21-CYLINDER BORE IN cm , 32-PISTON STROKE IN cm
Speed Engine)
MAIN ENGINE AND A/E STARTING AIR SYSTEM How starting air system works, interlocks, function of …..air distributer(to select timing n sequence), master starting v/v, safeties provided, why bursting disc or flame arrestor….their working, regulation (for cyl. Bore 230 mm or more+reversing then on all cyl.)and construction, what action if…..bursting disc bursts during maneuvering, starting air v/v gets stuck, how you will come to know, what extra precaution if m/e running with one starting v/v isolated, why negative cam for air distributor, crash maneuvering how, how starting and reversing takes place in MAN B&W n sulzer, regulations regarding reversing capacity of engine, why air bottle v/v is slow opening type, regulations regarding size of air bottle, material of….. air bottle(seamless low carbon manganese steel), starting air line, starting air v/v(cast steel body, stainless steel v/v n spindle), why overlap is necessary, timing dig. For uniflow, loop, and 4-st naturally n supercharged engines, how starting air is introduced in ME type engine(starting v/v is solenoid controlled,no air distributer), is thr a drain line in starting air line (yes, at lowest point in the pipe), starting difficulties,what starting arrangement on A/E, why not air kick started, ANS. In cases where the starting air supply has to be cut off to some cylinders, starting in all crankshaft positions cannot always be expected. If the engine does not turn on starting air in a certain crankshaft position, it must immediately be started for a short period in the opposite direction, after which reversal is to be made to the required direction of rotation. Should this not give the desired result, it will be necessary to turn the engine to a better starting position, by means of the turning gear. Remember to cut off the starting air before turning, and to open the indicator cocks. For checking- close master v/v, engage turning gear, open indicator cock, bring that piston to tdc, open master v/v, if air coming from indicator cock that means leaking.When an engine is in operation leakage of starting air valves is shown by overheating of the branch pipe connecting the starting air valve to the starting air rail. The heating occurs due to the leakage of hot gases from the engine cylinder into the starting air line connected to the starting air rail. During periods of manoeuvring the temperature of each supply pipe from the air rail to the starting air valve should be checked by feeling the pipe as close to the valve as possible. WHAT SHOULD I DO IF AN AIR START VALVE JAMS OPEN WHILST MANOEUVRING? The fuel pump should be lifted (fuel rack zeroed, puncture valve operated or whatever) on the affected unit and the bridge informed. The load should be kept at a minimum, as one unit is now out of operation. As soon as safe to do so, the engine should be stopped and the air start valve replaced.
ANS. BODY REQUIREMENTS FOR A REVERSIBLE ENGINE The main propulsion machinery is to be capable of maintaining in free route astern at least70% of the ahead MCR revolutions for a period of at least 30 minutes. The reversing characteristics of the propulsion plant are to be recorded during trails. The power developed in astern direction should be 60 %of ahead. SOLAS Requirements: Chapter Two (Reg. 28 & 03) 1. Sufficient power for going astern shall be provided to enable proper control of the ship in all circumstances. 2. Machinery should be able to reverse the direction of thrust of the propeller to bring the ship to rest from maximum ahead service speed in sufficient time and reasonable distance. This shall be shown and recorded.
11. Crash-Stop (FPP-Plants and Reversible CPP-Plants) The procedure is valid for: ! Control Room Control. See Items 8.2, 9.2 and 10.2. ! Control from Engine Side. See Items 8.4, 9.2 and 10.4. Regarding crash-stop during Bridge Control,see the special instruction book for the Bridge Control System. 1. Acknowledge the telegraph. 2. Give the engine a STOP order. The engine will continue to rotate (at slowly decreasing speed), because the velocity of the ship through the water will drive the propeller, and thereby turn the engine. 3. Check that the limiters in the governor are not cancelled. 4. When the engine speed has fallen to the REVERSING-LEVEL (15-30% of MCR-speed, depending on engine size and type of ship, see Plate 70305): ! Give REVERSING order. ! Give START order. 5. When the START-LEVEL is reached in the opposite direction of rotation (8-12% of MCR-speed) ! Give order to run on fuel.
CRANKCASE EXPLOSION, SCAVENGE FIRE, EGB FIRE CRANKCASE EXPLOSION -Safeties provided in crankcase, regulations, at what pressure crankcase door lifts, how many doors, total area of escape in relief door, how do u test the v/v, OMD alarm , what will u do ? How to check it’s false alarm, What are different types of oil mist detectors and where are they used and why? How oil mist formed in crankcase and what safeties provided and maintenance on them? Do all crankcase doors in A/E have relief v/v? What to conclude if fitted in alternative doors or only in fwd n aft? Why no crankcase relief v/v in air compressor and reefer compressor.
SCAVENGE FIRE -reasons(give at least 6), indications, action to be taken when passage through a narrow seaway, what if major fire takes place, what extinguishing arrangements is there, how to use that? WHAT PRECAUTIONS WHEN ENGINE IS RUNNING on less number of units?
ANS. MANUAL 704. Cyl. Oil properties( oilyness is imp.)? After how many cycle alfa lubricator injects fuel?( every 4th cycle) Why exhaust gas temp. is less at exhaust v/v(320*c) but more at entry to turbine(380*c)??pressure of exhaust gas after turbocharger(0.3 bar). Ans. Its bcoz of intermolecular collision. Also at nozzle the pressure decreses which increases the velocity. Now PV=NRT. As p decreses, t decreses. Can you change the fuel injection timing or stop the fuel flow in one of the 3 injectors in a single unit in RT-flex. Yes, we can stop the fuel through any one injectors at a time. WECS can give signal to any one of the rail valve separately and hence the particular injection control valve will operate and the particular fuel injector will inject the fuel. This improves the injection pressure at low rpm and loads and hence improve combustion.
Main brg, x-head brg seizure…action? How to know that there's an instrumental error from the crankweb deflection readings or we have not taken reading correctly?
to know dat error... We add p+s reading nd f+a reading..nd diff shuldn't vary much...if it vry much den may be dere s problem in gauge... or we have not taken reading correctly, also the reading on both sides around bdc shud come zero.
6. How to cut off a fuel pump? Why not cut off by closing fuel inlet valve to that cylinder? ANS. MANUAL 704 AND VOL 2,909-16. Q. water cooled piston vs. oil cooled piston adv & disadv. & why oil cooled piston were not used earlier if they r have so many advantages? Bore cooling? advan.? ANS. Water- advan- specific heat more than oil so less amount of water is needed, easily available n cheap, we can keep water temp. as high as 90*C so temp. diff is low whereas in case of oil upper temp. Limit is 65*C to prevent oxidation. Disadvan- chances of mixing with crankcase oil, need separate system with p/p etc. Bore cooling-advan- max. temp at piston surface can be reduced to 400*C from 500*C as in case of cage type cooling, problems with castings of internal ribs r not thr.in bore system cooling takes place by jet n shaker effect.
Q. A/E cyl. head has been removed. What all checks to be carried out? what on piston? ANS. Cracks, distortion, corrosion, cooling water side corrosion n scale etc. Q.after taking liner calibration f-a readings are more and p-s readings are less.... What is this phenomenon... And y does it happen? ANS. Trim is more, ship is moving too much in ballast condition.
Q. How to take cylinder liner calibration for M/E n A/E(both have same method)?consquences of operating with worn liner? how to calibrate template?max. wear(0.7% of cyl. bore).honing(gulia244)?running in(done for matching to reduce adhesive wear)(r.sen41)?liner material(gulia p249), antipolising ring(material is steel, r.sen70)? Q. is crankshaft able to move axially ,if it does what prevents it, how is thrust taken;full description? What is axial and torsion vibrations how they are reduced in engine? Moment compensator everything?
ANS.
Axial Damper: The Axial damper is fitted on the crankshaft of the engine to dampen the shaft generated axial vibration i.e. oscillation of the shaft in forward and aft directions, parallel to the shaft horizontal line. It consists of a damping flange integrated to the crankshaft and placed near the last main bearing girder, inside a cylindrical casing. The casing is filled with system oil on both side of flanges supplied via small orifice. This oil provides the damping effect. When the crankshaft vibrates axially, the oil in the sides of damping flange circulates inside the casing through a throttling valve provided from one side of the flange to the other, which gives a damping effect.(see r.sen 13.10)
Q .How was your engine piston cooling …line diagram, temp. and pressure, how is the telescopic pipe arrangement…how will make sure proper cooling .. a very important alarm on it? Explain crosshead lubrication. What modification ..(SEE 904,708,r.sen26)Why oil is supplied to shoes, not guide in xhead lubrication?bore relief? tangential runout?clearance(m/b 0.4-0.6,crankpin0.2-0.4,crshd0.2-0.3? Main engine's main bearing clearance. BOTTOM END BEARING CLEARANCE?
ANS. it will make the system complex bcoz then we will have to make quills like arrangement at many points. Also we have to make lub. Oil enter crosshead at last so supplying to shoes is better. Q.excessive liner lubrication in main engine? EFFECTS? desired properties of cylinder lube oil(oilyness,viscosity, tbn, viscosity index)? Where r quill. If at bottom what happen, why thr(p152 r.sen)how lub oil spreads on cylinder....what is clover leafing?
3. Types of indicator cards, purpose if each, draw all diagrams on single ordinate and abscissa with timing diagram for 2 stroke engine, which diagram suggests error in ir indicator instrument, how to take atmospheric line, what is 90 deg in phase and 90 deg out of phase, draw power card and draw card at a situation when you are taking card and engine tripped on some mechanical trip? what will be the maximum pressure you vil get then..? What is mean effective pressure..how to find
out mip?why we do not use indicator instrument for A/E(see sanyal p309? Why draw card is called 90 degree out of phase? In books it is written that ... draw card is taken with indicator drum 90 degree out of phase with the piston stroke, so it is called out of phase diagram.. My DOUBT...while taking draw card the indicator drum is rotated manually with the help of string attached to it.So if the rotation of the indicator drum is controlled by us,then how come it is said to be exactly 90 degree out of phase. this is purely on experience...nothing else....people took draw cards on experience and after so many trail and error practices nothing else...
Q. why tappet clearance...what u check before tappet clearance(engine cold, n piston on
firing tdc).... procedure... what is tappet clearance, what is its effect if increased or decreased? adjustment, tappet on my generators(0.4 in inlet n 0.9 on exhaust), how will u remove exhaust valve of generator. Tappet adjustment in engine having two inlet and exhaust v/vs(first balance yoke then adjust tappet)? what checks you will make on inlet and exh v/vs springs during overhaul(check length,twist). how they held in position?
Q.what is viscosity? Types? Viscosity index? SFOC and hw to calculate? cetane no,what if less? Fire point, ignition point, flash point, pour point,oiliness? Fuel knock and how u know it(by Fluctuation in rpm, after burn(spark from the funnel, smoke from exhaust). ignition delay.def.wt governs it?hw it can b minimised?what property of fuel oil is responsible for it? Q. expansion tank purpose (give six)..why we call it expansion tank? It is also called compensation tank. ANS.1. SINCE IT IS SITUATED AT HIGHEST POINT IT MAINTAINS CONSTANT HEAD ON THE SYSTEM AND SO REDUCE CHANCES OF AIR INGRESS OR STEAM FORMATION. 2.ALLOW FOR EXPANSION. And place for adding chemical for treatment. 3.PROVIDE A PLACE FOR ADDING MAKE UP FEED,BCOZ OF LEAKAGE AND EVAPORATION.
1.T/C lubrication(manual708)?what is surging....and hw it occur? and what will u do if continuous surging takes place? outboard bearing inboard bearing? From main lub oil system? In case M/E z stopped ….what provision z provided for its lubrication? T/C MAKE (met type)water n dry washing (see r.sen,tur. Side dry 24-48 hrs n wet every week) kab karte h. running indications dat it cleaned? pressure of exhaust gas after T/C(0-350mmWC). function of inducer(guide air smoothly to centre of impeller) and impeller(p181r.sen). P-V diagram of impeller.,inducer, diffuser, locking of t/c, blade fixing.
Q. Butt clearance will increase or decrease after 8000 hrs? What about stuffing gland rings? ANS. Butt clearance of piston ring (intial 0.5-1% cyl. Bore)will increase and those of stuffing box rings( 3 and 4 mm) will decrease with time. When butt clearance of stuffing gland becomes zero then we change the ring. Q. Uniflow scavenging, name other 2, which 1 is better and why, which 1 has more power stroke and why? ANS.LOOP FLOW and cross flow. Uniflow is better because there is less intermixing of scavenge air and exhaust gas.BecOz there is no change in the direction of scavenge air in the cylinder.and when cyl. Length is more than loop n cross scavenging becomes difficult. Uniflow has more power stroke bcoz of better scavange efficiency and use of super long stroke. Q. why is a balance weight fitted ? why not in main engine? ANS. balance weight r fitted only in a/e bcoz during exhaust stroke piston tries to fly out n also to reduce 1st order moment. In m/e 1st order moment r compensated by providing idle gear in chain drive arrangement.2nd order moment is also compensated by providing a smaller idle gear which rotate at double the engine rpm and is fitted at chain drive.
Q. what is difference between valve rotocap and spinner and why rotocap on A/E and spinners on M/E, what is the driving force in both of them..Maintenance and parts of valve rotocap..?no. of cotter and why only
those no. of pieces, purpose of cotter?? ANS.SPINNER ARE JUST VANES,NORMALLLY 6-8 IN NUMBER. M/E EXHAUST V/V IS BIG.AMOUNT OF EXHAUST IS MUCH MORE SO IT CAN ROTATE THE V/V.BUT IN A/E AMOUNT OF EXHAUST IS LESS SO IT IS NOT POSSIBLE TO ROTATE SPINNER BY EXHAUST IN A/E SO WE USE ROTOCAP. Cotter is In a/e, it holds
the exhaust v/v spindle, its in 2 pieces held in place by a cir-clip. Q. why 2stroke engines for propulsion and 4stroke engines for power generation..?CAN WE PUT PROPELLER IN FWD OF SHIP (propeller efficiency will increase but hull efficiency will decrease)? ANS. M/E SHUD BE SLOW SPEED ENGINE FOR BETTER HULL EFFICIENCY. N 2ST engine are more efficient at slow rpm. At high rpm scavenging becomes difficult. GIVE LONG STROKE CONCEPT, TWO ST. MORE POWER PRODUCED. Q.LO tests ( all five with name and how pensky martin test carried out ). 83. with respect to A/E Piston what is the name of the top most piston ring? How will one identify which piston ring goes in which groove if the rings get intermixed????
Top most ring is known as compression ring.Every piston ring has engraved marking....that can be matched with that given in manual. Also can be compare with the sequence in which the piston ring of other piston of the unit is arranged.
Q. piston ring calibration?? Groove clearences : Necessary because – to ensure free in and out movement of the ring in the groove to suit the liner bore. - to allow the gas to pass in the clearance space to press the ring against the liner. If their is cabon deposits in the groove or the groove clearance is too low then gases may pass directly between liner and piston ring outer surface and pushing the ring in to the groove causing Ring collapse. If the Ring clearance is too high then hammering and reduction of piston ring landing surface area in grooves, resulting breaking of ring and liner crack.
Vertical Groove clearance : around 0.4mm and ring should be renewed if it reaches 0.7mm Butt clearance : Will allow thermal expansion. If too large -à blow past. Between 0.5 – 1% of the liner bore. MAXIMUM ALLOWABLE BUTT CLEARENCE IS NOT USUALLY SPECIFIED AS LIMIT OF 15% WEAR ON THE RADIAL THICKNESS OF THE PISTON RING AUTOMATICALLY PUTS A LIMIT TO THE BUTT CLEARENCE
Q. why in a/e crankshaft is drilled for lubrication but not in M/E? ANS. By drilling a hole in crankshaft, its strength is reduced and crack and failure may occur. So we use it only in a/e and not in m/e. Q. T/C lub oil. dis-color..reasons... labyrinth sealing..material n how many.? ANS. Exhaust gas leaking due to leaking labyrinth seal, oxidation, lub. Oil burning due to high temp. forming deposits, if lub. Oil cooling by water then may be due to water contamination. Q. thrust bearing ,purpose ,is it fitted in A/E(yes),purpose there ? thrust brg .... working(last main bearing towards alternator is thrust bearing,it is provided bcoz during power stroke
axial opening of web will occur,so thrust will be there.to absord that thrust it is provided,see r.sen p292) . What is the role of holder bridge in a thrust block and how thrust is transferred to the ship’s hull.(SEE R.SEN p54). Q. overhauling of A/E fuel injector and testing, M/E fuel injector overhauling and testing? Did fuel
injectors can be separately injected in both? (YES in ME type) will it increase the combustion pressure? Q. stuffing box diagram with rings name,, scrapper ring ,,sealing ring clearances? 1- how quills and lubricator works with diagram,how pressure is developed in lubricator and how pressur is maintained in quills? liner ovality? why liner wear in f-a part? in 1 unit it is found to be more than other..y? how to rectify?safeties?tools? ANS. It is boundry lubrication. Liner wear down is normally more in p-s direction but in tanker during long ballast passage it is more in frwd- aft direction due to trim. Mainly in aft. 47. what s running direction interlock? hw s d arrangement? hw it s working?(refer arahna) If the direction of rotation of the engines contrary to the command from the Telegraph, we consider it as the'wrong' direction. In this situation, the fuel cut out servo must operate to shut-off fuel, in case the engine is already running. In addition, the starting air is not allowed to be released, thus preventing the re-starting of theengine in the wrong direction. The Running direction interlock in this engine is connected to the camshaft, and will be operated by the movement of the camshaft. If the camshaft does not reverse, then oil pressure does not act on the fuel cut-off servomotor, as can be seen in the sketch below. Thus fuel is cut-off.
Q.black smoke(excess oil,less air), white smoke(excess moisture),blue smoke(lub.oil burning),yellow(excess sulphur). 2-what are the causes of liner wear down ? when piston rings are stuck or broken what it is called exactly(engineering term)? ANS.1. CORROSIVE WEAR( high n low temp. corrosion),ADHESIVE WEAR(DUE TO IMPROPER LUBRICATION),ABRASIVE WEAR. Q. crankcase inspection of auxilairy engine, what is pinching of connecting rod(moving con. Rod with crowbar sideways), elongation gauge's use for measuring bottom end bearing bolts. 2. NO. OF TIE RODS IN A 6 cyl M/E, purpose? how u will come to know that its slack, how slackness is measured? What is pinching screw? Action if tie rod is slack (retighten)? How to remove broken tie-rod? Can we run engine with broken tie-rod (yes, but reduce load)? Can u see any tie rod from above? Are their tie-rods in A/E(no bcoz single casing type n have underslung crankshaft)? ANS. (2n+2) n = no. of cylinder. SEE MANUAL VOL 2,912-3
Did your engine can be adjusted for Exhaust valve timings? Why?(YES)
ANS. NORMALLY WE DON’T CHANGE but we change if chain slack. here we also take virtual tappet clearance. Taken in running engine at full load. Q. resin chocks?how it better than conventional one??where fitted,hw fitted and y fitted??(SEE ARHANA) 5. Radial T/C vs Axial T/C? Advantages? Emergency lub. Of turbocharger? Why coil spring is being replaced by spring air in M/E? Can u see ne moving part in exhaust V/V from outside? What it represents? ANS. We can see rotation check rod from outside. During working it rotates showing that v/v is working. We can also check that v/v s closed or not if needed during adjustment. 3.what is SAC vol in injectors..? The “Sac” is a small volume within the fuel flow path of an electronic fuel injector. In this study, it is defined as the volume between the valve seat (fuel shut off point) and the entrance to the final metering orifice of the injector. This sac causes fuel injectors to deliver uncalibrated excess fuel .
Q. What is super long stroke and its advantages. Its effects and changes that have been made in engine design to counter its effects. ANS. Superlong stroke= stroke/bore ratio is more then 3.8. advantages= cheaper fuel can be burnd as more time is available for burning, hull efficiency is more when we have slow turning large dia. Propeller but we can’t increase mean piston speed above certain limit. Now since m.p.s = 2x stroke x rps. So to reduce rpm we increase stroke.
q. why turning moment is more while running ahead than astern?? Why torque on rudder is more while running astern?? turning moment is more in running ahead due to neutral point which is about L/6 dist. from fwd and when running astern it is from aft...........and running astern greater force act at rudder so higher torque....... Q. how to calculate SFOC, POWER? How to calculate power if indicator fucked.?( torsiometer) Q. Difference b/w MIP n MEP? ANS. MIP=the pressure which when acting on the piston will perform the same work as performed during the cycle. MEP= theoretical pressure acting on the engine during power stroke.
Q. overhaul of globe v/v &gate v/v. and inspection in spindle?
ANS.
globe v/v -Remove the wheel nut and the wheel handle.Open the bonnet bolts and the top portion of the valve
along with the valve seat, stem etc will come out. The bottom portion of the valve will be separate.Hold the bonnet in a vice and open the gland bolts. Then loosen the gland flange and the gland bush. The valve stem should then be screwed clockwise and it would come out from below along with the valve disc.bcoz thread Is not in full portion so it will damage. Remove the set screw that is securing the valve disc to the stem. Remove all the gland packing’s with a gland packing extractor. Gate v/v Open the wheel nut and remove the hand wheel. Open the gland bolts and slacken the gland flange and the gland bush. Open the bonnet bolts and remove the bonnet along with the bonnet and the valve wedge. Unscrew the valve stem from beneath the bonnet. inspection in spindle 1.Check all the threaded parts for damage and if there is any damage on the thread then the threads must be dressed by a needle file. 2. Check the stem for straightness. The simplest method of checking is by rolling on a flat surface, but the correct method is to put it on a lathe and center it. Thereafter with the help of a dial gauge put on a magnetic stand at a suitable point, check the distortion. 3. Check the stem for scratches, as these can damage the gland packing. Any scratches must be removed with an emery paper or oil stone. 4.The valve and the valve seat must be inspected and if found to be in fairly good condition, they must be ground together by using a guide for centering and a suitable grade lapping paste. A 1200 grit lapping paste would be suitable in most conditions (carborandum). How we knw that lapping is done- 1. Apply Prussian blue on seat. Turn v/v by one turn. If all v/v gets colored then ok else v/v or seat is not properly even. So more lapping. 2. Mark pencil mark at some places on seat. Put v/v n turn half round. If all mark gone then ok else do more lapping. SAME LAPPING CHECK MEHTOD FOR EXHAUST V/V.
ELECTRIC ARC WELDING Q. Procedure and safeties for electric arc welding. Which current source is preferred, AC or DC.(AC bcoz more compact plant, high efficiency, less initial cost and less maintenance). Butt weld and lap weld? Name various parts where such welds are carried out? soldering?? ANS. Procedure- in electric arc welding, electric arc is used as a source of heat to melt base metal and if filler metal is used then filler metal also. Power source has two cables with holders. An electrode is used which has filler metal at the core and a flux coating (of metal alloy, cellulose etc) outside to protect the molten metal from oxidation. Electrode’s bare part is clamped to electrode holder. The other holder is connected to base metal. Electrode current= KxD. K= 40-60. D= 5mm dia. for thickness more than 5mm. Power source- normally we use high voltage and low current system. But for welding we need high current, low voltage system. So we use transformers for AC and welding generator n rectifier for DC. For DC open ckt voltage is 50V(so DC is more safe).For AC system, open circuit voltage is around 80V(bcoz voltage shud b high enough to strike an arc and low enough to b safe for welder).
Safeties-worn in addition to the personal protective equipment, Welding should not be carried out in hot/humid conditions which might cause sweat or damp clothing. Under no circumstances whatsoever should a welder work in wet conditions. Wear welder's goggles or a face shield. Buttweld-the weld is formed by placing two pieces of metal with their edge side by side n then welding the edges together. Lap weld-made by placing one piece of metal on the other so that they overlap .edge of upper is then welded to the surface of lower. Q. What are pms and cms…. What are all the system you had in your ship according to pms ..and cms? Ans. Class societies allow special status to ships with well implemented PMS. Survey of various machinery components is performed usually with regular Class surveyor inspection, and it is based on schedule given in Continous Machinery Survey. Surveyor comes to ship several times per year and inspects various machinery components, determining their condition. Inspection is scheduled every five years and the system is intended to assure good functionality of ship's machinery and therefore safety of the ship. As PMS is increasing overall safety and reliability of the ship, Class societies allow another form of Survey to be performed on the ships with well established PMS. Most of CSM inspections (all except steering gear and pressure vessels) is carried out by Chief Engineer, based on regular PMS jobs, and Class surveyor is coming on board the ship only once a year to inspect items Chief Engineer is not entitled to and to check what items were inspected since last Class inspection. Q. engine room overhead crane safeties n maintenance ?why lower n upper limit switch is provided? What type of brake n its working?
Crane takes the load due to the friction b/w the rope windings and the drum. So the number of windings should never go less then certain number. So we provide lower limit switch. Upper limit switch is to trip the motor on reaching max. up. 1)electromagnetic brakes are used which are fitted inside the rotating drum. They keep compressing a spring by power n when power goes, the spring applies the brake. 2) Emergency stop is provided in the remote so that the operator can stop the crane at any time. 3)motor is fitted with distance limit switch in both transverse and longitudinal direction, up and down direction so that the travel of the trolley and hence crane should not overshoot the rack’s end. Mechanical stoppers are provided for both directions in case the electrical distance limit trips fail. 4) motor is fitted with thermal protection trip. When the motor windings get overheated, trip will activate saving the motor winding from burning.Load limit switch is also fitted which will trip the motor if the load to be lifted is above the crane capacity. 5) Additional tools like i-bolts, shackle, wire sling, belts etc. used for lifting must be checked before use. No one walks or stand below the crane when it is in the loaded condition. ACETELENE STORAGE Q.how acetelene(C2H2)stored in cylinder??why it is stored in form of acetone?? what is pressure and safety? Flashback arrestor….where placed n working? ANS. ACETYLENE When burned with oxygen, produces a hot flame, having a temperature around 3000°C. Acetylene odor that is readily detected even when the gas is highly diluted with air. Pure acetylene is self-explosive if stored in the free state under a pressure of 2bar.A slight shock is likely to cause it to explode. Acetylene becomes extremely dangerous if used above 1atm(1 bar).Cylinder Design Acetylene can be safely compressed up to 18 bar when dissolved in acetone and stored in cylinders filled with porous material, such as charcoal, portland cement or firebrick. These porous filler materials aid in the prevention of high-pressure gas pockets forming in the cylinder. Acetone is a liquid chemical that dissolves large portions of acetylene under pressure without changing the nature of the gas. Being a liquid, acetone can be drawn from an acetylene cylinder when it is not upright. You should not store acetylene cylinders on their side, but if they are, you must let the cylinder stand upright for a minimum of 2 hours before using. This allows the acetone to settle to the bottom of the cylinder. NOTE: Acetone contaminates the hoses, regulators, torch, and disrupts the flame. Q. Where should a Flashback Arrestor be placed? Its Working? The flashback arrestor should be placed at the closest point to the flame, if due to un-avoidable circumstances the Arrestor cannot be places close to the cutting nozzle or the flame then it should be placed of the main pipe line, and also on the fuel gas bank, vessel, cylinder.
Flashback arrestor quenches the flame using the following methods a) By reducing the velocity of the flame, reducing the flame velocity even lower than the minimum flame velocity of the fuel gas b) Stops the flame propagation into or through a pipe. By placing a flame arrestor at the end of the flammable mixture pipe feeding a flare or burner, flame can be prevented from moving into the pipe regardless of the mixture velocity. OR By passing a potentially flammable mixture through a water chamber or some sort of heat sink. This dissipates the heat and quenches the flashback. OR By blocking the fuel gas path, with a suitable thermal fuse plug, casing the flashback to die out. OR By blocking the flow of fuel gas in the opposite direction by acting like a non return valve. Online flame arrestors (passive) – (most commonly used) Mechanical flame arrestors are filled with metal or ceramic, which absorbs heat from a flashback, quenching it to a temperature below what is needed for ignition. This stops the flame. With a low enough hydrocarbon/air mixture flow rate, if a flame travels to the face of the arrestor, it can become stable at that point. Heating of the arrestor body and internals results. Once the arrestor temperatures increase enough, ignition temperature can be reached on the upstream side of the arrestor and the flashback can proceed. For this reason, a temperature switch is often installed on the flame side of each arrestor (adding an "active" element). Q. Type of pump for emergency bilge suction,M/E fuel supply p/p,M/E fuel circulating p/p. lub. oil system of m/e type of pump .why so? why not c/f p/p? if so then y? where to be fitted? what must b the minimum capacity(MY SHIP capacity 280m3/h at 4 bar)?y that much only? ANS. M/E LUB. OIL P/P,FUEL SUPPLY P/P,FUEL CIRCULATING P/P- ITS SCREW P/P AND E/M BILGE P/P IS CENTRIFUGAL P/P(see p367reeds). m/e lub. Oil p/p can be centrifugal p/p but then its impeller is open type and is provided at bottom by increasing the size of spindle so that there is no problem of priming. Q. Bilge injection valve dia.?features? ANS. EM/GNCY BILGE INJECTION V/V- IT’S A SDNR V/V.DIA –ATLEAST 2/3 OF DIA OF MAIN SEA WATER INLET.VALVE HAND WHEEL OF THIS V/V AND MAIN SEA WATER INLET V/V MUST BE ATLEAST 0.46m ABOVE FLOOR.E/M BILGE INJECTION V/V IS FIITED TO HIGHEST CAPACITY P/P(MY SHIP 310m3/h).v/v is fitted after p/p suction v/v so that thr is no need to open suction v/v of p/p. emergency bilge suction pump has no suction filters fitted before and after the valve. Emergency bilge suction is used only at the time of engine room flooding.
Q.what is proof stress? destructive and non destructive tests?swl? ans. proof stress can be found by referring to the stress/strain curve at the point where strain is = 0.2% original volume (the material has grown 0.2% in volume) proof stress will be given as a measurement of energy (MPa,KPa etc.) as it specifically refers to the amount of energy required to stress the material to 0.2% its original volume. This value approximates to the yield stress in materials not exhibiting a definite yield point. SWL is determined by dividing the minimum breaking strength (MBS) of a component by a safety factor assigned to that type and use of equipment. The safety factor generally ranges from 4 to 6 unless a failure of the equipment could pose a risk to life; in that instance the safety factor would be a 10. Q. which all parts to be dye tested during decarb?(crankshaft,piston top surface,piston grooves,Bearings).what is meant by removing excess dye(dye colour is RED, developr white)?how developer draws it up from crack? Ans. If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects. In addition, this may also produce false indications severely hindering your ability to do a proper inspection. The developer draws penetrant from defects out onto the surface by reducing surface tension of the dye and by capillary action to form a visible indication, commonly known as bleed-out. Any areas that bleed-out can indicate the location, orientation and possible types of defects on the surface. [the indication size is not the actual size of the defect]
FRESH WATER GENERATOR Q. why is necessary to maintain temperature of shell of fwg, if temperature is increasing possible cause and solution. fresh water gen yield z reduced, possible causes? what was d disch rate of ur ejector pump? fwg principle and wrking?Routine maintenance on a fresh water generator?With the time the dia. of the nozzle of air ejector enlarged ,how to check (erosion)?Overhaul of fresh water generator. fwg starting? How 2 make fwg water portable..what is dolomite filter(it increase ph n ad mineral)how it add minerals 2 water....what r the minerals(K,Ca,Na etc)? ANS. IF SHELL TEMP. IS LESS-FRESH WATER PRODUCTION WILL REDUCE. IF SHELL TEMP. IS HIGH- ABOVE 80C,THEN FORM HARD SCALE DEPOSITS OF MAG.HYDROXIDE(MgOH),CALCIUM SULPHATE.AT LOWER TEMP. FORM SOFT DEPOSITS OF CALCIUM CARBONATE.) IF TEMP.IS INCREASING THEN CAUSES- 1.SCALE FORMATION IN SHELL ,2. IMPROPER AMOUNT OF FEED WATER SUPPLY. 3. JACKET WATER TEMP. INCREASING. Q. CENTRIFUGAL PUMP TROUBLESHOOTING??
TROUBLE Does not deliver any liquid
CAUSE Insufficient priming liquid Insufficient pump speed Excessive discharge pressure (such as a partially closed valve or some other obstruction in the discharge line) Excessive suction lift Clogged impeller passages Wrong direction of rotation Clogged suction screen (if used) Ruptured suction line Loss of suction pressure
Insufficient capacity
Air leakage into the suction line
Crackling noise from the pump casing
Insufficient speed of the pump Excessive suction lift Clogged impeller passages Excessive discharge pressure Mechanical defects (such as worn wearing rings, impellers, stuffing box packing,or sleeves)
Does not develop enough discharge pressure
Insufficient speed of the pump Air or gas in the liquid being pumped Mechanical defects (such as worn wearing rings, impellers, leaking mechanical seals, and sleeves)
Works for a while and then fails to deliver liquid
Air leakage into the suction line Air leakage in the stuffing boxes Clogged water seal passages
Insufficient liquid on the suction side Excessive heat in the liquid being pumped
M/E & A/E AIR COOLER CLEANING (BOTH AIR N WATER SIDE) Q.how M/E and A/E (see water side n air side in aux. engine folder)air cooler cleaning done.What chemical used (ACC 9,),what is interval of cleaning, what is manometer normal pr. (160mm aq)and what pr. it should be cleaned ?How will u come 2 know air cooler needs cleaning? ANS. SEE VOL 2.910-1. Air cooler cleaning p/p is provided for cooling air side of m/e air cooler. p/p has two suctions.one from a tank and other from fresh water line.first the tank is filled with fresh water and chemical acc9 is added to it. Then it is circulated from tank to tank for proper mixing. Then it is pumped to air cooler where we have nozzles on the upper side of cooler. The drain goes to bilges. After cleaning, fresh water is supplied to nozzles for washing. FOR BOTH M/E AND A/E, AIR SIDE CLEANING-if pressure drop across air cooler becomes double. WATER SIDE CLEANING-if temperature of air at cooler outlet increase considerably.
PUNCTURE V/V
&
VIT FUEL PUMP
Q. puncture valve(see909)? Vit? what is breakpoint? (gulia.p219) puncture valve is fitted in the top cover of the pump. It consists of a piston which communicates with the pneumatic/electric system of the engine. In the event of actuation of the shut-down system, or the "Fuel Oil Leakage Alarm System",or when STOP is activated, compressed air is supplied to the top of the piston, causing the piston with pin to be pressed downwards and `puncture' the oil flow to the fuel valve. As long as the puncture valve is activated, the fuel oil is returned through bores to the pump housing, and no injection takes place. Vit- in conventional fuel p/p,start of injection is fixed and end of injection i.e the amount of fuel injected in the cyl. Is controlled by a rack depending on engine load. In vit system two racks are there. one controls the end of injection by rotating the plunger in the barrel as per engine load. the other one called the vit rack is connected to threaded barrel(barrel is threaded here) by a threaded sleeve. as the sleeve cannot move axially, and the barrel is prevented from rotating, then as the sleeve rotates, the barrel moves up and down, thus altering the position of the spill ports relative to the plunger, and varying the start of injection. Advantage of vit- Savings in fuel, as SFOC decreases by around 5g/bhp-hr at 90% MCR.the system is set up so that there is no change in injection timing at low loads(40%MCR).this is to avoid frequent changes of pump lead during manoeuvring. As the engine load increases above 40%,the start of injection advances i.e. early injection. When the engine load reached approx.85%MCR at which engine is dsigned to have reached pmax.,retardation of injection timing takes place so that max. combustion pressure is kept constant between 85% and 100% MCR.vit racks are operated by pneumatic signal between 0.5bar(min. vit setting) to 5 bar(max. vit setting).vit operation is only active for engine in ahead direction and control is fron bridge or ECR.when running astern or from local control, the maneuvering system delivers preset pressure to vit actuators. Breakpoint- it is the load after which the pmax is maintained constant. So it is normally 85% of MCR in normal vit. But it can be adjusted in super vit. Fuel pressure is kept b/w 7-8 bar. Below 7 bar cavitation may occue.above 8 bar shock absorber may not function properly.
WEAR RING & MECHANICAL SEAL & LANTERN RING
Q.what is the function of wear ring in pumps?where fitted?parts of mechanical seal? inspection in mechanical seal during overhauling, how you will make sure it is usable or not, Mechanical seal.. pms routine.kya dekhoge ki mech. seal change karna hai? types of c/f p/p? lantern ring fitting?? ANS. Wear rings are typically found on pumps with closed impellers. It decrease the amount of leakage loss around the impeller. And also as name indicates 'WEAR' which is a ring can sacrifice its size by taking friction generated between stationary and rotating elements. The replacement of rings is cheaper than replacing impellers/casing. Wear rings r fitted to the impeller and/or the pump casing. Parts of Mech. Seal- Rotating and fixed face: The rotating face is connected to the rotating shaft while the fixed face is connected to the pump housing. Function of mech.seal- prevent liquid under pressure from leaking out of the pump, or from drawing air into the pump when under vacuum conditions. Damage to mech.seal can occur due to- Abrasives- abrasive particles in the liquid being pumped infiltrates with the liquid between the seal faces and grind away the carbon primary ring. The normal shiny face of the primary ring and mating ring. Heat Damage-Excessive heat can damage the primary ring and the elastomer parts. The primary ring is made primarily of carbon. Should the pump be operated without liquid - even for a very short period of time - the primary and mating ring faces are denied lubricant. This causes the faces to become very hot. The binder mixed with the carbon breaks down and the face of the primary ring turns to a dull black powder. Lantern ring is provided in centrifugal p/p stuffing gland. Located at center of gland and It is a hollow ring which receives liquid from discharge side of p/p and cool, lubricate the gland. It is provided bcoz the gland may not get proper cooling as p/p may be under vacuum. Q. Removal of CENTRIGUGAL Pump for Inspection?
1 Isolate pump electrical circuit breaker on main switch board and attach a warning notice. (Do Not Operate or Men at Work). 2. Switch off and lock pump supply at its local supply panel. Attach a warning notice to pump local supply panel. 3. Close suction and discharge valves, chain and lock hand wheels. 4. Open pump suction and discharge pipe drain valves to bilge and when water ceases to flow; crack open the pipes / pump flange joints carefully to ensure that pump has drained off and is safe for opening. 5. Fix a shackle to lifting pad eye above pump and hang chain block; ensuring SWL of block, slings and shackles are satisfactory. 6. Use a center-punch to mark coupling and casing, then remove the coupling bolts. 7. Disconnect, fixed tag and remove motor supply cables; taping over bare ends with insulating tape. 8. Connect shackle and sling to motor eyebolt and lift motor clear of pump using overhead chain block. Lay motor on its side out of harm’s way, protecting machined surfaces on both pump and motor coupling halves against damage. (Cardboard and masking tape is quick and efficient method.) 9. Disconnect all external fittings from pump casing e.g. cooling pipe, pressure gauge, oil reservoirs and air cock. 10. Remove bolting from top cover and remove cover. Scrape off old gasket and check mating surfaces, and renew gasket on assembly. (Light smear of grease on gasket / faces) 11. The pump shaft with impeller can be lifted out of casing. 12. Dismantle the impeller, and remove the wear ring. 13. Remove the gland packing and disregard; replacing it on rebuild. Q. Inspection Procedure for CENTRIFUGAL Pump and Motor? ANS. Pump 1. Impeller, pump shaft and internal volute/casing can now be inspected for erosion, pitting and wear. 2. Rectify pitting or erosion in the impeller and casing with brass putty. 3. Check main drive shaft bearings and thrust bearings for wear and replace if required.
4. Check wear ring clearance using feeler gauges; in my day at sea it was general practice is to replace with new rings at major overhaul. 5. Check impeller / shaft key and keyways for damage and undue wear, Unscrew impeller shaft securing nut and check threads are in satisfactory condition; retighten to manufacturers torque settings. 6. Give all parts a good clean removing any dirt/ medium residue 7. Enter date of overhaul and parts renewed in the pump maintenance record card. Drive Motor 1. Grip motor drive shaft /coupling firmly and check for excess axial and longitudinal movement. Rotate shaft at speed by hand, allowing it to run to a stop whilst listening for excess noise from bearings. Any doubt on either counts, the bearings should be replaced. 2. Megger check motor windings to ensure no dampness is present and windings are in good condition. Any suspect readings indicate a full motor strip to check condition of rotor and stator. 3. If these checks are satisfactory, grease bearings as required. Some bearings are now sealed for life and will not require greasing.
Q. crankcase inspection of aux. eng and m/e(see new folder)? ANS. before opining door check for leakage, open door then check sealing rings of door, check condition of lub. Oil, tightness of b.e.bearing bolt locking arrangement, check thr elongation, check sideways movement of piston rod with a crow bar, check b.e. bearing clearance, check bolt tightness of main bearing bolt and take clearance, move piston to tdc n use torch and check liner for water leakage, if water leaking from inside then liner crack n if leaking from outside then sealing o-ring leaking, then take gear drive mechanism backlash, in the end start priming pump n check lubricating nozzles n see if lub. Oil is coming properly from all points, if lub. Oil is coming more from a bearing then it means that bearing cl. has increased. SAFETY V/V OF ECONOMISER Q.why is EGB safety v/v lifting pressure is more than that of boiler safety v/v lifting pressure? The Exhaust Gas Boiler is circulated with feed water by Boiler Water Circulating pump and the pump takes its suction from Boiler Steam drum. Hence the pressure of feed water in the EGB, will be the pressure of steam drum and circulating pump discharge pressure, which will be higher than boiler steam drum pressure. Hence the Safety valve setting of EGB will be higher than that of its counterpart in Boiler. EGB takes suction from the boiler drum and after passing through the economiser tubes the water is fed back into the same drum. In order to have an efficient heat transfer the economizer tubes need to be filled with the water completely.Since heat transfer q=mct where m is the mass of the water.If the economiser tubes are supplied with the water having same pressure then the water in the tubes will be converted into water and steam. If steam is present in the tubes, then as per the above equation 'm' decreases finally the amount of heat transfer 'Q' will decrease. So heat taken away from the water decreases as a result it results in overheating of tubes. So in order to prevent steam formation the water is supplied at higher pressure ( At higher pressure the boiling point of water will increase).For increasing the pressure,the return line from the economiser to the boiler drum is provided with a spring loaded valve which increases the pressure in the line. Because of this the safety valve of egb which is kept on the return line of the boiler kept at high pressure.The water which is at high pressure when enters into the steam drum back, its pressure reduces as a result boiling (Vapourisation) of water will take place inside the drum producing steam.
ACTION IN CASE OF BLACKOUT
In case of Blackout following precautions and actions should be taken:1. 2. 3. 4. 5. 6. 7. 8.
Never panic in such situation, be calm and composed. Emergency generator will restore the power in no time. Inform Officer on bridge briefly about the condition. Call for man power and inform the chief engineer. If the main propulsion plant is running, bring the fuel lever to zero position. Close the feed of the running purifier to avoid overflow and wastage of fuel. If auxiliary boiler was running, shut the main steam stop valve to maintain the steam pressure. Find out the problem and reason for blackout and rectify the same. Before starting the generator set, start the pre- lubrication priming pump if the supply for the same is given from the emergency generator; if not, then use manual priming handle (provided in some generator). 9. Start the generator and take it on load. Then immediately start the main engine lube oil pump and main engine jacket water pump. 10. Reset breakers and start all the other required machinery and system. Reset breakers that are included in preferential tripping sequence. (Non-essential machinery).
Q. what will u do in case of grounding n E/R FLOODING? Ans. GROUNDING how we will come to know- Increased load on engine,turbocharger surging,heavy vibration,bridge will come to know from echo sounder so call bridge.Stop m/e. Change over to high sea chest. Call engineer’s alarm. Start taking soundings of all e/r db tanks and bilges. Note down the time and soundings,repeat sounding after 15 min. to check change in sounding.make sure sounding pipe caps are closed. wait for bridge instruction.they may ask for deballasting or astern kick. E/R FLOODING 1.Bilge high level alarm will come. 2.Go to bottom platform, find out here flooding is taking place,if any lakage is seen,activate engineer alarm,inform bridge. Start pumping out bilges using emergency bilge suction. Lower bilge level. Find out the leakage,isolate the pipe line and rectify. IF BULKHAED LEAKING-use collision mat, cement bags.
SHOOT BLOWING OF ECONOMISER Q. HOW TO Shoot BLOW EGB? ANS. Soot blowing not to be done if there is an indication of soot fire. SOOT BLOWING IS NOT ALLOWED IN PORT OR PILOTAGE PASSAGE. FOR USA,VESSEL TO BE AT LEAST 50 NM FROM LAND.ENGINE IS TO BE RUNNING AT FULL LOAD. HOW TO DO01. INFORM BRIDGE THAT YOU ARE ABOUT TO START SOOT BLOWING OF THE BOILER SO THAT CORRECTIVE ACTION BY THE BRIDGE WATCHKEEPER CAN BE TAKEN AND ALL SOOT EXHAUST SHOULD BE AWAY FROM THE VESSEL.
02. 03. 04. 05.
DRAIN THE CONDENSATE FROM THE STEAM INLET AND RETURN LINES OF THE SOOT BLOWER STEAM PIPING. OPEN STEAM INLET TO SOOT BLOWER SLOWLY AND LET ALL THE CONDENSATE PASS ON TO THE RETURN LINE BY KEEPING THE LINES OPENED. OPEN THE STEAM INLET FULL ONCE ENSURED THAT THE CONDENSATE IS COMPLETELY DRAINED. MOVE THE SOOT BLOWERS BY HAND, AND CHECK THE CONTENTS WHICH ARE COMING OUT OF THE FUNNEL.
CLOSE ALL STEAM INLET AND EXHAUST PIPING TO THE SOOT BLOWER AND CHECK PRESSURE DROP. WHEN TO DO- 1. IN VERY WATCH 2. WHEN PRESSURE DROP INCREASES BY 15mmWG. 3. WHEN GAS OUTLET TEMP. AFTER EGB IS 15*C HIGHER THEN CLEAN EGB GAS TEMP.
Q. retractable soot blowers working ? The blower carriage consists of three separate components: the lance hub assembly, the gearbox and the electric motor.The lance hub housing contains the lance hub, which is supported by two special roller bearings. Because the lance tube is fully retracted from the furnace and cooled through the blowing medium, the long retractable soot blower can be used in areas with higher flue gas temperature than any other soot blower type. Retractable property improves the cleaning effect and reduce erosions due to high temperature flue gases. The blowing medium is supplied through an automated poppet valve.
Q. Hole in a sea water line how will u repair? If hole is big? Hole is small??If line is not pressuresd ?Material of sea water line?? Ans. If hole is small1.use rubber piece and jubilee clip
2.rubber piece and C-clamp
3.use rubber piece and marling rope 4.use pipe repairing kit-it has fiberglass tape and epoxy. And then weld later. If hole is big1.cement boX
2.change pipe from flange to flange
3.cut that pipe and fit new pipe and weld. 4.take a pipe of little larger dia,cut it from middle and fit it and then weld. Hole in bulkhead- use cement bags, or collision mat etc. Material of sea water line-mild steel, galvanized from both sides and painted.
Q. Gun metal, where used, composition? Properties? Example of similar metal? ANS. Gun metal-10 %tin,88 % copper,2 % zinc. Strong and corrosion resistant. Used earlier in bearings castings boiler fittings, sea water pump casing. Originally used chiefly for making guns, gunmetal was eventually superseded by steel. Gunmetal casts and machines well and is resistant to corrosion from steam and sea water.
MONEL METAL- CU:NI= 2:1 IT IS RESISTENT TO SEA WATER CORROSION AND EROSION. STAINLESS STEEL – CHROMIUM=18%, NICKEL- 8%, CARBON- 0.1% and rest iron. Stainless steel when comes in contact with air or water forms a layer of protective chromium oxide which prevents it from corrosion. NIMONIC ALLOY- carbon 0.1%, chromium- 20%, iron -3%, titanium- 2.4% , aluminium- 1.4%, nickel- 75%. Resistant to corrosion at high temp., creep resistant, good strength n hardness at high temp. Q.Definition of suction head and characteristics? ANS. Npsh available- it is the head that the p/p shud provide by causing drop in preesure to raise liquid from tank level. The head that a pump must provide by providing pressure drop on the suction side to raise the liquid from the supply well to the level of the pump. Also known as suction lift.
Q. Safety and relief valve difference?? ANS. Safety Valve - it is characterize by rapid, full opening action. Relief Valve - liquid applications, opens in proportion to the increase of system pressure over the opening pressure, so it opens gradually.
Q. advantages of hydrophore system? ANS. CAN TRANFER water to any height on ship, no need to use tank on top it will move CG up. Q. As a duty engg. what to do if hole in rudder(rudder breach )and how u will come to know? how to take propeller and rudder drop? ANS. Indications- motor ampere increases, sluggish operation, trim by aft, engine load increases. Actions- reduce rudder movements, reduce water from aft peak tank.
Propeller drop- taken by poker gauge. First the propeller is brought at the reference point. For some engine this reference point is marked on the propeller and for some engine we have to bring the piston of cyl. Nearest to fltwheel at TDC. Then remove rope guard at take propeller drop.(max.2 mm for oil type, n for water type it depends upon dia. Of shaft.for above 305mm it is 8mm) Rudder drop- taken by trammel gauge. This takes the form of an 'L' shape bar of suitable construction. When the vessel is built a distinct centrepunch mark is placed onto the ruder stock and onto a suitable location on the vessels structure, here given as a girder which is typical. The trammel is manufactured to suit these marks As the carrier wears the upper pointer will fall below the centrepunch mark by an amount equal to the wear down.
