Control Valves Sizing & Selection

CHAPTER 1

CLASSIFICATION OF VALVES 1.1

INTRODUCTION

Efficient and economic running of any process plant depends on the efficiency of the control element in responding to regulating (control) requirements or isolating requirements of the process .One such control element is the valve. Isolating valve is used for on/off purpose. A control valve is always a pressure-reducing device. A valve is either automatic or manual operated device for controlling the process fluids like liquid, gas, corrosive chemicals, slurries, liquid metals, and radio active materials etc through pipes. Valves usually allow movement of fluid in one direction.Control valves must be selected taking into consideration the control purpose, process conditions, pipe sizes and all other related factors. It is very important to select an optimum size for the control valve, which is the final control element in a control loop. If the final control element is not of proper size for a particular process application, or if the selected valve does not function as planned, the total effort goes in vain. A control valve may have pneumatic, hydraulic, electric or other externally powered actuator that automatically positions the valve plug as dictated by the signal transmitted from the controller. These signals may be derived from process variables such as pressure, temperature, flow, and level. Control valves are used primarily to throttle energy in a fluid stream and not for shut off purpose. Due to this the control valve body assembly is considerably different from the shut-off valve. Valves may operate at pressures in the vacuum region to pressures of 6000kg /cm 2 or more, temperatures from cryogenic region to those of molten metals. The sizing of a valve is a part of valve selection. Sizing is accorded more importance because the very function of the valve selection proceeds depends on the accuracy of sizing. Optimum sizing of a valve will give the correct controllability and better performance of the system. On the other hand using a higher size valve will abnormally increase the cost. 1.2

CLASSIFICATION OF VALVES

Valves can be classified according to nature of the closure members employed. Almost all valves will fall into one of the fallowing basic eight categories

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1.2.1 BALL VALVE It is basically a ported sphere inside the housing. Rotation of the sphere by 90 0 changes the position from open to close.Ball valves are used in a wide range of applications including flow control, pressure control and shut-off. These valves generally have a very low pressure drop and low leakage.The seat of the ball valve is subject to extrusion in throttling applications. 1.2.2 BUTTERFLY VALVE It consists of a disc which rotates about a shaft in the housing, and close against a ring seal (seat) to shut off the flow.These are generally used in large diameter lines and in systems where leakage is relatively unimportant,viz. pen stocks of hydro-stations, C.W. lines in thermal stations. These valves require high actuation force. 1.2.3 GATE VALVE It is characterized by a sliding disc or gate, which is moved by the actuator perpendicular to the direction of flow. These are used primarily as stop valves. I.e. fully open or fully closed . Gate valves have slow response characteristics and require large actuating force. 1.2.4. GLOBE VALVE There are three types of valves in the globe family,viz. globe, angle and Y type. The closure member, usually a disc or a plug is moved by an actuator stem perpendicular to a ring shaped seat. Primarily it is a general-purpose flow control valve .It is faster in opening and closing than the gate valve. Globe valves are often heavier than other valves of the same flow rating. 1.2.5 PINCH VALVE These valves are characterized by one or more flexible elements such as diaphragms, rubber tubes, which can be moved together to press against a stop to pinch off the flow. These valves are used in systems carrying slurries, gel etc. It is relatively low cost, has low-pressure drop and can be tightly closed. Flexible members are subjected to wear and require periodical replacement. 1.2.6 POPET VALVE Mainly used in pressure control, safety and relief functions. Has excellent leakage control, and low pressure drop.

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1.2.7 TAPPER PLUG VALVE Similar to ball valve except that the closure member is a tapered plug instead of a ball and there is no through port in the plug. These are useful in high temperature, lowpressure applications. These are not usually suited for steam services. 1.2.8 SWING VALVE Primarily used as check Valves to block flow in one direction.It suffers from high leakage and is subjected to contamination build upon the closure member and in the clearances. Further depending on their construction the valves can also be classified as sliding stem or rotary type. 1.3

VALVE SELECTION PARAMETERS

The Valves are selected mainly considering the following parameters. A.

Type: Single seated, double seated (Figs No. 1.1 to 1.3), Sliding stem type, Rotary type, Angle type (Figs 1.4 to 1.6) etc.

B.

Size: Capacity to handle the flow rate.

C.

End connection type: Flanged, Screwed, Welded, etc.

D.

Pressure Rating: Determined by the Temperature and Pressure of the medium.

E.

Capacity: Cv Value determined by designed flow rate.

F.

Flow Characteristics: Equal percentage, Linear, Quick opening, etc.

G.

Plug Type: Contour, ‘V’ ported, Soft seated Tight Shut-off, etc.

H.

Actuator: The valve plug, Stem and the Valve Body have to be designed to with stand the thrust of the Actuator.

I.

Materials of the Body & Trim: This depends on the nature of the fluid handled. Body material is normally C.I., C.S., CSS or other special alloys suited to the fluid handled. For high Temperature applications the body is made of creep resistant alloy steel containing chromium and Molybdenum. Trim (internal parts) is made of corrosion resistant stainless steel. In order to withstand wire drawing and erosion the valve plug and seat rings are hardened with stellite.

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FIG: 1.1 Model :VDN Double Seated Low Noise Valve (Rating : ANSI 600 or Less )

Double seated low noise valves are featured with very low operating noise (aerodynamic noise) when they are used to handle compressible fluids (such as steam, air, natural gas, and ethylene gas). These valves operate still more silently than VDC cage valves. The cage and valve plugs are of a multiple hole construction. The components for “restriction, divergence” and “expansion” are laid out in a rational manner to accomplish low noise pressure reducing action. Components are interchangeable with those of the VDC cage type valves.

FIG : 1.2 Model :VDN Double Seated High Pressure Low Noise Valve (Rating : ANSI 900 - 2500 )

Double seated high pressure low noise valves are featured with very low operating noise for higher pressure rating of ANSI 900-2500 when they are used to handle compressible fluids (such as steam, air, natural gas, ethylene gas and etc.). Components are interchangeable with those of the VDC high-pressure cage valve. 4

FIG: 1.3 VDC: Double seated cage valve. Rating: ANSI 600 Or less

Double seated cage valves can be used for general applications as top and bottom guiding double seated valves. However, balanced holes in the plug can eliminate the unbalanced thrust in great efficiency and provide dependable operation against vibration and attrition with flashing fluids or at high pressure differentials. The valves can provide bubble-tight shut-off with the seat. The body is constructed for simpler disassemble, faster checking and easier part replacement. Also, the change of flow characteristics and capacity can be exchange of the cage only.

Fig:1.4 Model :VAV Venturi Throat Type Angle Valve

Venturi throat type angle valves are used for directing horizontally flowing fluid to the downward direction. It is particularly used for slurries and viscous or flashing mediums.

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FIG: 1. 5 Model :VAC Cage Type High Pressure Angle Valve

These are cage type angle valves with forged body suitable for high-pressure service. The valve plug is provided with balancing holes so that the unbalanced thrust caused by fluid can be reduced. The unit can be made in large sizes, and affords dependable operation at high pressure or high-pressure differentials.

FIG:1.6 Model :VAC Cage Type Angle Valve

In cage type angle valves, the plug is provided with balancing holes so that the unbalanced thrust caused by fluid will efficiently cancel out each other. The design affords dependable operation at high-pressure differentials without requiring a large actuator. The valve plug is housed entirely in the cage, and strongly resistant to vibration and wear. 6

Table 1.1 Valve selection guide Ball

B’fly

Gate

Globe

Pinc

Plug

Poppet

Swing

Check Valve

P

P

P

P

h P

P

G

G

Contamination Free

G

F

G

G

G

G

F

P

Corrosive Fluids

G

P

P

G

P

P

G

P

Hydrogenic Fluids

G

P

P

G

P

P

G

P

Gasses

G

G

G

G

G

G

G

G

High ∆P

P

P

F

G

P

F

F

P

High Flow

G

G

G

G

G

G

G

G

High Pressure

G

P

P

G

P

P

G

P

High Temperature

G

G

G

G

P

P-G

G

G

Leaktight

G

P

G

G

G

G

G

P

Light Weight

G

G

F

P

F

G

G

G

Liquid

G

G

G

G

G

G

G

G

Low Actuation Force

F

P

P

P

P

P

G

G

Low Cost

G

F-G

G

F-G

S

G

G

G

Low ∆P

G

G

G

P

G

G

G

G

Low Flow Control

G

G

P

G

P

G

G

G

Rapid Opening

G

G

P

F-P

G

G

G

Relief

P

P

P

P

P

G

P

safety valve Seat

P

P

P

P

P

P

G

P

F

P

P

G

P

F

F-C

P

F-G

P

P

P

G

P

P

F

Smal physical size

G

G

P

P

P

G

G

G

Steam service

G

P

P-F

G

P

P

G

P

Tarqiling

P

P

P

G

F-P

P

G

P

Vibration free

F

P

P

G

G

G

P

P

Erosion

resistance Slurries

P= poor. Not recommended

P

F = fair, Better choice available

G = good, Recommended for use under normal conditions.

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CHAPTER 2

CONTROL VALVE SELECTION AND APPLICATION 2.0

INTRODUCTION

Valve selection depends upon the function the valve has to perform after it has been installed, the properties and working conditions of the working fluid. The material of the valve also depends on the working fluid. General valve functions can be On-Off service, Throttling service, Prevention of reverse flow, Pressure control and special functions that include Directional flow control, Sampling service, Limiting flows, Sealing vessel and other miscellaneous functions. 2.1

FLUID PROPERTIES

Specific gravity, viscosity, corrosiveness and abrasiveness etc. of liquid / gas / slurry handled through the valve should be known. An analysis of the system should be made, to determine passage of more than one fluid through the valve. 2.1.1 FLUID FRICTION LOSSES Various types of valve exhibit varying degree of pressure drops due to friction to the flowing medium. A system requirement of permissible pressure drop must be taken into consideration during valve selection. 2.1.2

FLUID PROPERTIES AND VALVE MATERIAL

The valve material selection is directly related to the fluid properties of corrosiveness and abrasiveness. The combination of operating pressure and temperature will also influence in determining the permissible materials of construction. . 2.2 OPERATION CONDITIONS Establishment of actual operating conditions of each valve will simplify valve selection procedure. One normally encounters the following while selecting the Control Valves for different applications. a. b. c. d. e. f. g.

Leakage Rangeability Cavitations Noise, Vibration & Flow Velocity High Pressure High Temperature Low Temperature

8

h. i.

Low Flow Viscous and slurry streams

2.2.1 LEAKAGE Any flow through a fully closed control Valve when exposed to the operating pressure differentials and temperatures is referred to as Leakage. It is expressed as a cumulative quantity over a specified time period for shut off designs and as a percentage of full capacity for conventional control valves. (Refer American national standard control valve seat leakage Appendix-1). 2.2.2 FACTORS EFFECTING LEAKAGE Normally the valve co-efficient (leakage) is applicable to fully closed valve. This figure applies only to the new valves or valves operating at ambient temperatures with clean working fluids. After a few years of service valve leaks vary drastically as effected by the factors such as erosion of seat materials and due seating forces, fluids carrying abrasive particles, temperature variations, pipe line forces. The general experience is that either the valve body is at a different temperature than the trim or the thermal expansion factor for the valve plug is different from the expansion factor for the body material. In such cases it is usual practice to provide additional clearance to accommodate the expansion of the trim, when designing a valve for hot fluid services. If this valve is operated at low temperatures the leakage will be higher. Temperature gradient across the valve can also generate strains that promote leakages. eg: three way valves used for combining services where the two fluids involved are at different temperatures. Strain thrusted on control valves by pipes will lead to leakage. Hence, sufficient supports to pipe line should be provided such that the control valve will not be loaded with excessive bolting strain when connecting it or placing it in the pipeline. Seating materials are selected for compatibility with service conditions and stellite or hardened stainless steel is an appropriate choice for non-lubricating, abrasive, hightemperature and high pressure drop services. These hard surface materials increase the life of valves by reducing the risks or cuts occurring on the seating surfaces. 2.2.3 RANGEBILITY Rangebility of a control valve is defined as the ratio between the maximum &minimum flows within the limits of the inherent flow Characteristics of the Control Valve. The rangebility of a regular cage type and contoured type Trim is 30:1. a. It tells the points at which the valve is expected to act on off or lose control completely.

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b. It establishes the points at which the flow – lift characteristics starts to deviate from the expected. 2.2.4 NOISE The noise is generated by the passage of process fluids through the interior of the valve. Three main types of noise occur due to mechanical vibration, cavitation and aerodynamics. Each can be avoided or alleviated but the methods are very expensive. 2.3

VALVES FOR HIGH PRESSURE AND TEMPERATURE

Control Valve for high pressure and high temperature applications require special selection of materials and design to ensure long and trouble free service. 2.3.1

VALVE BODY

Materials chosen for the valve body should have enough tensile yield and creep resistance to withstand high temperature. Alloy castings as per ASTM A217 are usually specified for body components of valves handling steam and other non-corrosive fluids at temperature between 400 to 500 0 C. These alloys meet the pressure and temperature ratings listed under carbon-moly and chrome-moly steels of ANSI B 16.5. , Grade WC1, a carbon moly alloy and grade C 5, a chrome-moly alloy are the most commonly used. Grade C 5 is often used on valve bodies handling steam condensate and boiler feed water in power plants even though the pressure and temperatures are low. Molybdenum provides creep strength at high temperatures and chromium adds to corrosion resistance and strength. All these steels are of welding quality and should be annealed after welding. Chrome-moly alloys have higher hardness, which helps to withstand flashing and cavitation of high-pressure liquids like feed water. The end connection used for high temperature valve is butt-welding. Welded connection avoids leakages through flanged joints subjected to thermal cycling. 2.3.2

BONNET

Bonnet materials are same as that of valve body materials. For temperature above 2000 C, an extension bonnet with radiating fins is used. Where this construction is not practical special high temperature packings are used. Braided asbestos with inconel wire reinforcement and lubricated with graphite permits operation up to 540 0 C. Graphoil a new form of solid carbon packings may be employed at temperatures of 800 0 C and above. 2.3.3 BOLTS The bolting used on Cast steel and alloy steel bodies is generally as per ASTM A 193.The grade commonly used up to 450 0C is B7 and B14 for higher temperatures. Nuts used on studs are generally as per ASTM A 194, grade 2H for temperatures up to 450°C and grade 4 or 8 for higher temperatures.

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2.3.4 TRIMS FOR HIGH PRESSURE DROP Flashing and cavitations occurs under high-pressure drop of liquids as in the case of feed water valve. It further causes hydrodynamic noise. To avoid this, the trim is so designed that the pressure drop is made to occur in steps. The pressure drop at each stage is so designed that the pressure of the liquid does not drop below the saturated vapour pressure at the Temperature.

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CHAPTER 3

CONTROL VALVE FLOW COEFFICIENT 3.0

INTRODUCTION

Once the type of valve is chosen for an application the next step is to determine correct size. Control valve sizing will give the optimum port size for better controllability and performance of the system. Using higher size will abnormally increase the cost and lower size will not meet the requirements of the process. Also, based on discriminating analysis of past experience it is necessary to get correct data for arriving at correct sizing of a valve. For example, if it is assumed that the flow is large but the pressure drop across the valve is excessively low then both these factors lead to a larger valve size. This will result in higher investment, hence the actual flow rate and pressure must be known to arrive at correct size. 3.1

VALVE COEFFICIENT / FLOW COEFFICIENT OF VALVES (Cv)

Cv is actually a means of knowing the relative capacity of each size of valve. By definition it is “the number of GPM of water at 60° F that will pass through the valve with a pressure differential of 1 psi”. Cv for liquids (Water) V √G/DP OR V = Cv √DP/G OR DP = G ( V / Cv) 2 Cv =

Where

Cv : Flow coefficient of valve DP: Pressure drop (psi) at maximum flow G : specific gravity at fluid temperature V : flow volume (U.S.g.p.m) at fluid temperature

Different valve designs will have different Cv. The numerical example is worked out below for evaluation of Cv. Example Calculate the Cv value for the following conditions, Maximum flow = 600 g.p.m. Fluid Temperature = 500°F Specific gravity = 0.7 at 500° F Pressure drop = 70 psi Cv = V √G/DP = 600 x √ 0.7 / 70

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= 60 3.2

DETAILS REQUIRED FOR SIZING OF VALVE The following information are required for optimum sizing of the valve. i)

Flow application data a) Flow rate b) Pressure c) Temperature

ii)

: Maximum, minimum & normal : Upstream, downstream at maximum, minimum and Normal flow. : Of the fluid

Fluid data a) Name of the fluid b) Fluid phase : liquid, gas, or slurry etc. c) Density, specific gravity, specific weight, molecular weight etc. d) Viscosity (Liq) e) Vapour pressure (Liq)

iii)

Piping influence: Presence of reducers or other disturbances at the valve which will change the rated capacity.

iv)

Valve selection information. a) Range ability b) Corrosion & erosion resistance. c) Special requirement (tight shut off, low noise etc)

v)

Sizing calculation Manufacture`s sizing co-efficient, sizing formulas, monographs etc.

3.3

VISCOSITY CORRECTION

Viscosity represents a factor of flow resistance of a fluid. One can experience a well-known fact that water flows out of a bottle rapidly than honey, at the same temperature. The reason is viscosity of honey. If water and honey are allowed to pass through same type of valve with same temperature and with same pressure, more water flows out than honey in the given time. For the same quantities of water and honey to flow out of the valve in the same period, the valve opening for honey flow must be made larger, than that of water flow.

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No viscosity correction is required for a fluid having viscosity less than 100 ssu (saybolt second universal). In other cases, viscosity correction should be made to get reliable results /flow. Steps for calculation of viscosity factor are given below. 1. Calculate the Cv value as mentioned in example of section 3.1 using flow and pressure drop. 2. Calculate viscosity factor R by using equation B for process fluid having viscosity more than 200 ssu or equation A if the viscosity is less than 200 ssu after converting the unit into cs (centistokes) µcs =( (0.22) (µssu) – 180/µssu)) Equation A: factor R = (10,000) (v) / √ Cv x µcs Equation B: factor R=(46,500)(v)/ √Cv x µ ssu where , v: flow volume (g.p.m) µssu : viscosity (say bolt seconds universal ) µcs: viscosity (centistokes) 3. On the viscosity correction curve (Fig3.1), read the correction factor at intersection point of factor R 4. Multiply the Cv value calculated in step (I) by the correction factor. 5. Use this corrected Cv to select the valve type / size from the published Cv data. Example Calculation of Cv value when maximum flow, specific gravity at operating temperature, pressure differential across the ports and viscosity of fluid are known. Conditions of process: Maximum flow

= 42g.p.m (100° F)

Fluid temperature

=100° F

Specific gravity

= 0.95 (at 100° F)

Pressure differential

= 5 psi

Viscosity

= 2800 ssu (100°F)

Cv = v √g/∆p = 42√0.95/5 = 18

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Cv Correction factor

VISCOSITY CORRECTION FACTOR Fig 3.1 Cv after applying viscosity correction is as below 1. Cv = v √g/∆p = 42 √0.95/5 = 18(approx) 2. Since the viscosity is greater than 200 ssu,calculate factor using equation B Factor R = 46,500 X 42 √18 x 2800

= 163 (approx)

3.

from the correction curve (fig) the Cv correction factor to be 1.30

4.

The corrected Cv value is calculated to be 18 x 1.30 = 23.4

From the Cv value a valve can be chosen by matching the calculated Cv to that of the manufacturer’s Cv verses port size chart for different valves. This may result in more than one type, which may have to be restricted by selecting suitable type of valve for particular application as Table 1.1 3.3

FLASHING OF LIQUID

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The state of fluid depends on its temperature and pressure. When the temperature is below the boiling point, the fluid is in the liquid state. When the temperature is higher than the boiling point, the fluid is in the gas state. The boiling point, is a function of the pressure, as the pressure is higher, the boiling point is higher. In certain applications the fluid enters the valve inlet, in liquid state, and flows out as a mixture of gas and liquid or in gaseous state. This indicates that the fluid while passing through the control valve changes its state partially or fully to a gaseous state between inlet and out let of the control valve. In this circumstance, a problem of whether the fluid is to be regarded as liquid or as a gas for valve sizing arises. It is impracticable to accurately measure flashing, and reliable formulae for valve sizing for flashing fluids are not available. In such cases the formula for flashing water described below gives a closer solution. When hot water at or near saturation temperature flows through a control valve with, pressure reduction, thermo dynamic consideration indicates that a mixture of water and steam will exist at the outlet of the valve. For determining Cv value and valve sizing in such cases, the allowable pressure drop is calculated, result is compared with the desired pressure drop, and smaller of the two is used as ∆P in flashing liquid equation. 1. The allowable pressure drop, when the in let temperature is lower than the saturation temperature by 5°F or over, is determined as shown. Allowable pressure drop = 0.9 (P1- Ps) Where, P1 Ps

= Inlet pressure (Psia) = Saturation pressure (Psia) corresponding to inlet temperature

EXAMPLE Calculate the Cv value known conditions are: Inlet temperature = 330° F Inlet pressure

= 165 Pisa

Outlet pressure = 95 Pisa Pressure drop

= 70 Pisa

Maximum flow = 350 g.p.m water Solving the for Cv 1. Pl = 165 psia (saturation temperature = 366°F) Ps = 103 psia (saturation pressure corresponding to inlet temperature 33 0°F

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2. The inlet temperature (330°F) is lower than the saturation temperature by 36°F. 3. Allowable pressure drop =0.9(165-103)=55.8 Psi. 4. Since allowable pressure drop is lower than the desired pressure drop therefore, this figure is used for Cv calculation in this case. C v =46.8. When the inlet temperature is lower than the saturation temperature by 5°F or less, the equation given below is used to determine the allowable pressure drop Allowable pressure drop = 0.06 P1 Where P1 = pressure (Psia) at inlet EXAMPLE Calculate Cv value known conditions is. Maximum flow Inlet temperature Inlet pressure Pressure drop

= = = =

70g.p.m. water 340°F 120 Psia 30 Psia

Solving for Cv 1. 2. 3. 4. 5.

P1=120 Psia (saturation temperature=341°F) The inlet temperature is lower than saturation temperature by 1°F. Allowable pressure drop = 0.06 x 120=7.2psi This pressure drop figure is lower than the actual pressure drop (30 psi) and, therefore, this figure is used for calculation. Solving the equation (for liquid) for Cv, Cv = 26

3.4 LIQUIDS OTHER THAN FLASHING WATER As mentioned earlier, accurate measuring methods of flashing water are not available, therefore empirical methods are used for sizing of valve. A method often used for flashing liquids other than water involves a) flashing degree is estimated b) C v values for liquid and gas are separately calculated and c) the two C v values are added to obtain the required Cv value. This method results in a large Cv and valve size becomes slightly larger than actually required. In this method it is assumed that steam or gas existed already when the liquid entered the valve and that the flow speed of steam or gas is same as that of liquid. EXAMPLE Fluid Maximum flow Flashing rate Fluid temperature Pressure drop Inlet pressure Outlet pressure

ammonia 100 g.p.m 10% 83° F 50psi 150psig. 100psig.

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Specific gravity (gas) Specific gravity (liquid) Solving for Cv

0.596 0.89

1. Estimate the liquid and gas flow volumes of the valve. (a) 90% of 100 g.p.m = 90 g.p.m of liquid. (b) 10% of 100 g.p.m=10 g.p.m of gas. As converted into scfh 10g.p.m of gas =97.810 scfh 2. Calculate the Cv value for liquid G 0.89 = 90 =12 ∆Ρ 50

Cv =V

3. Calculate the Cv value of gas by the formula Cv =

Q 963

GTa 97810 = P( P1 + P 2 ) 963

0.596( 460 + 83) = 15.22 50(164.7 +114.7 )

Q = quantity of gas in standard cubic feet /hour at 14.7psia and 60 OF G = specific gravity at 60 deg. F Ta = Absolute temperature (460+ OF) P = Pressure drop P1= Inlet pressure(Psia) at maximum flow P2 = Out let pressure(Psia) at maximum flow 4. Addition of the above two values gives the C v value 12.00+15.22=27.22 3.5

VALVE SIZING FOR GASES

Gas is a compressible fluid and its density depends up on pressure. As the gas flows through the control valve, its density varies as its pressure falls. All formulae for valve sizing for gasses assume average densities. Valve size becomes smaller if the upstream density is used, it becomes larger if the downstream density is used. The density cannot be ascertained accurately. It is assumed that the gas is of ideal nature and the relationship between pressure and density is linear. The formulae are based on an assumed density of average pressure, which is (P1+P2) / 2.The assumption has been proved to be effective through actual application tests.

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Equation 1 When the pressure drop is less than a half of the inlet pressure ( inlet absolute pressure ) Cv =

Q 963

GTa ∆Ρ( P1 + P 2 )

Equation 2 When the pressure drop is equal to or more than a half of the inlet absolute pressure : Cv =

Where:

Q GTa 835P1

Cv : Flow coefficient of valve G : Specific gravity at 60 0 F(air = 1.0) P1 : Inlet pressure(psia) at maximum flow. P2 : Out let pressure(psia) at maximum flow. P : Pressure drop (psi) at maximum flow. Q : Flow ( ft 3 / hr ) at 14.7 psia ,60 0 F Ta : Absolute temperature (460+ 0F)

EXAMPLE Maximum flow = 1,500,000 scfh. Pressure drop = 40 psi. Specific gravity = 0.6 (at 60 0F). Inlet pressure = 140 psig. Outlet pressure = 100 psig. Inlet temperature = 200 0F. Cv =

1,500,000 963

0.6( 460 + 200 ) = 295 40(154.7 +114.7 )

Since ΔP is smaller than a half of P1 (inlet absolute pressure) equation 1 is used. EXAMPLE Calculate the Cv value . known conditions are: Maximum flow = 105 scfh. Pressure drop = 800 psi Specific gravity = 1.0 at 600F. Inlet pressure = 103 psig. Outlet pressure = 200 psig. Fluid temperature = 2200F. Since ΔΡ is greater than a half of P1, equation 2 is used. 19

Cv = 10 5

3.6

1.0( 460 + 220) = 3.1 835(1014.7 )

STEAM

Valve sizing for steam applications, the formulae is derived from liquid formulae employing appropriate unit conversion factors. Formulae are developed on assumption that steam follows the law of the ideal gas. Errors encountered in this method of valve sizing for steam applications are found to be negligible. 1.

When the pressure drop is less than a half of the absolute inlet pressure Cv =

W (1 + 0.0007 s )

2.12 ∆Ρ( P1 + P 2)

2. When the pressure drop is the same or more than half of the absolute inlet pressure W (1 + 0.0007 s ) Cv = 1.84 P1 Where: W = lbs/hr P1 = inlet pressure (psia) P2 = Outlet pressure (psia) Cv = flow coefficient of valve. S = super heating EXAMPLE Maximum flow = 45x103 lbs/hr Outlet pressure = 250 psig. Inlet pressure = 380 psig. Pressure drop = 130 psi. Superheating = 2000F. Cv =

W (1 + 0.0007 S )

2.12 ∆Ρ( P1 + P 2 )

=

45,000(1 + 0.0007 × 200 )

2.12 130( 394.7 + 264.7 )

= 83

Since ΔΡ is smaller than a half of P1 equation 1 is used. Example Calculate the Cv value. Known conditions are Maximum flow = 6 x 103 lbs/hr Inlet pressure = 100 psig. 20

Outlet pressure Pressure drop Superheating Cv =

= 20 psig. = 80 psi. =3

6 ×10 3 (1 + 0.0007 × 300 ) = 34.4 1.84(114.7 )

3.7 CONVERSION OF Cv FORMULA In this section the formulas for computation of Cv in metric units are given. FOR LIQUIDS Cv = 1.17V

G P1 − P 2

WHERE V = Maximum flow, m3/hr. G = Specific gravity.( water =1) P1= Inlet pressure, kg/cm2 P2 = Outlet pressure, kg/cm2. 3.7.1 2

VISCOSITY CORRECTION FORMULAE 1. First solve for the Cv, assuming no viscosity effect. 2. Solve for factor R from equations, A` or ,B` for viscosity in centi stokes / ssu .). 44,000V

 ( A') Cv Mcs 204,600V R=  ( B ') Cv Mssu R=

: Maximum flow,m3/hr : Centistoke at flowing temperature Cv : Cv value uncorrected for viscosity. Mssu :SSU at flowing temperature Eq A` valid for viscosity < 200 SSU Eq B` valid for viscosity > 200 SSU. V Mcs

3. Intercept of factor R with the viscosity curve gives the correction factor. 4. Multiply Cv by the correction factor of step 3. 5. Use this corrected Cv to select the valve size from the metric Cv table . FOR GASES

21

1. The following formula shall be used for calculation with no corrections when maximum flow is given at the standard conditions ( 760 mmHg and 15.6 0C) When

ΔΡ < P1 / 2

Cv =

∆P ≥

When

Q 287

G ( 273 + tf ) ∆Ρ( P1 + P2 )

P1 2 CV = Q

( 273 + tf )G ) 249 P1

Q : Max. flow (m3 /hr) at 760 mmHg, 15.60C G : Specific gravity(air = 1) tf :Fluid temperature( 0C ) P1 : Absolute inlet pressure (Kg/cm2 abs) at maximum flow. P2 : Absolute outlet pressure(kg/cm2 abs) at maximum flow ΔΡ = Pı - P2 (kg/cm2) FOR STEAM For the case∆Ρ <

p1 2

Cv =

WK

13.67 ∆Ρ( P1 + P2 )

For the case ∆ P = ≥ P1 / 2 Cv =

WK 11.9 P1

W : Maximum flow(kg /hr) P1 :Absolute inlet pressure(kg/hr abs) P2 :Absolute outlet pressure(kg/cm2 abs) ΔΡ = Pı - P2 (kg/cm2) (NOTE: P1 and P2 denote the pressure at maximum flow.) 22

the

K: 1 + (0.0013 x superheat0 C) FOR VAPORS

Cv =

W V1 + V2 1210 ∆P

When P2 < ½ P1, use p1/2 in place of ΔP, V2 used must be that corresponding to P1/2 W : Maximum flow (kg/hr) V1 : specific volume (cm3 / gr at P1) V2 : specific volume (cm3 / gr at P2) P1 : Absolute inlet pressure (kg / cm2 abs.) P2 : Absolute outlet pressure (kg / cm2abs.) ΔP : P1 - P2 (kg/cm2) P1 and p2 denote the pressure at maximum flow. Note Kv VALUE: wherever the valve capacity is expressed in Kv it denotes the maximum flow rate of water through the valve in m 3/ hr under a pressure differential 1kg/cm2. The relation between Cv and Kv is given as Cv = 1.17 Kv. 3.8

BUTTERFLY VALVE Cv

Flow Co-efficient of butterfly valve for regulating and on of services are derived from the below formulae. 1. Cv = 17D (for 60 % opening) Cv - flow co-efficient,

D - port diameter in inches (regulating service)

2. Cv = 27D (for 90% opening)(on-off service) 3.9

SPECIAL FEATURES OF BUTTERFLY VALES 1.

Valve is specially meant for low-pressure drop application at low static head.

2.

It is very economical because cost of metal required for valve body us very less in comparison with globe type valve body.

3.

Tight shut off is achieved by providing resilient sealing on the body or vane.

4.

Whenever valves are used for high temperature service it is supplied with metal searing having sear leakage, confirming to reputed internal standards.

5.

Design is very compact. 23

6.

Actuator torque required is very less in comparison with any other valve.

7.

Valve is well balanced at fully closed condition.

8.

Valve can be used for throttling service between 10-60 opening beyond this it causes instability and no control.

9.

It reduces the pumping cost because pressure drop across the valve is very less.

10. It has maximum flow capacity. 11. Space required for the valve is minimum on the pipeline. 12. Installation and handling is very easy.

Table 4 –Typical Cv values for different Valves and port sizes. Port Three way valves size VTM VTD ANSI 300lb Or Lower

Adjustable port valves VzA

½

Port size (mm.dia.)

80

24

butterfly valves VBL VBM VBH JIS 10 Kg/cm2 160

VBS JIS 10 Kg/cm2 VBZ ANSI 300, 600 lb 160

¾

6.3

100

280

260

1

10

125

450

410

1¼

-

150

610

580

1½

23

200

1,040

960

2

40

100

250

1,700

1,550

2½

63

130

300

2,480

2,250

3

90

70

140

350

3,300

3,000

4

160

130

250

400

4,350

4,000

5

250

200

420

450

5,500

5,000

6

360

270

570

500

6,800

6,200

8

640

480

1,000

550

8,200

7,400

10

1,000 750

1,600

600

9,800

9,000

12

1,440 1,080

650

11,400

700

13,300

750

15,300

800

17,300

900

21,900

1,000

27,000

CHAPTER 4

OTHER METHODS FOR VALVE SIZING 4.0

INTRODUCTION

25

Once the Cv of a valve is known, the amount of flow at a given pressure drop can be found, conversely, the pressure drop can be determined for a specific flow. On the other hand, for a specified flow and pressure drop, the flow coefficient can be computed and the type and size of the valve to be used can be determined from published Cv data. In this chapter various formulas for valve sizing and equivalent orifice method of valve sizing is described. 4.1

DETERMINATION OF PROCESS PARAMETERS FOR VALVES

Various parameters like differential pressure, flow of viscous fluids and selection of suitable valve from published Cv data for 2” valve is dealt here by means of numerical examples. The Cv values for 2” valves are given in Table 4.1 below.

TABLE 4.1 : TYPICAL Cv VALUES FOR 2 in. VALVE TYPE

Cv

Angle valve Ball check valve Ball valve (full port) Ball valve (standard port) Butterfly valve Coaxial valve Cone poppet check valve Flat poppet check valve Gate valve Globe valve Pinch valve Plug tapper valve Swing check valve y-valve 45° angle 60° angle

64.0 154.5 228 120 145 154.5 166 133 210 44.34 181 70 138.2 72.0 70.2

EXAMPLE To calculate the expected pressure drop in a 2 in. full port ball valve is to carry water at a rate of 556 gpm. From Table 4.1 Cv = 228, thus: ∆P =

556 228

= 2.44 ∆P = 5.95 psi

26

EXAMPLE A 2-in. globe valve is allowed a pressure drop of 64 psi when carrying water. To calculate the gallons/ minute of oil (specific gravity 0.8, kinematic viscosity 0.82) that will pass through the valve and the expected pressure drop. The kinematic viscosity of water is 0.93. From Table 4.1 Cv = 44.34, thus: ρ2 ρ1

∆P2 =

1/ 4

 µ2 ρ1     µ1 ρ1 

1 = S

 v2  v  1

∆P1

1/ 4

   

∆P1 1/ 4

1  0.93    0.8  0.82  = 82.56 psi =

64

82.56 0.8 Q = 450.43 gpm Q = 44.34

EXAMPLE Determination of an appropriate type of 2 in- valve to carry 100 gpm of water with a pressure drop of 1.98 psi across the valve. Cv =

Q ∆P

100 1.98 = 71 =

From Table 4.1 it is seen that a 60° angle valve will meet the requirements. Table 4.2 EQUATIONS FOR VALVE SIZING

27

Computation of Q – flow quantity in gpm. Computation of deo – equivalent orifice Computation of d - trail and error method of equivalent orifice. Computation of W - lbs./hr

∆P = 1.8 × 10 −5 CV =

29.9d 2 L K

ρ 62.4∆P

CV = W =

W =

KQ 2 d 4L

C f AP1 RT1 C f AP1 RT1

 2   gγ   γ +1

(γ +1)(γ −1)

2 gγ  P2  γ − 1  P1 

  

  

(γ +1) / γ

  

∆P S ∆P P

Q = 7.9C v Q = Cv

P −  2  P1

∆P S

Q = 29.81C f d 2 Q = Cv

2/γ

 62.4  ∆P  ρ     ∆P ρg

Q = 236d 2 l d EO = 1.292

dL K

d EO = 0.2365 CV d EO = C ( d L )1.07  Q d =  29.81C f  2

1/ 2

   

 Q  ρ ∆P =  C    V  62.4

1/ 4

 S     ∆P 

28

4.2

EQUIVALENT ORIFICE METHOD

Since the flow through a sharp edge orifice can be conveniently calculated with good accuracy, it would be desirable to relate flow through a valve to that through a sharp edge orifice. This can be done to high accuracy with the use of the equivalent orifice method. This procedure consists of three basic steps. The first step is to compute the sharp edge orifice diameter. This can be found from one of the following equation (see Table 4.2 for alternate forms of equation) for liquids, depending on known quantities. Q = 29.81C f d 2

∆P S

formula for gasses under sonic flow conditions. W=

C f P1Π d 2 4

RT1

 2   gγ   γ +1 

( γ +1) / ( γ −1) )

29

The next step is to determine the equivalent orifice diameter from one of the following equations depending on known quantities. 1.292d L d EO = 4 K = 0.2365 CV = 0.3162

F

. If dEO can be computed, an adjustment is made in one or more parameters until dEO is made equal to d. This can be done by changing d L for a value of known K or by changing K to meet a required line size. If neither is known, K may be computed from

A2 C 2V A2 K = 449.44 2 F K = 1459.24

or

and the line size chosen to meet this K-factor. Alternatively, a new valve and K factor may be chosen to fit a line size. If dEO cannot be computed from known information, a trial and error procedure can be used. Set d EO equal to d and use figs.4. 1 and 4.3 to choose a valve. From its coefficient C and d EO find the proper line diameter, or conversely, from a required line diameter find the valve type from the coefficient C. once the valve coefficient and line diameter are known, the K-factor for the valve may be found from fig.4.2. In summary, to fully size a valve for a given flow and pressure drop, determine the coefficient C, the K-factor of the valve, and its line diameter. Note that one or two, but not all of these may be specified before hand. All three may be specified if the flow and/or pressure drops are not specified. Example A 1½ -in full port ball has a valve flow coefficient C of 1.7. The number of gallons per minute of water it will pass with a pressure drop (∆p) of 1.2 psi is found as follows. From fig.4.3 for C = 1.70 ,dEO = 2.62 in . Hence

Q = 29.81C f d 2

∆P S

= 29.81(0.6)(2.62) 2 1.2 Q =134.5 gpm

30

31

Valve flow coefficient C. The value for Valves is based on full ported design. Fig 4.1

32

Vlave Configuration C

Head Loss Fdactor K

HEAD LOSS FACTOR FOR VALVES Fig 4.2

33

Inside diameter of line , d L(in)

d Eo= C(dL)1.07)

(In) EO

Equipments orifice diameter ,d

Valve flow coefficient C

BUTTERFLY VALVE Cv-

Inside Diameter dL ( in)

Inside diameter of line dL (in) FIG 4.3

34

CHAPTER 5

PLUGS AND THEIR CHARACTERISTICS 5.0

INTRODUCTION

A plug is a closure member of a valve. This part of the valve actually closes the orifice to stop the flow. Depending on the shape of the plug different flow characteristics can be obtained. Here three main contours viz. Equal percentage, linear, quick opening normally encountered in process application are explained. 5.1

EQUAL PERCENTAGE CONTOUR PLUG

This is designed to give a constant rate of change of flow for unit change in lift, i.e. equal increments of lift produces a ‘rate of change’ in flow which is proportional to the amount flowing before the change occurred. It provides the necessary control characteristic where control is required over a wide range and meets the majority of installation requirements. Contours of 50:1 ratio are generally available. This plug is usually employed in the following applications.

   

Where the pressure drop across the valve is a small portion of the total e.g. generally less than 40%. Where the pressure drop across the valve varies widely e.g. storage vessel run – down or varying set point conditions. Where the required valve capacity is uncertain as it is more difficult to oversize a valve for this characteristics. Where ever considerable lag exists in the system and for reasons when the rate or derivative action is in the controller.

35

Fig 5.1 5.2 LINEAR CONTOUR PLUG In linear contour plug the flow characteristics are linear.the fluid flow is in direct proportion to the valve lift. Equal increments of lift produces equal increments of flow through out its range. This is usually employed in the following applications a) Where the pressure drop across the valve is always more than 40% of the total pressure drop . b) Whenever corrective action requires to be linear and at the same rate throughout the range of opening e.g. the level control of a constant cross sectional vessel.

36

c) Where the process lag is small and the proportional band is less than 10% . 5.3

QUICK OPENING PLUG

The flow characteristics in this type of valve will be maximum flow for minimum travel. The plug is basically a flat disc with the addition as a linear contour for the first 25% of the stroke to counteract severe line shock. Hence it is also called as semi throttle poppet or beveled plug. This trim is employed in normal on- off control applications. The plugs are of reduced stroke and cylinder actuators are used for quick action. 5.4

TRIM

Trim generally refers to the removable internal parts of a valve which come in contact with the flowing fluid. The components included in trim are different depending on the type of valve, but they usually include packing retaining ring, stem, stem lock pin, guide bushing, valve plug and seat ring(cage). The standard materials used for trim are 304 SS, 316 SS and precipitation hardened stainless steels(440-C for guide bushing) Selection of the most suitable material must be made with due consideration of the temperature, pressure differential across the valve plug and corrosive conditions.

37

VALVE PLUG AND SEAT RING (CAGE) Fig 5.4

38

5.5

CAGE AND PLUG

Cages are employed in the control valves to reduce the aero dynamic noises and to reduce the unbalanced forces which causes vibration in trim parts. Flow characteristics of a cage valve are determined by the shape of the opening provided within the cage, and can be either “equal percentage” (%V) or “linear” (LV). The plug is available with Teflon seat.

Valve characteristics Fig 5.5

39

5.6 PLUGS FOR ON-OFF SERVICE The plugs for this purpose are available in two types: with Teflon seat and with stellite seat. Both types can provide bubble-tight shut off. On-off plug with Teflon seat This type is used when the fluid temperature is under 120 deg c and an absolute seal must be ensured. For sizes larger than 11/2 inches, the linear contoured plug with Teflon seat is used for on-off services. On-off Plug with satellite seat This type is used when the use of the Teflon seat plug is unfeasible. The satellite is finished with particularly careful lapping.

Fig 5.6

Steam Jacket A steam jacket accessory is to be used with fluid causing condensations when cooling down. 5.7

SPECIALITIES OF HIGH PRESSURE FEED WATER CONTROL VALVES

Feed water control valves face particular problems such as high and variable pressure drops, high velocities, sudden temperature changes and flashing conditions all of which impose severe mechanical and thermal shocks on the valves. Special care has to be taken to decrease the turbulence to the minimum and thereby increase the life of the internals as well as the body. Many design innovations have been incorporated by renown manufacturers for such duties, which are explained below. 5.7.1

MUFFLE CHAMBER TRIM (Fig 5.7)

This is a cage guided throttle plug type, designed to reduce the discharge pressure of flashing fluids where noise is a problem. The cage normally is extended downstream of the seat and a series of baffles incorporated in the bore. Long operational 40

life is attained by using solid satellite for the valve seat and linings of the baffle orifices. Pressure reflections from the baffles together with careful design of the plug combine to effect a considerable noise reduction at valve outlet. 5.7.2

SPEICAL CAGE TRIM (ANTI-FLASH TRM)(Fig 5.8)

This embodies a cylindrical seat-ring and a guide with several tapped holes. The size and number of holes (or ports) are dependent upon the flow coefficient and flow characteristics. The holes are tapped (ports are rough finished) to provide turbulence within themselves and the direction of flow so as to allow each high velocity jet to impinge on each other within the seat ring throat, which in turn acts as energy absorber of the flow medium. The upstream potential energy developed by the inlet pressure is converted to heat via fluid friction by massive turbulence within the throat of the seat ring itself, which provides for continuous contact between parts within the valve and fluid. Hence, discouraging cavity formation. It also provides pressure reducing with no pressure recovery, thus precluding low pressure and within the valve which may fall below the vapour pressure of the fluid 5.7.3

CASCADED TRIM (Fig 5.9)

This is designed to overcome the severe conditions imposed by extremely high pressure drops, thus offering longer valve life with minimum maintenance. An extension of the valve plunger in a guide downstream of the main valves seat and a series of annular grooves or steps in one of them help produce a cascade effect each step contributing to a pressure drop with minimum of vibrations. Thus the drop across the valve seating surface is a fraction of the total and the internal stream velocities are greatly reduced to attain minimum erosion, cavitation and noise. In all the above designs, special materials for internals such as satellite, 17.4 PH SS, Colmonoy-6 or 440-C are adopted to resist the duty and give trouble-free service.

41

Fig 5.7,5.8 and 5.

42

CHAPTER 6

VALVE INSTALLATION 6.0 INTRODUCTION The satisfactory performance of control valve depends on proper installation. Correctly sized and selected control valve might fail in performance, if the installation has not been carried out as per the requirement and established practices. And further it may lead to serve damage to the piping or equipment installed down stream of control valve. Safety of manpower and equipment is one of the prime considerations in any industrial installation. While designing a control valve, adequate safety factors should be taken into consideration, in selecting the material for body, and for internal parts of control valve, keeping in view the pressure and temperature of the fluid to be handled. Even after taking all precautions during design and manufacturing stage, of a control valve, there is a possibility of leakage through gland or gaskets during commissioning or at a later stage of operation. 6.1 INSTALLATION PRECAUTIONS It is important and very essential, that the location for installing the valves be selected in such a way that leakage does not harm the operator and equipment located near by.In the event of shut down, control valves are likely to retain system pressure. This pressure must be released before attempting for any maintenance work on these control valves. Particularly in case of tight shut off valves installed along with block valves, trapping of fluid at considerably higher pressure is possible. Even at low pressure toxic fluids can endanger the life of a technician while opening the valve. In such application adequate venting and draining facilities are essential in the piping system. Further, these vents and drains may have to be terminated in safer locations. It is a known fact, that the control valve can be considered as a variable orifice and as such piping arrangement recommended for orifice assemblies would apply to valve installation also to a great extent. It is always preferable to allow 10 to 20 pipe diameters of straight run upstream and 3 to 5 pipe diameters of straight run down stream of control valve. Straight run at inlet ensures the steady inlet pressure of the fluid at different flow conditions. It is ideal to provide control valves with the facility for manual operation. In that case location of control valve be easily identifiable by the operator. Suitable monitoring instruments should be provided in the vicinity, so that the operator can observe that change in the parameter while manually operating the control valve. 6.2 PREVENTIVE METHOD FOR THERMAL EXPANSION the valves used for isolation application and handling high temperature fluids, will experience the entrapment of fluid in the bonnet portion of the valve. This fluid temperature may rise due to adjacent pipe or an external source. This will cause fluid thermal expansion. Therefore the internal pressure in the bonnet section will rise and the

43

valve will not open due to high stem torque required. Following measures are adopted to avoid over pressurization due to liquid thermal expansion. 1. For the valve to which hydrostatic test pressure is applied from same direction as flow, a balance hole is provided to connect the disc pressure applying side of the disc to the chest of main valve body.(refer fig. in next page). 2. For the valve to which hydrostatic test pressure is needed to be applied from both inlet and outlet or from opposite side of flow, the outside balance pipe (a stop valve is installed in between) should be provided from chest of main valve body to the up-stream side, and when testing hydraulically, the balance valve should be closed and while operating this valve be fully opened and locked.(refer fig in next page). 3. For the valve of which flow direction may be changed by the operational condition, the balance pipes with an intermediate stop valve shall be provided from the chest of main valve body to both inlet and outlet of main valve, the stop valve in high pressure side during operation shall be normally opened.(refer fig in next page).

44

45

CHAPTER 7

CONTROL VALVE INSPECTION PROCEDURE 7.0

INTRODUCTION Control valves are essentially metallurgy intensive, and they have to withstand extreme temperature, high-pressure, stresses and other usual environmental conditions. In fact control valve applications call for special alloys containing FERROLIUM, TITANIUM, ZERCONIUM etc, to cater the multifunctions of the valve. From design point of view, and user point of view to ensure the quality the control valves should be inspected to establish their viability for specific application. Inspection mainly comprises of, material inspection, parts inspection, functional testing. 7.1. MATERIAL INSPECTION 7.1.1 PHYSICAL AND DIMENSIONAL CHECK Valve components are made from castings and forge materials. Hence external appearance inspection is required to check surface defects like blowholes, crack, shrinkage’s, flow directions, batch no’s etc. Apart from these, dimensions, shapes, profiles checks on random samples must be done depending on the importance of the parameters checked. 7.1.2 NON-DESTRUCTIVE TESTING (NDT) NDT is a versatile tool for maintaining the Quality of parts manufactured, and is used for find out sub-surface and surface defects of material. Some of the important NDT techniques are a) Radiographic examination b) Ultrasonic testing c) Magnetic particle test d) Liquid penetrate check. All the these tests help in finding the internal soundness of the material, parts and detect defects like blow and gas holes, porosity, cracks, shrinkage’s, etc. 7.1.2.1 RADIOGRAPHIC EXAMINATION X-rays OR Gamma rays are used for this type of examination. When a film exposed to radioactive isotope like Cobalt 60 or Iridium 192, an invisible change is produced in the film. When developed, the defects of material are exposed as dark patches, indicating the defects and their intensity. The tests are carried out as per ASTM standards class-III, ASTM reference standards E446 etc.

46

7.1.2.2. ULTRASONIC TESTING This test is based on the fact, that impedance offered by the metals of standard reference to the metals with the defects such as blowholes, cavities, to the sound waves are different. This helps in identifying the subsurface defects in terms of depth and magnitude. Valve body and bonnet castings and forgings are normally tested by this method. 7.1.2.3 MAGNETIC PARTICLE INSPECTION This test is carried out to find out the discontinuities in the ferro magnetic materials. Normally used to find out surface defects of the objects. This inspection is of three steps. a) b) c)

Establishing a suitable magnetic field in the test object. Applying magnetic particles to the surface of the test body. Examining the test object surface for accumulation of the particles.

7.1.2.4 LIQUID (DYE) PENETRANT INSPECTION This is one of the oldest methods of NDT process. This is a routine check based on penetrants seeping in to a discontinuity in the object body. Normally surface cracks or porosity are detected by this method. 7.1.3

PARTS INSPECTION

All the components of valves need to be made precisely so that it would facilitate a perfect assembly of mating parts. All the parts are subjected to a) Dimensional inspection for length, diameter threads etc. b) External appearance inspection. c) Pressure resistance test. d) Elasticity inspection e) Accuracy test f) Unit inspection 7.1.3.1 PRESSURE RESISTANCE TEST Valve bodies have to be tested hydraulically for their internal soundness by applying twice the design pressure of the valve for a period 10 minutes conforming to the applicable standards.

47

7.1.3.2 ACCURACY TEST Flow characteristic of the valve is dependent on the contour of the valve plugs and seat finishing. Therefore conformity to the design dimensions is very important. Up to 3inch size, plug is inspected in the profile projected by magnifying the object to 10,20 or 30 times with optical profile checking device. Sizes above 3 inch will be directly checked.Surface roughness and straightness of stem are also checked for good sealing and longer life. 7.1.4 FUNCTIONAL TESTING 7.1.4.1 SEAT LEAKAGE TEST Once the valve is assembled it is subjected to seat leakage test with plug in closed position, without the actuator. If it is a single seated valve, the leakage is checked by applying air pressure, and the double seated valves with water pressure. In the case of single seated valves leakage is measured with Rota meter calibrated to 0.01 l /min, and for double seated valves leakages are measured with measuring JARS which will give direct result. For leakages, less than 0.01 l /min, the leakage is measured by fixing a blind flange with a 6mm diameter copper tube to one valve flange. This tube is immersed in water and the air bubbles per min through water is counted, which gives direct readings of the leakage through valve. 7.1.4.2 ACTUATOR TEST (pneumatic actuator) Main parts of the actuator are the diaphragm casting, diaphragm and spring. The diaphragm chambers (casting) with diaphragm are tested with cyclic loading for about 10,000 times to assess their life span. After the test the diaphragm is checked for physical damage (this test is done on random basis for every 10 pieces). The valve spring is subjected to load at intervals of 25%, 50% and 100% in both directions and the relationship for the movement with respect to load will reveal the linearity as well as hysterisis if any present. Test for threshold sensitivity to determine no deflection must be conducted for adjustment of spring tension. 7.1.4.3 VALVE PERFORMANCE INSPECTION It consists of stroke test, valve open start and return point, linearity, hysterises,and evaluation of flow coefficient ie.Cv. 7.1.4.4 STROKE TEST The travel of the valve stem is tested by applying 0.2 to 1 kg/cm2 air pressure signal to the actuator.The travel should be within +or- 3% of the rated travel. Then by applying 1.2kg./cm2 the over travel also will be checked to ascertain the life of the valve. Valve

48

stroke is shown in figure below. Normally the allowable over travel will be given by manufacturer and depends on the type of valve.

Fig 7.1 7.1.4.5 VALVE OPEN START AND RETURN POINT The open start point of valve and return point must be within the prescribed tolerance in respect to the input pressure settings. 7.1.4.6 LINEARITY CHECK The actual travel of 25%. 50% and 75% input, the valve travel in the opening and closing direction are tested. The travel must be within the tolerances with respect to the set travels. The graph shows the linear movement of valve stem in ideal conditions with the input of 0.2 to 1,0 kg / sqcm & curves of stem travel with +1% and –1% deviations. Ideally the travel must be linear.

49

Fig 7.2 7.1.4.7 FLOW CO-EFFICIENT MEASUREMENT The flow co-efficient “Cv” is defined as the number of US gallons per minute of water that will pass through fully open valves for 1-psi pressure drop. The valve to be tested will be mounted on the pipeline of it size. Clean water is pumped under control pressure; the pressure drop is adjusted to one psi across the valve, using throttling valves and manometer. The flow rate is then measured with precession flow meters and the test can be carried out for 25%, 50%, 75% openings to find out the relation at respective opening. 7.2 CONTROL VALVE AUXILLARY INSPECTION The control valve performance mainly depends on the functional aspects at the connected auxiliaries, such as Valve positioner, Air filter regulator, Air lock relay, and position transmitters. 7.2.1. VALVE POSITIONER A valve positioner provides (auxiliary air supply) necessary pressure to the actuator so that the valve operates strictly as per the control signal in all circumstances even if abnormal conditions such as excess Gland friction etc, occurs. Further, air

50

flow rate for pilot assembly, top &bottom nozzle leakage checking is carried out to find out the air consumption and actual leakage respectively. No air leakage is permitted over the top and bottom nozzles when the signal is either minimum or maximum. 7.2.2 AIR FILTER REGULATOR These are tested to find out Regulator flow characteristics, Normal Air consumption (more than 0.92 l / min is not permitted) and overall leakage. 7.2.3 REGULATOR FLOW CHARACTERISTICS The inlet of the regulator is connected to the air supply and outlet to the rotameter and pressure gauge. A supply pressure of 1.4 or 2.6 kg/cm2 is set at the inlet without flow through regulator. Then air flow of 50 Nl / min is allowed through regulator, and the pressure drop across the regulator should not exceed 10%. 7.2.4 OVERALL LEAKAGE The air supply pressure is maintained to the maximum at its capacity or at 10kg.cm2, which ever is low, and soap solution is applied all over the joints. No leakage is allowed. 7.2.5 AIR LOCK RELAY These relays are used with control valves to lock in the loading pressure when the supply pressure fails. (i.e. Lock in last position / Stay put condition). This relay is subjected to pressure tight test, performance test, flow measurement and cyclic test. 7.2.6 POSITION TRANSMITTER (motion transmitter) The position transmitter can be either pneumatic or electrical. In pneumatic system pressure gauge is used for position indication. If electrical transmitter is used then position indication is by either a voltmeter (which indicates % of valve plug travel) OR a travel limit switch (with light indication representing the valve plug position). The position transmitter must be calibrated and checked for its performance.

51

CHAPTER 8

NOISE IN CONTROL VALVES 8.0 INTRODUCTION The noise levels in industrial location must be maintained to acceptable limits considering the safety of human beings and structures in industrial area etc. The noise is increasingly being regarded as a pollutant, which detracts from the quality of life. Noise is an unwanted sound. The fluctions in the atmospheric pressure due to noise produces unwanted auditory sensation the effect of this depends on the sound intensity and the power transmitted in the direction of travel of noise. The unit of noise power is dB. 8.1 NOISE MEASUREMENT Most Noise measurements are given in decibels (dB). The reasons for using a relative instead of on absolute scale is because of the magnitude of its pressure range involved. The smallest sound pressure by which a normal person can respond is 0.0002 µ bar. At above 200 µ bar the sound is felt, as well as heard, while above 2000 µbar the pressure levels are unbearable . It will be convenient to measure the actual sound pressure compare it with reference level (0.0002µ bar), and then express the result in decibels. Thus sound pressure level (spl) can be given by scale between 0 and 120 dB in mathematical term p

Spl = 20 log po Where p = measured pressure in µ bar p0 = 0.0002 µ bar An increase of 3 dB represents a doubling of the sound intensity. Sound is attenuated as the distance from the source to the observer is increased. When making noise measurements from a valve, it is usual to take readings at points situated 45 0 from the pipeline (both upstream and downstream) and at a radius of 1 meter away from the valve body.

8.2 Sources of valve noise Major sources of valve noises generated by the passage of the process fluid through the valve can be due to a) mechanical vibration, b) cavitation, and c) aerodynamic.their causes remedies are discussed here. 8.2.1

MECHANICAL VIBRATION It is induced by the pulsations of the flowing fluid. Some times it can lead to resonance of valve trim and fatigue failure of stem, guides, etc The slackness in the bearing or guides can give rise to oscillation of the internals. In severe cases the trim may go into resonance followed by rapid fatigue failure.

52

Reductions of guide clearance for better guiding, increasing the stem size, change of mass or stiffening up of the plug, reversal of flow direction are some of the possible solutions. Resonance phenomena generally occur at frequencies between 2000 and 7000 cycles/sec. 8.2.2

CAVITATION

The collapse of vapour bubbles in the liquid due to pressure recovery in downstream, of the valve orifice results in cavitation. The velocity of fluid stream increases while passing through the control valve. The velocity is maximum at veena contracta, hence pressure is less. If the pressure is less than the vapour pressure of the fluid, vapours are formed causing voids or cavities in the stream. Once the down stream pressure recovers vapour cannot exist. Then the voids / bubbles are forced to collapse or implode. This implosion is the final stage of cavitation and produces noise, vibrations and occasionally leads to mechanical damage to valve parts. Cavitations can be alleviated by reducing the pressure drop across the valve, by selecting low recovery trims/multiple velocity head loss trims. 8.2.3

AERODYNAMIC NOISE

This is caused by the re conversion of kinetic energy through turbulence into heat, down stream of throttling orifice handling compressible fluids. Aerodynamic noise also produced by a gas (compressible fluids) accelerating to super sonic velocity at critical or higher pressure drops through the trim. The resulting shock waves and general turbulence at the fluid boundary generate sound which travels down stream. This noise is worst of all, ranging from whistling sound to a heavy roar (eg. During boiler safety valve discharge). Sound pressure levels of 130dBA have been noticed in severe cases. Before final selection of valve, if the examination of flow data suggests the probability of noise problem,adopting some of the methods listed here can alleviate this problem. a) By fitting special internals, improved trims with in the valve. b) c) d)

By fixing one are more fixed area devices in the down stream to reduce the differential pressure across the valve in turn to reduce the noise Heavy wall piping down stream of the valve. Reducing the differential pressure across the valve by manipulating the upstream and down stream pressures wherever possible.

It is always better to anticipate a noisy situation and cater for it than have to try to remove the difficulty later on, because the problems involved in rectifying an already noisy installation can be considerable.

53

54

BODY AND BONNET OR COVER MATERIALS SYMBOLSTEEL

RELATED AMERICA STANDARDS

APPENDIX 1

TEMPERATURE

LIMITATIONS

APPLICATION

ASTM A382 –LCB ASTM A 16-WCB

-50 to 350

-50 to 350

Low temperature

-20 to 1000

-30 to 540

Steam , water, oil vapor gas and general services.

LCB

carbon

WCB

carbon

WC1

carbon Molybdenum ½ % Mo

ATM A217 –WC1

-20 to 1000

-30 to 540

High temperature

WC6

Chromium Molybdenum 1.1/4% Cr.1%Mo

ASTM

-20 to 1200

-30 to 645

Steam, Water, Oil Vapor, Gas and General services

WC9

Chromium Molybdenum 2.1/4% Cr.1% Mo

ASTM A217-WC 9

-20 to 1200

-30 to 645

C5

Chromium Molybdenum 5% Cr.1/2% Mo

ASTM A217-C 5

-20 to 1200

-30 to 645

C12

Chromium ASTM -20 to 1200 Molybdenum A217-C 12 9% Cr.1% Mo Selection of materials will be dependent upon actual service conditions

-30 to 645

corrosive –Erosive oil refinery service

APPLICATION Trim

MATERIAL stainless steel 18-10-Mo(316)FMB)

SERVICE standard trim material for most applications. high corrosion resistance. On clean liquids will Withstand pressure drop of 200 psi; on clean gases, critical pressure drop and beyond

TEMP.RANGE (°F) APPROX

-100 to 800

Stainless steel 18-8-Nb (347)(FCB)

similar to above, but with slightly different corrosion resistance properties.

Stainless steel 8-8-Ti (321)(FDP)

As above

-300 to 800

Brinell hardness 400/450. good resistance to erosion; for high pressure drop service. Fair corrosion resistance. Max trim size 4 in.

-20 to 800

hardened stainless steel (420)(FH)

-300 to 800

stellite face on Stainless steel (18-10-Mo)

cobalt-chromium-tungsten alloy. Brinell hardness 360/400. good resistance to erosion for high pressure drop service on liquids, steam or gasses

on seats only -100 to 800.on seats and guides –100 to 1500

commonly face on stainless (18-10-Mo)

As above , but high nickel chrome alloy brinell hardness 535/630

on seats and guides -100 to1500

Manganese Bronze

low pressure and temp. service, should not be used where abrasive particles are present in the fluid

-200 to 350

Monel

70% nickel, 30% copper alloy. High corrosion Resistance, especially on alkalis and salt solutions. Recommended for reducing agents rather than Oxidizing

-300 to 1000

Hastelloy ‘b’

65% nickel, 30% moly alloy. High pressure Resistance against mineral acids (hydrochloric, Phosphoric, sulphuric). Not recommended for oxidizing agents.

-300 to 1000

Hastelloy ‘c’

65% nickel, 18% moly 15% chrome alloy. High Corrosion Resistance against oxidizing agents, nitric acid ,free chlorine, and acid solution of ferric and cupric salts

-300 to 1000

Nickel

High corrosion resistance against strong concentration of hot caustic soda and other alkaline. or neutral salts. Not recommended for strong oxidizing agents

-300 to 1000

III Bolts and Nuts Stud bolt

1% chrome ¼ % moly steel

Nuts

High tensile High treated steel

Most regular applications. special alloys supplied when required for special corrosion resistance.

APPENDIX 2 SPECIFIC GRAVITY OF WATER AT VARIOUS TEMPERATURES

°F 62 100 110 120 130 140 150 160 170 180 190

°C 17 38 43 49 54 60 66 71 77 82 88

G 1.000 0.995 0.992 0.990 0.987 0.983 0.980 0.977 0.974 0.970 0.966

°F 200 210 220 230 240 250 260 270 280 290 300

°C 93 99 104 110 116 121 127 132 138 143 149

G 0.963 0.959 0.955 0.951 0.947 0.943 0.938 0.933 0.929 0.924 0.919

°F 310 320 330 340 350 360 370 380 390 400 410

°C 154 160 166 171 177 182 188 193 199 204 210

G 0.913 0.908 0.904 0.896 0.890 0.884 0.878 0.871 0.864 0.857 0.849

°F 420 430 440 450 460 470 480 490 500 550 600

°C 216 221 227 232 238 243 249 254 260 288 316

G 0.843 0.836 0.828 0.820 0.812 0.804 0.796 0.788 0.780 0.736 0.688

APPENDIX 3

SPECIFIC GRAVITY OF COMMON LIQUIDS (AT 15 C /16F) Acetic Acid

1.06

Ether

0.73

Naphtha

0.76

Astron

0.79

Ethyl Alcohol

0.789

Nitric Acid

1.50

Alcohol (Commercial )

0.83

Fluoric Acid

1.50

Olive Oil

0.919

Alcohol (Pure)

0.79

Gasoline

0.72

Palm Oil

0.97

Ammonia

0.89

Gasoline (Natural)0.68

Pentane

0.624

Benzene

0.69

Glycerin

Petroleum Oil

0.82

Benzoic Acid

1.27

Hydrochloric Acid 1.19

Phosphoric Acid 1.76

Bromine

2.97

Hydrofluoric Acid 0.99

Rape Oil

0.92

Carbolic Acid

0.96

Kerosene

0.80

Sulphuric Acid

1.84

Carbonic Acid

0.92

Linseed Oil

0.94

Tar

1.00

Carbon Disulphide

1.26

MC Residuum

0.935

Turpentine Oil

0.87

Carbon Tetrachloride

1.60

Mercury

13.57

Vegetable Oils

0.93

Chlorine

1.56

Methyl Alcohol

0.796

Vinegar

1.08

Chloroform

1.50

Mineral Oil

0.92

Water

1.00

Distillate

0.85

Muriatic Acid

1.20

Water (Sea)

1.03

1.26

APPENDIX 4 PHYSICAL PROPERTIES OF COMMON GASES Name Acetylene Air

FORMULA C2H2 -

Approx. molecular Wt. 26.0 29.0

.

Specific gravity relative to air 0.90 1.00

Specific heat ratio (at 1 atm) 1.26 1.40

Ammonia Argon Butane Carbon di oxide Carbon monoxide Chlorine Cyalogen Ethane Ethyl chloride Ethylene Fluorine Helium Hydrobromic acid Hydrochloric acid Hydrogen Hydrogen sulphide Krypton Methane Methyl chloride Natural gas Neon Nitric oxide Nitrogen Nitrous oxide Oxygen Pentane Phosgene Propane Propylene Sulphur dioxide Xenon

NH3 A C4H10 CO2 CO Cl2 C2N2 C2H6 C2H5Cl C2H4 F2 He HBr HCl H2 H2S Kr CH4 CH3Cl Ne NO N2 N2O O2 C5H12 OCCl2 C3H8 C3H6 SO2 Xe

17.0 40.0 58.0 44.0 28.0 71.0 52.0 30.0 64.5 28.0 38.0 4.0 81.0 36.5 2.0 34.0 83.5 16.0 50.5 19.5 20.2 30.0 28.0 44.0 32.0 72.0 99.0 44.0 42.0 64.0 131.0

0.59 1.38 2.08 1.52 0.97 2.49 1.81 1.04 2.36 0.97 1.31 0.14 2.71 1.27 0.069 1.19 2.82 0.55 1.78 0.67 0.696 1.036 0.97 1.52 1.10 1.56 1.45 2.26 4.53

1.30 1.67 1.11 1.30 1.40 1.35 1.26 1.22 1.13 1.22 1.66 1.40 1.41 1.32 1.68 1.32 1.20 1.27 1.64 1.40 1.40 1.28 1.40 1.09 1.29 1.66

APPENDIX 5 CRITICAL PRESSURE OF VARIOUS FLUIDS Bars (abs) Acetic Acid Acetone Acetylene Air Ammonia Argon Benzene Butane

58.0 47.7 62.28 37.7 112.8 48.6 48.3 36.4

lbf/im2 (abs) 841 691 911 547 1636 705 701 528

Carbon dioxide Carbon monoxide Chlorine Dowtherm 'A' Ethane Ethylene Freon Helium Hydrogen Hydrogen chloride Isobutene Methane Methyl alcohol Neon Nitrogen Nitrous oxide Oxygen Pentane Phosgene Propane Propylene Refrigerant 12 Refrigerant 22 sulphur dioxide water

73.9 35.4 7702 32.1 49.5 51.2 40.0 2.3 13.0 82.6 37.5 46.4 79.7 26.3 34.0 72.7 50.4 33.5 56.8 42.6 45.6 40.7 49.4 78.7 221.3

1072 514 1119 465 717 742 580 33 188 1198 543 673 1156 381 493 1054 730 485 823 618 661 590 716 1141 3210

APPENDIX 6 AMERICAN NATIONAL STANDARD FOR CONTROL VALVE SEAT LEAKAGE PURPOSE This standard establishes a series of seat leakage classes for control valves and defines the test procedures. SCOPE AND LIMITATIONS 1. Selection of a leakage class is not restricted as to valve design but acceptable values for various commercially available designers are suggested for each class. 2. The standard cannot be used as a basis for predicating leakage at conditions other than those specified.

3. The standard does not apply to control valves with a rated Cv less than 0.1 DEFINITIONS CONTROL VALVE 1.

A valve with a power positioning actuator for moving closure member to any position relative to valve port or seat in response to and in proportion to an external signal. The energy for a control valve actuator is derived from an independent source.

2.

Control valve body subassemblies on which an actuator is to be mounted at some later date are with in the intent of this definition.

3.

Cv An experimentally determined valve sizing coefficient. (Ref. ISA S39.1, 2, 3 and 4)

4.

Rated valve capacity. The quantity of test fluid (air or water) that would pass through the valve at rated travel under, stated pressure conditions as determined by the appropriate equations and manufactures ratings.

5.

Rated travel. The valve travel at which the manufacturer’s rating is established.

6.

Seat leakage. The quantity of test fluid passing through an assembled valve in the closed position under the conditions as defined.

LEAKAGE SPECIFICATIONS & CLASSES The maximum allowable seat leakage as specified for each class shall not exceed the seat leakage in Table 1 using the test pressure as defined in section 5. For Class II through IV each and every valve shall be tested. CLASS I A modification of any class II, III, or IV valves where design intent is the same as the basicclass, but by agreement between user and supplier, test is required. CLASS II This class establishes the maximum permissible leakage generally associated with commercial double seat. Double seat control valves or balanced single port control valves with a piston ring seal and metal –to- metal seal, use the test procedure type A. CLASS III

This class establishes the maximum permissible leakage generally associated with class II, (4.2.2) but requires higher degree of seat and seal tightness. Use test procedure Type A CLASS IV This class establishes the maximum permissible leakage generally associated with commercial unbalanced single - port, single seat control valves and balanced single – port control valves with extra tight piston rings or other sealing means metal –to-metal seats. Use test procedure Type A CLASS V This class is usually specified for critical applications where the control valve may be required to be closed, with out a blocking valve, for long periods of time with high differential pressure across the seating a surfaces. It requires special manufacturing assembly and testing techniques. This class is generally associated with metal seat, unbalanced single – port, single seat control valves or balanced single port designs with exceptional seat and seal tightness. Use test procedure Type B using water at the maximum operating differential pressure. CLASS VI This class establishes the maximum permissible seat leakage generally associated with resilient seating control valves either unbalanced or balanced single-port with “O” rings or similar popular seals. Use test procedure Type C.

TABLE – 1 Leakage class

Maximum seat leakage

Test procedure

CLASS I

See Paragraph 4.2.1

None

Class II See 4.2.2)

0.5% of rated valve capacity

Type A (See5.1)

Class III (See 4.2.3) Class IV (See 4.2.4)

0.1% of rated valve capacity

0.01% of rated valve capacity

Type A (See5.1) Type A (See5.1)

Class V

Class VI

5 x 10 -4 ml per minute of water per Inch of orifice diameter per psi differential (5x10-12 m3 per second of water per mm of orifice diameter per bar differential). Leakage as per paragraph 5.3.4 as expressed In ml per minute versus port diameter.

Type B (See5.2) Type C (See5.3)

TEST PROCEDURES Test procedure type A. •

Test medium shall be clean air or water at 10-52 0C (50-125° F).

•

Pressure of test medium shall be 3-4 bar (45-60 psig) or the maximum operating differential pressure whichever is less.

•

Leakage flow and pressure data shall be accurate to ± 10 percent of reading.

•

The test fluid shall be applied to the normal or specified valve body inlet. The valve body out let may be open to atmosphere or connected to a low headlessmeasuring device.

•

The actuator shall be adjusted to meet the operating conditions specified .The full normal closing thrust as applied an air pressure, a spring or other means shall then be applied. No allowance or adjustment shall be made to compensate for the increase in seat load obtained, when the test differential is less than the maximum valve operating differential pressure.

•

On valve body assemblies made for stock, tested without the actuator. A test fixture should be utilized which applies a net seat load not exceeding the manufacturer, s normal expected load under maximum service conditions.

•

On water test, care shall be taken to eliminate air pockets in the vale body and piping.

•

The leakage rate thus obtained can then be compared to the calculated values for Class 11,111, and 1V, in table 1.

TEST PROCEDURE TYPE B •

The test fluid shall be clean water at 10-520 (50-125f)

•

The water test differential pressure shall be the maximum service pressure drop across the valve plug, not exceeding the maximum operating pressure at room temperature as determined by ANSI B16.1, B16.5, or B16.34, or some lesser pressure by individual agreement (7 bars or 100 psi pressure drop minimum). Pressure measurement accuracy is to be in accordance with paragraph 5.1.3.

•

Test fluid shall be applied to the normal or specified inlet of the valve body. The valve plug shall be opened and the valve body assembly filled completely with water, including outlet portion and any downstream connecting piping and then closed.

•

The water test differential pressure as specified in 5.2.2 is then applied with the actuator adjusted to meet the operating conditions specified. The net actuator thrust shall be the specified maximum. Net actuator thrust above the specified maximum is not to be used.

•

When leakage flow is stabilized, the quantity should be observed over a period of time sufficient to obtain the accuracy under paragraph 5.1.3.

•

The leakage rate thus obtained shall not be greater than the value calculated from the definition of maximum seat leakage for class V as shown in table 1. The orifice diameter is understood to be the diameter at the point of seating contact at the nearest 2 millimeters(1/16 inch)

TEST PROCEDURE TYPE C- CLASS VI •

Test medium shall be air or nitrogen gas at 10-50 deg c (52-125 F)

•

Pressure of the test medium shall be the maximum rated differential pressure across the valve plug or 3.5 bar (45 psi) whichever the least.

•

The test fluid shall be applied to the normal or specified valve body inlet, and the outlet connected to a suitable measuring device.

•

With the control valve adjusted to meet the operating conditions specified (see paragraphs 5.1.5, and 5.1.6) and with sufficient time allowance for stabilizing flow, the leak rate shall not exceed the values in Table 2.

TABLE 2

Normal port diameter Millimeters inches

leakage ml per minute

bubbles per minute

25

1

0.15

1

38

1.5

0.30

2

51

2

0.45

3

64

2.5

0.60

4

76

3

0.90

6

102

4

1.70

11

152

6

4.00

27

203

8

6.75

45

Bubbles per minute as tabulated are a suggested alternative based on a suitable calibrated measuring device, in this case 0.25 inch (6.3 mm) O.D. x 0.032 inch (0.8 mm) wall tube submerged in water to a depth of from 1/8 to ¼ inch (3 to 6 mm). The tube end shall be cut square and smooth with no chamfers or burrs and the tube axis shall be perpendicular to the surface of the water. Other operators may be constructed and the number of bubbles per minute may differ from that shown in table 2 as they correctly indicate the flow in ml per minute. Provisions should be made to avoid over pressurizing of the measuring devices resulting from inadvertent opening of the valve plug. APPENDIX 7 TYPICAL SPECIFICATION FOR CONTROL VALVE. Client: Project: Purpose: Quantity: FLOW DATA : Fluid: Temperature: In let pressure(P1) Pressure drop (sizing) Diff pressure (shut off) Flow rate (max) (nor.) S.G/Density/MW/Viscosity : Cv cal/ Design II. VALVE SPECIFICATIONS: Size body/port: Model

Thermal station. TPS 2x210. MW. Condensate drain of SCAPH. 2x2 Condensate. 2250 C 15 ata. 0.927 kg/cm2 (6 % of p1)as fluid is flashing. 15 ata. 12000 kg/ hr. 0.8771 15.4/24 1 ½” x 1 ½” depends on application &in consultation with supplier

End connections: Body material: Trim material: Characteristics: Plug guiding: Bonnet: Gaskets: Action on air failure: Isolating valve:

ANSI 300 RF A 216 Gr WCB(scph 2) AISI 316 Stelited. Lc’ on-off.’ Top. Finned. V-543.* Close. yes

ACTUATOR: Model: Spring range(Kg/Cm2)

Electrical / pneumatic Type ‘ A ’with linear movement Max. Thrust 2000 Kg .Stroke – 25mm.

ACCESSORIES : Positioner.

Torque switches with holding relays, motion Transmitter (0 – 120 Ω), position indicator. OR Pneumatically operated etc. Yes(Top). Yes (2 nos) Yes. As applicable.

Hand wheel Side/Top: Limit switch IBR certificate: Extra information:

APPENDIX 8 VALVES FOR DIFFERENT APPLICATIONS. Location of application R.H Emergency block valve

Characteristic

Actuator

Flash flow linear

Diaphragm type VP – 6

I.L.P.

VP - 7

I.L.P.

Diaphragm

Black&Barough

Feed water control valve

=%

Feed water control valve

Linear

S.H. Spray control valve R.H. Spray control valve SCAPH drain

Flash flow = % ,, L.C. on-off

,, Electrical

Make/supplier Black&Barough

,, I.L.P.(Roper)

Hot- well make-up control

=%

VA1D

“

Steam to wagon heating

=%

VA2D

“

C.B.D.expander drain level

L.C.

VA1R

“

Auxiliary steam to deaerator Pr.

=%V

VA2D

“ .

,,

VA4D

“

%V

VP.7

“

,,

VP.6

“

HTP

“

control Cold reheat steam to ,, F.W.C. valve Lo-load feed control Aux.steam to fuel oil-

,,

%C

-suction header (this may not be a rule to use the same type of valve in all similar applications. users are requested to understand each application, and select the suitable valve.)

APPENDIX 9

DIAPHRAGM- Nylon Reinforced Neoprene, Extra Large Area Assures Accurate Positioning Of Inner Valve. SPRING ADJUSTMENT-Allows 3 To 15 PSI Inner Valve Travel For All Line Pressures TRAVEL INDICATOR-Handy Reference between Full Open to Full Closed. PACKING CLAND-Graphite Asbestos or Teflon Packing Rings Assure A Tight Seal with Minimum Friction. INNER VALVE- V-Ported With Top And Bottom Skirt Guide. BOOT-Available In A Selection Of Materials And End Connections. DIVERTING PATTERN-One Inlet, Two Outlets, V-Port Inner Valve Provides Modified Linear Flow Characteristic For Each Outlet. MIXING PATTERN-Two Inlets, One Outlet, V-Port Inner Valve Provides Modified Linear Flow Characteristic For Each Inlet. LUBRICATOR-(Not Shown) Valve Application Determines Type Of Lubricant Furnished. Lubricator Isolation Valve Supplied With Cast Steel Control Valves. DIVERTING OPERATION The Inner Valve Is Located Outside The Two Seat Rings. For A Throttling Positions The V-Port Plugs Always Close Against The Flow Of The Common Inlet, Adding To Operational Stability. The Possibility Of ‘Slamming’ And ‘Hammer’ Are Eliminated Even When The Inner Valve Is Just Off The Seat. MIXING OPERATION The Inner Valve Is Located Inside The Two Seat Rings. For All Throttling Positions The V-Port Plugs Always Close Against The Incoming Flow. Internal Forces Developed By The Two Inlet Oppose Each Other, Creating Little If Any Unbalance And Thereby Assuring Against The Possibility Of ‘Slamming’ And ‘Hammer’ When The Inner Valve Approaches The Critical Position Just Off The Seat.

Valve size½” ¾” 1” 1 1/4”1 ½”2” 21/2”Mixing 5.37.211.320.130.548.078.8Diverting5.57.611.921.132.050.482.7Valve size3”4”5”6”8”10”12”Mixing1011422143766629311100Diverting10614922539669 59781270

APPENDIX 10

Throttle Plug Control Valve recommended for low pressure drop applications. The machined contour around the plug periphery makes the valve suitable for fluids carrying suspended solids.

APPENDIX 11

V PORT CONTROL VALVE

V-port Control valve used for precise throttling control. Typical applications such as feed water control, steam pressure radiation, heater level control, etc. APPENDIX 12 VOLUMETRIC RATE OF FLOW

Litre Per second t/s

Litre Per minute t/min

Cubic meter Per hour M3/h

Cubic foot Per hour Ft3/h

Cubic foot Per minute Ft3/m

UK gallon Per minute US gal/min

1 0.017 0.278 0.008 0.472 0.076 0.063 0.002

60 1 16.667 0.472 28.317 4.546 3.785 0.110

3.6 0.06 1 0.0283 1.6690 0.2728 0.2271 0.0066

127.133 2.1189 35.3147 1 60 9.6326 8.0209 0.2338

2.1189 0.0353 0.5886 0.0167 1 0.1605 0.1337 0.0039

13.2 0.22 3.666 0.104 6.229 1 0.833 0.024

UK gallon Per minute US gal/min 18.85 0.264 4.403 0.125 7.480 1.201 1 0.029

US barrel per day US barrel/d 543.439 9.057 150.955 4.275 256.475 41.175 34.286 1

FORCE Newton N 1 1000 9.807 4.448

Kilonewton kN 0.001 1 0.0098 0.0044

Kilogram-force * Kgf 0.102 101.97 1 0.454

Pound-force lbf 0.225 224.81 2.205 1

MOMENT OF FORCE Newton Meter (N M) 1 1000 9.807 0.113 1.356

Kilonewton Meter (kN m) 0.001 1 0.0098 1.13*10-4 0.0014

Kilogram force Meter (Kgf m) 0.102 101.972 1 0.0115 0.138

Pound force Inch(Lbf in) 8.85 8851 66.8 1 12

Pound Foot (Lbf ft) 0.738 737.6 7.233 0.083 1

APPENDIX 13

Bibliography 1.

Valve users manual edited by J.kemplay.

2. 3.

Lyons Encyclopedia of valves by Jerry L. Lyons , P.E. Carl . L. Askland.jr. Control valves lecture notes by S. Raghavachari

4.

Course meterial of ILP.

5.

Technical brochures of – a) Blakeborough valves. b) Publications of BHEL. C) Fisher governor d) ILP product catalogue. e) Masoneilan f) Bailey Britain g) Bacon rotork controls h) Keltron control

6. Technical papers from power magazines. 7. NPTI control & instrumentation manuals 8. Control valves lecture notes by S. Karthikeyan ILP. 9. Control valves lecture notes by T.S.Nambiar ILP 10. Control valves lecture notes by G.K.Pillai ILP.