Valve_sizing_details - Material Selection Guide

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Material Selection Guide

Stainless SteelB9 (ST STL BS EN 10088 1.4541) -40C to +150C*Nitrile -10C to +100CFluorocarbon -20C to +150CEPDM -30C to +115C

BrassR1 (BRASS BS EN 12164 CW614N) -40C to +150C*Nitrile -10C to +100CFluorocarbon -20C to +150CEPDM -30C to +115C

AluminiumT0 (AL.UMINIUM L168-T6511) -40C to +150C *Nitrile -10C to +100CFluorocarbon -20C to +150CEPDM -30C to +115C

Carbon SteelK3 (BS970 230M07) -10C to +100C *Nitrile -10C to +100CFluorocarbon -10C to +100CEPDM -10C to +100C

Ductile Cast iron BS EN 1563 P8 EN-JS1025 EN-GJS-400-18 LT -20C to +150C*Nitrile -10C to +100CFluorocarbon -20C to +150CEPDM -20C to +115C

Cast Stainless Steel9H BS EN 10213-4 1.4408 -40C to +150C*Nitrile -10C to +100CFluorocarbon -20C to +150CEPDM -30C to +115C

Aluminium BronzeS4 (NES 833) -40C to +150C*Nitrile -10C to +100CViton -20C to +150CEPDM -30C to +115C

Grease - Dow Corning MS4 -50C to +200C

Standard valves are suitable for all non-aggressive gaseous and liquid media,including;

Minor VariationsA change in seal type meets the requirementstypically with CO2 or non-aggressive media at high or low temperatures (-50C to + 150C)

Major Variations from standard and specialvalvesMore compatible materials can also be usedfor valve parts in contact with aggressivemedia, eg;

Stainless or Mild Steel bodies replacingBronze or Brass for compatibility withAmmonia and similar ammoniacal fluids, or to prevent contamination of gaseouscoolant in Nuclear systems.

Metal to Metal seats and metal diaphragms replacing rubber or plasticseats and diaphragms. Valves with thisbuild are also compatible with steam, hotgases and fluids, as well as a wide varietyof aggressive media.

In addition, many designs have beendeveloped for special purposes. Consult IVPTechnical Sales on the availability of new orexisting designs.

OxygenBefore specifying a valve for this aggressivehazardous medium, it is advisable to consultIVP Technical Sales for expert advice.

IVP pressure regulators are available for most media. This guide covers a wide variety of operating environments. For other applications consult IVP Technical sales.

GASES FLUIDS

Air Diesel Oil

Argon Ethyl Alcohol

Butane Fuel Oil

Helium Hydraulic Oils (except proprietary oils)

Hydrogen Kerosene

Methane Mineral Oil

Nitric Acid Petrol

Nitrogen Soap and Detergents

Propane Water

Temperature Ranges (Materials)

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RangeFor pressure regulators the working pressurerange is given as zero to maximum. With allstandard valves, zero outlet pressure isachieved by totally unwinding the control springor venting the dome. Even at full inlet pressure,all valves seal bubble tight. Valves capable ofhigh pressure settings can be less accurate atlow pressure settings.

AccuracyThe value given is the pressure drop ofregulating valves, at full flow(b in the valveperformance diagram)

RepeatabilityThe value given is the accuracy with which eachvalve returns to its set point after any flowdemand, (a in the valve performance diagram).

Important notesDome loaded valves accuracy and repeatabilityare not a function of pressure setting. Thepercentage inaccuracy applies to the setting atwhich it is used. However, because of theconstant sealing load force, accuracypercentage cannot be applied below 7 bar(100psi)

Spring loaded valves accuracy and repeatabilityare a function of the valve load springmaximum, where as Dome loaded valvesaccuracy and repeatability are not a function ofpressure setting.

Pressure dependancyDefinitionValve dependency is a characteristic wherebyoutlet pressure will increase as inlet pressuredeclines and vice versa.

CausesDependency caused by decreasing inletpressure

A balanced valve is not completely balanced.The lower half of the valve is a slightly smallerdiameter than the top half. This has the effect ofensuring a greater load on the inlet side of thevalve, ensuring that it will close in the event offailure. However, should the inlet pressure fall,the load on the underside of the valve willdecrease, making it more difficult to close. This will result in an increase of outlet pressure.

Dependency caused by increasing inletpressure

Should inlet pressure increase, the load on theunderside of the valve will be greater. In thisinstance, the load on the valve will be moredifficult for the dome pressure to overcome,resulting in a decrease of outlet pressure. Thisproblem is worse with an unbalanced valve asthe increased area under the valve on the inletside helps to keep the valve closed.

Valve Size and FlowKv and Cv coefficients are given. Effective forfluids, they are not as accurate as the valvesizing guide and are not recommended for gasflow control.

Product DescriptionsProduct descriptions in this catalogue are givenin good faith, for general guidance, but are notto be taken as binding. IVP reserves the right toamend product specifications or designswithout notice.

Definition of Terms

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For clarity, Diagram 1 shows inaccuraciesexaggerated. In practice, losses are extremelysmall, as in Diagram 2.

At set point 1, a regulating valve will sealcompletely, without creep to higher values evenunder prolonged no-flow. When flow begins, theremoval of the sealing load causes animmediate, slight drop in pressure to 2.

As flow increases from points 2 to 3, pressurefalls a little further as the valve spring or gascharge in the dome expands to open the valve.Further flow demand after point 3 producesrapid loss of pressure, as the fully opened valveoperates as a choked orifice. Valves are notnormally used under this condition.

Flow reduction returns the valve to point 1,along the higher pressure curve through point 4,the hysteresis loop being caused by valvefriction.

Line pressure variations have a further effect on performance. With regulating valves, setpressure rises as inlet pressure falls, and fallswhen inlet pressure rises. In back-pressurevalves, set pressure falls as downstream linepressure increases.

Balancing the valve greatly reduces controlledpressure dependence on pressure in the non-controlled line.

Dome-loaded valves generally give higheraccuracy with better set point repeatability.

Valve Performance

Theoretical operating characteristics of regulating and relief valves are illustrated in the diagram.

Diagram 1

(a) Repeatability(b) Accuracy(c) Internal friction loss

Diagram 2

(d) Full flow(e) Pressure dependency

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Valve Sizing Guide

Those wishing to size valves themselves will find the following information useful. Eachdatasheet gives the area of the valve seat,known as orifice area, and defined as the flowarea between valve and seat when fully open.Port area is defined as the area of the portconnection or, if smaller, the internal passagearea. It is always the effective (not nominal) areathat is quoted.

Valve Sizing Charts are based on:

i) Reading off flow capacity through orifice area at prevailing pressure drop.

ii) Reading off flow capacity through port area at prevailing pressures.

iii) Maximum flow is the lesser of (i) and (ii).

Data sheets also give flow coefficients (Cv andKv). These are effective for fluids; they are notas accurate as the Valve Sizing Guide methodson the following fluids and are notrecommended for gas flow control.

Sizing for low ViscosityFluidsOrifice Flow CapacityUsing Flow Chart 1, read off the maximumwater volume flow (Q) which will pass throughthe valve orifice area (A) at prevailing pressuredrop (deltaP).

Port Flow CapacityUsing Flow Chart 2, read off the maximum flowcapacity (Q) which will pass through the portarea (A) at the desired velocity (V).

Note: For media other than water, flow capacityshould be corrected

Velocity should not normally exceed 5m/s(15ft/sec) to avoid noise/ cavitation.

The maximum flow of liquid at the prevailingpressure drop (P) is the smaller of the flowsthrough the orifice and ports.

Sizing for GasesGas sizing must be treated differently to that ofliquids and the following stages must beconsidered.

Correction for Non-ChokedOrifice

For the purposes of calculation does the flowneed correcting due to the pressure ratio?

Pressure Ratio (Y)=Outlet absolute pressure (P2) P2Inlet absolute pressure (P1) P1

Using chart 4, read the Volume Flow Factor (W)against the Pressure Ratio (Y). To determine themaximum possible air flow through the orificemultiply maximum air flow (Q) by the volumeflow factor (W). (Air flow is expressed inStandard Atmospheric Conditions).

Example 100 Bar (a) Inlet60 Bar (a) Outlet 50 Nm3 /min Flow of Hydrogen

60/100 = 0.6 = Pressure Ratio (Y)

Using chart 4, a pressure ratio (Y) of 0.6= a Volume FlowFactor (W) of 0.95

The corrected flow (Q) therefore will be 50 x 0.95 =47.5Nm3/min

Correction for other Gases1. For purposes of calculation, gases other than

air will need correcting due to the subjectgases relative density.

First determine the Correction Factor (V). See table1.

Correction Factor (V) = Flow Factor (Z)Relative Density (X)

To obtain the maximum flow through an orificeat the prevailing pressures, (Expressed inStandard Atmospheric Conditions) multiply thegas flow by the correction factor (V).

IVP Pressure Regulator

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Y =



Using our earlier example, the flow of Hydrogenalready corrected for Non.Choked flow is nowconverted to an equivalent air flow.

Hydrogen flow of 47.5 Nm3/min (Q) x (0.204 Flow factor (Z))

(0.068 Relative Density (X))

=142.5 Nm3/min Equivalent Air Flow

Using the flows and pressures in our examples,on flow chart 3 indicates the valve orificerequired. To find the minimum orifice area (A) forthe Choked Flow air flow (Q) at the absoluteinlet pressure (P) to be used.

(Q) At 100 Bar Abs = 140mm2

Ports Volume Flow Capacity Using flow chart 5, read off MaximumPermissible Flow (Q) through port area (A) atprevailing outlet pressure. Correction need notbe applied for different gas densities. As withthe orifice, we find the port requirement for 50Nm3/min at 60 Bar abs outlet = 170 mm2

The Maximum Volume Flow of gas through avalve at prevailing pressures is the lesser of theflows through orifice and port areas.

Relative DensityGas Symbol Relative Flow

Density FactorX Z

Air 1.00 1.00Hydrogen H2 0.068 0.204Nitrogen N2 0.96 0.98Oxygen O2 1.10 1.05Helium He 0.138 0.395Argon A 1.38 1.25Neon Ne 0.69 0.88Krypton Kr 2.90 1.82Xenon Xe 4.55 2.09Carbon Dioxide CO2 1.52 1.21Carbon Monoxide CO 0.96 0.96Ammonia NH3 0.59 0.75

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Z

X

Port area

Flow (Q) of 142.5Nm3/min at 100 Bar Abs = 140mm2 orifice area


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Valve sizing

Chart 1

Flow of Liquid Through an Orifice

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Sizing chartFlow of Liquid Through Valve Ports

Chart 2

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Valve sizingAir Flow Through Valve Orifices

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Chart 3



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Valve sizing

Chart 4

Flow Factors for Orifice Flow against Pressure Ratio


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Chart 5

Sizing chartAir Flow Through Valve Ports


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Valve_sizing_details - Material Selection Guide