Liquid Sizing.pdf

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TS2

TS2 Control

Control Valve

Valve Selection

Selection

for

Incompressible Fluid Flows

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Introduction

The company was formed in 1967 under the name of Introl Ltd. Its object was to provide a specialised control The company was formed in 1967 under the name of Introl Ltd. Its object was to provide a specialised control valve service for

valve service for the rapidly expanding Energy Industries (Petroleum, Gas, Electricity) the rapidly expanding Energy Industries (Petroleum, Gas, Electricity) and for the and for the ever-changinever-changingg Chemical Industry. The company very quickly

Chemical Industry. The company very quickly achieved a reputation throughout these industries for high qualityachieved a reputation throughout these industries for high quality control valves of

control valves of the conventional type and particularly for purpose designed high technology control valves.the conventional type and particularly for purpose designed high technology control valves. Introl have founded on a concept of in house design capability. Designs and prototypes have always been Introl have founded on a concept of in house design capability. Designs and prototypes have always been developed within the company and this remains an essential element of the company’s present day policy. developed within the company and this remains an essential element of the company’s present day policy. Acco

Accordrdingingly a lly a largarge dee develvelopopmenment ant and ded desigsign den depapartmrtmenent is stt is staffaffed bed by quy qualialifiefied end engingineeeers whrs who aro are ave availailablable fore for customer consultation on

customer consultation on problem applications.problem applications.

Kent Introl has always recognised the importance of maintaining high standards of quality and was the first Kent Introl has always recognised the importance of maintaining high standards of quality and was the first control valve company to

control valve company to be awarded the British Standards approval of quality be awarded the British Standards approval of quality control systems — BS5750 Partcontrol systems — BS5750 Part 1 by the British Standards Institution in 1986. This was supplemented by approval of the systems to ISO 9001. 1 by the British Standards Institution in 1986. This was supplemented by approval of the systems to ISO 9001. Retention of these certifications requires continual maintenance of all Quality Assurance Systems to the Retention of these certifications requires continual maintenance of all Quality Assurance Systems to the satisfaction of the

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Scope of Manual

The automatic control of modern processing plants relies heavily on the control valve as the final control The automatic control of modern processing plants relies heavily on the control valve as the final control element. These control valves may be required to operate continuously or intermittently to regulate process element. These control valves may be required to operate continuously or intermittently to regulate process parameters such as flow rate, pressure level, temperature, etc. The introduction of computer technology within parameters such as flow rate, pressure level, temperature, etc. The introduction of computer technology within the industry and the demand for designs capable of handling a wider range of process requirements has the industry and the demand for designs capable of handling a wider range of process requirements has necessitated a higher level of accuracy in the sizing and selection of these critical elements.

necessitated a higher level of accuracy in the sizing and selection of these critical elements.

The methods of control valve sizing and sound pressure level prediction for liquid and compressible fluids have The methods of control valve sizing and sound pressure level prediction for liquid and compressible fluids have previously been discussed in Introl Engineering Reports EN12 and EN9b respectively. This technical selection previously been discussed in Introl Engineering Reports EN12 and EN9b respectively. This technical selection manual has been produced to provide a document incorporating all relevant aspects of valve sizing and manual has been produced to provide a document incorporating all relevant aspects of valve sizing and selection, including revisions and additions e.g. multi-phase fluid sizing.

selection, including revisions and additions e.g. multi-phase fluid sizing. In addition to

In addition to sizing and sound sizing and sound pressure level calculation procedures, this manual provides information requiredpressure level calculation procedures, this manual provides information required during the specification of a

during the specification of a control valve for a control valve for a particular application includinparticular application including selection guidelines, and materialg selection guidelines, and material considerations.

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Contents Contents Contents Contents

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_{______4}

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TS20 Control Valve Selection for Incompressib

TS20 Control Valve Selection for Incompressible Fluid Flows

le Fluid Flows ________________

_____________________

_____4

4

TS20.1 - Nomenclature _________________________________________________________________ 5 TS20.1 - Nomenclature _________________________________________________________________ 5 TS20.2 - Liquid Flow Valve Sizing Procedure _______________________________________________ 6 TS20.2 - Liquid Flow Valve Sizing Procedure _______________________________________________ 6 TS20.3 - Process/Application data requirements ______________________________________________ 7 TS20.3 - Process/Application data requirements ______________________________________________ 7

TS21 Liquid

TS21 Liquid Sizing

Sizing ________________

__________________________________

___________________________________

______________________

_____8

8

TS21.1 - Liquid Flows__________________________________________________________________ 8 TS21.1 - Liquid Flows__________________________________________________________________ 8

TS21.

TS21.1.1 1.1 - - IntroIntroductioductionn ______________________________________________________________________________________________________________________ ____ 88 TS21.1.2 - Flow Path Through a Control Valve __________________________________________ 9 TS21.1.2 - Flow Path Through a Control Valve __________________________________________ 9 TS21.1.3 - Flow Regimes - Normal, Semi-critical, critical _________________________________ 10 TS21.1.3 - Flow Regimes - Normal, Semi-critical, critical _________________________________ 10 TS21.1.4 - Cavitation & Flashing ____________________________________________________ 11 TS21.1.4 - Cavitation & Flashing ____________________________________________________ 11 TS21.1.6 - Viscous Flow___________________________________________________________ 13 TS21.1.6 - Viscous Flow___________________________________________________________ 13 TS21.1.7 - Pipework Configuration___________________________________________________ 14 TS21.1.7 - Pipework Configuration___________________________________________________ 14 TS21.2 - Valve Sizing Equations_________________________________________________________ 15 TS21.2 - Valve Sizing Equations_________________________________________________________ 15 TS21.2.1 - Cavitation Index_________________________________________________________ 15 TS21.2.1 - Cavitation Index_________________________________________________________ 15 TS21.

TS21.2.1 2.1 - - FlasFlashing Indexhing Index ___________________________________________________________________________________________________________________ _ 1515 TS21.2.3 - Valve Flow Coefficient ___________________________________________________ 17 TS21.2.3 - Valve Flow Coefficient ___________________________________________________ 17 TS21.2.5

TS21.2.5 - - Viscous Viscous Flow Flow CorrectionCorrection ___________________________________________________________________________________ _________________ 1919 TS21.2.7 - Pipework Correction Factor________________________________________________ 21 TS21.2.7 - Pipework Correction Factor________________________________________________ 21 TS21.

TS21.A A - - AppeAppendiciendiciess __________________________________________________________________________________________________________________________ ________ 2323 TS21.A.1 - Semi-critical Flow_______________________________________________________ 23 TS21.A.1 - Semi-critical Flow_______________________________________________________ 23 TS21.A.2 - Pressure Drop Considerations______________________________________________ 24 TS21.A.2 - Pressure Drop Considerations______________________________________________ 24 TS21.A2 - Contaminate Flow _______________________________________________________ 24 TS21.A2 - Contaminate Flow _______________________________________________________ 24

TS22 Liquid Velocity

TS22 Liquid Velocity _______________

________________________________

__________________________________

_____________________

____25

25

TS22.1 - Factors Influencing Velocity Limitations _______________________________________ 25 TS22.1 - Factors Influencing Velocity Limitations _______________________________________ 25 TS22.2

TS22.2 - - Velocity Velocity CalculationCalculation ________________________________________________________________________________________________________ ______ 2626 TS22.4

TS22.4 - - Flashing Flashing FlowFlow ______________________________________________________________________________________________________________ __________ 2828 TS22.5 - Procedure _______________________________________________________________ 29 TS22.5 - Procedure _______________________________________________________________ 29

TS23 Liquid Noise

TS23 Liquid Noise ________________

__________________________________

____________________________________

_____________________

___30

30

TS23.1 - Categories of Noise Vibration________________________________________________ 30 TS23.1 - Categories of Noise Vibration________________________________________________ 30 TS23.1 -

TS23.1 - Methods of Methods of Abating LAbating Liquid Generateiquid Generated Noised Noise ______________________________________________________________________ __ 3131 TS23.3 - Liquid Noise Prediction ____________________________________________________ 32 TS23.3 - Liquid Noise Prediction ____________________________________________________ 32 TS23.4 -

TS23.4 - Procedure for Procedure for Fixed Area Fixed Area Pressure Pressure Drop StagesDrop Stages ___________________________________________________ _________________ 3333 TS23.5 - Procedure for Tubotrol Valves _______________________________________________ 34 TS23.5 - Procedure for Tubotrol Valves _______________________________________________ 34

Liq

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TS20 Control Valve Selection for Incompressible Fluid Flows

Selection of a control valve for an incompressible fluid (liquid) flow application involves a number of factors, Selection of a control valve for an incompressible fluid (liquid) flow application involves a number of factors, which should be considered in a logical sequence. This section of the Technical Manual provides the which should be considered in a logical sequence. This section of the Technical Manual provides the information necessary to consider these factors, which include Cv calculation, fluid velocity and noise level information necessary to consider these factors, which include Cv calculation, fluid velocity and noise level prediction. It is important to note that omission of these aspects could lead to incorrect selection of a control prediction. It is important to note that omission of these aspects could lead to incorrect selection of a control valve for a

valve for a particular application.particular application.

The process and application information necessary to fully specify the size and type of valve required is The process and application information necessary to fully specify the size and type of valve required is detailed, together with a flow

detailed, together with a flow chart indicating the sequence of steps involved.chart indicating the sequence of steps involved.

The calculation includes consideration of the various flow regimes, together with the effects of processes such The calculation includes consideration of the various flow regimes, together with the effects of processes such as cavitation or flashing. Additionally, where appropriate, techniques are detailed for evaluating the effects of as cavitation or flashing. Additionally, where appropriate, techniques are detailed for evaluating the effects of both highly viscous fluids

both highly viscous fluids and pipework configuration on the calculated Cv value.and pipework configuration on the calculated Cv value.

To ensure correct selection of valve size and to maximise operational life, fluid velocity calculations and To ensure correct selection of valve size and to maximise operational life, fluid velocity calculations and limitations are detailed for the various

limitations are detailed for the various flow regimes.flow regimes. Add

Additiitiononallally in thy in the sele selectection ion of a coof a contrntrol vaol valvelve, the p, the prorobleblem of enm of envirvirononmementantal noil noise muse must be tst be takeaken intn into acco accouount.nt. Therefore, a noise prediction technique forms part of the

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Nomenclature

Unit

Unit Description Description Imp Imp MetricMetric C

Cv v Valve Valve Flow Flow Coefficient Coefficient U.S. U.S. units units U.S. U.S. unitsunits

C

CV VISC V VISC Viscous Viscous Flow Flow Coefficient Coefficient U.S. U.S. units units U.S. U.S. unitsunits C

Cvr vr Valve/Reducer Valve/Reducer Flow Flow Coefficient Coefficient U.S. U.S. units units U.S. U.S. unitsunits K

Kvv Valve Valve Flow Flow Coefficient Coefficient S.I. units S.I. units S.I. S.I. unitsunits

C

CII Cavitation Cavitation Index Index p.s.i p.s.i BarBar C

Cf f Valve Valve Pressure Pressure Recovery Recovery Factor Factor - -

--C

Cfr fr Valve/Reducer Valve/Reducer Pressure Pressure Recovery Recovery Factor Factor - -

--d

d Valve Valve bore bore size size inches inches mmmm

D Pipe

D Pipe bore bore Size Size inches inches mmmm F

F Pipe/Reducer Pipe/Reducer Correction Correction FactorFactor - - --K

Kii Coefficient Coefficient of of Incipient Incipient CavitationCavitation - - --K

K_in_in Inlet Inlet Head Head LossLoss - - --K

K11 Inlet Loss CoefficientInlet Loss Coefficient - - --K

K22 Outlet Loss CoefficientOutlet Loss Coefficient --K

KSS Coefficient of Cavitation (1.1 KCoefficient of Cavitation (1.1 K11)) --N

NTT Valve/Trim Valve/Trim Style Style Correction Correction FactorFactor --N

NRR Valve Valve Reynolds Reynolds numbernumber --n

n Number Number of of Pressure Pressure Drop Drop StagesStages --V

VKK Viscous Viscous Correction Correction FactorFactor --P

P11 Upstream Upstream Pressure Pressure p.s.i.a p.s.i.a BarABarA

P

P22 Downstream Downstream Pressure Pressure p.s.i.a p.s.i.a BarABarA

Thermodyn

Thermodynamic amic Critical Critical Pressure Pressure p.s.i.a p.s.i.a BarABarA Vapour

Vapour Pressure Pressure of of Fluid Fluid p.s.i.a p.s.i.a BarABarA (at flowing

(at flowing temperaturtemperature)e) Supercoole

Supercooled d Vapour Vapour Pressure Pressure p.s.i.a p.s.i.a BarABarA ∆

∆P P Pressure Pressure Drop Drop Across Across Valve Valve p.s.i. p.s.i. BarABarA ∆

∆Ps Ps Sizing Sizing Pressure Pressure Drop Drop p.s.i. p.s.i. BarBar ∆

∆PPlimitlimit Limiting Limiting Pressure Pressure Drop Drop p.s.i. p.s.i. BarBar

for Critical Flow for Critical Flow ∆

∆PPvr limitvr limit Limiting Limiting Pressure Pressure Drop Drop p.s.i. p.s.i. BarBar

across Valve

//

ReducerReducer T

T11 Inlet Inlet TemperaturTemperature e °F °F °C°C

Q

Q Volume Volume Flow Flow Rate Rate U.S. U.S. gall./min gall./min mm33/hr/hr W

W Mass Mass Flow Flow Rate Rate lb/hr lb/hr kg/hrkg/hr G

G Specific Specific GravityGravity - - --v

v Fluid Fluid Velocity Velocity ft/sec ft/sec m/secm/sec SPL

SPL Sound Sound pressure pressure level level dBA dBA dBAdBA B

B Liquid Liquid noise noise efficiency efficiency termterm - - --H

HLL Liquid Liquid noise noise trim trim style style correction correction dB dB dBdB

T

T Liquid Liquid noise noise valve valve opening opening reduction reduction dB dB dBdB Z

Z11 Liquid Liquid noise noise bulk bulk flow flow factorfactor - - -- A

App Pipe Pipe attenuation attenuation dB dB dBdB

G

reek

C

Ch

ha

arra

ac

ctte

errs

s

θ

θ Pipe Pipe Reducer Reducer Angle Angle degrees degrees degreesdegrees µ *

µ * Dynamic Dynamic Viscosity Viscosity centi-Poise centi-Poise (1x10(1x10-3-3_Ns/m_Ns/m22₎₎

p

p Fluid Fluid Density Density lb/ftlb/ft33 kg/mkg/m33

ν

ν * * Kinematic Kinematic ViscosityViscosity centi-Stokes (mmcenti-Stokes (mm22_/s)_/s)

* usually given in metric units * usually given in metric units

TS20.1

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Liquid Flow Valve Sizing Procedure

The following flowchart details the overall The following flowchart details the overall sequence of steps used during the selection of a sequence of steps used during the selection of a

control valve for a particular application. For control valve for a particular application. For individual consideration of liquid sizing, liquid individual consideration of liquid sizing, liquid velocity and liquid noise, reference should be velocity and liquid noise, reference should be made to Sections TS21, TS22 and TS23 made to Sections TS21, TS22 and TS23 respec-tively.

tively.

START START

Select Trim Style* Select Trim Style*

Calculate Cavitation Index Calculate Cavitation Index

Determine the Valve Flow Coefficient Determine the Valve Flow Coefficient

Is cavitation Is cavitation

Index Index

Select Design CV and Valve Select Design CV and Valve

Determine Cf Value at Valve Opening Determine Cf Value at Valve Opening

Re-calculate Cavitation Index and Valve Flow Coefficient Re-calculate Cavitation Index and Valve Flow Coefficient

Calculate Pipework Correction Calculate Pipework Correction

Is Design CV OK? Is Design CV OK?

Calculate Flow Velocities Calculate Flow Velocities

Is Velocity Is Velocity

Calculate Sound Pressure Level Calculate Sound Pressure Level

Is SPL OK Is SPL OK

END END

Select Different Trim Style Select Different Trim Style N

N

Yes Yes

Select Design CV & Valve Size Select Design CV & Valve Size

N N Yes Yes N N Yes Yes N N Yes Yes

* Pressure drop limit 50 Bar (725 psi) per * Pressure drop limit 50 Bar (725 psi) per stage

stage

TS20.2

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Process/Application Data Requirements

The information required to fully specify the size and type of valve for liquid service applications can be broken The information required to fully specify the size and type of valve for liquid service applications can be broken down into different categories. For valve sizing and selection, this information can be classified as essential, down into different categories. For valve sizing and selection, this information can be classified as essential, preferred or additional. The following chart categorises the information required into these three areas. The preferred or additional. The following chart categorises the information required into these three areas. The information presented here relates to valve selection only and for

information presented here relates to valve selection only and for actuator selection refer to TS8O.actuator selection refer to TS8O.

P

Prroocceesss s UUnniitts s FFlloow w UUnniitts s -- TTeemmp p UUnniitts s --F

Flloow w CCoonnddiittiioon n MMaaxx NNoorrmmaall MMiinniimmuumm 1 Quantity

1 Quantity 2

2 Line Line FluidFluid 3

3 Flow Flow RateRate

4 Inlet 4 Inlet 5 Outlet 5 Outlet 6 6 Pressures Pressures P P 7

7 Temp. Temp. at at InletInlet 8

8 Specific Specific GravityGravity 9

9 10

10 Vapour Vapour PressurePressure 11

11 Critical Critical PressurePressure 12

12 DP DP Actuator Actuator SizingSizing 13

13 Design Design Press./Temp.Press./Temp. 14

14 Line Line Size Size In/Out/Sch.In/Out/Sch. 15

15 16

16 Predicted Predicted SPL SPL (dBA)(dBA) 17

17 Calculated Calculated CvCv 18 Viscosity 18 Viscosity 1

199 VVaallvveeSSiizzee CC..MM.. TTrriimm 20

20 Body Body Form Form Design Design CVCV 21

21 Catalogue Catalogue No.No. 2

22 2 EEnnd d CCoonnnnss. . SSttyyllee RRaattiinngg 23

23 Rated Rated Press. Press. Temp.Temp. 24

24 Body Body MaterialMaterial 25

25 No No of of Seats Seats DesignDesign 26

26 Type Type RingsRings

27

27 Char’s Char’s Flow Flow Dir Dir 28 28 Trim Trim Material Material 29

29 Type Type of of BonnetBonnet 30

30 Packing Packing Lub. Lub. /Lub /Lub NoNo 31

31 Max. Max. LeakageLeakage 32

32 Stem Stem Dia Dia Valve Valve DutyDuty

Abs

Absoluolute te minminimuimum fm flow low infinforormatmation ion (es(essensentiatial)l) Information required for full

Information required for full analysis (preferred)analysis (preferred) Add

Additiitionaonal dl desiesign gn infinformormatiationon Full valve specification

Full valve specification

TS20.3

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TS21

Liquid

Sizing

TS21.1

Liquid

Liquid Flows

Flows

This section covers the various factors to be considered when sizing and selecting a valve for liquid service This section covers the various factors to be considered when sizing and selecting a valve for liquid service applications. Procedures are detailed for determining the valve flow coefficient

applications. Procedures are detailed for determining the valve flow coefficient (Cv)(Cv) along with the necessaryalong with the necessary corrections required to account for

corrections required to account for viscous effects and viscous effects and valve pipe reducer combinations. Additionally, calculationvalve pipe reducer combinations. Additionally, calculation procedures are presented to ensure that cavitation and flow erosion are avoided. procedures are presented to ensure that cavitation and flow erosion are avoided.

TS21.1.1

Page

Page 9

9

Introduction Introduction

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Flow Path Through a Control Valve

The flow path through a control valve is highly complex, The flow path through a control valve is highly complex, including regions of high turbulence, flow separation including regions of high turbulence, flow separation and impingement. To allow description of the behaviour and impingement. To allow description of the behaviour of the fluid properties through a control valve, a greatly of the fluid properties through a control valve, a greatly simplified sketch of the flow path through a control valve simplified sketch of the flow path through a control valve is presented in Figure 21.1. This figure presents the is presented in Figure 21.1. This figure presents the flow being directed under the plug and indicates areas flow being directed under the plug and indicates areas within the valve, which are referenced in the within the valve, which are referenced in the subsequent discussion.

subsequent discussion.

As the fl

As the flow pasow passes frses from thom the valve valve inlet to the inlet to the trim ine trim inletlet the static pressure reduces due to frictional and turning the static pressure reduces due to frictional and turning losses. Fluid approaching the trim contracts in a similar losses. Fluid approaching the trim contracts in a similar manner to that shown schematically in Figure 21.2. manner to that shown schematically in Figure 21.2. During this contraction the static pressure decreases During this contraction the static pressure decreases and the fluid velocity increases as illustrated in Figure and the fluid velocity increases as illustrated in Figure 21.3. Subsequently, as the flow passes through the 21.3. Subsequently, as the flow passes through the minimum geometrical flow area the streamlines minimum geometrical flow area the streamlines continue to contract, until at a point just downstream continue to contract, until at a point just downstream from the trim outlet the streamlines become parallel. from the trim outlet the streamlines become parallel. This minimum flow area is referred to as the This minimum flow area is referred to as the venavena contracta.

contracta. At At thithis pos point int the the minminimuimum sm stattatic pic presressursure ane andd maximum

maximum flowflow velocity occur. The pressure at the venavelocity occur. The pressure at the vena contracta in relation to the upstream pressure and the contracta in relation to the upstream pressure and the fluid vapour pressure is important in determining the fluid vapour pressure is important in determining the flowrate through the valve.

flowrate through the valve.

Downstream of the vena-contracta the flow area Downstream of the vena-contracta the flow area expands resulting in a reduction in flow velocity and an expands resulting in a reduction in flow velocity and an increase in static pressure. The amount of pressure increase in static pressure. The amount of pressure recovery is a function of the valve trim style, and is recovery is a function of the valve trim style, and is quantified by the term the valve pressure recovery quantified by the term the valve pressure recovery coefficient (Cf) coefficient (Cf) where:-vc vc f f

p

C

∆

=

This factor is an important term in valve sizing This factor is an important term in valve sizing particularly in reference to critical flow and the particularly in reference to critical flow and the occurrence of cavitation or flashing, both of which are occurrence of cavitation or flashing, both of which are discussed later.

discussed later.

Fig. 21.1 Idealised Flow Path Through a Control Valve Fig. 21.1 Idealised Flow Path Through a Control Valve

Fig. 21.2 Contraction of Streamlines Fig. 21.2 Contraction of Streamlines

Fig. 21.3 Variation in Static Pressure and Velocity Fig. 21.3 Variation in Static Pressure and Velocity

TS21.1.3

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TS21.1.4

Page

Page 11

11

A

A liqliquid uid flow flow can can gengeneraerally lly be be tretreateated d as as beibeingng incompressible if there is no vapour formation. However, incompressible if there is no vapour formation. However, vapour bubbles are produced if the local static pressure vapour bubbles are produced if the local static pressure falls below the fluid vapour pressure. This occurrence is not falls below the fluid vapour pressure. This occurrence is not uncommon in control valve flows and leads to changes in uncommon in control valve flows and leads to changes in the behaviour of the flow. Different flow regimes, dependant the behaviour of the flow. Different flow regimes, dependant upon the level of vapourisation, are used to describe the upon the level of vapourisation, are used to describe the behaviour of the fluid as it passes through a control valve. behaviour of the fluid as it passes through a control valve. Normal Flow

Normal Flow

Normal flow describes the case when the fluid is assumed Normal flow describes the case when the fluid is assumed to be incompressible (no vapour formation). Under this to be incompressible (no vapour formation). Under this condition the volume flow rate is proportional to the square condition the volume flow rate is proportional to the square root of the pressure drop across the valve, see Figure 21.4. root of the pressure drop across the valve, see Figure 21.4. Semi-critical Flow

Semi-critical Flow

When the static pressure at the vena contracta (the When the static pressure at the vena contracta (the minimum flow area) falls just below the fluid vapour minimum flow area) falls just below the fluid vapour pressure, bubbles form and the flow can no longr be pressure, bubbles form and the flow can no longr be assumed to be incompressible. This represents the start of assumed to be incompressible. This represents the start of semi-critical flow and corresponds to the break down in the semi-critical flow and corresponds to the break down in the relationship between flow rate and pressure drop shown in relationship between flow rate and pressure drop shown in Figure 21.4.

Figure 21.4.

The onset of the semi-critical zone also coincides with the The onset of the semi-critical zone also coincides with the occurrence of incipient cavitation when the vena contracta occurrence of incipient cavitation when the vena contracta static pressure is just lower than the fluid vapour pressure. static pressure is just lower than the fluid vapour pressure. In the semi-critical flow regime any subsequent reduction in In the semi-critical flow regime any subsequent reduction in downstream pressure leads to increased levels of downstream pressure leads to increased levels of cavitation and reduced rate of increase in flow rate as cavitation and reduced rate of increase in flow rate as indicated by the curve between points 2 and 4 in Fig 21.4. indicated by the curve between points 2 and 4 in Fig 21.4.

Critical Flow Critical Flow

Critical flow occurs when the pressure drop is increased Critical flow occurs when the pressure drop is increased beyond the semi-critical zone, refer to point 4 on Figure beyond the semi-critical zone, refer to point 4 on Figure 21.4. At this stage the pressure at the vena contracta has 21.4. At this stage the pressure at the vena contracta has reached its minimum value, referred to as the reached its minimum value, referred to as the “supercooled” vapour pressure, see Figure 21.5. Beyond “supercooled” vapour pressure, see Figure 21.5. Beyond this point, as the downstream pressure is reduced no this point, as the downstream pressure is reduced no further change in flow rate occurs. Also any subsequent further change in flow rate occurs. Also any subsequent increase in pressure drop results only in greater levels of increase in pressure drop results only in greater levels of cavitation or flashing.

cavitation or flashing.

Most valve sizing techniques omit the semi-critical flow Most valve sizing techniques omit the semi-critical flow regime and assume that normal flow occurs up to point 3 of regime and assume that normal flow occurs up to point 3 of Figure 21.4 and that critical flow occurs thereafter. This Figure 21.4 and that critical flow occurs thereafter. This omission greatly simplifies the calculation procedure, and omission greatly simplifies the calculation procedure, and generally results in errors less than 2% in the Cv generally results in errors less than 2% in the Cv calculation. A calculation procedure for the semi-critical flow calculation. A calculation procedure for the semi-critical flow regime is pres

regime is presented in Appendix 21 ented in Appendix 21 .A. .A. 1.1.

Fig. 21.5 Static Pressure Variation for Different Flow Fig. 21.5 Static Pressure Variation for Different Flow Regimes

Regimes Fig. 21.4 Different Flow Regimes as a Function of

Fig. 21.4 Different Flow Regimes as a Function of Root of Pressure Drop

Root of Pressure Drop

Flow Regimes Flow Regimes

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As previ

As previousously detailly detailed, vapoued, vapour r bubbubblebles s are generare generateatedd within the liquid if the local static pressure falls below within the liquid if the local static pressure falls below the fluid vapour pressure. This subsequently results in the fluid vapour pressure. This subsequently results in the phenomena known as either cavitation or flashing. the phenomena known as either cavitation or flashing. In addition to the effect these have on valve sizing, In addition to the effect these have on valve sizing, structural damage to the valve or adjacent pipework structural damage to the valve or adjacent pipework may occur. In order to accurately size the valve and may occur. In order to accurately size the valve and minimize the effects of flashing and cavitation, minimize the effects of flashing and cavitation, consideration of these phenomena is essential.

consideration of these phenomena is essential. Flashing

Flashing

If the downstream static pressure remains below the If the downstream static pressure remains below the fluid vapour pressure, see Figure 21.5, then these fluid vapour pressure, see Figure 21.5, then these vapour bubbles will remain in the downstream flow, and vapour bubbles will remain in the downstream flow, and the process is referred to as flashing. Incorrect selection the process is referred to as flashing. Incorrect selection of valve trim style d/or materials for these applications of valve trim style d/or materials for these applications could result in serious erosion damage to valve trim and could result in serious erosion damage to valve trim and possibly to the valve body. The characteristic of flashing possibly to the valve body. The characteristic of flashing damage is that of a smooth polished appearance as damage is that of a smooth polished appearance as shown in Figure 21.6.

shown in Figure 21.6. As pre

As previoviouslusly detay detaileiled, corrd, correct seect seleclectiotion of a n of a valvalve/ve/tritrimm style is fundamental for valves on flashing duty. High style is fundamental for valves on flashing duty. High pressure recovery valves are generally considered to pressure recovery valves are generally considered to be more susceptible to flashing erosion damage than be more susceptible to flashing erosion damage than low pressure recovery designs. The cage guided low pressure recovery designs. The cage guided design of trim is used extensively on high duty flashing design of trim is used extensively on high duty flashing applications whereby the flow is directed over the plug applications whereby the flow is directed over the plug

to dissipate the energy within the confines of the trim. to dissipate the energy within the confines of the trim. Experience has shown that in the case of flashing flows Experience has shown that in the case of flashing flows it is good practice to use a single stage of pressure it is good practice to use a single stage of pressure letdown and utilise trim materials with good erosion letdown and utilise trim materials with good erosion resistance. Figure21.7 illustrates a high duty trim design resistance. Figure21.7 illustrates a high duty trim design

used on flashing applications. To aid the engineer in used on flashing applications. To aid the engineer in selecting the correct trim and material combination, a selecting the correct trim and material combination, a flash index presented in Table 21.2.

flash index presented in Table 21.2.

Fig. 21.7 High Pressure Drop Trim Design used on Fig. 21.7 High Pressure Drop Trim Design used on Flashing Flow

Flashing Flow Cavitation

Cavitation

In the event that the pressure recovery is sufficient to In the event that the pressure recovery is sufficient to raise the static pressure above the vapour pressure, raise the static pressure above the vapour pressure, see Figures 21.5, then the vapour bubbles will collapse, see Figures 21.5, then the vapour bubbles will collapse, this process being known as cavitation. The onset of this process being known as cavitation. The onset of this phenomena is referred to as incipient cavitation, this phenomena is referred to as incipient cavitation, and occurs when the pressure drop from the valve inlet and occurs when the pressure drop from the valve inlet to the vena contracta is equal to

to the vena contracta is equal to

))

((

₁₁ 2 2 vv ii f f

K

P

C

−

where K

where Kii. is the coefficient of incipient cavitation.. is the coefficient of incipient cavitation.

Collapsing vapour bubbles release extremely high Collapsing vapour bubbles release extremely high levels of energy and noise. If these bubbles implode in levels of energy and noise. If these bubbles implode in close proximity to a solid surface then the energy close proximity to a solid surface then the energy released tears away the material leaving a rough pitted released tears away the material leaving a rough pitted surface as shown in Figure 21.8.

surface as shown in Figure 21.8.

Fig. 21.6 Trim Erosion Due to Flashing Fig. 21.6 Trim Erosion Due to Flashing

Fig. 21.8 Typical Cavitation Damage to a Valve Trim Fig. 21.8 Typical Cavitation Damage to a Valve Trim

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avitation and Flashing avitation and Flashing

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Solution for Cavitating Flows

With regards to valves on potentially cavitating duties With regards to valves on potentially cavitating duties correct selection of valve/trim style and material correct selection of valve/trim style and material combination is a requisite. High pressure recovery combination is a requisite. High pressure recovery valves are inherently more susceptible to cavitation valves are inherently more susceptible to cavitation damage than low pressure recovery designs. A damage than low pressure recovery designs. A comparison between the variation of the static pressure comparison between the variation of the static pressure through a valve, for both high and low recovery valves, through a valve, for both high and low recovery valves, is shown in Figure 21.9. This figure reveals the greater is shown in Figure 21.9. This figure reveals the greater potential for the flow to cavitate with a high recovery potential for the flow to cavitate with a high recovery trim design.

trim design.

Thus, the low pressure recovery cage guided design of Thus, the low pressure recovery cage guided design of trim is used to remove cavitation potential, whereby the trim is used to remove cavitation potential, whereby the flow is normally routed over the plug so that any flow is normally routed over the plug so that any cavitation, jet impingement and/or highly turbulent cavitation, jet impingement and/or highly turbulent zones occur within the confines of the trim. In the event zones occur within the confines of the trim. In the event of high potentials of cavitation, usually associated with of high potentials of cavitation, usually associated with high pressure drops, further consideration to the trim high pressure drops, further consideration to the trim design is required. The principle is to utilise a low design is required. The principle is to utilise a low pressure recovery design and to apportion the pressure pressure recovery design and to apportion the pressure drop over a number of stages, so that the static drop over a number of stages, so that the static pressure within the valve does not fall below the liquid pressure within the valve does not fall below the liquid vapour pressure. This principle can be achieved in a vapour pressure. This principle can be achieved in a variety of ways including the use of variable area stages variety of ways including the use of variable area stages of pressure letdown within the trim (HFD, HFT designs), of pressure letdown within the trim (HFD, HFT designs), fixed area stages of pressure letdown either within the fixed area stages of pressure letdown either within the valve or downstream elements and/or a combination of valve or downstream elements and/or a combination of both. The variable area solution provides a higher both. The variable area solution provides a higher performance than fixed area units and inherently have a performance than fixed area units and inherently have a much

much wider wider rangeability.rangeability.

Fig. 21.9 Comparison between Low and High Recovery Fig. 21.9 Comparison between Low and High Recovery Valve Designs

Valve Designs

The cavitation index (C

The cavitation index (CII) see TS21.2.1, is used to) see TS21.2.1, is used to

indicate the potential of the flow to cavitate. When indicate the potential of the flow to cavitate. When selecting a valve for a set of operating conditions the selecting a valve for a set of operating conditions the cavitation index should be brought to within acceptable cavitation index should be brought to within acceptable limits by using the principles discussed previously. limits by using the principles discussed previously. Thus, the first resort is to utilise single stage cage Thus, the first resort is to utilise single stage cage guided trims such as the ported or HF design. If these guided trims such as the ported or HF design. If these fail to eliminate cavitation, then the two stage HFD or fail to eliminate cavitation, then the two stage HFD or three stage HFT should be considered. If these should three stage HFT should be considered. If these should fail to meet the criteria, then additional stages of fail to meet the criteria, then additional stages of pressure letdown can be incorporated either in the form pressure letdown can be incorporated either in the form of the Turbotrol valve presented in Figure 21.10 or fixed of the Turbotrol valve presented in Figure 21.10 or fixed area stages.

area stages.

Fig. 21.10 Seven Stage Turbotrol Valve Fig. 21.10 Seven Stage Turbotrol Valve

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The flow rate of a fluid through a valve is proportional to The flow rate of a fluid through a valve is proportional to the square root of the pressure drop within the normal the square root of the pressure drop within the normal flow regime, assuming the flow to be turbulent. The flow regime, assuming the flow to be turbulent. The factor that determines the turbulence level within the factor that determines the turbulence level within the fluid is related to its viscosity and its effect requires fluid is related to its viscosity and its effect requires consideration during the sizing of a control valve for consideration during the sizing of a control valve for liquid service. In considering the flow of a fluid through a liquid service. In considering the flow of a fluid through a valve there are two distinct groups of forces affecting valve there are two distinct groups of forces affecting the motion of the fluid particles. These are viscous the motion of the fluid particles. These are viscous forces, which are proportional to the fluid velocity ( forces, which are proportional to the fluid velocity (∝∝V),V), and inertia forces, which are proportional to the square and inertia forces, which are proportional to the square of the velocity (

of the velocity (∝∝ VV22), see Figure 21.11. The), see Figure 21.11. The predominance of one of these forces over the other predominance of one of these forces over the other leads to two different types of flow. If the viscous forces leads to two different types of flow. If the viscous forces dominate, the flow is termed

dominate, the flow is termed laminarlaminar (or viscous), if the(or viscous), if the inertia forces dominate the flow is termed

inertia forces dominate the flow is termed turbulent.turbulent. TheThe influence of these two flow types on control valve sizing influence of these two flow types on control valve sizing should not be overlooked. If the viscous effects are should not be overlooked. If the viscous effects are ignored then gross undersizing of a control valve can ignored then gross undersizing of a control valve can occur.

occur.

Laminar Flow (Viscous) Laminar Flow (Viscous)

Laminar flow generally occurs with fluids having high Laminar flow generally occurs with fluids having high viscosities and/or low flow velocities. Under such viscosities and/or low flow velocities. Under such conditions the movement of individual particles are conditions the movement of individual particles are along clearly defined lines (streamlines) , see Figure along clearly defined lines (streamlines) , see Figure 21.12. There is no movement transverse to the 21.12. There is no movement transverse to the streamlines, although particles in different streamlines streamlines, although particles in different streamlines may have different velocities. In the case of laminar flow may have different velocities. In the case of laminar flow in a pipe, the fluid layer in contact with the wall is at rest in a pipe, the fluid layer in contact with the wall is at rest and the velocity of the various

and the velocity of the various streamlines increasestreamlines increase progressively as the pipe centre in reached. The progressively as the pipe centre in reached. The resistance to the flow is due to viscous shear forces resistance to the flow is due to viscous shear forces between adjacent layers of fluid.

between adjacent layers of fluid.

Fig 21.12 Diagramatic Representation of Laminar & Turbulent Fig 21.12 Diagramatic Representation of Laminar & Turbulent Flows.

Flows.

Turbulent Flow Turbulent Flow

Turbulent flow occurs at relatively high velocities and Turbulent flow occurs at relatively high velocities and with fluids having low viscosities. It is characterised by with fluids having low viscosities. It is characterised by the mixing of fluid particles between adjacent layers or the mixing of fluid particles between adjacent layers or streamlines, the particles gaining or losing momentum streamlines, the particles gaining or losing momentum in the process. The particles thus have velocity in the process. The particles thus have velocity components transverse to the streamlines as well as components transverse to the streamlines as well as along the streamlines. The inertia forces are too large along the streamlines. The inertia forces are too large for the viscous forces to restrain the particles motion. for the viscous forces to restrain the particles motion. Fig. 21.11 Deviation from Normal Flow Relationship

Fig. 21.11 Deviation from Normal Flow Relationship Due to Viscous Flow

Due to Viscous Flow _{Reynolds Number}_{Reynolds Number}

The occurrence of laminar or turbulent flow is indicated The occurrence of laminar or turbulent flow is indicated by the value of the ratio of inertia to viscous forces; by the value of the ratio of inertia to viscous forces;

µ µ ρν ρν

d

ces

Viscousfor

Inertia

₌

=

Re

This ratio is referred to as the Reynolds number, after This ratio is referred to as the Reynolds number, after Osbourne Reynolds who first demonstrated this Osbourne Reynolds who first demonstrated this effect.This relationship has been applied to the valve effect.This relationship has been applied to the valve flow problem, and a modified form of the Reynolds flow problem, and a modified form of the Reynolds number, applicable to control valve terminology, is used number, applicable to control valve terminology, is used as the basis of determining whether the flow through a as the basis of determining whether the flow through a valve is laminar or turbulent. Thus, the basic valve flow valve is laminar or turbulent. Thus, the basic valve flow sizing equations apply to turbulent flow and a correction sizing equations apply to turbulent flow and a correction factor is then introduced if viscous forces are dominant. factor is then introduced if viscous forces are dominant. The procedure used for this calculation is presented in The procedure used for this calculation is presented in TS 21.2.4. TS 21.2.4.

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Viscous Flow Viscous Flow

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A

A concontrotrol l valvalve preseve presents a nts a sinsingle compgle componenonent t witwithin ahin a piping system. In determining the function of the valve, piping system. In determining the function of the valve, the overall piping arrangement should be considered. the overall piping arrangement should be considered. The pressure loss across the different piping The pressure loss across the different piping components such as adjacent isolating valves, elbows components such as adjacent isolating valves, elbows and tees can usually be determined for different flow and tees can usually be determined for different flow conditions by utilising head loss coefficients. However, conditions by utilising head loss coefficients. However, certain components not only introduce pressure loss certain components not only introduce pressure loss but will also effect the capacity of any adjacent valve but will also effect the capacity of any adjacent valve due to changes in the velocity pressure head (dynamic due to changes in the velocity pressure head (dynamic pressure). This will tend to have a greater affect on the pressure). This will tend to have a greater affect on the performance of the valve under choked flow conditions. performance of the valve under choked flow conditions. The piping components most likely to cause this are The piping components most likely to cause this are reducers and expanders, see Figures 21.13 and 21.14.

reducers and expanders, see Figures 21.13 and 21.14. Fig. 21.13 Line Size Fig. 21.13 Line Size ValveValve

Alt

Althouhough gh it it wouwould ld be be pospossibsible le to to testest t valvalves ves andand adjacent fittings, to determine the correction factors, it is adjacent fittings, to determine the correction factors, it is more practical to estimate them. A calculation of the more practical to estimate them. A calculation of the correction can be made by assuming that the reducer correction can be made by assuming that the reducer and expander result in a sudden contraction and and expander result in a sudden contraction and sudden enlargement in series. The pressure drop sudden enlargement in series. The pressure drop across these can then be determined by using the across these can then be determined by using the following expression.

following expression.

∆

∆p=p=k k ρ ρv v 22 (where k is the head loss coefficient.)(where k is the head loss coefficient.)

The head loss can be incorporated into the valve sizing The head loss can be incorporated into the valve sizing formula by means of a pipework correction factor. formula by means of a pipework correction factor. Under critical flow conditions the effect of the Under critical flow conditions the effect of the contraction on the pressure recovery coefficient also contraction on the pressure recovery coefficient also becomes important.The pressure recovery will be becomes important.The pressure recovery will be modified by the reducer and expander, and modified by the reducer and expander, and consequently, a combined pressure recovery coefficient consequently, a combined pressure recovery coefficient is required. This is used in the calculation of the limiting is required. This is used in the calculation of the limiting pressure drop which is used to determine whether pressure drop which is used to determine whether choked flow occurs due to vapourisation of the fluid. A choked flow occurs due to vapourisation of the fluid. A procedure for determining the effect of the pipework is procedure for determining the effect of the pipework is detailed in TS 21.2.7.

detailed in TS 21.2.7.

Fig. 21.14 Valve fitted

Fig. 21.14 Valve fitted with Pipe Line Reducerswith Pipe Line Reducers

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Pipework onfiguration Pipework onfiguration

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TS21.2

Valve

Valve Sizing

Sizing Equations

Equations

The sizing procedures detailed in the following sections The sizing procedures detailed in the following sections are dependant on the valve trim style. In these are dependant on the valve trim style. In these procedures an engineer would generally start with the procedures an engineer would generally start with the standard trim design (contoured) and depending upon standard trim design (contoured) and depending upon pressure drop, cavitation, flashing, or sound pressure pressure drop, cavitation, flashing, or sound pressure level a higher duty trim design may be selected. The level a higher duty trim design may be selected. The starting point for the trim selection is the determination starting point for the trim selection is the determination of the cavitation index or flashing index, both of which of the cavitation index or flashing index, both of which are detailed here. In the case of high pressure drop are detailed here. In the case of high pressure drop applications refer to Appendix 21 .A.2 for a guide to the applications refer to Appendix 21 .A.2 for a guide to the trim design and material selection.

trim design and material selection.

The cavitation index (C

The cavitation index (CII) indicates the potential of the) indicates the potential of the

flow to cavitate under a certain set of operating flow to cavitate under a certain set of operating conditions. C

conditions. CII should be used to sshould be used to select a trim select a trim style thattyle that

will eliminate any potential of the flow to cavitate. A full will eliminate any potential of the flow to cavitate. A full explanation of cavitation, the cavitation index and explanation of cavitation, the cavitation index and methods to remove/ reduce cavitation has been given methods to remove/ reduce cavitation has been given above.

above.

For a single stage of pressure letdown (i.e. microspline, For a single stage of pressure letdown (i.e. microspline, contoured, ported, or HF trim) use the equation below contoured, ported, or HF trim) use the equation below to calculate the cavitation index. Read the values of Cf to calculate the cavitation index. Read the values of Cf and K1 for the trim style selected from Table 21.2. and K1 for the trim style selected from Table 21.2.

21.01 21.01

))

((

₁₁ 2 2 vv ii f f I I

p

C

K

P

C

=

∆

−

Note: - when the valve opening has been determined Note: - when the valve opening has been determined the corrected value of Cf (see Figure 21.16) should be the corrected value of Cf (see Figure 21.16) should be used in the above formula.

used in the above formula. A neg

A negatiative vve value oalue of Cf CIIindicates no cavitation, whereas,indicates no cavitation, whereas,

a positive value indicates possible cavitation damage; a positive value indicates possible cavitation damage; the higher the value the greater the potential of the higher the value the greater the potential of cavitation damage. The allowable level of the cavitation cavitation damage. The allowable level of the cavitation index is a function of the trim design and material. For index is a function of the trim design and material. For single stage trims C

single stage trims CIIvalues up to the levels shown invalues up to the levels shown in

Table 21.1 the valve should operate satisfactorily Table 21.1 the valve should operate satisfactorily without any significant wear. If the value of C

without any significant wear. If the value of CIIis higheris higher

than these limits then a higher class of anti-cavitation than these limits then a higher class of anti-cavitation trim such as the HFD or HFT should be used. When trim such as the HFD or HFT should be used. When selecting multi-stage trims it is good practice to selecting multi-stage trims it is good practice to eliminate all cavitation. The equation below is used for eliminate all cavitation. The equation below is used for these trim styles (where n is the number of pressure these trim styles (where n is the number of pressure letdown stages in the trim).

letdown stages in the trim).

))

((

₂₂ 2 2 vv ii f f I I

P

n

p

P

K

C

n

P

C

=

∆

−

+

∆

−

21.0221.02

If the cavitation index is still positive when specifying an If the cavitation index is still positive when specifying an HFT trim then either fixed area restrictions or a turbotrol HFT trim then either fixed area restrictions or a turbotrol valve should be considered. When determining the valve should be considered. When determining the cavitation performance of either a turbotrol or fixed area cavitation performance of either a turbotrol or fixed area devices then each pressure letdown stage should be devices then each pressure letdown stage should be evaluated separately using equation 21-01.

evaluated separately using equation 21-01.

Table 21-1 Allowable Levels of Cavitation Table 21-1 Allowable Levels of Cavitation Material

Material Cavitation Cavitation Index Index (C(CII))

Single

Single stage stage Multi-stageMulti-stage psi

psi bar bar psi psi barbar 316L

316L 5 5 0.3 0.3 3 3 0.20.2

17.4

17.4 PH PH 8 8 0.5 0.5 5 5 0.30.3 Full

Full stellite stellite grade grade 6 6 20 20 1.4 1.4 10 10 0.70.7 Full

Full stellite stellite grade grade 12 12 26 26 1.8 1.8 12 12 0.80.8 Monel

Monel 8 8 0.5 0.5 5 5 0.30.3

Ferralium

Ferralium 10 10 0.7 0.7 8 8 0.50.5

In the selection of a valve for a flashing application the In the selection of a valve for a flashing application the trim style and material should be chosen to eliminate! trim style and material should be chosen to eliminate! reduce erosion potential. In determining the correct reduce erosion potential. In determining the correct solution the influence of both the valve pressure drop solution the influence of both the valve pressure drop and percentage flash should be accounted for. A guide and percentage flash should be accounted for. A guide to this selection can be obtained by using the Flash to this selection can be obtained by using the Flash Index presented in Figure 21.15a/b. The Flash Index Index presented in Figure 21.15a/b. The Flash Index combines the effects of pressure drop and % flash and combines the effects of pressure drop and % flash and indicates the appropriate trim design, trim material and indicates the appropriate trim design, trim material and overlay.

overlay.

Fig. 21.15a Flash Index. Contoured Trim Fig. 21.15a Flash Index. Contoured Trim

Fig. 21.15b Flash Index. HF Trim Fig. 21.15b Flash Index. HF Trim

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avitation Index avitation Index Procedure Procedure Flash Index Flash Index

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TS21.2.3

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Table 21.2 Valve Pressure Recovery and Incipient Cavitation Coefficients Table 21.2 Valve Pressure Recovery and Incipient Cavitation Coefficients

Valve

Valve Type Type Trim Trim Style Style Trim Trim Size Size Flow Direction Flow Direction CCf f KK11

Microspline

Microspline All All sizes sizes Over Over 0.95 0.95 0.950.95 Full

Full UnderUnder_Over_Over _0.85_0.850.90.9 _0.81_0.810.80.8 Contoured

Contoured

Reduced

Reduced UnderUnder Over Over 0.9 0.9 0.8 0.8 0.8 0.8 0.82 0.82 Ported

Ported All All sizes sizes Over Over or or under under 0.93 0.93 0.90.9 Series 10

Series 10

HF,

HF, HFD, HFD, HFT HFT All All sizes sizes Over Over or or under under 1 1 0.950.95 Full

Full UnderUnder_Over_Over _0.85_0.850.90.9 _0.81_0.810.80.8 Contoured

Contoured

Reduced

Ported All All sizes sizes Over Over or or under under 0.93 0.93 0.90.9 Series 14

Series 14

HF

HF All All sizes sizes Over Over or or under under 1 1 0.950.95 Ported

Ported Full Full Over Over or or under under 0.92 0.92 0.90.9 HF

HF All All sizes sizes Over Over or or under under 0.97 0.97 0.950.95 XHF

XHF All All sizes sizes Over Over or or under under 0.98 0.98 0.950.95 HFD

HFD All All sizes sizes Over Over or or under under 0.99 0.99 0.950.95 Series 12

Series 12

XHFD,HFT,XHFT

XHFD,HFT,XHFT All All sizes sizes Over Over or or under under 0.97 0.97 0.950.95 Contoured

Contoured _Reduced_ReducedFullFull Over and underOver and under 0.90.9_0.8_0.8 0.870.87_0.84_0.84 Series 20

Series 20

HF,

HF, HFD, HFD, HFT HFT All All sizes sizes Over Over and and under under 1 1 0.950.95 Series

Series 30/31 30/31 ‘V’ ‘V’ Port Port All All sizes sizes Mixing Mixing and and diverting diverting 0.91 0.91 0.90.9 4

4 Stage Stage All All sizes sizes Over Over 1* 1* 0.95*0.95* Series 51/57

Series 51/57

7

7 Stage Stage All All sizes sizes Over Over 1* 1* 0.95*0.95* Vane

Vane <30%<30%_Open_Open ThroughThrough 0.980.98_0.9_0.9 _0.75_0.750.90.9 Series 61/62

Series 61/62

Vane and baffle

Vane and baffle <30%<30%_Open_Open ThroughThrough 1**1** 0.98** 0.98** 0.9 0.9 0.9 0.9 Contoured Full

Contoured Full UnderUnder

Over Over 0.9 0.9 0.45 0.45 0.8 0.8 0.84 0.84 Reduced

Ported All All sizes sizes Over Over or or under under 0.92 0.92 0.90.9 HF

HF All All sizes sizes Over Over or or under under 0.96 0.96 0.920.92 HFD

HFD All All sizes sizes Over Over or or under under 0.98 0.98 0.950.95 Series 70/71

Series 70/71

HFT

HFT All All sizes sizes Over Over or or under under 0.99 0.99 0.950.95 Ported

Ported All All sizes sizes Over Over or or under under 0.92 0.92 0.90.9 HF

HF All All sizes sizes Over Over or or under under 0.96 0.96 0.920.92 XHF

XHF All All sizes sizes Over Over or or under under 0.97 0.97 0.920.92 HFD

HFD All All sizes sizes Over Over or or under under 0.98 0.98 0.950.95 Series

Series 72/73/74 72/73/74

XHFD

XHFD ,HFT, ,HFT, XHFT XHFT All All sizes sizes Over Over or or under under 0.99 0.99 0.950.95 Cylindrical

Cylindrical All All sizes sizes Through Through 0.95 0.95 0.900.90 Fixed area

Fixed area

Flat

Flat All All sizes sizes Through Through 0.92 0.92 0.900.90 *

* stage stage valuesvalues

** varies with baffle size ** varies with baffle size