IC WARREN CON S

VALVE SIZING & SELECTION TECHNICAL REFERENCE

TABLE OF CONTENTS

I ntroduction

Va lve Ftow Termino logyThe S izing Process

Operating Cond itions

F lu id PropertiesRangeab i l i tyCv and F low Sizing Formu las

Cv Formu las for L iqu id Ftow

Cv Formulas for Vapor F lowCv Formu las for Two Phase F low

F low Velocity Formu las

F low Ve locity for Liqu id F lowFfow Velocity for Vapor F low

Nomenclature

Conversion to Cg and Cs

Seat Leakage

Actuator S izingAP Tables

App l ication Gu ide for Cavitation , Flash i ng and Compressible Flow ServicesL iq u id F low

Cavi tation

Cavi tat ion Defin it ion

Cavitation Countermeasures

Appl ication ofWarren Trims in Cavitation ServiceCavitation Avo idance

Cavitation Toterant

Cavitat ion Containment

Cavi tation Prevention

The Cavitation Phenomena

Flu id and Pressure Profi les

Choked Flow and I ncipient CavitationCavi tat ion Damage

Flashing

F lash ing Defin it ion

F lash i ng Countermeasures

Body MaterialTrim Se lection

Appl ication ofWarren Va lves in Flash ing S erviceBody Materia l :Trim Se lection

The Flashing Phenomena

Liqu id F low Ve loci ty - Body MaterialCompress i b le F low Noise

Compress i b le F low No ise D iscussionCompress ib le Flow Noise CountermeasuresApp l ication ofWarren Trims i n Compressib le Flow Appl ications

Standard Trims :

Mu lt iple Orifice TrimsCompress ib le Flow Velocity Lim its :Two Stage Trims and Backpressure Orifices :

The Compressible Flow Noise Phenomena

TABLES

Trim Rangeabi l i ty Tab le 1F lu id Properties Table 2FL Factors Ta ble 3

F langed Body I n let and Outlet Diameters Table 4AI Iowab le Seat Leakage Classes Tab le 5Liq u id F low Ve locity Lim its Tab{e 6

F IG URES

Cavi tation

INTRODUCTION

A Contro l Valve performs a specia l task , control l i ng the flow of flu ids so a process variable suchas flu id pressure , fluid leve l or temperature can be contre l led . In add it i on to control l i ng the flow, acontrol valve may be used to shut off flow. A control va lve may be defined as a valve wi th apowered actuator that responds to an external s ig naL The signal usua l ly comes from acontrol l e r. The control l e r and valve together form a basic controt loop. The control va lve is

se ldom fu l l open or closed but in an intermed iate position controt l i ng the flow of flu id through thevalve. I n this dynamic service cond ition , the va lve must withstand the eros ive effects of theflowing flu id wh i le maintain ing an accurate position to mainta in the process variab le .

A Contro l Va lve wi l l perform these tasks satisfactori l y i f it i s sized correctly for the flowing andshut-off cond i tions. The valve sizing process determines the requ i red Cv , the requ i red FL , F l owVeloe i ties , F low Noise and the appropriate Aetuator S ize

VALVE FLOW TERM INOLOGY

Cv: The Flow Coefficient, Cv , i s a d imensionless val ue that relates to a valve's flow capacity . I tsQ

most bas ic form is Cv - where Q=F low rate and AP=pressure d rop across the va lve . See

pages 6 , 7 & 9 for the equations for l i qu id , g as , steam and two phase flow. The Cv valueincreases i f the flow rate i ncreases or if the AP decreases . A s izi ng app l ication wi l l have a

Requ i red Cv wh i le a valve wil l have a Rated Cv . The valve's rated Cv must equal or exceed therequ i red Cv .

Ft. : The FL , Liqu id Pressure Recovery Coefficient, i s a d imension less constant used to ca lculate

the pressure drop when the va lve 's l iqu id flow is choked . The F L is the square roet of the ratio ofva lve pressure drop to the pressure d rop from the in let pressure to the pressure of the venacontracta . See page 7 for the F L equation . The FL factor is an ind ication of the vatve's venacontracta pressure relat ive to the outlet pressure, lf the FL were 1 .0 , the vena contracta pressurewou ld be the same as the valve's outtet pressure and there wou ld be no pressure recovery . Asthe FL value becomes sma l le r the vena contracta pressure becomes increas ing ly Iower than thevalve's outlet pressure and the valve is more l i kely to cavi tate . A valve's Rated F L varies with thevalve and trim style , it may vary from .99 for a special mu ltip le stage tdm to . 60 for a ba l l va lve .

Rated F L : The Rated F , is the actua l F L value for a particular va lve and trim style .

Requ i red F L : The Requi red F L is the F L val ue calcu lated for a particu tar service cond ition . I t

i nd icates the requ i red FL needed to avo id choked flow. I f the Rated F L is less than the Requ i redFL , the l iqu id flow wi l l be choked wi th cavitation .

Vena Contracta : The vena contracta is where the jet of flowing flu id is the smallest immed iately

downstream of the trim's thrott le point . At the vena contracta , the flu id's ve locity is the highestand the flu id's pressure is the Iowest.

Vapor Press ure : A flu id's vapor pressure is the pressure where the flu id wi l l change from a

l iqu id to a vapor. The l iq uid wi l l change to a vapor be low the vapor pressure and a vapor wi l l3

change to a l iqu id above the vapor pressure . The vapor pressure i ncreases as the temperatureincreases .

C hoked F low: Liqu id flow wi l l become choked when the trim's vena contracta is fi t l ed wi th

vapor from cavitat ion or flashing . Vapor flow a lso wi l l become choked when the flow ve locity atthe vena contracta reaches son ic. A choked flow rate is l im ited ; a fu rther decrease of the outlet

pressure does not increase flow. Choked flow is a lso ca l led cri tica i flow.

Cavitation : Cavitation is a two stage phenomena with l iqu id flow. The first stage is the

formation of vapor bubbles in the l i qu id as the flu id passes through the trim and the pressure isreduced be low the flu id 's vapor pressure . The second stage is the col lapse of the vapor bubb lesas the fluid passes the vena contracta and the pressure recovers and increases above the vaporpressure . The col lapsing bubb les are very destruct ive when they contact meta l parts and thebubble co l lapse may produce h igh noise levels .

F lash i ng : F lash i ng is simi la r to cavi tation except the vapor bubbles do not col l apse , as thedownstream pressure rema ins less than the vapor pressure. The flow wi l l remain a mixture ofvapor and l iqu id .

Lam i nar F low: Most flu id flow is tu rbulent. However, when the l iqu id flow ve locity is very slow orthe flu id is very viscous or both , the flow may become laminar. When the flow becomes taminar,the requ i red Cv is la rger than for tu rbu lent flow with sim i la r cond itions. The ISA sizing formu lasadjust the Cv when laminar flow exists.

THE SIZING PROCESS

The fi rst s izing step is to determine the requ i red Cv value for the appl ication . Next determine if

there are unusual cond itions that may affect va lve selection such as cavitation , flash ing , h igh flowveloci ties or h igh flow noise . The valve s izing process wi l l determine the proper va lve s ize, valvetr ito size , va lve tr im style and actuator size . Warren's Va lve Siz ing Prog ram wi l l accuratelyca]cu late the Cv, fiow ve loci ty and flow noise. The program wi l l a l so show messages whenunusual cond itions occur such as cavitat ion , flash ing , h igh velocity or h igh noise . The resu ltsfrom Warren 's Valve Sizing Program are on ly one element of the valve select ion process .Knowledge and judgment are a lso req u i red . Th is overview wi l l g ive the user some of the s izi ngbas ics .

The l iquid , gas and steam Cv ca lcu lation methods , i n th is manual , a re in accordance with I SA$75 . 0 1 and the gas and steam flow no ise ca lcu lations are in accordance withISA $75 . 1 7 . These two ISA Standards are i n agreement with I EC-534 . These standards haveworldwide acceptance as the state of the art in Cv and F low No ise determination .

Operati ng Cond itions

The most important part of Valve S izi ng is obtain ing the correct flowing cond itions. I f they arei ncorrect or incomplete , the sizing process wi l l be fau l ty. There are two common problems . Fi rsti s having a very conservative cond ition that overstates the Cv and provide a valve less than ½open at maximum requ i red flow. The second is sta ting only the maximum flow cond i tion that has

min imum pressure drops and not stating the min imum flow cond i tions with h igh-pressure d ropsthat often induce cavitat icn or have very h igh rangeab i l i ty requ i rements .

F lu id P roperties

Table 2 l ists many flu id p ropert ies needed for va lve s izing . These fl uid properties are inWarren's Valve Sizing Prog ram's database and do not need manua l entry.

Rangeabi l ity : Rangeab i l i ty i s the ratio of maximum to mi nimum control l ab le Cv . Th is is a lsosometimes ca l led Cv Rati o or Tumdown. The maximum flow for Warren Controls' vaives is at

maximum travel . The minimum contro l l able Cv is where the Flow Characteri st i c (Cv vs. Travel)i n it i a l ly deviates or where the va lve trim cannot ma inta in a consistent flow rate . Th is is partial ty a

function actuator stiffness as wel l as va lve "stiction" . The Tfim's rangeabi l i ty i s not a lways theuseabte range as seat erosion may be a govern i ng factor with respect to erosive flu ids and h ighdrops in the near-closed position . A valve with a sign ificant pressure d rop shou ld not be used tothrott le near the seat for extended periods of time .

The rangeabi l i ty va lues , l i sted in Table 1 , apply to the rated Cv, not the requ i red Cv . For

example , an app l i cation may requ i re a maximum Cv of 1 70 . A 4" Equa l Percentage Trim maybe se lected that has a maximum CV of 1 95. Using the rangeabi l ity va lue for this tr im , theminimum Cv is 1 95/1 00= 1 9 . 5 , not 1 70/1 00= 1 7 .

Valve app l ications subject to pressures from nature , such as gas and oi l p roduction , a re usua l lysized for ful l flow at about 80% open as the pressure may be unknown when the va lve is sizedand the pressure may vary with time .

Those va lve appl i cations wi th fai r ly consistent in let pressures , such as process control andpower appl icat ions are usual ly sized at ful l travel . The va lve specifier usua l iy includes a fa i rmarg in of safety in the stated sizing cond itions . I f the valve suppl ier includes add itional safety ,such as fu l l flow at 80% open , the valve may be at fu l l flow at tess than ½ trave l g iving poorperformance .

TRIM RANGEABILITY Tab le 1

Valve Trim

Equal Percent - Unbalanced .

Equal Percent - Doub le Seat Balanced I

Equal Percent - Balanced Cage Contro lLi near - Unba lanced

Equal Percent - Unbalanced Cage Reta i ned Seat

Linear - Unba lanced Cage Reta ined Seat

Rota ry E -Plug , Equat Percent, Flow to Open

Rotary E -Pluq , Equa l Percent, F low to Close

Rotary E -P lug , Linear, Flow to Open

Rotary E -P lug , Li near, F low to C lose

Rangeab i l i ty1 00: 1

1 00: 1

1 00: 1

1 00 : 1

1 00: 1

1 00: 1

1 00 : 1

1 00 : 1

1 00 : 1

1 00 : 1

Cv AND FLOW SIZING FORMULAS

The fo l lowing formu las are for information and for understand ing the sizing process . Warren 'sVa lve S izing Program is recommended for the ca lcu lat ion process . Flow no ise equations arenot l i sted be low as they are high ly complex and shou ld only be made on our verified computerprogram . Formu las are shown both for calcu lation the Cv when the flow rate is known and forcalculating the ftowwhen the Cv is known .

Cv Form u las fo r L iqu id F l ow

Requ i red FL - " P1 - PvFF FF = 0.96 - 0.28 fI f the Rated FL is ta rger than the Requ i red Fd

Q F G' FRCv : F - _--p2 or Q = Cv Fp Of

When the Rated F L iS sma l ler than the Requ i red F L , choked flow exists i n the vena contracta

l imiting the flow.

I f the Rated FL is smal ler than the Requ i red F L :

Cv Fp FL (Rated) P - FF Pv or Q = Cv Fp FL (Rated) p -G-FF PvAP for choked Ilow = F ( 1=1 - FFPv ) = ps iAP for incip ient cavitat i cn = Kc (P - Pv ) = ps i(See d iscussion in "Choked F low and I ncipient Cavitation" section )

Cv Formu las for Vapor F low

x - P1 - P2 Lim i t x _< xTPI

k x

FK - 1 .4 Y = I 3 FK xT

I f the flow rate is in volumetric un its , SCFM , then

Q G/ g T Z or Q = 1 360 Cv Fp P Y. TCv - 1 360 Fp P1 Y x Z

I f the flow rate is in mass flow un i ts, Lb . /H r. , thenW

Cv - 63.3 Fp Y .,/r p ) ' or W = 63.3 Cv Fp Y -q P1 X1

To convert SCFH to Lb./H r. : W=0 . 0764 Q Gg = Lb./Hr.

Cv Form u las for Two Phase F low

Pressure Drop for I i qu id phase= A P, = F (P1 - FF Pv )

Pressure Drop for vapor phase = A P0 = FK XT P1

ff = we ight fraction of tota l flow as l iqu id

f0 = weig ht fraction of totat flow as vapor

W t f' foCv - 63.3 F -Ap -x 1 f 4 APo 'I Q y2FLOW VELOC lTY FORMULAS

F l ow Veloc i ty for L iqu id F low

L iq u id Flow Velocity through the Valve :0.408 Q

Vv - Di- Ft/Sec.

L iqu id Flow Veloci ty through the Pi pe :0.408 Q

Vp = 2Dp

- Ft /Sec.

F low Veloc i ty for Vapor F low

Downstream Specific Vo lume for a Gas Vapor: V2 = 1 0.72 T ZM P2

= Ft.3 /Lb.

Downstream Specific Vo lume for Steam : V2 = Refer to Keenan & Keyes' Steam Tab les

Vapor Ftow Ve locity th rough the Valve:3.06 WV2 0.234 Q Gg

Vv - Dî - Dí - Ft./M i n.

Vapor F low Ve loci ty through the P ipe : Vp 3.06 W V2 0.234 Q Gg- - - Ft./M i r[

Di Di

Son ic Ve l ocity of a Vapor F l u id : VSON c = 4650 V2 = FL /Min.

Mach Number: = Vapor F low Ve loci ty, Vv or VpVSONIC

Nomenc latu re

Cv = Valve F low Coeffic ient.

D B -- Ins ide Diameter of Va lve Body Outlet = I nches . See Tab le 4 .

Dp = I nside D iameter of Outlet P ipe = I nches .

FF =Liq u id Cdtica l Pressure Ratio Factor:Fk = Ratio of specific Heats Factor.

FL = L iq u id Pressure Recovery Factor.

FL Requi red = The F L factor to avoid Choked F low.

FL Rated = The FL factor rated for i nd ividual Trim Styles . See Tab le 3 .

Fp = Piping Geometry Factor, I f the va lve s ize and pipe size are equal us 1 . 0, if not referto I SA $75. 0 1 section 4 . 3.

FR = Reynolds Number Factor, N ormal ly = 1 . 0 but varies with vepJ slow flu id velocities orvery viscous flu ids . Refer to ISA $75 . 0 1 section 4 .4 .

Gr = Specific Gravity of a Liq uid re lative to water at 60 ° F .

G = Spedfic Gravi ty of a Vapor re lative to a i r at 60 ° F 1 4 . 7 PS IA .

k = Ratio of specific Heats . See Tab le 2 .Kc = Cavitation Index. See Tab le 3 .

M = Molecu lar Weight. See Table 2 .

P 1 = Valve ln let Pressure (psia) .P2 = Va lve Outlet Pressure (psia) .Pc =Flu id ' s Crit i ca i Pressure (ps ia) See Tab le 2 .Pv =Ftu id 's Vapor Pressure (psia) .Q = Volumetric Flow Rate : Liqu ids (GPM) Vapor(SCFM)T = Flu id Temperature in Deg rees Rankine . ° R = ° F + 460 .

V2 =Specific Vo lume of vapor, e i ther gas or steam = Ft. 3 / Lb .W = Mass FIow Rate = Lb./H r.

x = Pressure Drop Ratio .XT = Maximum Pressure Drop Ratio , varies with Trim Style . See Table 3 .Y = Fluid Expansion Factor for vapor fiow.Z = Compress ibi l i ty Factor for vapor f]ow. Usual ly 1 . 0 . Refer I SA Handbook of Control

Va lves , 2nd Ed itJon , pages 488-490 .X = Specific Weight = Lb . /Ft . 3Subscripts :

1 = I n let cond i tions

2 = out let cond it ion s

V = vaive

p = pipe

f = l iq u id

g = vapor

b = body

F low velocity of a vapor, gas or steam , phys ica l ly cannot exceed sonic velocity or Mach 1 . 0 .Vapor flow is phys ica l ly l im ited at sonic ve locity and becomes choked . The choked son ic

t im itation may apply either at the valve tdm or at the valve body's outlet . When the flow rateincreases with the veloci ty at the valve's outlet at sonic, the vatve 's outlet p ressure wi l l rise

increasing the fluid densi ty and a l lowing a h igher flow rate sti l l l imited at son ic ve locity .

The I SA noise pred ict ion formu las for vapor flow Ioses accuracy at Mach numbers la rger than. 33 . .

Name

of

Flu id

F LU ID PROPERT IES

AcetyleneAi r

Ammen ia

ArgonBenzene

Butane

ButanoI

Butene - 1

Butylene OxideButadiene

1 -Butene

n-Butane

Isobutane

n-Butanol

I sobutyleneCarbon Dioxide

Carbon Monoxide

Carbon Tetrach lo ride

Chlo r ine

Ch lorobenzene

Ch loroform

ChloropreneCyclobutaneCyclohexaneCyclopentaneCyclopropaneCrude O i l

Ethane

Ethanol

EthylbenzeneEthyl Chlori d eEthyl OxideEthyleneEthylene GlycolTriethylene GIycolFreon 1 1

Freon 1 2

Freon 22

Hel i um

HeptaneHydrazineHydrogenHydrogen BromideHydrogen Ch lor ideHydrogen F lorideHydrogen I od ideHydrogen Su lph ide

Flu id

Form

Liq u idGas

G

G

L G

G

L G

G

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

Mo lecu la r Cri ti ca i

Weig ht Pressure

M Pc ps ia26 . 038 905 . 04

28 .966 546 . 79

1 7 .03 1 1 637 .48

39 .948 706 . 34

78 . 1 1 4 7 1 3 . 59

58 . 1 24 529 . 39

74 . 1 23 639 . 62

G 56 . 1 08 583 .4

63 .6

54 . 092 652 . 5

56 . 1 08 583 .4

G 58 . 1 243 55 1 . 1

G 58 . 1 24 529 . 1 0

638 . 3

56 . 1 08 580 .5

G 44 . 01 1 070 . 38

G 28 .01 507 . 63

1 53 . 82 66 1 . 37

G 70 . 906 1 1 1 6 . 79

1 1 2 . 559 655 . 62

1 1 9 . 38 786 . 1 1

6 1 6 . 5

56 . 1 08 723 . 24

84 . 1 62 590 . 30

70 . 1 35 654 . 1 5

42 . 08 1 797 . 7 1

G 30 . 07 707 , 79

46 . 069 925 . 34

1 06 . 1 68 523 .2

G 64 . 5 1 5 754 . 20

1 052 .2

G 28 . 054 732 .44

62 . 069 1 1 1 7 .2

G 1 37 . 37 635 . 00

G 1 20 . 92 596 . 90

G 86 .48 7 1 6 . 00

G 4.003 33 . 36

G 1 00 . 205 396 . 8

32 . 045 2 1 32 . 06

G 2. 0 1 6 1 88 . 55

80 . 9 1 2 1 240

G 36 .46 1 1 205 ,27

20 . 006 94 1 . 30

1 27 . 9 1 1 205 . 27

G 34 . 076 1 296 . 64

Tab l e 2

Cri t i ca i

Temperature

Tc (F)95 . 27

-220 . 99

270 . 59

-1 88 . 23

552 . 1 1

274 . 9 1

553 . 55

295 . 6

339

295 . 6

305 .7

274 . 90

292 .6

87 . 7 1

-220 .45

54 1 . 85

29 1 . 29

678 . 32

505 . 1 3

367 . 82

536 .45

460 . 88

256 . 37

90 . 05

469 .49

651 . 1

369 . 05

49 . 9 1

338 . 00

234 . 00

204 . 80

-450 . 33

5 1 2 . 7

7 1 6 . 09

-399 .73

1 93 . 76

1 24 . 79

370 .49

303 . 35

229 . 9 1

Ratio of

specificHeats

k

1 .26

1 .4

1 . 3 1

1 . 668

1 . 08

1 . 1

1 . 1 1

1 . 1 2

1 . 1 1

1 . 1

1 . 1 1

1 . 1 2

1 . 295

1 , 395

1 . 067

1 . 355

1 . 1

1 . 1 4

1 . 1 1

1 . 1 8

1 . 1 3

1 . 072

1 . 1 3

1 .22

1 . 1 4

1 . 1 4

1 . 1 8

1 . 66

1 . 05

1 .4 1 2

1 .4

1 .4 1

t .32

Name

of

F lu id

IsopreneMethane

Methano l

Methyl Chlo ride1 -Methytch lo rideO-Methylene Ch lor ideNapthaleneNatural Gas

Neon

Nitric Oxide

N itrogenN itrogen D ioxideN itrous Oxide

n-Nonane

n-Octane

OxygenPentane

Pheno l

Propanen-Propano lPropenePropylenePropyl OxideSea Water/Brine

Su lfuric Acid

Su lfur D ioxide

Su l fur Trioxide

Tolulene

Water

M-XyleneO-xyleneP-xylene

F lu id

Form

L iqu idGas

L

L G

L

L G

L

L

L

G

G

L G

L G

L

L G

G

G

L G

G

L

L G

L

G

L

L

L

L

L G

L

L

L G

L

L

L

Molecu lar

Weight

M

1 6 . 043

32 . 042

50 .49

84 .922

1 28 . 1 7

1 9 . 5

20 . 1 79

30 . 006

28 , 0 1 3

46 . 006

44 . 0 1 3

1 28 . 259

1 1 4 . 23

3 1 . 999

72 . 1 5 1

94 . 1 1 3

44 ,097

42 . 1

42 . 08 1

1 8

64 , 059

80 . 058

92 . 1 4 1

1 8 . 0 1 5

1 06 . 1 68

1 06 . 1 68

1 06 . 1 68

Cri t i ca i

P ssure

Pc ps ia532 . 1

667 . 1 7

1 1 53 . 05

968 . 85

889 . 08

91 0 . 9

587 .40

670

400 . 30

94 1 . 30

493 . 1 3

1 479 . 8

1 050 . 08

335 . 1

362 . 60

730 . 99

488 . 78

889 . 56

6 1 7 . 86

75 1 . 3

66 1

667 . 1 7

7 14 . 7

3200

1 1 42 . 90

1 1 90 .7

587 .40

3208 .24

5 1 4 .4

540 . 8

5 1 0

C rit ica i

Temperature

Tc (F)

- 1 1 6 . 77

463 . 0 1

289 . 67

458 . 33

887 .45

-80

-379 . 75

-1 35 . 67

-232 . 5 1

3 1 6 . 52

97 . 6 1

6 1 0 .6

456 , 35

-1 8 1 . 39

385 .6 1

789 , 56

205 . 97

1 98

1 97 . 5 1

705 .47

3 1 5 . 59

423 , 8

609 . 53

705 ,47

650 . 9

674 . 7

649 . 5

Ratio of

specificHeats

k

1 . 3 1

1 ,2

1 .27

1 .667

1 .4

1 ,29

1 . 04

1 . 05

1 . 397

1 . 07

1 . 09

1 . 1 3

1 . 1 4

1 , 1 54

1 ,33

1 ,29

1 ,06

1 , 335

1 , 072

1 . 049

1 . 073

FL , Kc & XT Facto rs

Valve Trim Style

Tab le 3

1 840

1 843

2820

2920

2922

2923

3800

5800

* = no value r vapor flow

FL Kc XTRated

.?? . ?? . ??

. ?? .?? . ??

.?? . ?? . ??

.?? . ?? . ??

,77 . 77 ,77

,?? . ?? . ??

,?? . ?? ,??

. ?? . ?? . ??

* * = no value for l iq u id flow

l 0

F l a nged Body I n let a nd O utlet D iameters Tab le 4Nomi na I ANS I Pressure Class

Body S ize 1 50 3001 1 .06" 1 . 06"

1 .5 1 . 63" 1 .63"

2 2 .06" 2 . 00"

3 3 .00" 3 . 00"

4 4 .00" 4 . 00"

6 6 . 00" 6 . 00"

8 8 . 00" 8 . 00"

SEAT LEAKAGE

The F luids Control I nstitute (FC I ) Standard ANSI/FC1 70 .2 estab l i shes a Va lve's a l lowab le seat

Leakage Rate . The standard recogn izes rive deg rees of seat tightness .

ALLOWABLE SEAT LEAKAGE CLASSES Tab le 5

Leakage Class Maximum Seat Test Test Re lative Seat

Leakage F l u id Pressure TightnessClass I l 0 . 5% of rated Cv Water 45 to 60 PS I 1 . 0

Class I I I 0. 1 % of rated Cv Water 45 to 60 PS I 5 . 0

Ctass IV 0. 01 % of rated Cv Water 45 to 60 PS I 50

C lass V 0 .0005 ml /m in/inch Water Max Operating 300 , 000of tdm size/ AP(PSI) AP

C l ass VI about 0.9 mi/miri � A i r 50 PS I 600 ,000

Leakage rate varies by va lve size , Refer to the Standard ANS I/FC1 70 . 2 .Warren offers Class I I , C lass I I I , Class IV, & Class IV

The Re lative Seat Tightness is at a 50 AP . For example , a C lass IV leakage rate is 1 /50as much as Class I l

Class VI is for resi l i ent seated valves ; the other classes are for metal l i c seats .

ACTUATOR SIZING

The actuator s izing process matches our actuator's force output with our va lve tr im 's requi red

stem forces. The resu l t is the maximum obtainable pressure drop at the d ifferent seat leakageclasses . The process cons iders the va lve's sh ut off cond ition . The flowing cond it i ons alsorequi re an adequate match between the actuator and trim forces but the shut off condition isdominant and determines the al lowab le .

UA = Unba ta ncedArea (Ba ta ncedTrim) = ( (Cage ID) 2 - (Seat I D) 2 ) (4) = In2UA = Unba lancedArea (Unba lancedTrim) = (Seat I D) 2 (4) = In2C L = Seat Contact Load = ( Seat I D) í ( Load Factor) = Lb . / I n . of oi rcumference

Load Factors vary with seat leakage classPF = Packi ng Friction (Teflon Packing)= 20 Lb .

] ]

PF = Packing Friction (G rafo i l Packi ng)= (Stem Dia . ) (P 1 ) (Packing He ight) ( . 1 5)PF for Grafoi l Packing friction shou ld never be less than 25 Lb .

RF = P l ug Sea l Ring Fri ction = (Cage I D) ( 2) ( =) + ((Cage 1 13) 2 - ( Sea l Groove) 2 ) 4 (0. 03) APDi rect Actuator Output = (Effective Diaph . Area) (Actuator Press . - F i na l Spring Pressure)Reverse Actuator Output = (Effective D iaph . Area) (I n i tial Fina l S pring Pressu re)

The " l nitiat Spri ng Pressure" is the actuator pressure when the va lve stem beg ins to move .The "Fina l Spring Pressure" is the actuato r pressure when the valve stem reaches fu l l travel .

/ \

/Actuator OutDut l - PF - RF - CLAI Iowab le AP - " - " For Ba lanced Trim Flow te C lo se

UA

AI Iowable AP = "- ' '(Æctuator " "uutput) - PF - CL For Unba lanced Trito Flow to OpenUA

Be sure that the al lowable pressure drop cannot exceed the Body's ANSI pressure rating .

AP Tab l es are avai lable in the ind ividua l techn ica l bu l letins of each respective va lve series .

APPLICATION GU IDE FOR CAVITATION , FLASH ING ANDCOMPRESS I BLE FLOW SERVlCES

Valve appt ications invo lving cavi tation , flashing and noise reduction of compress ib le flow requ irespecial sizing and app l i cat ion cons iderations and , i n most cases , special tr ims are requ i red .The fol towing section d iscusses these phenomena with a definition , a l i st of poss ible

countermeasures , tips , and a techn ical d iscussion of the phenomena . Cavitation and fiash ingare i n the "Liq u id F low" Section and compress ible flow noise reduction is i n the "Compress i b leF low No ise" Section .

L IQU ID FLOW

Cavitation and flash i ng appl i cations requ i re accurate pred iction to determ i ne when they occurand proper va lve selection to supp ly the best trim for the appl ication .

CAV ITAT ION

Cavi tation Defi n ition

Cavitation is a two stage phenomena with l iqu id flow. The first stage is the formation of vaporbubb les i n the l iquid as the ftuid passes through the trim and the pressure is reduced below the

flu id's vapor pressure . The second stage is the ce l l apse of the vapor bubbles as the flu idpasses the vena contracta and the pressure recovers and increases above the vapor pressure .The col lapsing bubb les are very destructive when they centact meta l parts and the bubblecol lapse may produce h igh noise levels .

C av itat ion Countermeasu res

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There are severa l ways to dea l with cavi tation .

Method 1 : Cav i tat io n avo i dance : Cavitation can be avoided by select ing a valve style that has

FL (rated) va lues g reater than requ i red for the appl ication . Th is is an especial ly usefu l advantageof g lebe valves over ba l l and butterfly valves .

Cavitat ion can a lso be avoided with the insta l l ation of an orifice plate downstream of the va lvethat shares the pressure d rop . The va lve's pressure drop is reduced to the po int of avo id ingdamag ing cavitat ion . The downstream ori fice p late a lso shou ld be s ized to avoid damag ingcavitation . Th is may not be su i table for app l i cations with a wide flow range as the Iow flowcond ition may put the entJ re pressure drop en the valve .

Method 2 : Cavi tation To l erant : Standard trim desig ns can to lerate mi ld cavitat ion

app l ications . These app l i cations wi l l have increased flow noise from the mild cavitation butshou ld not have damage from cavitat ion .

Method 3 : Cav i tation Conta i nment: A trim des ign that a l tows cavitation to occur but in a

harmless manner can be effective in preventing cavitation damage and reducing cavitationno ise . Cavi tat ion conta inment designs are l im i ted to cavi tation appl ications of moderateintensity .

Method 4: Cav itation P revention : A trim des ign that takes the pressure drop in severa l steps

or stages can avo id the formation of cavitation . These trim designs are more expens ive thanother methods but may be the only a lte rnative in the more severe cases of cavi tation .

App l i catio n of Warren Trims i n Cavitat ion Serv ice

Cavitation Avoidance: Wherever possib le , try to reduce unnecessadly h igh-pressure drops toavo id cavitation in the first p iace . Severa l design constra ints can be re-evaluated in th is process

Cavitation Tolerant : Hardened trims are tolerant to cavitation service where the F L ( requ i red )

exceeds the F L (rated) and the in let p ressure is 1 50 psiq or less for 1 7-4 Trim or 300 ps i ,q or

less wi th Ste l l i ted (Al loy 6) or Ceramic Trito. At these inlet p ressures , the sevedty of cavitation

may be sma l l enough to ensure reasonable trim l ife . Use the Warren Valve S izing program andassistance from the App l ication Eng i neering department to determi ne .

The unba lanced Plug Control Trims with tungsten carbide or ceramic can withstand cavitation upto an in let pressure of 2000 ps ig . However, these trims wi l l not reduce no ise . Oversized bod ies

are recommended to avo id body eros ion .

Cavi tati on Conta i nment : Special cavi tation reduction tr ims are appropriate where the F L

(requ i red) exceeds . 94. The flow no ise from cavitation wi l l be reduced by the use of such tdms .F low noise calcu tation is automatic with Warren's Va lve S izi ng Program . However, at this time ,Warren does not offer any specia l cavitat ion reduction trim .

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Some cavitat ion reduction trim wi l l make multip le sma tl cavitation plumes that wi l l not as read i lycause erosion damage and wi l l generate less noise than a trim with plug or cage port contro l .Typica l ty, i n a G lobe va lve , this trim is used on ty in the flow down d i rection .

Cavitati on P revention : Specia l tr ims wi th mu l t ip le stages might be requ i red to su it a particu larapp l ication , or pa i red valves may need to spl it-d rop in sedes . These tr ims and two va lvesolut ions wi l I cost s ign ificantly more than the other options d iscussed but wi l l be appl i cabte incond it ions beyond the others . Consu l t with App l ication Eng ineering for any cavitatingapp l i cations to see what may be done .

THE CAVlTAT ION PHENOMENA

FLU ID AND PRESSURE PROF I LE

A control va lve creates a pressure drop in the fluid as it controls the flow rate . The profile of thefluid pressure , as it flows through the valve , is shown in the fo l lowing gra ph. The flu id acceteratesas i t takes a pressure drop through the valve's trim , I t reaches i ts highest ve loci ty just past thethrotUe point , at a po int ca l led the vena contracta . The fluid is at its Iowest pressure and h ighestvelocity at the vena contracta . Past the vena contracta the flu id decelerates and some of the

pressure drop is recovered as the pressure increases . For g lobe valves , the pressured ifference from the inlet pressure P 1 to the vena contracta pressure Pvc is about 1 25% of the P tto P2 pressure drop . The pressure in the vena contracta is not of importance unti l i t is Iower thanthe flu id's vapor pressure. Then the flu id wi l l qu ickly form vapor bubbles and , if the pressureincreases above the vapor pressure , the vapor bubb les instantly col lapse back to l iqu id . This i scavitation . I t wi l ] occur when the vapor pressure, as shown in the fol lowing graph , is more thanthe vena contracta pressure but less than the outlet pressure , P2 . When the Vapor pressure isless than the vena contracta pressure , there is ful l l iquid flow with no cavi tation .

1 4

Cavitation in control va lves can have four negative effects ;� Restricts flu id flow

� Causes severe vibrations

� Erodes metal su rfaces

� Generates high no ise levels .

CHOKED FLOW AND I NC lP I ENT CAVITATION

The l iq u id flow rate wi l l i ncrease as the pressure drop increases . However, when cavi tationvapor bubbles form i n the vena contracta , the vapor bubbles wi l l i ncreasi ngly restrict the flow ofl iq uid unti l the flow is fu l ly choked wi th vapor. Th is cond ition is known as "choked fiow" or "cri ti ca iflOW" .

When the flow is fu l ly choked , the flow rate does not increase when the pressure drop isincreased . The relationsh ip of flow to . - P2 is l i near unti l cavitation beg ins to form at the po int

of incipient cavitation . As more cavitation forms , the more the flow curve bends unti l i t ishorizontal and ful ly choked with the flow not increasing with add itiona l pressure drop .

The iarger the F L factor, the greater the pressure d rop that can be taken before choked flowoccu rs . Note the d ifferences in Tab le 3 .

The point of " l nci pient Cavitation" can be pred icted wi th the AP incipient in the equation in the"Cv Formu las for Liquid Ftov¢' us ing the Kc factor. Va lues for Kc are shown i n table 3 .Cavitation wi l l beg i n at the point of " l ncipient Cavitation" and increase i n intens ity to the po i nt ofchoked flow. Cavi lation at point of " l ncipient Cavitation" is not damag ing and is aimostundetectab le . At some point between i ncipient and choked , the cavitation may damage mosttrim styles . The Iocation of the "Damage" point varies with trim style and material . A larger Kc ispreferred so the i ncipient cavi tat ion range to choked flow is as smal l as poss ibie .

As the point of damag ing cavitation is not easi ly defined , sizing and app l ication methods use theCritica i Pressure Drop and the Requ i red F , to rate tr ims for cavitation service . The Kc value isnot used for trim se lection on ly flow noise pred iction .

CAVITATION DAMAGE

Cavi tation damage problems are more l i kely to occur with water flow as water has a we l l-definedvapor pressure and the vapor bubb le co l tapse is instantaneous . Hydrocarbon fl u ids have a lessprecise vapor pressure and are often a compound wi th severa l vapor pressures. Cavi tationdamage with hydrocarbon fl u ids is usua l ty less severe than water, as the bubble col lapse is notas sudden and can be cushioned by other vapors . However the vib ration and flow noiseproblems remain .

The flu id's i n iet p ressure is proportional to the amount of energy ava i labie to cause cavitat iondamage . H igher inlet pressures wi l l p roduce more intense and more damag ing cavi tation . Theamount of cavitation is re lated to the degree the requ i red F L exceeds the rated F L . As therequ i red F L exceeds the rated F L , the amount of cavitation increases . A va lve wi th a rated F L of

1 5

. 90 in an app l ication requ i ring a F L of .96 wi l l have more cavitation than an appl i cation requ i ring

. 92 . There wi l l be more cavitation but not more flow!

The generatien and imp losion of the vapor bubb les wi l l cause vib ration to the valve's PIug thatmay cause wear between the P lug and Cage or Gu ide and can cause Stems to break.

The implesion of the bubbles when near or en a meta l surface can generate extreme ly highshock stresses i n the meta l surface that usual ly damages the meta l with severe eros ion of themetal . This phenomenon , when severe , can destroy trims with in hours ! The generation andimplos ien of the vapor bubbles wi l l cause s ig n ificantly e levated flow noise i n add ition to vibration .

The cavi tation bubbles wi l l form a vapor piume in the l iquid . The larger the piume , the nois ier theflow and the more l i ke ly it i s to cause eros ion damage . The size of the pi ume is dependent entrito style and severi ty of cavitation . Cavitat ion reduction trim des igns wi th many sma l l orificeswi l l have s ign ificantly smal ler vapor plumes with less noise and a reduced damage potentia l thana standard trim . Warren does not currently offer such trim .

There is not much pos itive to say about cavitation . Va lves improperly appt ied or wi thoutadequate cavi tat ion protection can lead to earty fa i l u re .

FLASH ING

Flash i ng Defi n i tion

Flash ing is a one -stage phenomenon somewhat simi la r to cavi tation . The d ifference is thedownstream pressure does not recover enough to be above the fluid's vapor pressure . Thevapor bubbles in the l iq u id do not col l apse and they rema in in the fluid as vapor. Genera l ly on lypart of the flu id vaporizes so the resulting flow downstream of the valve is two phase , vapor andl i quid . Flash ing is sim i la r to cavi tation in some respects but i s not q u ite as severe . There aremeans to prevent or retard cavitation but not flashing ! I f the valves outlet pressure is below thevapor pressure , flashing wi l l occur regard less of the valve's trim .

F lash i ng Countermeasures

There are several measures that shou ld be made in flash ing app l ications .

Body Materia h The flash i ng process can cause body erosion that may reduce the body's wa l lth ickness to tess than requ i red by codes . The flu id in the valve body downstream of the trim ishigh ly tu rbulent as a two-phase fiow mixture of vapor and l iqu id . The turbulent m i xture can easi lyerode body materials , such as carbon steel , that may not have sufficient erosion resistance .

Trim Selecti on : Avoid the use of Balanced Plug Control Trim in flashing appl i cations as the

flash ing process may make the trim unstable . H igh-pressure drops in flash ing service is bestserved with special cage control tr im with mu l tiple sma l l orifices , that reduce the tr im's vib rationfrom the flu id 's turbu lence , or at least Unbalanced P lug Control Trims with tungsten carbide orceramic.

1 6

APPLICATION OF WARREN VALVES IN FLASH ING SERVIC E

Body Materia l : The flash ing process can cause body eros ion that may reduce the body's wal l

thickness to less than requ i red by codes . Al l flash i ng service shou ld have stai n less steel orChrome-Moly (WC6) bod ies ; Carbon stee l i s not su i table .

Trim Selection : If the pressure d rop is 50 PS I or less , standard Cage Contro l Trim is su itable .

P l ug control Trim is not recommended for flash ing service . For pressure drops greater than 50psi , U nba lanced P lug Contro l Tri ms with tungsten carbide or ceramic are recommended .

TH E FLASH ING PHENOMENA

Liqu ids in flashing service undergo a transformation from al i l iqu id flow to two-phase flow offlashed vapor and the remaining l iqu id . The l iqu id wi l l flash unti l thermodynamic equ i l i br ium isachieved with the vapor fu l iy saturated . Often the majority of the volume wi l l be vapor and someof the remain ing i i qu id wi l l be suspended as drop lets in the vapor. As the velocity of the vaporcan reach as h igh as son ic ve locity, the t iquid droplets can cause severe erosion the valve bodyand the downstream pipe . The flashing process is h igh ly tu rbu lent wi th the l i qu id impacti ng thevalve trim at high ve loci ty. The effects of the turbu lent flash ing l iq uid can cause trim instabi l i ty if itimpacts the control surfaces of the Plug . For th is reason , Plug Contro l Trim is not ideai forflashing service. Specifica l ly designed cavitat ion reduction trim wi l l d i stribute the flashingprocess into a large number of sma l l jets reducing the total turbu lence and reducing the vibrationeffects on the Plug and the erosion effects to the body. Often flash ing service wi l l be in the flowdown d irection through an ang le style body. The object is the get the flashing through the valve

without sign ificant contact with the body. As Warren does not have an angle body or anticavitation trim , out best so lution is through avoidance . Flash i ng service wi th pressure drops lessthan 50 PS I wi l t have less severe turbu lence so the standard Hardened Trims with flow down wi l l

be su itable .

L IQU ID FLOW VELOC lTY - BODY MATERIAL

High l iqu id flow ve locities in va lve bod ies can cause metal erosion even though there may be nocavitat ion or flashing . Liq u id flow veloci ty in valve bod ies shou ld be l im ited to the velocit iesshown in Table 6 to avoid flow erosion . The body's flow velocity, for l i qu id flow, can becalcu lated . The body flow velocity at the smal lest flow passage , usual ly the body i nlet or outlet ,should not exceed the ve loci ties in Tab le 6 .

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LIQU ID FLOW VELOClTY LIMITS

Body Materia l

Carbon Stee l

Stain less or

WC6 (C r-Mo)

Tab le 6

Appl i cation Lim its

Pressure Drop InfTequent> 500 PS I < 500 PS I < 2% of time

I 30 Ft/Sec 40 Ft/Sec 50 Ft/Sec45 Ft/Sec 60 Ft/Sec 90 Ft/Sec

COMPRESSIBLE FLOW NO ISE

Compressi b le F l ow Noise Discuss ion

F low no ise from compress i ble flow is a major appi icat ion considerat ion . The flow no ise must beaccurateiy pred icted and the appropriate valve tr im chosen to meet the customers req u i rementsand assure good valve operation .

Compressible flow no ise is generated by flu id tu rbu lence , the more turbulence the more no ise .Flu id tu rbu lence is i ncreased by h ig her flow rates and by a h ig her fluid pressure d rop throughva lve trim . As the valve's pressure drop reaches the crit i ca i cond iti on and the speed of sound isreached i n the flow stream's vena contracta , shock waves are produced that increases the noiseleve l above that produced by turbulence alone .

Compress i b le F low Noise Countermeasu res

There are severa l methods to reduce compressib le fiow noise .

Mu ltip le Orifice Trims : A trim with a h igh number of sma l t flow orifices wi l l produce less flownoise than a trim of equal flow capacity with either fou r or one flow orifices. The sma l l holesproduce smal ler flow jets that generate proportiona l ly less noise , as the sma l l hc les are less

efficient in converting mechan ical power to acoustical power than large holes . These trimdes ig ns genera l ly have mu l t iple sma l t odfices and are significantly qu ieter than standard p lug orcage control trims .

Backpressu re Ori fice : The flow noise increases rap id ly with increased pressure d rop

especiai ly when the critica i p ressure drop is exceeded . However if two devices can share thetota l pressure d rop , the fiow no ise can be s ign i ficantly reduced . This can be accompl ished witha fixed odfice p late downstream of a control valve . At maximum flow the valve and orifice platecan have about the same pressure drop and generate less noise than taking the tota l d ropacross the va lve alone . At Iower ftow rates , the noise from flow through the va lve wi l l p robably beless than at fu l l flow even though the va lve's pressure drop i ncreases as the pressure dropacross the fixed orifice plate decreases . The backpressure ori fice plate may be i n the form of acyl indrical d iffuser. The backpressure orifice device aiso shou ld be sized for flcw no ise .

Two Stage Trim : A two-stage va lve wi t l reduce flow noise beyond the noise reduction of themu lt iple orifice trim . The two-stage tr im is s im i lar to two multiple ori fice tri ms , one ins ide of theother. The i nner stage takes the majority of the pressure drop with the outer stage acting as ad iffuser to reduce flow turbu lence .

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At present, Warren does not offer any such Iow noise or anti -cavitation trim .

APPLICATION OF WARREN TRI MS I N COMPRESSIB LE FLOW APPLICATIONS

Low no ise considerations shou ld be appt ied when the pred icted no ise leve l exceeds thecustomers requi rement or when the noise level exceed 1 1 0 dBA.

Standa rd Trims : Calcu late the flow noise for the specified ccnd it ions. The standard P lug

Control , flow up , or the Cage Controi , flow down, may meet the customer's noise requ i rements orour 1 1 0 dBA l im it . I n th is case no further measures are requ ired provid ing the downstream flowve loci ty is not excessive .

Compress i b le F low Veloc i ty L im its : I f flow noise is be ing control led , the flow velocity in the

va lve body and downstream p ip i ng shou ld be l imited to 1 /3 sonic ve locity for DB I I and 1 /2 son ic

ve loci ty for DB I trims . H igher ve locities wi l l generate sign ificant flow noise in the pipe eventhough a Iow noise trim is instal led . Appl ications with Iow outlet pressures can read i ly have hiq hdownstream veloci t ies . Son ic ve locity at the vaive's outlet can produce flow no ise as h ig h as1 35 dBA as the shock waves from the son ic vetocity wi l l propagate downstream as the pipe actsas a megaphone ! The body's flow ve loci ty , for compressi b le flow, can be ca lcu lated usi ng thebody outlet d iameter from Tab le 4 .

Two Stage Tr ims and Backpressu re Ori fices : Two stage trims and backpressure ori fices

requ i re specia l ana lyses and des igns not ava i l ab le as standard . The use of two stage trims anddownstream orifices may reduce the flow no ise an add itiona 1 1 0 d BA beyond the reduction of anoise reduction trim . Consu it Warren 's Appl icat ion Eng ineeri ng for app l ications requ i ring no isereduction .

THE COMPRESS IBLE FLOW NO ISE PHENOMENA

A contro l valve's purpose is to create a pressure drop, the pressure drop creates flu id turbu lenceand the turbu lence generates flow noise . The resuitant fíow no ise is inevitable but can bemin imized by trim and va lve selection .

FIow noise produced by a va lve wi l l be transmi tted through the wa l l of the downstream p ipe .Very l i ttle noise wi l l come through the va lve body wa l l as the area of the pipe's wa l l istremendousiy la rger and the pipe's wal l thickness is less .

H igh flow noise from compressib le ftow presents two problems . Mechan ica l vib rations fromexcessive noise ievels can qu ickly destroy the trim and a lso may damage accessories mounted

on the valve's actuator. The major prob lem from h igh fiow no ise is hearing damage to people inthe vicin ity of the valve . OSHA has establ i shed noise l im its that vary fTom 1 1 5 alBA to 85 dBAdepend ing on the length of dai ly exposure , the 1 1 5 dBA is for 1 5 mi nutes exposure and 85 d BA

is for an 8 hour exposure . The usua l requ i rement is 85 alBA as it i s d ifficu l t to l imit a person'sexposure . Ear protection can heip protect a person's heari ng , but wi th today's tegal l i abi l i tyru l i ngs , the owner of the process is l iabie for people's hearing damage even i f they exceedposted exposure times and do not use provided ear protection . We shou ld be concerned if the

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pred icted no ise leve l exceeds 1 1 0 dBA even i f the customer does not impose a I im it . F low

no ise exceed ing 1 1 0 dBA, for any s ign ificant time can damage the va lve tr im and accessories .

Warren uses both I SA's Cv formu las from ISA S75 .0 1 and I SA's Control Valve AerodynamicNoise Pred iction formu las from ISA-S75 . 1 7 . I SA-S75 . 1 7 was publ i shed in 1 989 and has

become recogn ized as the best compress ib le flow noise pred ict ion method . The major contro lva lve compan ies , Fisher and Masonei lan , had deve loped , in the 1 960's , emp i ri ca l noise

pred ict ion techn iques based on laboratory test data . Formu las were written to fit the test data .

I n the 1 980's ISA developed a theoretica l no ise pred iction method , with the combined input frommany va lve companies, that is more accurate than the previous empirical methods. The I SAnoise pred iction method appl ies on ly to standard plug or cage contro l trims . Low flow noisedesig ns requi re an add itional factor to be subtracted from the I SA value .

20