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Euratom

Calculationof

Kv Cv c oeffic ients

European standardsFor

Control valves sizing

Denis HENRY

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EuratomOutlineOutline

General desc ription of Cv coeffic ient

Valve flow charac teristic s

European standard for valve sizing

Conclusion

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Euratom

In addition to the service conditions, the flow control valve specifications gathers the

following characteristics :

- valve size (DN)- sort of valve (butterfly, rotatable, plug )

- plug profile

- flow direction

General description (1)General description (1)

The valve flow capacity is defined by the value of the Cv coefficient which is applicable

for any kind of fluid.

with the valve device, the manufacturer has to provide the technical data including :- Fd factor depending on the hydraulic diameter.

- FL factor taking in account the choked flow due to cavitations phenomena.

- XT factor taking in account the choked flow in case of cr itical pressure drop.

- Cv coefficient (full opening or 80% opening)

For a defined fluid, the characteristic of a flow control valve is the pressure drop as

function of the flow capacity for several stroke values.

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EuratomGeneral description (2)General description (2)

Valve flow coeffic ients(liquid flow)

p

QAv =

Q (m3/s) Virtual cross section in m2 of volumetric

(kg/m3) flow rate flowing through the valvep (Pa) (use I.S. units)Q (m3/h) Numerical value in m3/h of water at 15 C (w) (kg/m3) flowing through the valve at pkv = 105 Pap (Pa)w

=

p

pQK

vkv

Q (gal/min) US Numerical value in US gal/min of water at 15 C (w) (lb/ft3) flowing through the valve at p = 1 psip (psi) (usually applied)w

=

p

1QCv

Conversion

1078.2K

A 5

v

v = 1040.2C

A 5

v

v = 1065.8C

K 1

v

v =

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EuratomGeneral description (3)General description (3)

valve flow charac teristics

Digital

(on/off)

Linear flow

(lin.)

Equal percentage

(=%)

Relative Cv = f (Relative opening h )

Interest for c ontrol system

( )hC

C

fov

vf==

Cv Current Cv valueCvfo Full opening Cv value

h Relative opening %

Rangeability

0v

v0

1

C

CR

mo

fo

==

Cvfo Full opening Cv valueCvmo Minimal opening Cv value0 Maximum relative Cv

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EuratomValve flow characteristicsValve flow characteristics

Linear flow

hm0 +=

01m =

0

01

R

=

With the slope

And the rangeabili ty

gives

1R

1-.Rh

0

0

=

h (%) Valve stroke

Relative Cv

Equal perc entage

hn

0

= e

=

0

1lnnWith

And the rangeabili ty

gives

( )

( )00

Rln

.Rln

h

=

h (%) Valve stroke

Relative Cv

0

01

R

=

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EuratomEU Standards for valve sizing (1)EU Standards for valve sizing (1)

Two-phase flow

No g enerally ac c epted

standard m ethod exists.

All desc ribed methods

inc lude a lot ofuncertainty

Single-phase flow

Liquid Service Gas/ Vapour Service

Taking into ac c ount of

- thermophysic al properties of fluid

- plug profile of the valve

- piping geom etry (includingc onvergent/ divergent devices)

- Reynolds numbers

Standards referenc es

Industrial-process control valves. Part 2-3 : flow capacity. Testprocedures.

NF EN 60534-2-3

Industrial-process control valves. Part 2-1 : flow capacity. Sizingequations for fluid flow under installed conditions.

NF EN 60534-2-1

Industrial-process control valves. Part 1 : terminology of the

valves of regulation and general considerations

NF EN 60534-1

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EuratomEU Standards for valve sizing (2)EU Standards for valve sizing (2)

NF EN 60534 2-1

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1.5 kg/s

13.5 kPa

2 kPa 2 kPa

PID ACB_TF

CV 719 :DN 80Tin : 4.6 KPin :395 kPa

Pout :381.5 kPaQm :3 kg/ s

Cv :95

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EuratomConclusionsConclusions

The main supplier of flow control valve like VEKA or VELAN use their own code which

refers to EU standards.

In the frame of EFDA tasks concerning the the design of the ITER cryodistribution, the

valve sizing are performed according to the EU standards.

CEA implemented an Excel-macro for the Cv calculation in accordance with the EU

standards.

A comparison of several Cv values will be carried between those given by the suppliers

and the results of CEA calculations.