GPSA Control_Valve_Sizing(1).xls

8/12/2019 GPSA Control_Valve_Sizing(1).xls

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CONTROL VALVE SIZING

(GAS AND LIQUID SERVICE)

Reference: GPSA Engineering Databook, 11th Edition

Gas Service (Volumetric Flow):

Qg= Cg* ((520 / G*T)0.5

)*P1*Sin [(3417 / C1)*((P / P1)0.5)]DEGAlternativelyCg= Qg/ ((520 / G*T)

0.5)*P1*Sin [(3417 / C1)*((P / P1)0.5)]DEG

Gas Service (Mass Flow):

Wg= 1.1*Cg*((1*P1)0.5)*Sin [(3417 / C1)*((P / P1)0.5)]DEGAlternatively

Cg= Wg/ 1.1*Cg*((1*P1)0.5)*Sin [(3417 / C1)*((P / P1)0.5)]DEGwhere

Qg= Volumetric Gas Flow Rate, ft / hr@ 14.7 psia, 60F (SCFH)Wg= Mass Flow Rate, lb/hr.

Cg= Gas Sizing Coefficient

G = specific gravity of gas (air = 1.0)

T = absolute temperature of gas at inlet, R

P1= absolute pressure of gas at inlet of valve, psia

C1 = Cg/Cv Ratio of Gas Sizing Coefficient to Liquid Sizing Coefficient.

DP = required pressure drop across control valve, psi

r1= density at valve inlet pressure & temperature, lb/ft

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Typical C1& Cgvalues for valves in gas service:

C1 Cg1

C1 Cg1

1 32.7 270 31.9 528 Notes:

1 1/2 33.0 578 32.4 10202 33.2 851 32.0 2050

2 1/2 32.5 1600 32.0 2830

3 32.9 2150 31.5 3970

4 33.8 4100 33.2 6260

6 35.3 8200 34.4 13000

8 34.0 8300 36.6 18100

1 31.3 363 - -

1 1/2 28.9 1050 - -

2 30.3 1620 - -

3 27.9 3180 - -

4 28.1 5010 - -

6 28.4 8960 - -8 29.5 15100 - -

10 27.8 26900 - -

12 28.2 46300 - -

2 25.2 965 - -

2 1/2 25.2 1770 - -

3 25.2 3120 - -

4 25.2 6400 - -

5 25.2 10800 - -

6 24.5 17500 - -

8 24.5 31100 - -

10 24.5 48500 - -

12 24.5 75300 - -14 24.5 89000 - -

16 24.5 124000 - -

Linear Flow Characteristic:

Applications of Linear Flow Characteristic Control Valves:

Liquid level control & for certain flow control applications requiring constant gain.

Ball

Butterfly

1. At approximately 70% of valvetravel.

2. C1& Cgvalues vary with

percentage of valve travel.

3. For a more detailed analysis

of capacity of a given valve at

other percentages of travel

consult manufacturer's data.

The linear flow characteristic implies that the flow rate is directly proportional to the valve travel or opening.

This proportional relationship produces a characteristic with a constant slope so that with constant

pressure drop (delta P), the valve gain will be the same at all flows. Valve gain is the ratio of an

incremental change in flow rate to an incremental change in valve plug position. Gain is a function of

valve size & configuration, system operating conditions & valve plug characteristic).

Valve Style

Valve

Body

Size,

inches

Flow Characteristic

Equal Percentage Linear

Globe

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Selection Criteria for Linear Flow Characteristic Control Valve:

3. When 2 control valves are used in pairs as a 3-way valve.4. For compressor recycle (spill-back) applications.

5. For compressor anti-surge control valves.

6. For pump minimum safe continuous recirculation flow applications.

Equal-Percentage Flow Characteristic:

Applications of Equal-Percentage Flow Characteristic Control Valves:

Calculation steps for specifying gas service control valves:

1. Calculate the required Cgby using the sizing equation given above.

In this flow characteristic, equal increments of valve travel (opening) produce equal percentage changes in

the existing flow. The change in flow rate is always proportional to the flow rate just before the change in

position is made for a valve plug, disc or ball position. When the valve plug, disc or ball is near its seat &

the flow is small, the change in flow rate will be small; with a large flow, the change in flow rate will be

large.

These are generally used for pressure control applications. They are also used where a large percentage

of the total system pressure drop is normally absorbed by the system itself, with only a relatively small

percentage by the control valve. These are also recommended for applications where highly varying

pressure conditions can be expected.

2. Select a valve from the manufacturers catalog (see table above). The valve selected should have a Cgwhich equals or exceeds the calculated value.. The assumed C1value for the Cgcalculation must match

the C1value for the valve selected from the catalog.

1. When the ratio of differential pressure across the control valve at minimum flow over the differential

pressure across the control valve at maximum flow is equal to or less than 1.5.

2. When the differential pressure conditions across the control valve under all specified flow conditions

are more than two-third (2/3) of the differential pressure across the control valve in the closed condition.

7. For pressure reducing service where pressure drop is constant within +/- 15% over all specified flow

conditions.

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Liquid Service (Volumetric Flow):

QL= Cv* (P / G)0.5Alternatively

Cv= QL*(G / P)0.5

whereQL= Volumetric Liquid Flow Rate, gpmat inlet pressure & temperature

G = specific gravity of liquid (water = 1.0 @60F)

DP =

DPmax= Km( P1- rc*Pv)

where

Km = valve recovery coefficient (see table below for values)

rc= Critical pressure ratio = 0.96 - (0.28*(Pv/ Pc)0.5

)

Pv= Vapor Pressure of liquid at valve inlet temperature,psia

Pc= Absolute thermodynamic critical pressure, psia

Note: For flashing liquids the following equation should be used to determine the maximum allowable

pressure drop that is effective in producing flow.

If actual delta P is less than DPa,then the actual DP should be used in the equation above for calculating

flow or coefficient..

less than the maximum allowable pressure drop (DPmax)across control valve for sizing or

actual pressure drop, psi

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Typical Km& Cvvalues for valves in liquid service:

Km Cv1

Km Cv1

1 0.77 7.83 0.87 8.31 Notes:1 1/2 0.7 17.4 0.82 11.7

2 0.72 25.4 0.81 19.9

2 1/2 0.71 49.2 0.88 32.6

3 0.68 66 0.89 40.4

4 0.68 125 0.8 73.5

6 0.73 239 0.82 100

1 0.74 11.6 - -

1 1/2 0.72 36.3 - -

2 0.6 53.4 - -

3 0.67 114 - -

4 0.68 178 - -

6 0.68 316 0.73 2488 0.61 512 0.72 407

10 0.66 967 0.72 691

12 0.6 1640 0.71 1010

2 0.55 38.3 - -

2 1/2 0.55 70.4 - -

3 0.55 124 - -

4 0.55 254 - -

5 0.55 428 - -

6 0.55 713 - -

8 0.55 1270 - -

10 0.55 1980 - -

12 0.55 3070 - -

14 0.55 3630 - -

16 0.55 5070 - -

Calculation steps for specifying liquid service control valves:

Prepared by: Ankur Srivastava

Chemical Engineer

e-mail: [email protected]

Linear- Anti-

cavitation Trim

Globe

1. At approximately 70% of valve

travel.

2. Select a valve from the manufacturer's catalog, with a Cvequal to or greater than the calculated value.

1. Calculate the required Cvby using the sizing equation given above. The DP used in the equation must

be the actual valve pressure drop or DPmax, whichever is smaller.

Ball

Butterfly

Disclaimer : The information and methods included within this spreadsheet are presented for "cont

calculations. It is intended to be used by technically skilled persons at their own discretion. I do no

suitability or accuracy of these methods.

Valve Style

Valve

Body

Size,

inches

Flow CharacteristicEqual Percentage-

Standard

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mailto:[email protected]:[email protected]


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ol valve sizing"

warrant the

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GPSA Control_Valve_Sizing(1).xls