In deciding the size of the control valve that (Port Size) we need to calculate the Cv value of the process (Calculated Cv) by calculating Cv has educated more than 50 years, which is involved in. such as the Renault number (Reynolds number), flow rate (Flow), the Shock (Choking), the involved joints in pipes (Fitting) and the other by the values of these.

This reference standard IEC 60534-2-1: 1998 (International Electro technical Commission), which is standard valve manufacturer mainly quoted. The coefficient Cv IEC standards are highly complex.

I recommend using the control valve manufacturer has provided. However, to be considered under the verification e Cv easier we have a simple formula Cv value can be calculated following them.

## Cv value calculation

### A) Simple Cv Value Formula: Case of the Liquid

**Q _{L }: **Flow rate (m3 / H).

**△ ****P : **Differential pressure (kg / cm ^{2} )

**G _{L} : **Specific Gravity (Water = 1)

### B) imple Cv Value Formula: Case of the Gas

#### I) Non-choked flow ΔP <P1 / 2

**Q _{G }: **Flow rate (M

**H @ 15**

^{3}/**, 1atm.)**

^{o}C**△ ****P : **Differential pressure (kg / cm ^{2} )

**G _{G} : **Specific Gravity (Air = 1)

**T : **Temperature ( ** ^{o}** C)

**P _{M} :** (P1 P2) / 2

#### II) choked flow ΔP ≥ P1 / 2

**Q _{G }: **Flow rate (M

^{3}/ H @ 15

^{o}C, 1atm.)

**P _{1} : **Inlet pressure (kgf / cm

^{2}, ABS)

**G _{G} : **Specific Gravity (Air = 1)

**T : **Temperature ( ^{o} C)

### C) Simple Cv Value Formula: Case of the Steam (Vapor)

#### I) Saturation Vapor: Non-choked flow * ΔP <P1 / 2*

**Q _{s }: **Flow rate (kg / H)

**Y : **Vapor Correction factor (Water Vapor = 19.4)

**△ ****P : **Differential pressure (kg / cm ^{2} )

**P _{M}: **(P1 P2) / 2

#### II) Vapor Saturation: choked flow *ΔP **≥ P1 / 2*

**Q _{s }: **Flow rate (kg / H)

**Y : **Vapor Correction factor (Water Vapor = 19.4)

**P _{1} : **Inlet pressure (kgf / cm

^{2}ABS.)

#### III) Wet Vapor: Non-choked flow * ΔP <P1 / 2*

**Q _{s }: **Flow rate (kg / H)

**X : **Quality of Vapor (X = 1 is Dry Steam)

**Y : **Vapor Correction factor (Water Vapor = 19.4)

**△ ****P : **Differential pressure (kg / cm ^{2} )

**P _{M}: **(P1 P2) / 2

#### IV) Wet Vapor: choked flow *ΔP **≥ P1 / 2*

**Q _{s }: **Flow rate (kg / H)

**X : **Quality of Vapor (X = 1 is Dry Steam)

**Y : **Vapor Correction factor (Water Vapor = 19.4)

**P _{1} : **Inlet pressure (kgf / cm

^{2}ABS.)

#### v) Superheated Vapor: Non-choked flow * ΔP <P1 / 2*

**Q _{s }: **Flow rate (kg / H)

**Y : **Vapor Correction factor (Water Vapor = 19.4)

**△ ****P : **Differential pressure (kg / cm ^{2} )

**S : **Superheat ( ^{o} C)

**P _{M} : **(P1 P2) / 2

#### VI) Superheated Vapor: choked flow *ΔP **≥ P1 / 2*

**Q _{s }: **Flow rate (kg / H)

**Y : **Vapor Correction factor (Water Vapor = 19.4)

**S : **Superheat ( ^{o} C)

**P _{1} : **Inlet pressure (kgf / cm

^{2}ABS)

In the example for calculating it. Time calculation aware of it. The manufacturing unit will have a total abs.

##### Example # 1

Application : Fluid Water

Flow rate 50 M ^{3} / HR.

Inlet Pressure 10 kgf / cm ^{2} G.

Outlet Pressure 5 kgf / cm ^{2} G.

Pressure different 5 kgf / cm ^{2} G.

Temperature 120 degree C

Density 943 kg / M ^{3}

Because the fluid is a liquid So we will use the formula

Q _{L} = 50 M ^{3} / HR.

G _{L} = 943 kg / M ^{3} Convert to (UNIT Water = 1) = 0.943.

ΔP = 5 kg / cm ^{2.}

So,

Cv = 1.17 (50) x sqrt (0.943 / 5).

Cv = 25.4

================================================== =====

##### Example # 2

Application : Fluid Gas

Flow rate 48,000 Sm3 / hr

Inlet Pressure 32 kgf / cm2 Convert to absolute pressure = 33.03 kgf / cm2 (A).

Outlet Pressure 15 kgf / cm2 convert to absolute pressure = 16.03 kgf / cm2 (A).

Pressure different 17 kgf / cm ^{2.}

Temperature 240 degree C

Density 0.86 Air = 1

Because the fluid is a gas and *ΔP *** ≥ P1 / 2** so we will use the formula.

Cv = (48000 / (248 × 33.03)) x sqrt (0.86 x (273 240)).

Cv = 123.08

#### Articles You May Like :

Diaphragm Solenoid Valve Principle

Valve Technician Interview Questions

What is Butterfly Check Valve ?

Sir,

l am working in power plant plz send electrical questions and answers

Sir urged arrivals very useful

thank u sir

Hello Ramesh,

For Electrical Questions & Answers Please Click Here

Sir, I am aslam khan please explain hydraulic control valve working principles and also explain i/p working hydraulic oil possible

Please share the calibration procedure (steps) for calibration of flow Instrumentation like – orifice flowmeter ,venturi, Coriolis, vortex, Magnetic flowmeter.

Hi Bharadwaj

This is Ramu from Anrak. I have seen your website. Very much useful for all. You are doing very good job. Well done Bharadwaj. Be continue.

Dear sir,

Please sir share the DP type transmitter basic principal and how its work..??

Devanathan,

Dear sir,

please share Convertion table for all units like pressure,temp,mm water column, mercury column, psi to bar,and bar to kg–etc.

I have a customer who wants the ESD to close in 2 seconds. I know the cv of the valve and have the actuator chosen to operate the valve. I just need to know how to choose the correct cv of the pilot valve, solenoid and filter regulator to make the actuator and valve close I. 2 seconds. Can anyone help me?