Control Valve Cv calculation

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

Control Valve Cv Value Formula for Liquid

Q 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

CV Value Formula for Gas & Non Choked Flow

Q Flow rate (M 3 / H @ 15 o C , 1atm.)

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

CV Value Formula for Gas & Choked Flow

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

CV Value Formula for Steam & Saturation Vapour Non choked flow

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

CV Value Formula for Steam & Saturation Vapour choked flow

Q 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

CV Value Formula for Steam & Wet Vapour Non choked flow

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

CV Value Formula for Steam & Wet Vapour choked flow

Q 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

CV Value Formula for Steam & Superheated Vapour Non choked flow

Q 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

CV Value Formula for Steam & Superheated Vapour choked flow

Q 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

CV Value Formula for Liquid

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 Value Formula for Gas & Choked Flow

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 ?

Control Valve Tips and Tricks

Types of Control Valves Noise

Share With Your Friends

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address

8 thoughts on “Control Valve Cv calculation”

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

    Reply
  2. 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.

    Reply
  3. 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?

    Reply

Leave a Comment

Control Valve Cv calculation

 
Send this to a friend