control valve sizing

[cobraaa]

i need to calculate maximum flow for dia 3" control valve / PCV ?
Please help............

Rgds
JH

[dso]

use Q=Cv(DP/Rho)^1/2
for sizing the valve.

[mskhadke]

Is it for relief load calculations during condition of control valve fail open?

[lammer]

how should i calculate if the flow was during control valve fail open (fluid = GAS) ?

[mskhadke]

You can calculate the flow rate when CV fail to open by using the CV value at full open condition. Usually CV value is provided by the control valve manufacturer. You need to determine the upstream and downstream pressure and put in to the formula of CV value calculation to calculate flow rate. See control valve handbook for the formula.
Hope this will help you.
mskhadke

[mskhadke]

You can calculate the flow rate when CV fail to open by using the CV value at full open condition. Usually CV value is provided by the control valve manufacturer. You need to determine the upstream and downstream pressure and put in to the formula of CV value calculation to calculate flow rate. See control valve handbook for the formula.
Hope this will help you.
mskhadke

[lammer]

Thanks!

[amshah]

General rule of thumb is

Valve size in inch * Valve size in inch X10

that is for 1" Max Cv = 1X1X10 = 10 Cv
for 2" Max Cv = 2X2X10 = 40
3" = 3x3x10=90 Cv

This is rule of thumb, max Cv for selected valve size changes based on modified trims available with vendor but it remains 10 % here and there.

For sizing a valve based on your process data follow following link,

[link Point to another website Only the registered members can access]
control valve sizing software is available in Instrument forum

[link Point to another website Only the registered members can access]