"CV" valve calculation outline

[200272522]

How does one undertake a "CV" calculation. And what is a CV calculation regarding flow through valves.

 

[MortenA]

Cv= flow of water at 60 deg F in USgal/min at a pressure difference of 1 psi

Best regards

Morten

 

[JLSeagull]

Obtain a copy of the Fisher Control Valve Handbook online:

http://www.documentation.frco.com/groups/public/documents/book/cvh99.pdf

 

[twr]

Here's a link that helped me:

http://www.engineeringtoolbox.com/flow-coefficients-d_277.html

 

[JimCasey]

I always resist giving MortenA's example, Not that it is wrong, but it does seem to imply thatthe relationship between flow and Delta-P is linear. it's not.

If you get 1 gallon at 1 psi loss, you will get 1.414 gpm at 2 psi differential.

There are a family of Cv equations. Liquids, Gases, Steam, SUbcritical, Choked flow, etc. Most of the major control valve companies allow at least a trial version of their sizing software to be downloaded from their website. ANy decent program runs all the checks to determine the flowing conditions and applies the appropriate equation.

 

[bcd]

Cv is another way of expressing the amount of pressure drop, or in otherwords, flow resistance, you can expect through a valve or fitting. If the manufacturer cannot give you the value, you can calculate it using the data in Crane Technical Paper #410. However, I would be very surprised if the valve manufacturer does not have the data readily available for you.

bcd

 

[MortenA]

Jim

The definition of Cv is clear. The fact that sizing and choosing a control valve isnt just calculating a single Cv value is something else.

Best regards

Morten