Cg valve is 27,000 CFH at full cylinder

[subbuC3]

Hi

I am trying to find the maximum flow through the fisher control valve. i have given the Cg valve as 27,000 CFH at Full Cylinder. Could you please some one help me to find the Cg from given data.

Thanks

 

[StoneCold]

If Cg is really Cv, then we would need to know the upstream pressure and the down stream pressure at a given flow rate to back calculate the CV of the valve. If you know the CV of the valve, then you should be able to calculate the flow rate your self given the upstream and downstream pressures. If you post them then someone here can easily calculate the max flow for you at the given conditions.


Regards
StoneCold

 

[subbuC3]

Thank You StoneCold.

 

[ggordil]

You can download "Firstvue" software from the Fisher website. It is really helpful when it come to this type of problem. On the "schematic" calculation it is really easy to solve through for different values.

 

[JLSeagull]

I haven't used Cg for the last 15 years. This was a Fisher specific property for their gas sizing program. The PE exam requires use of the ISA formulas and data. Consider using the ISA equations even with Firstview for uniformity.

 

[Chatwin]

Cg is like a Cv value for a gas. It represents a value which is termed the Gas sizing coefficient.

There is a standard given formula to work out Cg given the temperature, Pressure Drop, Cl,(Cg/Cv)(dependant on the type of valve), Pressure in, and you will be able to work out the Expected Gas Flowrate.

I will refer you to Rules of Thumb for Chemical Engineers. IF you do a google book search you will find a good reference which you can use. (It however comes in American Units will is somewhat in convenient)

 

[kkimic]

subbuC3,

I normally use either firstvue as recommended by ggordil or the equations in Crosby Control Valve Hadnbook (

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

The last one is easy to follow and I have been using it for quite a long time.

Regards.