How to find Cg from given info

[subbuC3]

I have given the Cv as 0.115 and Cg as 27,000 CFH at full cylinder. This is a fisher control valve. Upstream pressure is 500 psig and relief pressure is 425.7 psig. I am trying to find the maximum flow through the control valve. The flow medium is air with 5% Helium. I have a template to find the maximum flow rate. But i need the Cg as constant. Could you please somebody help me in converting the Cg to constant. Stonecold and other guys explained me but I haven't understand exactly.
Thanks in advance

 

[shahyar]

There is a Sine formula by Fisher. You can use it to calculate max flow through a control valve (fail open). Something is wrong. The unit for Cg is not CFH.
Refer to below address:

http://www.fisherregulators.com/technical/sizingcalculations/

 

[Chatwin]

See the other post I have made in the other thread.

I hope this helps. You have to make a guess of Cl given the data avaliable. The valve vendor may be able to assist you will accurate values for Cl that they have used. Some just use 30.