Dear All,

I have found several different equations for Gas flow calculation through control valves, in terms of pressure, temp., valve coefficient(Cv), etc.

Now I have 2 questions:
1-What is the effect of valve opening on these equations.

2-What is the effect of valve characteristic(Linear, Equal percentage, Quick opening) on these equations?

Regards

 

1)No effect

2)No effect

To select a control valve you first run a calculation with the process data you have been given. This will give you the required CV at those conditions.

Next you select a control valve which has a CV equal to or greater than the calculated value. It is normal to say that your calculated CV will be equal to your selected control valve CV at say 70% opening to allow for some variation.

Also when you select the control valve you make a choice of which valve characteristic you need based upon the application where it is to be used.

 

David Todd,

Thanks.

I have the Cv of valve. So I don't want to select a valve. I just want to calculate the flow passing through the valve by knowing differential pressure, temp, Cv and valve opening (in percentage).

 

I don't see your problem. Just use the same formula that you have used to calculate the cv and just manupulate the formula to get the flow based on the various conditions.

 

Download the pdf file at the link below. All equations required can be found there. Transpose the formulae to calculate flow rather than CV.

http://www.documentation.emersonprocess.com/groups/public/documents/reference/d351798x012_11.pdf