Derivation of process conditions from valve CV

[minty]

I am trying to determine the inlet pressure to a throttle valve. The information I have is:
*valve CV
*fluid
*flowrate I want through the valve
*an approximate downstream pressure.

Is there any way I can calculate the upstream pressure or the pressure drop across the valve from this information? I have sent all this to the valve manufacturer for them to run through their program but was wondering if a manual calculation is do-able.

Thanks,
Michelle

 

[JimCasey]

Yes.
Use the Cv equation appropriate for your application, and solve for P1.

Post all the parameters you have and I will run it thru a sizing program. If the fluid is not commonly used, you might want to throw in the specific gravity.

 

[minty]

Hi Jim,

I did try using a Cv equation but was getting daft results. However, as I said in my original post, I sent the data to the valve manufacturer and they have now responded with a result from their software.

Thanks for your response anyway.
Regards,
Michelle

 

[MortenA]

Remeber that with a control valve you have one degree of freedom and you must either select your CV (degree of opening) or your downstream pressure.

It would be most common to have you pressure chosen and then calculate the Cv (degree of opening).

If you size the valve - calculate Cv for you normal flow case, up pressure and down pressure (this may require some brain activity since what is "normal/worst normal etc case"). Choose a mid range position for the valve say 70% and say that this should match your valve cv.

Best regards

Morten

 

[ddsancho]

Hi,

Hope this page can help you.
There are some explanations about Cv and Kv flow coefficents with online hydraulic formulas with several units as inputs.

http://www.valvias.com/flow-coefficient.php

Regards
Daniel

 

[minty]

Hi Guys,

Thanks for all your help. That's been really useful.

Best Regards,
Michelle