Pressure Drop Across An ESDV

[Berenger]

Hi all,

I am back with one more question (a simple one for those with experience) and will appreciate any help.

I am doing a sizing exercise for a gas plant and need to size some shutdown valves for a client. What pressure drop will be used in the CV calculations? Is it the operating pressure upstream of the valve? Since the plant/process is shut down when the valve is activated, logic tells me that the pressure on the downstream side should be zero. So, if our pipeline operating pressure is 800 psig, the pressure drop across the valve should be 800 - 0 = 800. Am I right?

If I am wrong, what is the rule of thumb? How do I calculate the pressure drop across the valve since only the pipeline pressure is know?

What about for liquid lines? Does the same logic hold?

 

[MikeClay]

One does not normally size an SDV. These valves are normally in line ball, plug, or gate valves. Their size is the pipeline size. The pressure drop is based on the flow and valve Cv. However, since these valves are shut down valves, when specifying the shut off differential pressure, use the maximum upstream and minimum downstream pressures.

--Mike--

 

[LittleInch]

I'm sorry but I don't really understand your issue. CV is only really needed for control valves, not ESD valves. ESD valve issues are normally about actuator sizing as they need to seal against flow and full pressure (design pressure one side - not max operating, zero the other) in a short period of time and with some form of stored energy, usually a spring (a big one). This has very little to do with valve CV.

Same thing for liquid lines.

Valve CV is only of use if you have flow. If you have flow past your ESD valves then you're in big trouble, but please let me know if I'v emisunderstood your question / issue.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way