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1

# Control Valve Rating

5 replies to this topic
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### #1 sargon 1979

sargon 1979

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Posted 08 October 2017 - 11:15 AM

Dear all
If a control valve is sized for specific operating conditions and it is required to change these conditions, what should i do?
Ex: a cv of control valve has been calculated according to dp=9 bar and flow rate=15000kg/hr with inlet pressure of 50 barg. If the inlet pressure decreases to 30 barg without any change in dp and the new calculated cv is less than the original one, does the control valve work?

### #2 Bobby Strain

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Posted 08 October 2017 - 12:56 PM

You can find free software at Emerson's website. Meanwhile, maybe you will provide all the information regarding the new conditions. And your calculations. Vapor? Liquid? Flashing? Mixed phase?

Bobby

### #3 fallah

fallah

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Posted 08 October 2017 - 01:36 PM

If a control valve is sized for specific operating conditions and it is required to change these conditions, what should i do?
Ex: a cv of control valve has been calculated according to dp=9 bar and flow rate=15000kg/hr with inlet pressure of 50 barg. If the inlet pressure decreases to 30 barg without any change in dp and the new calculated cv is less than the original one, does the control valve work?

sargon,

Because for given delta P and mass flow rate, the cv of control valve is changed for lower inlet pressure of the same fluid; appears the fluid to be in gas (or vapor) state; if so for lower inlet pressure the cv should be increased while you did mention it's less than the cv for higher inlet pressure. Please recheck and clarify...

### #4 sargon 1979

sargon 1979

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Posted 08 October 2017 - 08:18 PM

Hi fallah
In general, if i calculate the new CV according to new operating conditions of pressure, temperature and flow without exceeding the pressure class and without changing the service, and the calculated CV was less than the original one. Will the control valve work?
Thank you

### #5 Bobby Strain

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Posted 08 October 2017 - 10:58 PM

You ask a question which has no good answer from a professional. Naser cannot assure it will "work" as he has no idea about new conditions and your calculation. Regarding will it "work"? Certainly. The result just may not be satisfactory.

Bobby

### #6 fallah

fallah

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Posted 09 October 2017 - 01:30 AM

You ask a question which has no good answer from a professional. Naser cannot assure it will "work" as he has no idea about new conditions and your calculation. Regarding will it "work"? Certainly. The result just may not be satisfactory.

Agreed with Bobby; it might work in new conditions but not according to all pre specified process conditions...

Edited by fallah, 09 October 2017 - 01:32 AM.