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Setting Control Valve Position To Provide A Dp


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#1 drawingtheline

drawingtheline

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Posted 11 November 2014 - 03:26 PM

Hi,

 

I know the Cv of a valve and I am able calculate the pressure drop of water across the valve at 100% open.

 

I now want to partially close the valve to provide an additional pressure drop.

How can I calculate the position of the valve to provide a wanted DP.

 

In the first instance please keep in simple (this is a hypothetical question), assume a linear trim and no problems with cavitation etc,

 

Thanks



#2 shan

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Posted 11 November 2014 - 04:47 PM

You should find the valve curve with pressure vs. % valve opening from the valve vendor.



#3 Ajay S. Satpute

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Posted 11 November 2014 - 11:26 PM

Drawingtheline,

 

1. Refer http://www.cheresour...f-on-off-valve/ (post # 5).

2. As you know the Cv (100% valve opening) and pressure drop, you can calculate Q (in USGPM). [Cv = Q * (G/delta P)^0.5].

3. And it's a linear trim (Cv% = Valve opening %) so you can calculate Cv at different valve openings.

4. Assuming flow is gonna be same for different valve openings and as Cv is also calculated, you can calculate delta P (psi).

 

You might have to do some trial & error to get the desired delta P by manipulating Valve opening.

 

Regards.

 

Ajay S. Satpute



#4 drawingtheline

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Posted 12 November 2014 - 02:16 AM

OK thanks.

 

So if I now am able to calculate the Cv with the valve partially closed (giving me the DP I want);

 

Then is the % of the valve opening expressed as (Partial open Cv)/(Full open Cv) x 100 ?

 

Thanks



#5 Ajay S. Satpute

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Posted 12 November 2014 - 05:00 AM

Yes, for linear trim.

 

 

Regards.

 

Ajay S. Satpute



#6 drawingtheline

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Posted 20 November 2014 - 02:22 AM

OK thanks.

 

How do I go about this if I have equal percentage trim?

 

Rgds,

 

James



#7 Ajay S. Satpute

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Posted 20 November 2014 - 03:25 AM

Drawingtheline,

 

If you want approx. results, then use;

Equal percentage: Cv% = (Valve opening %)^3

 

And if you want more accurate results, then refer below links;

https://controls.eng...p/ValveModeling

http://www.cambridge.../chap5valve.pdf

 

 

Regards.

 

Ajay S. Satpute






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