Control Valve Sizing

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anand s

Dear all

I would like to know For a given application, whether there will be cavitation or flashing while sizing Control Valve. How can I find whether there will be flashing or cavitation in my sizing of Control Valve.

Since I am from engineering dept, anybody who has done sizing of Control valve and had experience. please disseminate ur experience / knowledge and also tell me where I can find information about this

Thanks

anand s

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William T. Dolan Raytheon Engineers & Co

A very good source of information is ISA publication "Control Valve Sizing & Selection" by Les Driskoll. It covers cavitation and flashing service in great detail.

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Brian T. Smith

Anand:
The control valve sizing programs check for flashing and cavatitation. Equations could be found in texts and manufacturers literature. You could discuss this with your local control valve suppliers. The control valve estimates of flashing and cavitation can be overstated. The best way to determine the percentage of flashing is to ask a Chemical Engineer to analyze this on a process simulator and give you the percentage.

Control valve sizing programs are available from manufacturers, for free. Usually they will analyse your application and present solutions.
For example see the web link below for a free download of Fisher FirstVue control valve sizing program:

http://www.emersonprocess.com/FISHER/products/firstvuesizing/firstvuesizing.
html

Brian Smith

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Bruce Durdle

As with some of the other posts, you really need to check with specific data for your valve.

However, you can do a very simple check to see if you are likely to have problems. If you can find a value for your proposed valve of the Pressure
Recovery Coefficient FL, you can estimate the minimum pressure at the valve throat.

Minimum pressure = Upstream pressure - (Pressure drop over valve/FL^2)

If this pressure is close to or less than the vapour pressure of the liquid, you have a problem.

Failing specific valve data, FL for a globe valve is about 0.85; for a butterfly 0.65; and for a ball 0.5

But don't take my word for it - if money is to be spent on this, make sure the valve supplier makes a commitment to the result in writing. (Then when
the valve develops wormholes through cavitation, you have a chance of some redress!)

Bruce.

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anand s

Dear William

Thanks for ur valuable suggestion.

regards

anand