Sizing a control valve (liquid dump valve on 2 or 3 phase O&G separators) 1

[engr2GW]

Hi,

I have never had to size these valves before, but I would really appreciate any input.

I understand that many manufactures have sizing programs that maks it easier and faster to size their own valves. But I want to be able to size them from first principles or equations, charts, etc. because there are some supplier that do not have such programs or softwares for sizing.
So; if I have P1, P2, dP, Q, S.G (specific gravity), what are the steps.
1. I know that I can select a valve and look up it's Cv in the manual and plug into the equation Cv=Q*sqrt(S.G/dP). is there a way to verify that one of the variables needs to be increased or reduced to ensure that the valve size for which I picked Cv is appropriate, e.g. critical velocity, erosional velocity, etc. Just a way to know that I can plug in and solve for dP, Q, or Cv and know that I will be fine.

Or can I solve for Cv from the equation above and compare it to the manufactures Cv for a given valve and know at what range/ratioo to stay...any rule or thumb? or other equations? or variables?

Thank you.

As much as possible, do it right the first time...

 

[BigInch]

You can estimate a size by calculating the Cv required for your flowrate with a corresponding available pressure drop, assume that is 30-75% of your valve's maximum Cv. Then make sure that the valve fits the bill for noise and erosion limits.
Everything you need to know is here,

http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[engr2GW]

Thanks,
When I solve for Cv and keep it within 30 to 75% of the valve's rated Cv, everything looks good. It appears the two things to worry about are:
1. Critical flow (choked flow?) for cavitation and flashing- where can I find a verification equation for this? the control valve handbook just what kind of valves to use, and not a way to tell that your valve sizing condition is sub-critical or has less chance of erosion

2. Noice, is there an industry standard for the minimum sound decibels and an equation to derive the same?

Thanks for you help

As much as possible, do it right the first time...

 

[bingbingwang]

1--- critical flow, choked or not, try FISHER control valve sizing software, it will tell you what condition your valve will work at. cavitation or flashing or not, depends on the process condition, it is just some number that you can estimate. when you choose your valve style or trim style , you gotta be careful with the "operating condition" mostly the pressure drop and down stream temperature/pressure condition is the trouble maker, you have to work together with process engineer to figure out the best design.
2---noise control, it is not so accurate calculation, it is just a prediction, it is related to velocity in the valve and pipe line. the standard can be searched on google. some formulars are recommended for noise estimation in those standards.
3---- 30%-75% is not always right, it actually depends on the charactor of the valve trim, for equal% time, normally 60%-80%, for linear trim 40%-60%, for quick opening trim, <30%?? depends on how quick you need the valve to open.----which means depends on how big your system is !

hope can help.


Get help and return with helps!!.

 

[bingbingwang]

sizing a valve for 2 or 3 phases is really a trouble headache or puzzle, experience is very important, pay double attantion to your process data----never trust too much of your process data. ---my experience told me the process data could be wrong for sizing valves.

Get help and return with helps!!.