Valve Flow coefficient Cv
Valve Flow coefficient Cv
(OP)
Hi All,
Go through this thread http://www.eng-tips.com/viewthread.cfm?qid=209037
We are having exactly same problem as per above thread. The Cv values we are getting through software are very less but they are matching when valve is treated as CONTROL VALVE and are 40/50% less when valve is considered as ON/OFF valve for given size/class. Most of the Cv values of ON/OFF valves are derived from formulas in Crane Technical paper 410.
Is there any seperate procedure / standard practice to measure Cv of ON/OFF valves?
Go through this thread http://www.eng-tips.com/viewthread.cfm?qid=209037
We are having exactly same problem as per above thread. The Cv values we are getting through software are very less but they are matching when valve is treated as CONTROL VALVE and are 40/50% less when valve is considered as ON/OFF valve for given size/class. Most of the Cv values of ON/OFF valves are derived from formulas in Crane Technical paper 410.
Is there any seperate procedure / standard practice to measure Cv of ON/OFF valves?





RE: Valve Flow coefficient Cv
RE: Valve Flow coefficient Cv
If I use procedure as per ISA/IEC for Cv computation of CONTROL VALVE, the values are 40/50% less than ON/OFF valves.
So I am confused which procedure to be simulated on software to get correct Cv values for ON/OFF Ball valve.
RE: Valve Flow coefficient Cv
Say 1 velocity head, water and a velocity in the pipe of 1 m/s in a 4" opening => dP= 1000*1^2 = 1060 Pa= .153 psi
and the flow rate is .0083 m3/sec or 110 gal/min
Cv= 110*sqr(1/0.153)=281
Best regards, Morten
RE: Valve Flow coefficient Cv
Perhaps include some actual numbers as an example to make clear what your problem is.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Valve Flow coefficient Cv
Theoretically and by formula I can get the desired Cv but when I give same inputs to CFD Software it simply doesn’t give me desired flow (Cv) for ON/OFF valve.
Katmar
For 12” ON/OFF ball valve Cv is around 22,000 whereas for same size CONTROL valve it is 12,000.
When we physically measure Cv of full open ball valve, as per ISA/IEC procedure we get Cv around 12,000.
When I simulate this condition in CFD software I get Cv around 12,000.
Now my question is what condition shall I simulate in software to get Cv = 22,000?
I’m asking this cause I have to freeze the PROCEDURE / METHOD in CFD software. The same procedure can be used for partial open valve. This is because now days some crazy people are asking for % opening vs Cv curve for ON/OFF valves also. God knows why they want this.
Thanks & Regards,
RE: Valve Flow coefficient Cv
Replacing 1 with 0.05 gives 1257 in the 4" case and 11310 in the 12" case (close to what you mention). If you had a value why do you ask?
The enggineering tool box (http://www.engineeringtoolbox.com/minor-loss-coeff...) dont mention the assumption - but its probably "old school rule of thumb values". A full bore modern large valve could have much migher Cv/lower loss. Solving my little excel sheet that i made just for you gives me a head loss coefficient of 0.01 (assumed ID=12" exactly)
If you know its 22,000 then use 22,000???
I have recently approved that a characteristic similar to "quick opening" was used in a case similar to what you describe. I think this is optimistic but acceptable.
RE: Valve Flow coefficient Cv
I want procedure to generate 22,000 value not 12,000 value. This procedure will be used for computation (in CFD software) of Cv at different openings to plot % opening vs Cv curve.
Cheers !!!
RE: Valve Flow coefficient Cv
Modeling the ball valve as a thick orifice gives me a required valve bore of 10.9" if the pipe ID is 11.94" and I want a Cv of 12,000. I would be surprised if your CFD numbers are so different from this. There seems to be good agreement amongst the ball valve manufacturers that the Cv for a full bore 12" ball valve is in the region of 22,000 to 24,000.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Valve Flow coefficient Cv