Calculating Cv

[DrJim]

I have a 24" weld neck flange (23.25" ID) and a stopper plate on the flange side that is 6.25" above the flange when open. The flow is coming out the flange and hitting this plate, and in effect, turning 90 degrees to exit. The stopper is supported by 5 ea 1.66" dia pipes above the bolt holes in the flange and parallel to the flow stream. How do I calculate Cv for this device?

 

[JimCasey]

23.25 id flange throat area is 424.6 square inches.
area between the flange face and the stopper plate is 456.51 in2, less 38.125 in2 obstructed by the standoffs, but on a larger bolt circle, I'll bet, so they cause little additional restriction.

With the miracle of modern technology you could throw all the parameters into a CFD program and come up with something, or whip out the old Crane "Flow of Fluids" handbook and do it the hard way. Or, come up with a way to measure the flowrate ad delta P through the fixture and use the Cv equation.

Either way, the Cv is going to be in the ball-park of the Cv of a 24" Butterfly valve: Durco publishes 20,500 for a 24" BX2000.

 

[TD2K]

I'd concur with Jim's estimate. The throat area of the flange is greater than the area for flow created by the plate (424 in2 versus 456 in2). The Cv for a wide open butterfly valve should be a reasonable estimate.