Greetings everyone. I've just started at a small valve manufacturing company. I'm building a test rig to do the classic "flow rate vs. pressure drop" test on our products (injection quills and pressure relief valves). I'll then be preparing brochures/data sheets for each product. (Small place, Engineering gets mixed with Marketing, heh). I've been given some time to do some research on how to best collect and present the data to customers, so naturally I've been reading a lot about the Masoneilan flow coefficient Cv, introduced in 1944.

Here's my issue: every text or website I've read has given the well-known equation to relate the Cv value of a valve to pressure drops and flow rates other than 1 USGPM and 1 PSI:
Q = Cv * sqrt(dp/G)

My question is: how accurate is this relation? Nowhere in the Masoneilan valve sizing handbook, the Fisher Controls "Control Valve Handbook", my undergraduate fluid mechanics text, or any website or Eng-tips thread that I can find does it mention the derivation. I don't think it comes from Bernoulli's equation, since there is obviously a huge energy loss across a control valve.

I know the equation is accurate enough for general use, since it's been around so long, but since I'm doing R&D work I was hoping to get a little more background. Does anyone have a reference for the 1944 paper where the concept was introduced?

One last question: I see in the Fisher controls manual the following: "To aid in establishing uniform measurement of liquid flow capacity coefficients (Cv) among valve manufacturers, the Fluid Controls Institute (FCI) has developed a standard test piping arrangement, as shown in Figure...". Does anyone know the paper in which this standard test piping arrangemen