Transcription of Flow Coefficients and Computations
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Flow Coefficients and Computations
The pipe size in the system ordinarily will determine the valve size. However, to assure accurate throttling or positioning, it is advisable to calculate the valve size. Formulas for liquid and gas are as follows:Liquid Flow Formula* Cv = Qa sg / PQa = Cv P/sg P = sg(Qa/Cv) Gas Flow Formula* Cv = Q/1360 sg(T)/ P 2/(P1+P2)Q = 1360 Cv P/sg(T) (P1+P2)/2 P = P1 P1 (sg T)(Q/[963 Cv]) * Fluid Controls Institute Inc Standard FCI 62-1 ** SCFH (standard cubic foot per hour) of gas is measured at 60 F ( ) and psia. CFH (cubic foot per hour) is measured at any temperature and of CFH to SCFH SCFH = ( ) ( R/Tactual) CFHactualNote: The design of the Straightway Valves are not conducive to good throttling In general, any reduction in outlet pressure below half the absolute inlet pressure will give no further increase in flow.
Cv rating Rate of flow depends upon the pressure drop. Cv is the amount of flow in gallons per minute through a valve which results in a 1 psi pressure drop. Throttling characteristics are shown in the same manner with Cv’s at various openings. Use formula shown below to compute actual flow at various pressure drops. Weir Valve Cv Ratings
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