Valve Pressure Loss Flow gekengineering（阀压力损失gekengineering流动）.pdf

Valve Pressure Loss Flow • The valve coefficient, Cv, is a number which represents the capability of a valve (or any flow component) to flow a fluid. The larger the Cv, the larger the flow at a given pressure differential. Cv is the number of U.S. gallons per minute that will pass through a valve with press drop of 1 psi. For example, a Cv of 150 would then equate to 150 gpm of water at 60° F with a differential pressure of one psi. • Cv is determined by counting the number of gallons that pass through the valve with 11 psipsi appliedapplied pressurepressure betweenbetween thethe valvevalve inletinlet thethe outletoutlet atat 00 psi.psi. CvCv isis aa mathematical constant. For a pressure drop other than 1 psi, a value can be calculated. • Cv factors typically apply to full open/full closed valves, e.g., solenoid valves, ball valves, etc. Valves held open without aid of pressure. • Cv does not apply to modulating or regulating valves, spring loaded check valves, etc., that incorporate a control spring or opposing gas charge or bellows since more than 1 psi is required just to start positioning the valve mechanism. Differential Pressure • Differential, Delta, D, refers to the pressure drop across a flow component – valve, screen, etc. Delta is the change in something; in this case a change,change, oror drop,drop, inin pressure.pressure. ToTo determinedetermine thethe DDPP across a valve, simply subtract the outlet pressure (P2) from the inlet pressure(P1). • The equation is P1-P2 = DP Pressure Drop and Back Pressure • Pressure drop across a valve is highly influenced by the area, shape, path and roughness of the valve. • Resistance to flow creates backpressure. Perforations, screens, tubing, valves, chokes and regulators all contribute to both backpressure and pressure loss. In production, verticalvertical flowflow cr