Related Resources: Fluids Engineering
Control Valve P1 P2 vs Flow Spreadsheet Calculator
About the worksheet
This worksheet approximates the behavior of P1 and P2 (pressure upstream and pressure downstream of a control valve) at different flow rates. This might be useful if valve Cv calculations need to be made at several flow rates, when only P1 and P2 are known at the maximum design flow and at zero flow. The principle behind the calculation is that pressure loss in a piping system is approximately proportional to flow squared. The worksheet may be freely copied and distributed to others.
Although the units on this worksheet are shown as gpm and psig, the calculation method is independent of units and the user can use any appropriate units.
How the Worksheet Works
The cells of most of the data used in calculations are given names that describe their contents, and these names are used in the formulas, so it should be easy for the interested user to follow the calculation method. The calculation method is also shown on the “Calculation Method” tab.
The worksheet makes 16 calculations for flows between zero and 150% of the given maximum design flow.
The “Intermediate Calculations” section determines “Resistance factors” for both the upstream and downstream piping systems with units of pressure/flow squared. Using these resistance factors the pressure losses in the upstream and downstream piping systems are calculated at each of the 16 flow rates (flow squared times resistance factor). From these pressure drops, P1 and P2 are calculated for each of the 16 flow rates and a graph showing the behavior of P1 and P2 is drawn. P1 will always slope downward with increasing flow and P2 will always slope upward with increasing flow. (The exception being when the pressure is the same at maximum and zero flow in which case the pressure graph will be a straight line with zero slope.)
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