8. The performance curves are useful in selecting a particular water pump. When a question regarding the performance of a specific pump must be answered, refer to the pump specifications for the particular model.

Determine how high the pump will sit above the water source (static suction head). Determine how high the discharge end will be elevated above the pump (static discharge head). Determine what the discharge capacity (gpm) of the pump must be.

Given the total head (suction + discharge), the discharge capacity can be estimated by referring to the performance curve.

Keep in mind, the actual discharge performance may be significantly less than predicted by using static head alone because of friction losses in the system.

Pressure can be calculated for total head by multiplying total head by .433. Pressure available at the end of the hose at zero flow for a given total head (less then the maximum total head) can be calculated by multiplying the total head by .433 then subtracting it from the maximum pressure.

Example: The maximum pressure for a WH20X is 71 psi (.433 x 164 total head in feet). The maximum available pressure at a total head of 120 feet is 71 - 52 (120 x .433) = 19 psi at zero flow.