Determining Pump Size
To select the most suitable pump(s) for your application, follow the steps below.
1. Establish the following factors: fluid type, flow rate required, hose (or pipe) lengths required, static suction lift, static discharge head and seepage.
2. Calculate the dynamic suction head, which equals the sum of the static suction lift and the friction loss added by suction pipe, valves and fittings needed for the installation. To begin, select a pipe or hose diameter based on the flow rate required, referring to a reference chart that plots flow, velocity and friction loss per 100' of length for various diameters of hose or pipe. Friction loss for valves and fittings is expressed in equivalent feet of straight pipe of the same diameter, which is obtained using reference conversion charts. The sum of the friction losses for suction pipe, valves and fittings is divided by 100 to calculate the friction loss in feet, which is added to the static suction lift to determine the dynamic suction head. To utilize centrifugal pumps, the dynamic suction head must be less than 25'. Submersible pumps must be used if the dynamic suction head is greater than 25'.
Tip: Using larger diameter suction pipe may reduce friction loss enough to lower the dynamic suction head to a workable range in applications with a high static suction lift (15' or larger).
3. Calculate the dynamic discharge head, which equals the sum of the static discharge head and the friction loss for discharge pipe, valves and fittings needed for the installation. The friction loss for the discharge line is calculated in the same manner as the suction side. Add this number to the static discharge head to determine the dynamic discharge head.
Tip: Long discharge lines add significant friction losses to a pump system. To reduce friction loss, use larger diameter pipe for all (or part) of the discharge line.
4. Calculate the total dynamic head, which equals the sum of the dynamic suction head and the dynamic discharge head.
5. Match a pump (or pumps) to the application by referring to the performance curve for a given pump, which plots total dynamic head and flow rates at various static suction lifts. Performance curves for diesel-driven pumps also plot pump performance at various engine rpms.