Once the pump type has been determined, its economic performance must be considered-specifically regarding the pump's head and flow rate, as well as the selection of the matching power unit. It is important to note the distinction between the rated head (total head) specified on the pump's nameplate and the actual discharge head (actual head) during operation; this difference arises from resistance losses as water flows through the piping system. Consequently, the actual head is generally 10% to 20% lower than the total head, resulting in a corresponding reduction in discharge volume.
Therefore, in practical application, estimates should be based on 80% to 90% of the rated head and flow rate. Regarding the power unit, one can select a motor based on the power rating specified on the nameplate; however, to ensure rapid startup and safe operation, the power unit's output may be slightly higher than the pump's requirement-typically by about 10%. Alternatively, if a power unit is already available, the pump should be selected to match that unit's power rating.
