Pump terminology

As with any field working with pumps requires an understanding of the terminology common to their applications.   It was explained earlier in this online pump school that pumps lift water with the aid of atmospheric pressure then pressurize and discharge it from the casing. The practical suction lift, at sea level, is 25 feet. The published specifications of most pump manufacturers will list this as maximum suction lift.   Pump performance is measured in volume as gallons per minute (GPM) and in pressure as head. In general a trade off occurs between head and flow with an increase in head causing a decrease in flow and vice versa.   head refers to gains or losses in pressure caused by gravity and friction as water moves through the system (see figure below). It can be measured in lbs/in2 (PSI) but is most commonly listed in feet of water.     To illiustrate this consider that a Multiquip 3 inch trash pump is rated with a maximum head of 90 feet. A pump must produce 1 PSI to push a column of water vertically 2.31 feet, therefore dividing the maximum head rating of a pump by 2.31 will provide the maximum pressure capability of the pump.   90 (ft/head) / 2.31 (ft/head) = 38.96 PSI   Similarly multiplying 2.31 by the maximum pressure capability of the pump will provide the maximum head rating of the pump.   2.31 (ft/head) / 38.96 PSI = 90 (ft/head)   Depending on how the measurement is taken suction lift and head may also be referred to as static or dynamic. Static indicates the measurement does not take into account the fritcion caused by water moving through the hose or pipes. Dynamic indicates that losses due to friction are factored into the performance. The following terms are usually used when referring to lift or head.   Static Suction Lift - The vertical distance from the water line to the centerline of the impeller.   Static Discharge Head - The vertical distance fromthe discharge outlet to the point of discharge or liquid level when discharging into the bottom of a water tank.   Dynamic Suction Head - The Static Suction Lift plus the friction in the suction line. Also referred to as a Total Suction Head.   Dynamic Discharge Head - The Static Discharge Head plus the friction in the discharge line. Also referred to as Total Discharge Head.   Total Dynamic Head - The Dynamic Suction Head plus the Dynamic Discharge Head. Also referred to as Total Head.