5 - Centrifugal pump operation and characteristics

Abstract

One of the most attractive features of a centrifugal pump is its ability to perform in a system under a wide range of operating conditions. Pumps are able to operate satisfactorily under varying operating conditions and with a range of fluid types. The pump is designed for a discrete value of flow rate, differential head, and speed. This is the best efficiency point of operation or “BEP.” The hydraulic properties of any centrifugal pump are studied taking the shaft speed of the pump N as a constant. After the speed is considered constant, the behavior of the differential head H with respect to the flow rate Q is obtained by throttling the discharge valve of the pump. The various openings of the discharge valve result in different flow rates and corresponding heads. One of the most important characteristics of a pump is its capacity. The capacity of a centrifugal pump decreases as the pressure at the pump discharge increases. The nature/shape of power-flow rate characteristic curves is also dependent on the specific speed of the pump. Centrifugal pumps having low to medium specific speeds have P–Q curves that rise upward. For higher specific speeds, the P–Q curves maybe approximately flat and horizontal. Changes in pump design results in differences in pump characteristics and gives rise to a wide range of hydraulic properties. To overcome this problem, nondimensional characteristics are defined.