CENTRIFUGAL PUMP CLASSIFICATION

Figure 9-1.—Centrifugal pump. outlet. Figure 9-1 shows the arrangement of components in a centrifugal pump. CENTRIFUGAL PUMP CLASSIFICATION.— Centrifugal pumps may be classified in several ways. For example, they may be either single-stage or multistage. A single-stage pump has only one impeller; a multistage pump has two or more impellers housed together in one casing. In a multistage pump, each impeller usually acts separately, discharging to the suction of the next- stage impeller. Centrifugal pumps are also classified as horizontal or vertical, depending on the position of the pump shaft. Impellers used in centrifugal pumps may be classified as single-suction or double-suction, depending on the way in which liquid enters the eye of the impeller. Figure 9-2 shows single- suction and double-suction arrangements of centrifugal pump impellers. The single-suction impeller (view A) allows liquid to enter the eye from one side only; the double-suction impeller (view B) allows liquid to enter the eye from both sides. The double-suction arrangement has the advantage of balancing the end thrust in one direction with the end thrust in the other direction. Impellers are also classified as CLOSED or OPEN. A closed impeller has side walls that extend from the eye to the outer edge of the vane tips; an open impeller does not have side walls. Most centrifugal pumps used in the Navy have closed impellers. CONSTRUCTION.— As a rule, the casing for the liquid end of a pump with a single-suction impeller is made with an end plate that can be removed for inspection and repair of the pump. A pump with a double-suction impeller is generally made so one-half of the casing may be lifted without disturbing the pump. Since an impeller rotates at high speed, it must be carefully machined to minimize friction. An impeller must be balanced to avoid vibration. A close radial clearance must be maintained between Figure 9-2.—Centrifugal pump impellers. A. Single-suction. B. Double-suction. 9-2