Pump Casings

There are three general types of casings, but each consist of chamber in which the impeller rotates, provided with inlet and exist for the liquid being pumped. The simplest form is the circular casing, consisting of an annular chamber around the impeller; no attempt is made to overcome the losses that will arise from eddies and shock when the liquid leaving the impeller at relatives high velocities enter this chamber. Such casing is seldom used.

Volute Casings take the form of spiral increasing uniformly in cross-sectional area as the outlet is approached. The volute efficiently converts the velocity energy imparted to the liquid by the impeller into pressure energy.

A third type of casings is used to diffuser type or turbine pumps. In this type, guide vanes or diffuser are interposed between the impeller discharge and the casing chamber. Losses are kept to a minimum in a well designed of this type, and improved efficiency is obtained over a wider range of capacities. This construction is often used in multistage high head pumps.

Action of Centrifugal Pump

Briefly the action of centrifugal pump may be shown by drawing. Power from outside source is applied to shaft A, rotating the impeller B, within the stationary casing C. The blade of the impeller in revolving produces a reduction in pressure at the entrance or eye of the impeller. This causes liquid to flow into the impeller from the motion pipe D. This liquid is forced outward along the blades at increasing tangential velocity.