The pump casing refers to the outside shell of the pump. It has to seal off the inside of the unit to the outside with respect to pressure and fluids.
The structure of the casing differs depending on the type of pump. The casing of a centrifugal pump is visibly determined by the infeed and delivery of the flow to the impeller. Special importance is also attributed to the casing for these pumps because the gap between casing and impeller plays a major role in determining the efficiency of the pump. The casing of a positive displacement pump, on the other hand, encloses the displacing elements such as the piston. In practice, all pumps already provide an indication of the pump type by the shape of their casing.
Depending on the location, a pump casing can be made of cast or wrought iron, of chromium or duplex steel. Also some pumps can have a casing made of plastic.