Most end-suction, single-stage pumps are made of one-piece solid casings. At least one side of the casing must be open so that the impeller can be assembled in the pump. Thus, a cover is required for that side. If the cover is on the suction side, it becomes the casing sidewall and contains the suction opening. This is called the suction cover or casing suction head. Other designs are made with casing covers and still others have both casing suction covers and casing covers.
For general service, the end-suction, single-stage pump design is extensively used for small pumps with a 4- or 6-in (102 or 152 mm) discharge size for both motor-mounted and coupled types. In these pumps, the small size makes it feasible to cast the volute and one side integrally. Whether or not the seal chamber side or the suction side is made integrally with the casing is usually determined by the most economical pump design.
For larger pumps, especially those for special services such as sewage handling, there is a demand for pumps of both rotations.A design with separate suction and seal chamber heads permits the use of the same casing for either rotation if the flanges on the two sides are made identical. There is also a demand for vertical pumps that can be disassembled by removing the rotor and bearing assembly from the top of the casing. Many horizontal applications of the pumps of the same line, however, require partial dismantling from the suction side. Such lines are most adaptable when they have separate suction and casing covers.