The present invention relates to single-stage or multistage centrifugal pumps in general, and more particularly to improvements in sump pumps or submersible motor pumps. For the sake of simplicity, the pump of the present invention will be referred to as a submersible motor pump with the understanding, however, that it can be used with equal advantage as a sump pump.
A submersible motor pump comprises an electric motor which is located at one end of an elongated tubular pump housing and a discharge head which is located at the other end of the housing and admits the fluid medium into a main, i.e., into a rising main if the apparatus is installed in a vertical pipe which contains the fluid medium to be pumped. The apparatus usually need not have a suction pipe because the medium to be pumped enters the first or the only stage of the pump by way of one or more strainers.
As a rule, a submersible motor pump comprises several stages whose components consist of metallic or synthetic plastic material. Such types of apparatus are often used to evacuate liquid (e.g., water) from deep walls. In most instances, the motor is mounted below the pump so that the liquid to be pumped can flow around the motor and cools the latter before it enters the first or lowermost pump stage.
U.S. Pat. No. 3,521,970 to Deters discloses a submersible motor pump wherein the cylindrical pump housing comprises internally threaded upper and lower end portions. The internal threads of the lower end portion mate with external threads of a suction manifold, and the internal threads of the upper end portion mate with the external threads of a complex discharge head. The pump shaft is attached to the output shaft of the motor by a specially designed coupling. The pump shaft is guided by the suction manifold and is mounted in suitable bearings. A drawback of the patented apparatus is that the cost of machining threads into the pump housing as well as into the suction manifold and discharge head is very high. Moreover, the machining of bearings for the pump shaft is costly and the component parts of the pump stages must be machined or otherwise produced with a very high degree of precision. Still further, the pump shaft must be accurately centered in the stages and in the suction manifold in order to prevent wobbling of impellers when the apparatus is in use.