The present invention relates to improvements in centrifugal pumps in general, and more particularly to improvements in centrifugal pumps which can be used for circulation of coolant in nuclear reactor plants, especially as primary recirculating pumps in pressurized water and boiling water nuclear reactors.
It is already known to provide the primary recirculating pump in a nuclear reactor plant with a spherical housing having an inlet for incoming fluid and an outlet for pressurized fluid. It is further known to assemble the inlet of two sections one of which is integral with the housing and the other of which is coaxial with the impeller or rotor. Reference may be had to German printed publication No. 1,653,785. A drawback of the pump which is disclosed in this publication is that the housing has a semispherical shape or resembles a cylindrical shell. This reduces the stability of the housing. Moreover, the outer section of the inlet is a pipe elbow which extends along an arc of 90.degree. so that it contributes excessively to the overall requirements of the pump and necessitates the circulation of excessive quantities of fluid. It has been found that excessive pressure peaks develop in the region where the elbow of the inlet communicates with the interior of a semispherical or cylindrical (shell-shaped) pump housing. Moreover, the distance between the plane of the fluid-receiving end of the outer section of the inlet and the outlet is quite substantial which necessitates the circulation of large quantities of fluid in the interior of the pump. Therefore, the pump which is disclosed in the aforementioned publication failed to gain acceptance in the industry and is not in actual use.
The commonly owned copending application Ser. No. 411,382 of Matthias et al. discloses a centrifugal pump wherein the pressure housing resembles a ring-shaped or spiral insert which is installed in an outer housing, and wherein the plane of the inlet coincides with the plane of the outlet. This is achieved by greatly increasing the dimensions of the pressure housing in a direction at right angles to the axis of the impeller. The pressure housing has a conical central portion which conveys fluid into the range of the rotary impeller. The outlet has a portion which extends through the pressure housing. A drawback of such construction is that the pressure housing is a ring or spiral whose stability does not match that of a hollow sphere.