Abstract: The pump described is of the canned motor type generally used for handling caustic materials where the motor is integrated into the pump, but must be totally sealed therefrom. The pump rotor is mounted on a hollow shaft that is supported by bearings on a hollow mandrel which has one end secured to the pump housing and the other end secured to a lug projecting from a rear shaft support plate. The lug is hollow and is provided with a plurality of ports that provide fluid communication between the motor housing and the pump inlet through the hollow mandrel. The shaft is arranged, when moved axially by the thrust developed by the centrifugal pump to open and close the ports regulating flow therethrough and thereby exerting a force on the shaft to counteract the thrust force generated during pumping.