In a submersible pump adapted for location in a sump or the like and including a motor case and a driving motor in said motor case; an impeller case having an upper,interiorlydisposed face, an inlet for receiving liquid material from the sump, and an outlet for discharging liquid material out of the sump; and an impeller located in said impeller case and defining a back shroud space with said face, said impeller beingrotatable for developing a low pressure vortex below said impeller adjacent said inlet.

The improvement comprising: vent means defining vent passage means providing communication between said back shroud space and the exterior of said impeller case; spray means coupled to said vent passage means and opening to the exterior of said impeller case for spraying liquid material from said back shroud space onto the exterior of said motor case for cooling said motor, and for venting air from saidback shroud space and to the exterior of said impeller case to facilitate repriming of said pump under conditions of air intake through said inlet; and liquid material discharge control means for controlling the quantity of liquid material discharged through said outlet, independently of the rate of rotation of said impeller, said control means comprising a compressor, conduit means terminatingat one end adjacent said low pressure vortex area and coupled at the other end to said compressor for injection of compressed air into said low pressure vortex for discharge through said outlet with said liquid material.

Submersible pump improvement according to claim 1 wherein said liquid material discharge control means includes air flow control means coupled to said conduit means, and further includes pressure sensing means responsive to the level ofliquid material in said sump to operate said air flow control means for regulating the rate of air flow through said conduit means.

The additional subject matter of the present applicationincludes material relating to means for discharging liquid material and venting air from the back shroud area adjacent the pump impeller to facilitate self-priming, reduce thrust bearing loads, and for cooling of the pump drive motor.