Submersible sewage pump is provided which is adapted for location in a sump or the like, and which includes a motor case, a driving motor, an impeller case, and an impeller located in the impeller case, the impeller defining a back shroud space between its upper face and the confronting, superjacent portion of the impeller case.
The usual submersible pump is sealed against fluid entry for operation in a submerged condition, and is designed to be cooled by the liquid material within which it is submerged. Dangerous overheating can occur if such a pump is not operated in a submerged condition, and such overheating may result in burning or explosion of the motor.
The apparatus includes a vent which opens at one end into the back shroud space and at the other end opens to the exterior of the impeller case. Whenever air is drawn or injected into the low pressure vortex area of the sewage pump for controlling the amount of liquid discharged, the air collecting in the back shroud space is constantly vented to facilitate operation of the impeller and reprime the pump.