Inlet shut-off valve for rotary piston pumps.

摘要

A shaft lip sealed is provided as an inlet shut-off valve seal in the working fluid inlet line of a rotary piston pump between the first pumping chamber of the vacuum pump and the inlet to the operating chamber. A piston valve is provided, having an axially inclined radial face, for engaging this seal and cutting off flow therebetween even under low pressures. This piston valve is actuated into sealing engagement with the shaft lip seal when operation of the vacuum pump ceases and a pressure relief vent is connected to the first pumping chamber.