Inventors:
Benjamin Bassan - Framingham MA
Assignee:
Varian Associates, Inc. - Palo Alto CA
International Classification:
F04C 2502, F04C 2702, F04C 2900
Abstract:
A gas ballast device for an oil sealed mechanical rotary vane vacuum pump prevents vapor condensation in the outlet port region of the low vacuum stage of the pump as a vane cyclically approaches the outlet port, whereby molecules of condensed vapor in the oil do not flow back to the inlet port of the low vacuum stage through the oil seal between the inlet and outlet ports. A flow path for atmospheric air leading to the outlet port region includes a tortuous, constricted fluid passageway. An outlet passage connecting the tortuous, constricted fluid passageway to the outlet port region is positioned so that an orifice thereof into the outlet port region is filled with and sealed by oil except during a small portion of each vane cycle immediately after the vane passes the orifice, whereby no movement of mechanical parts is employed to control air flow in response to the cyclical movement of the vanes past the orifice. The flow path for atmospheric air can be adjusted or closed at will, and includes a sleeve through which a portion of the passageway extends. The sleeve is spring biased in an upward direction to be normally urged against an air filter body, threadedly secured to a housing for the pump.