Abstract: An oil pool in a rotary vane, oil sealed mechanical vacuum pump casing is cooled by air drawn by a relatively low pressure and low speed laminar flow fan mounted on a motor shaft for the pump and positioned in a shroud between end plates for the motor and casing. The air pumped by the fan flows axially relative to the shaft through a horizotally extending slot at the bottom of the shroud and vertically extending slots on the sides of the shroud. The pumped air flows against vertically and horizontally extending fins respectively on the pump casing bottom and sides. The vertically extending fins at the bottom of the casing have bases slightly above the horizontal slot at the bottom of the housing so air flowing through that slot flows against the bases of the fins at a shallow angle. A vertical surface of the housing remote from the fan and the shroud has vertically extending fins that are aligned with the vertically extending fins on the bottom of the casing.

Abstract: A mechanical rotary vane vacuum pump has high and low vacuum stages for a pumped gas. Each stage includes a rotor for vanes cyclically driven about a common axis that is eccentric to a cylinder of a stator; the stator of each stage includes an inlet and outlet for the pumped gas. An oil seal between inlets and outlets for each stage is in a narrow gap between the stator and rotor. An interstage structure includes a flow path between the stages for the pumped gases and a shaft drivingly connected the rotors of the stages. An oil flow path comprises a first passage through the interstage structure leading radially to the shaft. The shaft includes diametrically opposed oil metering flats or cavities longitudinally aligned with an outlet of the first passage. A second passage through the interstage structure is longitudinally aligned with the cavities and leads tangentially from the peripheries of the shaft and a bore for the shaft.

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.