Cooling structure for an oil sealed rotary vacuum pump

An oil sealed, mechanical rotary vane vacuum pump having high vacuum and low vacuum stages for a pumped gas, each of said stages being located in a housing immersed in an oil pool, a casing in which the housing and oil pool are located, each of said stages including a rotor for vanes cyclically driven about a common axis that is eccentric to a cylinder of a stator, the stator of each stage including an inlet and outlet for the pumped gas, an oil seal between the inlet and outlet of the stages in a narrow gap between the stator and rotor, an interstage structure being the high and low vacuum stages, said interstage structure including a flow path between the stages for the pumped gases and a first shaft drivingly connecting the rotors of the high and low vacuum stages, an oil flow path between the pool and the stages comprising a first passage through the interstage structure leading radially to the shaft from a source of oil, said first passage having a first orifice into a bore in the interstage structure through which the shaft extends, the shaft including a recess longitudinally aligned with the first orifice so that oil is metered to the recess as the shaft is rotated, a second passage through the interstage structure longitudinally aligned with the recess and leading from the bore to one face of the cylinder of the low vacuum stage so oil metered to the recess flows to the cylinder of the low vacuum stage to form the oil seal and lubricate surfaces between the rotor and stator, the interstage structure including a third oil passage enabling oil to be sucked from the low vacuum stage to the high vacuum stage, said third passage having an inlet from the low vacuum stage on a first face of the low vacuum stage cylinder adjacent the interstage structure, the second passage having an orifice on a second face of the low vacuum stage cylinder opposite the first face, a conduit extending from a casing inlet through the oil pool to a housing inlet and thence to the high vacuum stage inlet, another shaft extending through the casing and housing to drive the high vacuum stage rotor and the low vacuum stage rotor via the first shaft, a motor having an output shaft aligned with and connected to the drive shaft for the pumping structure, the oil in the pool having a tendency to be heated as it flows from the pool to the interior of the housing, means for cooling the oil including:

• a fan mounted on the motor shaft and positioned between the motor and the casing for providing an air flow axially of the shaft without substantial centrifugal components, a shroud having a first opening for providing an axial air flow into the shroud away from the casing and toward the housing in response to the fan being driven by the motor, said shroud including outlets for providing axial flow from the bottom and sides of the shroud toward thhe casing for air pumped by the fan, the casing having vertically and horizontally extending fins respectively extending from bottom and side surfaces thereof, said fins being in heat exchange relation with air pumped by the fan through the shroud outlets.