Oil flow metering structure for oil sealed mechanical vacuum vane pump

An oil flow path for an oil sealed, mechanical rotary vane vacuum pump having high vacuum and low vacuum stages for a pumped gas, 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 low vacuum stage in a narrow gap between the stator and rotor, an interstage structure between the high and low vacuum stages, said interstage structure including a flow path between the stages for the pumped gases and a shaft drivingly connecting the rotors of the high and low vacuum stages, the oil flow path 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 and extending only part way around the shaft so that oil is metered by the recess as the shaft is rotated, a second passage through the interstage structure longitudinally aligned with the recess, and leading tangentially from the peripheries of the bore and shaft, means for connecting the second passage in fluid flow relation to the cylinder of the low vacuum stage so oil metered by the recess bursts into the second passage and flows to the cylinder of the low vacuum stage to form the oil seal and lubricate surfaces between the rotor and stator.