Oil-sealed rotary vane vacuum pumps are used in the vacuum heat treating as holding pumps at the exhaust side of the oil diffusion pump while the larger mechanical pumps are roughing (evacuating from atmospheric pressure) the main vacuum chamber.
“In an oil-sealed rotary vane pump (or dry vane mechanism) an offset rotor fitted with vanes that slide in and out of their housing within a stator ‘chamber’. The vanes rotate and ‘trap’ a quantity of gas that enters through the pump’s inlet port and the volume between the rotor and stator decreases. The resulting compressed gas exits the outlet port to the atmosphere. Oil is a fundamental part of rotary vane pumps and to ensure their most efficient long-term performance, as well as effective and trouble-free operation, follow these eight top-tips:”
Source: Vacuum Science World