Mechanical high-vacuum pumps with an oil-free swept volume

Abstract

In both corrosive and clean duties the widely used oil lubricated rotary pump has certain disadvantages. In corrosive applications aggressive vapors and/or abrasive particles tend to contaminate the lubricant of the pump, which shortens its service life, while in clean applications the lubricant may cause contamination of the vacuum process. To overcome these problems a new multistage pump has been developed to work from atmospheric pressure to 0.01 mbar without any lubricant within its pumping chamber. The pump is a multistage positive displacement rotary machine in which a number of intermeshing rotor pairs of different profiles mounted on common shafts are held in correct phase relation without contact by a pair of timing gears. The construction is robust designed for industrial as well as for clean vacuum processes which can benefit by the exclusion of lubricant, sealing, or working fluid from the swept volume of the pump. Handling of condensable vapors or dust laden gas is assisted by gas ballast and versatile orientation of pump mounting. Pump sizes of 80 and 180 m3 h−1 displacement have been developed. The paper explains the reasoning that led to the choice of different mechanisms which have been combined in the pump, its performance and construction.