These are oil - immersed, rotary vane type pumps. The rotor with twospring loaded vanes is mounted eccentric in the stator body. As the rotorrotates, the vanes sweep the crescent shape air space twice in each revolution.There is inbuilt non-return valve which prevents back flow of air. All movingparts are manufactured from graded material. These parts are preciselymachined, ground and assembled with close tolerances which results in increasedefficiency and long trouble free operating life