Abstract: The screw type vacuum pump comprises a pump casing having a suction inlet and a discharge outlet, and a pair of rotors incorporated within the pump casing and meshing with each other to rotate in synchronized manner. The vacuum pump evacuates a reaction vessel, to which process gas is applied, to obtain a negative pressure condition of a predetermined level. Upon operation of the pump, inert gas is introduced into a compression working chamber directly or through a sealing portion disposed adjacent the discharge outlet. The introduced inert gas is adiabatically compressed therein to generate heat to heat the rotors and a casing wall. Further the inert gas effects a reduction of partial pressure of the process gas in the pump. Accordingly, a side reaction product is prevented from accumulating on the rotors and the casing wall.

Abstract: The present invention provides a screw vacuum pump unit in which both a screw block and a driving motor are mounted on one side surface of a casing of a speed change gear, both axes of a male rotor and a female rotor in the screw block are arranged in vertical adjacency within a substantially perpendicular virtual plane, and suction ports and discharge ports are arranged on both sides with the vertical plane intervening therebetween, whereby maintenance can be facilitated.