Vacuum exhaust apparatus and drive method of vacuum exhaust apparatus

Abstract

Pairs of rotors (R 1 , R 2 , R 3 , R 4 , R 5 and R 6 ) driven rotationally by a motor ( 22 ) are disposed in the body ( 21 ) of a main pump ( 20 ) comprising a multistage Roots dry vacuum pump. A suction opening ( 23 ) communicating with the rotor chamber of the rotor R 1 is provided in the upper wall portion at the left end of the body ( 21 ). A delivery section ( 24 ) communicating with the delivery side of the rotor chamber of rotor R 6 on the final stage is coupled to an exhaust pipe ( 25 ) and is provided with a silencer ( 26 ) and further coupled to a check valve ( 28 ) through a pipe ( 27 ). The check valve ( 28 ) has its forward direction toward the atmospheric side. The delivery section ( 24 ), or a delivery section ( 24 ′) at the side intermediate stage, is coupled to an auxiliary pump ( 30 ) having an exhaust capacity smaller than that of the main pump ( 20 ). When the motor ( 22 ) is driven, gas exhausted through rotation of the rotors (R 1 -R 6 ) is carried sequentially to the downstream side from the rotor chambers and a vacuum processing chamber coupled to the suction opening ( 23 ) is exhausted. The delivery section ( 24 ) on the final stage is exhausted by driving the auxiliary pump ( 30 ), and the pressure is reduced. Consequently, the burden of the exhaust action on the rotor (R 6 ) on the final stage or the rotor (R 5 ) on the intermediate stage is lessened, and the power consumption of the motor ( 22 ) can be reduced significantly as compared with the prior art.

1 . The method of driving a vacuum exhaust apparatus including, a dry vacuum pump of the multi-stage positive displacement type, a first exhaust pipe connected with a last stage of an exhaust chamber for said apparatus and a second exhaust pipe connected at one end with a middle stage or with the last stage of said exhaust chamber and at the other end to approximately atmosphere, a check valve connected with said first exhaust pipe and permitting gas to flow only in a direction towards atmosphere, and an auxiliary pump connected with said second exhaust pipe in parallel with said check valve for pumping the middle stage or the last stage of said exhaust chamber, said method comprising:
 driving said auxiliary pump at a pumping speed of one to three percentages of the pumping speed of said drive vacuum pump while said dry vacuum pump is driven.