Rotary vacuum pump

Abstract

The rotary vacuum pump includes a pump housing, a rotary shaft, a thrust movement restriction mechanism and a first elastic member. The pump housing has therein a pump chamber. The rotary shaft has thereon a rotor rotatably disposed in the pump chamber. When the rotor is rotated with the rotary shaft, gas in the pump chamber is pumped thereby to draw gas into the pump chamber. The thrust movement restriction mechanism is provided for allowing the rotor to displace in the pump chamber in one thrust direction due to thermal expansion thereof during the operation of the rotary vacuum pump. The first elastic member is provided for urging the rotary shaft in the other thrust direction opposite to the one thrust direction.

1 . A rotary vacuum pump comprising:
 a pump housing having therein a pump chamber;   a rotary shaft having thereon a rotor rotatably disposed in the pump chamber, wherein when the rotor is rotated with the rotary shaft, gas in the pump chamber is pumped thereby to draw gas into the pump chamber;   a thrust movement restriction mechanism provided for allowing the rotor to displace in the pump chamber in one thrust direction due to thermal expansion thereof during the operation of the rotary vacuum pump; and   a first elastic member provided for urging the rotary shaft in the other thrust direction opposite to the one thrust direction.   
   
   
       2 . The rotary vacuum pump according to  claim 1 , wherein the thrust movement restriction mechanism has a stepped portion that is formed on the rotary shaft and a bearing that supports the rotary shaft, wherein the rotary shaft is prevented from displacing in the other thrust direction which is opposed to the one thrust direction by bringing the stepped portion into contact with the bearing directly or indirectly. 
   
   
       3 . The rotary vacuum pump according to  claim 1 , wherein the rotary shaft having the rotor is provided in plurality, wherein the rotors are engaged with each other in the pump chamber. 
   
   
       4 . The rotary vacuum pump according to  claim 3 , wherein the first elastic member is located around one end of each rotary shaft. 
   
   
       5 . The rotary vacuum pump according to  claim 4 , wherein a second elastic member is provided for urging each rotary shaft in the one thrust direction. 
   
   
       6 . The rotary vacuum pump according to  claim 5 , wherein the first and second elastic members are respectively located around opposite ends of the rotary shafts. 
   
   
       7 . The rotary vacuum pump according to  claim 5 , wherein each of the first elastic member and the second elastic member is provided by a spring. 
   
   
       8 . The rotary vacuum pump according to  claim 4 , wherein the first elastic member is located between the stepped portion and the bearing. 
   
   
       9 . The rotary vacuum pump according to  claim 1 , wherein the rotary vacuum pump is a multistage roots pump. 
   
   
       10 . The rotary vacuum pump according to  claim 9 , wherein the gas is transferred in the one thrust direction of the rotary shaft, wherein the thrust movement restriction mechanism is located at a position adjacent to the final stage of the multistage roots pump.