Roots pump and exhaust method

Abstract

According to one embodiment, a roots pump includes a first roots pump, a second roots pump, and a connection passage. The first roots pump includes a first casing which has a first pump chamber. The second roots pump includes a second casing which has a second pump chamber. The connection passage connects an exhaust hole which is provided in the first pump chamber to an intake hole which is provided in the second pump chamber.

What is claimed is: 
     
         1 . A roots pump comprising:
 a first roots pump including a first casing which has therein a first pump chamber, a first gas transfer member which is disposed inside the first pump chamber and rotates so as to transfer a gas in a predetermined direction, and a first support member which supports the first gas transfer member;   a second roots pump including a second casing which has therein a second pump chamber, a second gas transfer member which is disposed inside the second pump chamber and rotates so as to transfer a gas in a predetermined direction, and a second support member which supports the second gas transfer member; and   a connection passage connecting an exhaust hole which is provided in the first pump chamber to an intake hole which is provided in the second pump chamber.   
     
     
         2 . The roots pump according to  claim 1 , wherein in the connection passage, a cross-sectional area perpendicular to a gas transfer direction decreases as it goes from the first roots pump toward the second roots pump. 
     
     
         3 . The roots pump according to  claim 1 , wherein
 the first casing, the first gas transfer member, and the first support member are formed of a material without corrosion resistance, and   the second casing, the second gas transfer member, and the second support member are formed of a material with corrosion resistance.   
     
     
         4 . The roots pump according to  claim 1 , wherein
 the first pump chamber has a plurality of pump chambers,   the second pump chamber has a plurality of pump chambers, and   the connection passage is connected between a pump chamber constituting the first pump chamber at the most downstream side in a gas transfer direction of the first roots pump and a pump chamber constituting the second pump chamber at the most upstream side in a gas transfer direction of the second roots pump.   
     
     
         5 . The roots pump according to  claim 4 , wherein
 the pump chambers constituting the first pump chamber of the first roots pump are formed so that the volume becomes smaller as it goes toward the downstream side in the gas transfer direction, and   the pump chambers constituting the second pump chamber of the second roots pump is formed so that the volume becomes smaller as it goes toward the downstream side in the gas transfer direction and the volume of the pump chamber constituting the second chamber at the most upstream side in the gas transfer direction of the second roots pump becomes smaller than that of the pump chamber constituting the first chamber at the most downstream side in the gas transfer direction of the first roots pump.   
     
     
         6 . The roots pump according to  claim 1 , wherein
 the first roots pump further includes a first motor which rotates the first support member,   the second roots pump further includes a second motor which rotates the second support member, and   the capacity of the first motor is smaller than the capacity of the second motor.   
     
     
         7 . The roots pump according to  claim 1 , wherein
 the first support member includes a pair of rotary shafts which is a first rotary shaft and a second rotary shaft rotated, the first support member being supported by the first casing,   the first gas transfer member includes a pair of rotors which is a first rotor and a second rotor respectively supported by the first rotary shaft and the second rotary shaft,   the second support member includes a pair of rotary shafts which is a third rotary shaft and a fourth rotary shaft rotated, the second support member being supported by the second casing, and   the second gas transfer member includes a pair of rotors which is a third rotor and a fourth rotor respectively supported by the third rotary shaft and the fourth rotary shaft.   
     
     
         8 . The roots pump according to  claim 7 , wherein
 a first motor which rotates the first rotary shaft is connected to the first rotary shaft,   the first rotary shaft and the second rotary shaft are connected to each other through gears so as to rotate in the opposite directions,   a second motor which rotates the third rotary shaft is connected to the third rotary shaft, and   the third rotary shaft and the fourth rotary shaft are connected to each other through gears so as to rotate in the opposite directions.   
     
     
         9 . The roots pump according to  claim 8 , wherein the capacity of the first motor is smaller than the capacity of the second motor. 
     
     
         10 . The roots pump according to  claim 1 , wherein the connection passage is disposed so that a length direction of the connection passage is perpendicular to a length direction of the first support member and the second support member. 
     
     
         11 . The roots pump according to  claim 3 , wherein
 the first casing, the first support member, and the first gas transfer member are formed of ductile cast iron, and   the second casing, the second support member, and the second gas transfer member are formed of ductile cast iron subjected to Ni-plating.   
     
     
         12 . The roots pump according to  claim 7 , wherein a small gap is formed between the first rotor and the second rotor, between the first rotor and an inner wall surface of the first casing, between the second rotor and the inner wall surface of the first casing, between the third rotor and the fourth rotor, between the third rotor and an inner wall surface of the second casing, and between the fourth rotor and the inner wall surface of the second casing. 
     
     
         13 . The roots pump according to  claim 2 , wherein the connection passage is formed as a truncated conical tube. 
     
     
         14 . The roots pump according to  claim 1 , further comprising:
 N−2 number of k-th roots pumps including a k-th casing which has therein a k-th pump chamber, a k-th gas transfer member which is disposed inside the k-th pump chamber and rotates so as to transfer a gas in a predetermined direction, and a k-th support member which supports the k-th gas transfer member when N is set to an integer equal to or larger than 3 and k is set to an integer from 3 to N,   wherein the connection passage is provided between the respective roots pumps so as to connect an exhaust hole which is provided in the k−1-th pump chamber to an intake hole which is provided in the k-th pump chamber.   
     
     
         15 . The roots pump according to  claim 7 , wherein the first rotor, the second rotor, the third rotor, and the fourth rotor includes a plurality of teeth. 
     
     
         16 . An exhaust method comprising:
 transferring a gas, which is suctioned from a first intake hole of a first casing inside the first casing having a first pump chamber, to a first exhaust hole of the first casing while compressing the gas inside the first pump chamber;   transferring the gas which is exhausted from the first exhaust hole to a second intake hole of a second casing having a second pump chamber;   transferring the gas which is suctioned from the second intake hole inside the second casing to a second exhaust hole of the second casing while compressing the gas inside the pump chamber; and   discharging the gas from the second exhaust hole.   
     
     
         17 . The exhaust method according to  claim 16 , wherein the transferring gas from the first exhaust hole to the second intake hole is performed so as to increase the flow rate of the gas and to decrease the temperature of the gas. 
     
     
         18 . The exhaust method according to  claim 16 , wherein
 the transferring the gas inside the first casing having the first pump chamber is performed by a rotation of a pair of rotors which has a plurality of teeth and is supported by a pair of rotary shafts rotated is supported by the first casing, and   the transferring the gas inside the second casing having the second pump chamber is performed by a rotation of a pair of rotors which has a plurality of teeth and is supported by a pair of rotary shafts rotated is supported by the second casing.   
     
     
         19 . The exhaust method according to  claim 15 , wherein
 the first pump chamber has a plurality of pump chambers,   the second pump chamber has a plurality of pump chambers, and   in the transferring the gas from the first exhaust hole to the second intake hole, the gas is transferred from a pump chamber constituting the first pump chamber at the most downstream side in a gas transfer direction of the first roots pump to a pump chamber constituting the second pump chamber at the most upstream side in a gas transfer direction of the second roots pump.   
     
     
         20 . The exhaust method according to  claim 19 , wherein
 the pump chambers constituting the first pump chamber of the first roots pump are formed so that the volume becomes smaller as it goes toward the downstream side in the gas transfer direction, and   the pump chambers constituting the second pump chamber of the second roots pump are formed so that the volume becomes smaller as it goes toward the downstream side in the gas transfer direction and the volume of the pump chamber constituting the second pump chamber at the most upstream side in the gas transfer direction of the second roots pump becomes smaller than that of the pump chamber constituting the second pump chamber at the most downstream side in the gas transfer direction of the first roots pump.