Rotary vacuum pump, vacuum device, and pump connection structure

1. A rotary vacuum pump comprising:

a pump casing having an intake port flange to be fixed to a device for evacuation, said intake port flange having a first through-hole and a thickness,

a rotor situated in the pump casing for rotation, and having a rotating side evacuating device,

a fixing side evacuating device disposed in the pump casing for evacuation together with the rotating side evacuating device,

a first bolt inserted into the first through-hole, said first bolt having a diameter less than that of the first through-hole, and

a first gap forming device for forming a gap between the bolt and the through-hole so that the pump casing is fixed to the device for evacuation by the first bolt and the first gap forming device,

wherein said first gap forming device is a bush inserted between the first bolt and the first through-hole and including a bush part and a flange part integrally formed together, said bush part having a height less than the thickness of the intake part flange and being made of iron or stainless steel.

2. A rotary vacuum pump according to claim 1 , wherein said bush forms the gap having a length in the rotor rotation direction larger than a length in a diameter direction of the intake port flange.

3. A rotary vacuum pump according to claim 1 , wherein said bush is fixed to the first through-hole.

4. A rotary vacuum pump according to claim 1 , wherein said bush is integrated with a washer for the first bolt.

5. A rotary vacuum pump according to claim 1 , wherein said first gap forming device includes a large-diameter portion situated on a shaft of the first bolt adjacent to a bolt head of the first bolt and having an outer diameter substantially same as an inner diameter of the first through-hole.

6. A vacuum device comprising a vacuum chamber, the rotary vacuum pump according to claim 1 and fixed to the vacuum chamber, a pump supporting part fixed to an end surface of the rotary vacuum pump, a second through-hole formed in the pump supporting part for inserting a second bolt and having a diameter larger than that of the second bolt, and a second gap forming device disposed in the second through-hole for forming a gap between the second bolt and the second through-hole.

7. A pump connection structure for connecting first and second flange members for a rotary vacuum pump, comprising:

a bolt for connecting the first and second flange members,

a through-hole formed in one of the first and second flange members for inserting the bolt and having a diameter larger than that of the bolt, and

a gap forming device disposed in the through-hole for forming a gap between the bolt and the through-hole,

wherein said gap forming device is a bush inserted between the bolt and the through-hole, and including a bush part and a flange part at one side of the bush part, said bush part having a height less than a thickness of the first or second flange member where the through-hole is formed and being made of iron or stainless steel.

8. A pump connection structure according to claim 7 , wherein said first flange member is an intake port flange for the rotary vacuum pump which exhausts gas by rotating a rotor relative to a stator, and said second flange member is a member to which said rotary vacuum pump is connected.

9. A pump connection structure according to claim 7 , wherein said first flange member is a connection flange for a first piping member, and said second flange member is a connection flange of a second piping member for the rotary vacuum pump.

10. A pump connection structure according to claim 7 , wherein said bush forms the gap having a length in a rotational direction of a rotor of the rotary vacuum pump larger than a length in a diameter direction of the intake port flange.

11. A pump connection structure according to claim 7 , wherein said bush is fixed to the through-hole.

12. A pump connection structure according to claim 9 , wherein said bush is integrated with a washer for the bolt.

13. A pump connection structure according to claim 7 , wherein said gap forming device includes a large-diameter portion situated on a shaft of the bolt adjacent to a bolt head of the bolt and having an outer diameter substantially same as an inner diameter of the through-hole.

14. A pump connection structure according to claim 7 , wherein said bush part includes at least one annular projecting portion projecting radially outwardly therefrom, or annular dent.