Patent ID: 8662869
Filing Date: 2014-03-04
Classification: F01C,F04C

Abstract:
1. A multi-stage dry pump comprising: a plurality of pump chambers each including a cylinder and a rotor housed in the cylinder; a first rotor shaft that is a rotation shaft of the rotors; a fixed bearing that rotatably supports the first rotor shaft and restricts a movement thereof along an axis direction of the first rotor shaft; and a free bearing that rotatably supports the first rotor shaft and permits a movement thereof along the axis direction of the first rotor shaft, wherein: the plurality of pump chambers is disposed between the fixed bearing and the free bearing; a first pump chamber of the plurality of pump chambers which has a lower pressure and on the aspiration side is placed in proximity to the fixed bearing; and a gap in the axis direction between the rotor and the cylinder in a pump chamber which has a maximum compression work amount among the plurality of pump chambers is larger than a gap in the axis direction of the rotor and the cylinder in the other pump chambers of the plurality of pump chambers.