PURPOSE: To prevent the occurrence of abnormal wear, by a method wherein a throttle ring, attached between a rotary shaft and a side plate, is made of a material having an expansion coefficient smaller than that of the rotary shaft, and back pressure of a vane is reduced by decreasing a clearance between the throttle ring and the rotary shaft during high-speed rotation.

CONSTITUTION: With rotation of a rotor 2, operating gas is introduced into a pump chamber 7 through a suction passage 9, the gas is pressurized to be discharged to the outside, oil 12 in an oil sump 11 connected to a discharge passage 10 is introduced to the base of a vane support hole 2a through a clearance (c) between a throttle ring 13, attached between a rotary shaft 1 and a side plate 6, and the rotary shaft 1, and a back pressure is applied to vanes 3, 3... to press those vanes against the inner peripheral surface of a cam ring 4. In this case, since the throttle ring 13 is made of a material having an expansion coefficient smaller than that of the rotary shaft 1, as the discharge pressure and discharge temperature increase, the clearance (c) decreases and the back pressure of the vane also reduces, resulting in prevention of abnormal wear of the vanes 3, 3... during steady operation.