PURPOSE: To set precompressing pressure to the average value of working pressure without causing any problems of separation phenomenon of vanes.
CONSTITUTION: A cylinder 29 is provided with a path 50 for introducing pressure reaching precompressing process α in a pump chamber 46 into back pressure chambers 43a in respective vanes 44 constituting the pump chamber 46. Thus, the pressure getting higher than discharge pressure (back pressure) in the pump chamber 46 during the precompression process α when used under the condition of low working pressure is introduced through the path 50 into the back-pressure chambers 43a of the vanes 44 constituting the pump chamber 46 in the precompression process α to maintain always the pressure balance relation to the pump chamber 46 so that even if the pressure in the pump chamber 46 is increases the tip of the vane 44 is not separated from the inner peripheral surface of the cylinder 29.
HORIUCHI YASUHIRO
YOKOYAMA SO
