Gear pump

摘要

A two-stage gear pump has a pump section. The pump section has an internal space (51,52) that is located adjacent to a driven gear and about a cylindrical surface of the driven shaft. A discharge section of a first gear train is connected to a suction section of a second gear train with a communication passage (43). The internal space is connected to the communication passage with a pressure introduction passage (67,72). The pressure of the communication passage is introduced to the internal space by the pressure introduction passage, so that the pressure atmosphere of the internal space is an intermediate pressure atmosphere of the suction pressure and the discharge pressure of the pump section.