Abstract: A tandem pump apparatus having a first hydraulic pump for supplying operating fluid to a first actuator and a second hydraulic pump for supplying operating fluid to a second actuator in cooperation with each other is disclosed. Each hydraulic pump is provided with a flow rate control valve for refluxing a surplus of flow discharged from the pump to a suction side of the pump through a relief passage. A connecting passage connects the first relief passage downstream from the first flow rate control valve and the second relief passage downstream from the second flow rate control valve. A check valve is provided in the connecting passage for allowing operating fluid to flow from one of the relief passages that has a relatively great reflux flow rate to the other relief passage having a relatively small reflux flow rate, thereby ensuring sufficient supercharge into the two pump to achieve sufficient restraint of cavitation.

Abstract: A tandem pump apparatus is featured having a main suction passage connected to a fluid source. The main suction passage branches into first and second suction passages which, in turn, feed into first and second pumps. Each pump discharges a portion of the fluid to a return passage that is fluidly connected to the suction port of each respective pump. In each return passage, a return control valve is disposed to control the amount of fluid returned to the suction port. The tandem pump featured in this invention exhibits increased efficiency and decreased noise.

Abstract: When one chamber of vane pump is located at an end of a discharge process and is compressed at maximum, pressure in the chamber is higher than the discharge pressure of the pump. Vanes are supported in slits of a rotor. A passage connecting the one chamber and inner sides of the vanes in the slits supplies pressure to push the vanes onto an inner surface of a cam-ring of the pump.

Abstract: A fluid pressure driving system for a vehicle includes a reservoir tank in which an amount of fluid is stored, a variable capacity oil pump sucking the fluid from the reservoir tank and discharging the resultant fluid, a control device for adjusting a quantity of the fluid discharged from the variable oil pump, and a distributor valve having an inlet port for receiving the fluid from the variable capacity oil pump. The distributor valve discharges a fixed amount of the fluid and the remaining amount of the fluid from a first outlet port thereof and a second outlet port thereof, respectively. A first passage connects the first outlet port of the distributor valve and the reservoir tank. A second passage connects the second outlet port of the distributor valve and the reservoir tank. A power steering device is associated with a steering wheel and disposed in the first passage. A hydraulic motor is disposed in the second passage, and a cooling fan is mounted rotatably on the hydraulic motor.