Abstract: In a tandem type gear pump, the housing body has an inner middle partition wall portion integral with the body and having bearing means. The housing body is formed at the opposite axial end faces thereof with a pair of recesses each shaped like a pair of glasses, with a pair of covers being fixed to the axial end faces of the body to close the recesses. A pair of gear pump units are set in the recesses so as to be rotatable by the bearing means in synchronism with each other. The housing is provided with inlet and outlet port means in communication with the gear pump units.

Abstract: A bent axis type axial piston pump or motor wherein the cylinder block is rotatable in synchronizm with the torque plate about an axis inclined relative to the axis of rotation of the torque plate. The shaft of the torque plate passes through the inclined cylinder block without mutual mechanical interference and is supported by bearings at the opposite sides of the casing. The torque plate and the cylinder block are connected by a mechanism which ensures exact synchronization of rotation of the two members. A static pressure balance is established between the working fluid acting on the opposite sides of the torque plate, the cylinder block and the pistons, respectively. The angle of inclination of the cylinder block with respect to the shaft can be changed thereby to change the capacity of the pump or motor. The pump or motor of this invention may be provided in a tandem type.

Abstract: A gear pump or motor comprises a pair of gears intermeshing with each other, a case body accommodating the pair of gears, and a hard layer formed on an inner surface of the case body. The hard layer is made of a material to be as hard as not to be cut by tooth tips of the pair of gears. The hard layer may be a ceramic coating or a composite coating layer which performs a grinding like operation on the tooth tips.