Hydraulic motors and pumps

In a hydraulic motor or pump comprising a casing, a shaft, means journalling said shaft in said casing, an eccentric on said shaft, a bearing block within said casing and about said eccentric and having a bore permitting relative rotation between said bearing block and said eccentric, a plurality of hydraulic cylinders formed and grouped in said bearing block radially about said eccentric in a common plane normal to the axis of said shaft, a plunger slidable in each of said cylinders, said plunger having an outer end face, flat faces of abutments formed in said casing at its internal surface for engagement with said outer end faces of said plungers, respectively, means urging said plunger in the direction of said face of abutment of said casing during the operation of said motor or pump, and said bearing block having a port communicating between its bore and the interior of each of said cylinders, pressure liquid being admitted to the cylinders in turn one after another during the operation of said motor or pump, the improvement comprising a centrally disposed recess formed in said outer end surface of each said plunger in alignment with the axis of said plunger, a port formed in said plunger communicating said recess with said cylinder interior, said centrally disposed recess having an area almost equal to that of the pressure bearing surface of said plunger, a shoulder on each of said plungers to engage the cylinder wall at a limited length, restraining means formed between said casing and said bearing block for limiting the range within which said bearing block is allowed to rotate with respect to said casing, said restraining means including a number of laterally extending pins affixed to said casing and a number of generally semicircular cooperating recesses formed in the peripheral surface of said bearing block, said number of said pins and recesses being equal to the number of said hydraulic cylinders, said pins being engageable by said recesses such that during operation no more than two pins are in physical contact with their corresponding recesses, and said bearing block being carried about said eccentric such that the radially directed hydraulic forces exerted by the liquid acting on said block are always balanced with the liquid pressures within said cylinders during the operation of said motor or pump.