a positive fluid displacement device with single piece double - ended pistons connected to a crankpin for circular motion . pistons are nested together to maintain all pistons in the same plane perpendicular to the axis of the crankshaft . cylinders are driven in a reciprocating fashion by the pistons and are held loosely in a cylinder carriage along its axis with radial sealing engagement therebetween . pliable members mount port plates within a housing such that there is no direct contact therebetween or with a two - layer manifold . a flat surface of the port plate is urged against the cylinder head by a pliable member which exerts a force on the center of the port plate . grooves in the first layer of the manifold are sealed by the second layer to form fluid passageways . the cylinder head is guided in housing grooves with a pliable member . a sealing lip is integral with a piston head .