Abstract: A hydraulic piston and cylinder machine includes a plurality of pistons and cylinders, a ring of ports for alternatively supplying fluid into, and for allowing the fluid to be discharged from each cylinder, and a cam having a plurality of lobes to control the displacement of the pistons in a cylinder block with respect to the progression of the cylinder block along the direction of the cam or vice versa. Each of the pistons traverses each of the cam lobes during a full rotation of the machine to undergo a number of piston strokes equal to the number of lobes. A control valve is adjustable to route working fluid discharged through at least one of the fluid discharge ports of the machine to the exhaust fluid outlet of the machine during each full rotation of the machine via an isolated pressure zone of the machine.