Pressure compensated pump

A pressure compensated piston pump comprising a casing, a barrel rotatably mounted in the casing, a plurality of bores in the barrel, a piston mounted for reciprocation in each bore, a shoe mounted on the end of each piston, a hanger pivotally mounted in the casing, a thrust plate attached to the hanger, means for connecting the pistons to the thrust plate wherein the shoes slide over the thrust plate when the barrel is rotated and the pistons reciprocate in their bores when the hanger is on-stroke, the hanger is movable between an off-stroke position in which the pump displacement is a minimum and a full on-stroke position in which the pump displacement is a maximum, means for biasing the hanger to the full on-stroke position, a stroking piston which receives fluid and moves the hanger toward the off-stroke position when the pressure of the discharge fluid exceeds a predetermined maximum, a pressure compensator valve including a spool bore, a spool movable in the bore, means for setting the maximum discharge pressure of the pump, means for sensing the discharge pressure of the pump, a first control port, a first fluid passage connecting said first control port to the stroking piston, a second control port, a second fluid passage connecting said second control port to drain, a control land formed on said spool which cooperates with said first and second control ports to form first and second variable orifices which control the flow of fluid to and from the first and second control ports, first means for connecting discharge pressure fluid to one side of the control land, a second means for connecting low pressure fluid to the other side of the control land, and the spool is movable alternatively between a first position in which said control land blocks said first and second control ports, a second position in which said first and second control ports are open to the second connecting means and drain, and a third position in which the first and second control ports are open to the first connecting means that discharge pressure is supplied to the first control port to move the stroking piston towards the off-stroke position and simultaneously discharge pressure fluid is supplied to drain through the second control port.