Variable pressure sensitive pump

Claim 1

A hydraulic pump of a type having a housing and havIng an inlet end and an outlet end, a barrel within said housing having a central, longitudinally extending axis, a plurality of cylinders within said barrel forming pumping chambers, said chambers being annularly arranged with the longitudinal axes thereof being parallel to and equally spaced from the axis of said barrel, a piston reciprocably received in each of said chambers, rotatable cam means axially spaced from said barrel and engaging and reciprocating said pistons in suction and discharge strokes, a fluid reservoir, each of said pumping chambers having an outlet passageway through which fluid is dischargeable through the outlet end of the housing during a pressure stroke, a second passageway for each chamber having a first end terminating intermediate said outlet passageway and a second end terminating at said reservoir through which fluid in said reservoir flows in a first direction to the outlet passageway during a suction stroke of said pistons and through which fluid in said outlet passageway can return to said reservoir in a second direction during the pressure stroke of said pistons, means for each of said chambers for obtaining a variable output from said chambers by varying the amount of fluid returned to said reservoir during the pressure strokes of said pistons, said means comprising a third passageway having a first end leading to a control pressure and a second end communicating with said second passageway intermediate the length thereof, controller means disposed in said third passageway between said control pressure and said second passageway and moveable responsive to said control pressure, closure means in said second passageway operably connected to said controller means for opening and closing said second passageway between said outlet passageway and said reservoir, removable plate means over the output end of said housing containing first and second manifold means, said first manifold means combining the outputs of selected pumping chambers into plural groups and communicating said groups respectively with separate outlets leading to separate loads, said second manifold means directing separate control pressures respectively to the third passageways of said groups of selected pumping chambers.