Control valve arrangements for variable stroke pumps

A control valve arrangement for a variable-stroke positive displacement pump which includes a stroke-varying device operated by a servo pressure, said control valve arrangement comprising a body having a bore, a spool control element slidable in said bore, first and second inlets communicating with said bore, means for applying to said first inlet an operating pressure derived from the outlet pressure of said pump, means for connecting said second inlet to the outlet of said pump, said operating pressure urging said control element in a first direction, means biasing said control element in a second direction against said operating pressure, a first outlet for connecting said bore to a low pressure, a second outlet communicating with said bore, said control element being operable to derive said servo pressure at said second outlet from the pressures at said first inlet and said first outlet, movement of said control element in said first direction acting to vary the servo pressure at said second outlet in a sense to reduce the stroke of said pump, and means for reducing the pressure at said first inlet, said spool control element including means responsive to movement of said control element by more than a predetermined amount in said second direction for interconnecting said second inlet and said first outlet.