GB1283347A - A pumping system - Google Patents

Abstract

1283347 Hydraulic motor control circuit DOWTY MINING EQUIPMENT Ltd 31 Oct 1969 [21 Nov 1968] 55321/68 Heading F1P A hydraulic motor (not shown) requiring a sudden high flow input is supplied through a service line 6 by a pump 1 provided with snap-acting unloaden means 3 having a first position shown in which pump delivery is connected to line 6 and having a second position in which pump delivery is cut-off from line 6 and unloaded to a resevoir 7; the unloader means 3 being moved to its second unloading position by a pressure sensing device 4 responsive to a predetermined high-pressure in line 6 and being moved to its first position when pressure in line 6 is below a predetermined intermediate value below which value the service line 6 is also connected through a pilot valve 9 to an accummulator 8 which latter is isolated from line 6 at high-pressures therein; line pressures between the intermediate and high levels having no effect on the unloader position and accumulator connection. As shown the pilot valve 9 is spring- biased to its closed position and is opened by pressure in a branch line 11 of the pump delivery line 2. In a modification Fig.3 (not shown) the pilot valve is biased to its open position and is closed by pressure in a branch line of the service line. In further modification the unloader device comprise a snap-action electric switch controlling the motor driving the pump and responsive to pressure in the service line. The unloader may also comprise a clutch between the pump and its driving motor operated by means responsive to service line pressure. Again the unloader device may comprise means to over-ridingly hold the pump inlet valve open in response to service line pressure.