NO742760L

1473420 Fluid-pressure control circuits PEINER MASCHINEN UND SCHRAUBENWERKE AG 30 July 1974 [31 July 1973] 33652/74 Heading F1P In the circuit shown, Fig. 1, actuators 15, 16 are supplied by a reversible pump 1 and liquid is returned to or withdrawn from a reservoir 26 as required to compensate for the difference in volume between the chambers on opposite sides of the pistons. Assuming that the pump is acting to supply liquid to chambers 11, 12, through lines 4, 9, the return path from chambers 13, 14 is blocked by check-valves 45, 47. The resultant rise in pressure in the line 4 opens the pilot-controlled check-valve 47 through a pilot line 49. This allows liquid to return through a line 50 and a check-valve 51 to the pump, the excess flowing through a filter 34 to the reservoir. If the supply from the pump is reversed, pressure in a line 32 opens a pilotoperated check-valve 52 through a pilot line 44 so that the return from chambers 11, 12 can flow to the pump through lines 9, 4. The extra liquid required is drawn from the reservoir through a valve 2. Relief valves 6, 36 are provided. The valves 47, 52 are hydraulically locked by supplying pilot pressure to both sides of the operating piston through lines 48, 49 and 43, 44 respectively. Fig. 2 shows an embodiment in which liquid from chambers 11, 12 flows through a pilot-controlled checkvalve 27 and lines 29, 28, 17 directly to the chambers 13, 14 without going through the pump. Extra liquid is drawn from the reservoir as before. Return from chambers 13, 14 is as described with reference to Fig. 1.