SE7409792L

1473123 Fluid-pressure control circuits PEINER MASCHINEN UND SCHRAUBENWERKE A G 31 July 1974 [31 July 1973] 33870/74 Heading F1P A pair of actuators 15, 16, Fig. 1, are extended and retracted by a reversible pump 1 and the difference in volumn between the chambers on opposite sides of the pistons is compensated for by returning excess liquid to a reservoir 26 or switching extra liquid therefrom. If the pump is driven to supply liquid to the chambers 11, 12, return flow from chambers 13, 14 is blocked by a pilot-operated check-valve 19 until pressure in the supply line 4 rises to a value high enough to displace a piston 20 through a pilot line 21, so that the valve 19 is opened. Liquid now returns through lines 17, 32, excess returning to the reservoir through a pilot operated check-valve 36, which can open when a pilot line 31 is connected to the reservoir when the piston 20 opens valve 19. If the pump is reversed, pressure in a pilot line 44 opens a check-valve 45 so that liquid from chambers 11, 12 is returned to the pump through lines 9, 4. Extra liquid is drawn from the reservoir through a valve 2. Valves 19, 45 are hydraulically locked against reverse rotation of the pump by pilot lines which lead to both sides of the operating pistons. In the embodiment shown in Fig. 2 liquid from the chambers 11, 12 is returned directly to chambers 13, 14, through lines 29, 28 and pilotcontrolled check-valve 27, without passing through the pump.