GB1426699A - Hydraulic circuit including a priority system for series connected hydraulic systems - Google Patents

Abstract

1426699 Power steering systems CATERPILLAR TRACTOR CO 24 April 1974 [10 May 1973] 17967/74 Heading B7H In an hydraulic circuit having serially arranged steering and implement valves 82 and 148 a valve 190 between these valves is operative to maintain a pressure differential between the steering and implement circuits sufficient to ensure proper working of the steering circuit at all times. Valve 82 has inlet and work parts 89, 90, 92 controlled by spool 116 and includes a further spool with orifices 109 which opens the inlet to a discharge port 98 and line 144 as set out in Specification 1,051,690. Line 144 connects the inlet 146 of the open centre valve 148 and a pressure relief valve 180. Valve 148 has work parts 154, 156 controlled by valve 172 and a spool 152. Valve 190 is connected by a part 206 in a chamber 208 to the pump pressure line 78 and has inlet and outlet parts 198, 200, controlled by a spool 220 apertured at 228, 230, connected to lines 144, 176. The spool is spring loaded at 222 and is moved against the springs by pressure in chamber 208. In an example the steering valve pressure is limited to a predetermined value of 2750 p.s.i., relief valve 180 is set to open at 2040 p.s.i. and valve 190 is set to start opening at 2200 p.s.i. When the engine is operating at high idle with the steering circuit at relief pressure of 2750 p.s.i., valve 190 opens sufficiently to limit pressure in the implement circuit to 610 p.s.i.