LINK A 4K7091 - Caterpillar

Illustration 1 g00981385
Hydraulic schematic for the steering system (1) Steering cylinder (2) Line relief and makeup valve for the head end of the steering cylinder (3) Line relief and makeup valve for the rod end of the steering cylinder (4) Steering neutralizer valve for a left turn (5) Steering neutralizer valve for a right turn (6) Spool (7) Secondary steering pump (8) Load sensing shuttle valve (9) Spool (10) STIC steering pilot valve (11) Spool (12) Implement and steering neutralizer valve (13) Check valve (14) Check valve (15) Pilot oil pressure reducing valve (16) Steering system pressure tap (17) Steering relief valve (18) Secondary steering diverter valve (19) Steering control valve (20) Hydraulic oil cooler (21) Line to the implement pilot circuit (22) Pilot system pressure tap (23) Check valve (24) Steering pump (25) Implement pump (26) Breaker relief valve (27) Selector and pressure control valve (28) Line to the parking brake oil pressure reducing valve (29) Pilot and braking pump (30) Hydraulic oil filters (31) Hydraulic tank (32) Line to the braking systemThe steering pilot circuit controls the movement of spool (6) in steering control valve (19) .With the engine running, oil is drawn from hydraulic tank (31) by pilot and braking pump (29). Pilot and braking pump (29) supplies pilot oil through check valve (23) to pilot oil pressure reducing valve (15) .Pilot oil pressure reducing valve (15) reduces the pilot and braking pump oil to a reduced pressure.The pilot oil, now at a reduced pressure flows through check valve (14) to selector and pressure control valve (27) .As long as the pilot and braking pump is supplying pilot oil to the pilot system, the selector and pressure control valve will block the flow of alternate oil into the pilot system.If the pilot and braking pump fails, or pilot oil is not available, then selector and pressure control valve (27) will allow alternate pilot oil to flow into the pilot system from the lift cylinders. If oil is not available from the lift cylinders, then selector and pressure control valve (27) will allow alternate pilot oil to flow into the pilot system from steering control valve (19) .Oil from the selector and pressure control valve flows to implement and steering neutralizer valve (12). The implement and steering neutralizer valve prevents pilot oil from flowing to STIC steering pilot valve (10) and the implement pilot circuit when the operator station door is open.When the operator station door is closed, pilot oil from the implement and steering neutralizer valve flows to STIC steering pilot valve (10). When the STIC steering control is moved to either direction, STIC steering pilot valve (10) routes the pilot oil through steering neutralizer valve (4) for a left turn or steering neutralizer valve (5) for a right turn.Pilot oil flows from the steering neutralizer valve to spool (6) in steering control valve (19). The pilot oil pressure causes spool (6) to move. When the spool moves, it allows high pressure oil from the steering