CYLINDER AS-HYDRAULIC 2690382 - Caterpillar

Illustration 1 g00582851
Hydraulic Schematic for the Pilot System (1) Steering control valve (2) Valve spool (3) Check valves for the steering neutralizer valves (4) Left steering neutralizer valve (5) Right steering neutralizer valve (6) Steering pump (7) Steering pilot valve (8) Pressure switch for the steering system "STRG OIL PRES" (9) Steering pump (10) Selector and pressure control valve (11) Selector and pressure control valve (12) Hydraulic tank for the steering and brake systems (13) Unloader spool (14) Secondary steering diverter valveThe steering pilot system controls the movement of valve spool (2) in steering control valve (1). The pilot oil also directs the secondary steering oil flow back to the hydraulic tank.While the engine is running, oil is drawn from hydraulic tank (12) by steering pumps (6) and (9). Steering pump (9) supplies a constant source of pressure oil to selector and pressure control valve (11). Selector and pressure control valve (11) reduces the pump pressure oil to pilot pressure oil. Pilot oil flows from selector and pressure control valve (11) through an orifice to pressure switch (8) for the steering system. The orifice reduces the amount of false pressure indications which can be caused by pressure spikes in the system.Pressure switch (8) is monitored by the Vital Information Management System (VIMS). If the pilot oil pressure drops off below 700 103 kPa (100 15 psi), the VIMS will display a warning category 3.The pilot oil then flows to secondary steering diverter valve (14). The pilot oil acts on unloader spool (13) in the diverter valve. This causes the secondary oil flow to be directed back to hydraulic tank (12) for the steering and brake systems.If the flow of pilot oil to the unloader spool stops, the unloader spool will shift. This causes the secondary oil flow to be directed to the primary steering system and the pilot system.The steering pumps supply pressure oil to selector and pressure control valve (10). Selector and pressure control valve (10) reduces the pressure oil to pilot pressure oil. The pilot oil then flows to steering pilot valve (7). For a right turn, the pilot oil flows to right steering neutralizer valve (5). Then, the pilot oil flows to the left end of valve spool (2) in steering control valve (1). This causes the spool to move to the right. For a left turn, the pilot oil flows to left steering neutralizer valve (4). Then, the pilot oil flows to the right end of valve spool (2) in the steering control valve. This causes the spool to move to the left.Steering control valve spool (2) directs the high pressure oil to the steering cylinders. This causes the machine to turn.The return pilot oil flows to hydraulic tank (12) for the steering and brake systems.Note: If the engine is stopped, steering can only be performed when the machine is moving.For additional information on the VIMS, refer to Service Manual, SENR6059, "Vital Information Management System (VIMS)".