CIRCLE AS 2772120 - Caterpillar

Illustration 1 g00851877
Steering Control Valve in the Neutral Position
(1) Pressure regulating valve. (2) Inlet from pump. (3) Outlet to hydraulic tank. (4) Pilot port. (5) Spool. (6) Cylinder crossover relief valve. (7) Shuttle valve. (8) Springs. (9) Retainer. (10) Pilot port. (11) Return passage. (12) Port for right turn. (13) Oil supply passage. (14) Port for left turn. (15) Return passage. (16) Relief valve.
Note: This valve does not include secondary steering. Secondary steering will be covered later.While the engine is running, oil flows from the steering hydraulic tank to the steering pump. The oil flows to the steering control valve through inlet port (2).The flow of pilot oil to the spool is stopped when the STIC is moved to the center position. The flow of pilot oil is also stopped if a neutralizer valve is activated. When no pilot oil is acting on either end of the spool, centering springs (8) return the spool to the neutral position. As the spool returns to neutral, the pilot oil that had been acting on an end of the spool is forced across an orifice and back to the tank.Oil flow to port (2) is blocked at passage (13), when the spool is in the center position. Oil in the steering cylinder lines is also blocked in ports (12) and (14). The load for the cylinder is sensed by shuttle valve (7). The shuttle valve routes the signal back to the steering pump. This will cause the pump to destroke. During destroke, the pressure compensator will supply only enough oil for leakage.Note: If you are making a turn and if you release the lever, the machine will continue to turn. Therefore, releasing the lever will not return the machine to the straight forward travel.If the fan drive pump fails, pilot oil in the steering pilot system will flow from a port near pressure reducing valve (1) and to the pilot control valve. The pressure reducing valve maintains pilot pressure at 1650 150 kPa (239 22 psi).Left Turn Position
When the operator moves the control lever to turn left, pilot oil will flow from the pilot control valve, through the right neutralizer valve, and through dual check valves into port (10). The pilot oil is forced on retainer (9). The oil pressure pushes the springs (8) and the spool moves to the left.Oil in passage (13) can now flow past the spool into port (14). The oil in port (14) flows to the head end of the right side steering cylinder and the rod end of the left side cylinder.Oil from the rod end of the right side steering cylinder and the head end of the left side cylinder flows into port (12). The oil flows from port (12) back to the hydraulic tank.The machine articulates left and the machine begins making a left turn. When the control lever is released, pilot oil flow to port (10) stops. Oil pressure on the retainer (9) must be removed before the spool