RACE-BEARING 2158201 - Caterpillar

Illustration 1 g00270416
Pilot Valve for a machine that is equipped with wheel steering (1) Actuator. (2) Input shaft. (3) Plunger. (4) Spool. (5) Spring. (6) Metering spring. (7) Tank port. (8) Damping orifice. (9) Work port. (10) Damping chamber. (11) Pump inlet port. (A) Actuator assembly. (B) Valve section.Note: The internal components of the steering pilot valve are not serviceable.The steering pilot valve consists of actuator assembly (A) and valve section (B). These two sections work together in order to send oil to the steering control valve. Oil only flows through the steering pilot valve when the steering wheel is turned.As the steering wheel is turned, input shaft (2) turns. The turning of the input shaft causes actuator (1) to push down on plunger (3). This causes spool (4) to shift downward against effort spring (5). When the spool has shifted far enough, oil is allowed to flow from pump port (11) to the respective outlet port. Oil also flows through damping orifice (8) into damping chamber (10). Pressure at the outlet port is sensed in the damping chamber. This compresses metering spring (6). The metering spring is used to provide a smooth pressure increase at the outlet port as the spool is shifted.The steering pilot valve uses mechanical feedback to turn off the valve. The valve is turned off by returning the spool to the NEUTRAL position. If the steering wheel is turned to the left and the steering wheel is held in place, the machine will turn to the left. When the machine reaches the LEFT TURN position or the RIGHT TURN position that is indicated by the steering wheel, the valve is shut off. This happens as the input shaft rotates back to the NEUTRAL position.Note: The steering pilot valve will not provide manual steering when the engine is stopped and the machine is not moving. Steering with a stopped engine can be done only when the secondary steering system is installed and the machine is moving.Note: Secondary steering is an optional attachment that is available on the 834G Wheel Tractor only. Secondary steering is not available on the 836G Landfill Compactor.