CYL GP-LINES & 4800290 - Caterpillar

Illustration 1 g00976222
(1) Left steering cylinder (2) Right steering cylinder (3) Servo cylinder (4) Check and relief valve for the steering cylinders (5) Steering control valve (6) Centering spring (7) Strainer (8) Flow control valve (9) Pressure reducing valve (10) Steering control valve spool (11) Orifice (12) Pilot relief valve (13) Steering pump (14) Hydraulic tank (15) Steering metering pump (16) Check valve for the steering metering pumpHOLD Position
When the steering wheel is stationary there is no servo pilot oil flow against either end of steering control valve spool (10). Centering spring (6) will keep steering control valve spool (10) in the HOLD position. When the steering control valve spool is in the HOLD position, the oil flow from steering pump section (13) is stopped. The pressure increases in the line behind the steering control valve spool. This pressure increase moves flow control valve (8) which allows oil to flow back to the hydraulic tank. In the HOLD position, steering control valve spool (10) also blocks the oil to steering cylinders (1) and (2). This holds the machine in position. A small amount of oil flows through the charging slots in flow control valve (8). This gives pressure to both sides of steering cylinders (1) and (2). This pressure adds stability against outside forces that try to turn the machine. Also, this pressure shortens the time that is needed for a turn to begin.LEFT TURN Position
When the steering wheel is turned to the left, pilot oil is sent through check and relief valve (4) for the steering cylinders to the top of steering control valve spool (10). The oil pressure overcomes centering spring (6). This moves steering control valve spool (10) downward to the LEFT TURN position. Oil flows through internal strainer (7). Then, the oil flows through orifice (11) to the bottom of flow control valve (8). The flow control valve is controlled by pilot relief valve (12) and the load pressure. Flow control valve (8) now blocks oil from returning to the hydraulic tank. This allows the oil from steering pump (13) to flow through steering control valve spool (10) to head end of right steering cylinder (2) and also to the rod end of left steering cylinder (1). This pressure oil causes the steering cylinders to move and the machine turns to the left. The return oil from the steering cylinders passes back through steering control valve spool (10) and to the hydraulic tank.If an outside force keeps the machine from turning or a steering stop is contacted, the pressure in the cylinders will increase. This pressure increase is also felt against the right side of the flow control valve. This causes the flow control valve to shift downward allowing the oil to flow back to the hydraulic tank. If the pressure rises above the pilot relief valve setting of 13500 170 kPa (1958 25 psi), the relief valve will open allowing oil to flow back to the hydraulic tank.RIGHT TURN Position
The operation of