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| Illustration 1 | g00869240 |
Section View of the Pilot Valve (Oil Manifold) (1) Shuttle valve (2) Port to the steering system (3) Passage (primary pilot pressure) (4) Supply port from the pilot/brake pump (5) Primary pressure reducing valve (6) Secondary pressure reducing valve (7) Passage to hydraulic oil tank (8) Proportional solenoid valve (TILT RIGHT) (9) Proportional solenoid valve (LOWER) (10) Port to the main control valve (LOWER) (11) Port to the main control valve (TILT RIGHT) (12) Passage (pilot pressure) (13) Port from the lift cylinder (dead engine lower) (14) Port to the lowering control valve (15) Passage (secondary pilot pressure) (16) Passage from the lift valve spool (17) Plug (18) Pilot on/off solenoid valve (19) Port to the main control valve (TILT LEFT) (20) Proportional solenoid valve (TILT LEFT) (21) Return port to the hydraulic oil tank (22) Proportional solenoid valve (RAISE) (23) Port to the main control valve (RAISE) (24) Plug | |
Pilot Valve
Pilot Operation
Oil enters the pilot valve (oil manifold) at port (4) from the pilot/brake pump. Primary pressure reducing valve (5) reduces the pressure of the pilot oil to 3450 ± 200 kPa (500 ± 30 psi). The oil then flows through passage (3). The pilot pressure from the primary reducing valve is greater than the pilot pressure from the secondary reducing valve.
Shuttle valve (1) senses the two reduced pressures. Shuttle valve (1) will shift. This will allow the pilot oil from the primary reducing valve to flow through passage (12). Passage (12) ports the oil to on/off solenoid valve (18).
Excess oil from pressure reducing valves (5) and (6) flows to port (21). The oil flows to the hydraulic tank.
Pilot oil that is used in the steering system is drawn from port (2) by way of passage (3) .
Reference: For more information about the pressure reducing valves, refer to the Service Manual module Systems Operation, "Pressure Reducing Valve" for the machine that is being serviced.
On/Off Solenoid Valve
Pilot on/off solenoid valve (19) controls the flow of pilot oil to the proportional solenoid valves. When the implement lockout switch is in the LOCKED position the pilot on/off solenoid valve is in the CLOSED position. When the implement lockout switch is in the UNLOCKED position the pilot on/off solenoid valve will be ready to be energized.
When the engine is not running and when all control levers are in the HOLD position, the pilot on/off solenoid valve is closed. No oil is allowed to flow to the proportional solenoid valves. The implement cylinders will not operate.
When the engine is running and the pilot on/off solenoid valve has been energized oil will flow through proportional solenoid valves (8), (9), (20), and (22). The flow of oil to the end caps on the main control valve will increase as the joystick control is moved from the HOLD position. The pilot oil that flows to the end cap of the main control valve moves the stem proportionally to the movement of the joystick control.
When the key start switch is moved to the ON position, the on/off solenoid valve will not be energized until the joystick control has initially been moved. When the joystick control is moved back to the HOLD position, the on/off solenoid valve is in the OFF position.
Dead Engine Lower
If the blade is in the RAISE position and the engine is not running the blade can be lowered. The secondary pilot oil allows an operator to lower the lift arms when the engine is stopped.
The oil pressure from the lift cylinder rod end enters the pilot valve at port (13). The oil is reduced to 2070 ± 200 kPa (300 ± 30 psi) by secondary reducing valve (6). Shuttle valve (1) senses differential pressure between passage (15) and passage (3). The shuttle valve will shift. This will allow the oil to flow into passage (12). The oil in the passage is held there until the on/off solenoid valve is energized.
When the key start switch is in the ON position and the joystick control is moved to the LOWER position, the blade will lower.
Lift Function
When the joystick control is moved to the RAISE position, oil will flow through port (24) to the lift valve spool in the main control valve.
As the lift valve spool moves, oil from the chamber at the LOWER end of the lift valve spool returns through port (10). The return oil then flows through proportional solenoid valve (9) and back to return port (21) .
When the joystick control is moved to the LOWER position, oil will flow to solenoid valve (9) through port (10) to the lift valve spool in the main control valve.
As the lift valve spool moves, oil from the chamber at the RAISE end of the lift valve spool in the main control valve returns through port (24). The return oil then flows through proportional solenoid valve (23) and back to return port (22) .
Tilt Function
When the joystick control is moved to the TILT LEFT position, oil will flow to solenoid valve (20) through port (19) to the tilt valve spool in the main control valve.
As the tilt valve spool moves, oil from the chamber at the TILT RIGHT end of the tilt valve spool returns through port (11). The return oil flows through proportional solenoid valve (8) to return port (21) .
When the joystick control is moved to the TILT RIGHT position oil will flow to solenoid valve (8) through port (11) to the tilt valve spool in the main control valve.
As the tilt valve spool moves, oil from the chamber at the TILT LEFT end of the tilt valve spool returns through port (19). The return oil flows through proportional solenoid valve (20) to return port (22) .
Tip Function
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| Illustration 2 | g00869385 |
Valve Section for the Tip Function | |
The 824H II Wheel Dozer is equipped with a extra valve section. The valve section is attached to the body of the pilot valve by three bolts. The valve section is equipped with two proportional solenoid valves. The valve section controls the tip functions.
Tip Back
Pilot oil will enter the valve section through passage (28 ). When the implement select switch on the joystick control is pressed and the joystick control is moved to the left, a signal is sent to the proportional solenoid valve for the tip back function. The pilot oil is sent through the solenoid valve to the port (27). The pilot oil will flow to the appropriate spools on the main control valve. The oil that was in the pilot line for the tip forward will flow back through port (30), through the solenoid valve, through port (21), and back to the hydraulic tank.
Tip Forward
Pilot oil will enter the valve section through passage (28 ). When the implement select switch on the joystick control is pressed and the joystick control is moved to the right, a signal is sent to the proportional solenoid valve for the tip forward. function. The pilot oil is sent through the solenoid valve to port (30). The pilot oil will flow to the appropriate spools on the main control valve. The oil that was in the pilot line for the tip back function will flow back through port (27), through the solenoid valve, and back to the hydraulic tank through port (21) .
Reference: For more information about the components of the pilot valve (oil manifold), refer to the Service Manual module System Operation, "Solenoid Valves (Implement)" for the machine that is being serviced.