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| Illustration 1 | g00297153 |
Section View of the Pilot Valve (Oil Manifold) (1) Shuttle valve. (2) Signal cavity (primary pilot pressure). (3) Primary pressure reducing valve. (4) Secondary pressure reducing valve. (5) Supply port from the lift cylinder. (6) Return port from the ride control solenoid valve. (7) Passage to the hydraulic oil tank. (8) Supply port to the pilot control valve. (9) Supply port from the pilot/brake pump. (10) Signal cavity (secondary pilot pressure). (11) Signal cavity (pilot pressure). (12) Port to the lift valve spool. (13) Supply port to the ride control solenoid valve. (14) Return port to the hydraulic oil tank. (15) Float valve. (16) Vent port from the makeup valve. | |
The pilot valve (oil manifold) is part of the valve group that is located in the front end frame. The pilot valve (oil manifold) controls the flow of pilot oil to the pilot control valve.
Oil flows into the pilot valve (oil manifold) at port (9) from the pilot/brake pump. Primary pressure reducing valve (3) reduces the pressure of the pilot oil to 2600 ± 200 kPa (375 ± 30 psi). The pilot oil then flows through passage (2) to shuttle valve (1) .
Secondary pressure reducing valve (4) is used to supply pilot oil when the engine is stopped. The secondary pilot oil allows the lift arms to be lowered when the engine is stopped.
Secondary pressure reducing valve (4) receives high pressure oil from the lift cylinder through port (5). A check valve in the ride control diverter valve allows the oil to flow from the end of the lift cylinder with higher pressure.
The pressure of the oil is reduced to 2070 ± 200 kPa (300 ± 30 psi) by secondary pressure reducing valve (4). The pilot oil then flows through passage (10) to shuttle valve (1) .
Shuttle valve (1) senses the two reduced pressures. Shuttle valve (1) then allows the oil from the source of higher pressure to flow to the pilot control valve through supply port (8). Pilot pressure oil for the ride control solenoid valve flows through passage (11) to port (13) .
Excess oil from pressure reducing valves (3) and (4) flows through passage (7) to port (14). The oil then returns to the hydraulic oil tank.
If the lift control lever is detented in the LOWER position, the lift arms will be in the FLOAT position. The pressure in the LOWER end of the lift valve spool of the main control valve will increase to pilot system pressure.
The increase in pressure will be sensed in port (12). Float valve (15) opens in order to vent oil from a makeup valve in the main control valve. The oil flows through port (16) to tank return port (14) .
Oil from both ends of the lift cylinders can flow to the hydraulic oil tank. This allows the bucket to move up and down with the contour of the ground as the machine travels.