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| Illustration 1 | g00532051 |
Schematic for the 824G pilot hydraulic system (1) Main control valve (2) Control valve for the lift cylinder (3) Implement control valve (tilt) (4) Implement control valve (tip) (5) Pilot control valve (6) Hydraulic control lever lock (7) Pressure reducing valve (8) Pilot/brake pump (9) On/off solenoid for the left tilt function (10) On/off solenoid for the right tilt function (11) On/off solenoid for raising the blade (12) On/off solenoid for the lower function (13) On/off solenoid for the forward tip function (14) On/off solenoid for the backward tip function (15) Fan drive pump (16) Implement pump (17) Hydraulic oil tank | |
The purpose of the pilot hydraulic system is to direct low pressure hydraulic oil to a particular implement control valve in main control valve (1). The 824G Wheel loader schematic is used here but the schematic for the 825G Soil compactor and the 826G Landfill Compactor are similar.
Note: Main control valve (1) can be made up of a singular implement control valve or a group of implement control valves. The number of control valves on the machine is equal to the number of implement cylinders.
The pilot hydraulic system is made up of four major parts.pilot/brake pump (8), the pilot control valve (5), hydraulic oil tank (17) and main control valve (1) .
Oil flows through hydraulic oil tank (17) to pilot/brake pump (8). Pilot/brake pump (8) is a gear pump which supplies hydraulic oil to the pilot hydraulic system.
From pilot/brake pump (8), the pilot oil flows through pressure reducing valve (7). Pressure reducing valve (7) maintains a maximum pilot system pressure of 3450 ± 200 kPa (500 ± 30 psi).
When an on/off solenoid valve within the pilot control valve receives an electronic signal from the ECM (electronic control module), the on/off solenoid valve will begin to move. This will allow pilot oil to flow from the on/off solenoid to the main control valve.
The pilot control valves have three positions. Two of the positions will provide pilot oil flow to an implement control valve while the third position prevents any oil flow. On/off solenoid valve (11) or (12) will allow pilot oil to flow to implement control valve (2), if the control lever is moved to the lift position or to the lower position.
While the control lever is in the HOLD position, pilot oil is prevented from flowing to the main control valve.
The hydraulic implement system can be disabled, if you press the switch for hydraulic control lever lock. The solenoid will not receive any electronic signal when the switch for hydraulic control lever lock is activated. ON/OFF valve (6) is shifted upward due to spring pressure. A check valve in the ON/OFF valve (6) prevents the flow of pilot oil.