The load sensing signal system is composed of the following components:
- Implement control valve
- Accumulator (pilot oil)
- Steering metering pump
- Bogie control valve
- Pressure reducing valve (maximum signal pressure)
- Pressure reducing valve (steering signal pressure)
- Implement pump
- Solenoid valve (cold start)
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| Illustration 1 | g00799747 |
Load Sensing Signal System for 574 1FM411-UP Forwarder (1) Implement control valve (2) Pressure reducing valve (steering signal) (3) Priority valve (4) Steering metering pump (5) Resolver (6) Bogie control valve (7) Resolver (8) Pressure reducing valve (maximum signal) (9) Accumulator (10) Resolver (11) Implement pump (12) Solenoid valve (cold start) (13) Hydraulic oil tank (A) Signal pressure from brake accumulator charging valve (AA) Pressure tap (signal pressure) (BB) Pressure tap (implement pump pressure) | |
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| Illustration 2 | g00800126 |
Load Sensing Signal System for 554 Forwarder (1) Implement control valve (2) Pressure reducing valve (steering signal) (3) Priority valve (4) Steering metering pump (5) Resolver (6) Bogie control valve (7) Resolver (8) Pressure reducing valve (maximum signal) (9) Accumulator (11) Implement pump (12) Solenoid valve (cold start) (13) Hydraulic oil tank (A) Signal pressure from brake accumulator charging valve (AA) Pressure tap (signal pressure) (BB) Pressure tap (implement pump pressure) | |
When the operator turns the engine start switch, electrical current flows to solenoid valve (12). This activates solenoid valve (12). Solenoid valve (12) blocks signal pressure oil from the brake accumulator charging valve. This assists the starting of the engine by decreasing the load on the engine.
When the operator releases the key, current is cutoff to solenoid valve (12) and signal pressure oil flows from the brake accumulator charging valve through line (A) to the implement pump. The signal upstrokes the pump in order to charge the brake accumulators.
When the engine starts, there is no pressure in the load sensing signal system. Implement pump (11) is stroked to maximum output. As the implement pump begins to turn, the pressure in the signal system increases. Accumulator (9) is charged. The pump strokes to low pressure standby until a function is activated.
Accumulator (9) is fully charged by the pilot oil of the signal system. When the engine is stopped, accumulator (9) will stay charged for a period of time. If the boom is in the raised position and the engine stops, the pressurized oil in accumulator (9) will allow the boom to be lowered.
Note: The starter key switch must be in the ON position in order to lower the boom when the engine is stopped.
Note: On the 554 Forwarder and the 574 Forwarder, use pressure tap (AA) in order to measure the signal pressure. The pressure tap is located on the "PL" port at the end of implement control valve (1) .
When the operator uses the steering wheel, steering metering pump (4) sends a load signal to pressure reducing valve (2) and priority valve (3). The load signal in the priority valve controls the flow of pressure oil to the steering metering pump.
The pressure reducing valve limits the maximum pressure of the load signal from the steering metering pump. Therefore, the pressure reducing valve limits the maximum oil flow and pressure from the implement pump to the steering metering pump.
Note: The pressure setting of pressure reducing valve (2) is less than the pressure setting of pressure reducing valve (8) .
The load signal flows from pressure reducing valve (2) to the implement control valve. If a function that is controlled by the implement control valve is activated, the function will send another load signal into the load sensing system.
A resolver network in the implement control valve allows the highest signal pressure in the implement control valve to flow to resolver (5). The resolver allows the higher signal pressure from the implement control valve or bogie control valve (6) to be sensed by the pump.
The load signal from the implement control valve or the bogie control valve then flows to pressure reducing valve (8). The pressure reducing valve limits the maximum pressure of the load signal from the hydraulic system to the implement pump. Therefore, the pressure reducing valve limits the high pressure of the implement pump for the hydraulic system.
Note: The pressure setting of pressure reducing valve (8) is below the pressure setting of the pressure cutoff valve in the implement pump.