 | |
| Illustration 1 | g00954155 |
Load Sensing Signal System (1) Pendulum arm control valve (2) Shuttle valve (3) Shuttle valve (4) Relief valve (load sensing system) (5) Pressure tap (6) Implement control valve (7) Implement pump (8) Signal cutoff valve (9) Hydraulic oil tank (A) Pump supply line to Harvester head (B) Signal pressure line (C) Return oil line | |
When the machine first starts there is no pressure in the load sensing signal system. Implement pump (7) is stroked to maximum output. As the implement pump begins to turn, the pressure in the signal system increases. The pump destrokes to low pressure standby until a function is activated.
 | |
| Illustration 2 | g00975138 |
(5) Pressure tap. | |
Note: The signal pressure of the implement control valve functions can be measured with pressure tap (5). The pressure tap is located on the end of implement control valve (6) on the "PL" port.
When no functions are active, a small amount of pump pressure oil flows through a relief valve in pendulum arm control valve (1). The oil flows through the open center valve spools in the pendulum arm control valve. The oil then flows through signal cutoff valve (8) to the hydraulic oil tank. The small amount of oil flow allows warm oil to be circulated through the signal lines. The warm oil allows the implement pump to be more responsive to the flow requirements of the hydraulic system.
When a function on the harvester head is activated, the required pump output flows through signal line (B) to the shuttle valve (2). If a function that is controlled by the implement control valve is activated, the function will send another load signal into the signal system.
A resolver network in the implement control valve allows the highest signal pressure in the implement control valve to flow to resolver (3). The resolver allows the higher signal pressure from the implement control valve or pendulum arm control valve (1) to be sensed by the pump.
When a pendulum arm is moved, the flow of signal oil through the open center spools in the pendulum arm control valve is blocked. The pressure in the signal system increases to the setting of the pressure relief valve (4) that is in the pendulum arm control valve (1). The implement pump strokes to maximum output.
Signal cutoff valve (8) is controlled by the control system for the harvester head. The valve is used to stroke the implement pump to maximum output. When a tree is fed through the harvester head, the feed rollers stroke the pump to maximum output. When the saw cuts the tree, the pump is also stroked to maximum output.
A small time delay occurs when the feed rollers stop and the saw is activated. The implement pump would begin to destroke during this time delay and the saw would not reach maximum speed quickly. Therefore, the measuring and control system closes the signal cutoff valve. The pump is stroked to maximum output when the harvester head changes from feeding to sawing.
Pressure relief valve (4) limits the maximum signal pressure to the implement pump. If a pressure spike occurs in the load sensing system, the pump would upstroke rapidly without the pressure reducing valve. Therefore, the valve limits the high pressure cutoff setting of the implement pump.
Note: The pressure setting of pressure relief valve (4) is below the pressure setting of the pressure cutoff valve in the implement pump.
Machines with steering hand metering units contain an additional load sensing line. Signal oil flows from the steering metering pump. An additional resolver in the system allows the higher signal pressure from the following components to be sensed: the steering metering pump, the pendulum arm control valve and the implement control valve.
Reference: For more information on HMU steering, refer to the Service Manual module Systems Operation, "Steering System" for the machine that is being serviced.