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| Illustration 1 | g00543771 |
(1) Swing motor (2) Stick cylinder (3) Bucket cylinder (4) Boom cylinder (5) High pressure swivel (6) Boom drift reduction valve (7) Main relief valve (8) Main control valve (9) AEC pressure switch (implement and travel) (10) Travel makeup valve (11) Pilot control valve (stick and swing) (12) Pilot control valve (boom and bucket) (13) Brake pilot steering pump (14) Governor actuator (15) Swing charge filter (16) Oil cooler (17) Pilot manifold (18) Pilot accumulator (19) Main pump (20) Swing pump (21) Hydraulic tank (22) Return oil filter (23) Return oil manifold (24) Pressure switch for Swing (AEC) (25) Pilot oil filter (26) Swing charge pump (27) Blade/Stabilizer control valve (28) Pilot control valve (travel) (29) Transmission manifold | |
Main Pump
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| Illustration 2 | g00524867 |
Main hydraulic circuit (8) Main control valve (19) Main pump (20) Swing pump | |
The main hydraulic system is supplied by main pump (19). The main pump activates the following components:
- Stick cylinder (2)
- Bucket cylinder (3)
- Boom cylinders (4)
- Blade/stabilizer cylinders
- Travel motor
Main pump (19) is a variable displacement axial piston pump. Main pump (19) and swing pump (20) are mechanically connected in series through a flexible coupling.
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| Illustration 3 | g00524868 |
Typical example (7) Main relief valve (8) Main control valve (9) AEC pressure switch (Implement and travel) (10) Travel makeup valve | |
The oil that is delivered from the main pump enters main control valve (8). The oil is then sent to the respective cylinders and/or the travel motor. If the hydraulic demand is low the pump is automatically destroked and the oil could be returned to the hydraulic tank.
The main hydraulic pump is load sensing. The pump receives pressure signals in order to regulate the pump flow. The three following pressure signals are provided to the pump regulator:
- Load sensing pressure from the main control valve
- Power shift pressure from the main pump proportional reducing valve (PRV)
- Pump delivery pressure (PD)
When all the hydraulic control valves are in neutral, the load sensing pressure is low and the main pump flow is reduced to a minimum. When one of the hydraulic controls is activated, the load sensing pressure increases. The pump flow is regulated in proportion to the amount of movement in the pilot control valve in order to keep the pump margin pressure constant.
The main pump is also controlled by the controller. Input signals from the power mode switch and the engine speed pickup are sent to the controller. The controller processes these input signals. The controller then sends a electrical signal to the Proportional Reducing Valve (PRV). The PRV is a solenoid operated pressure reducing valve that sends a hydraulic signal to the pump in order to regulate the pump output. The hydraulic signal from the PRV is called power shift pressure (PS).
PS pressure works with the system pressure in order to regulate the pump flow. A decrease in PS pressure causes the main pump to destroke at a lower system pressure. An increase in PS pressure causes the pumps to destroke at a higher system pressure.
Swing Pump
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| Illustration 4 | g00543778 |
Typical example (1) Swing motor (15) Swing charge filter (19) Main pump (20) Swing pump (26) Swing charge pump (30) Inlet for the swing charge pump | |
The oil is supplied from swing pump (20). The oil activates swing motor (1). Swing pump (20) is a variable displacement axial piston pump that is mechanically connected to main pump (19). The swing pump is not self-charging. The pump is supplied oil by an attached charging pump (26) through swing charge filter (15) .
Pilot Pump
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| Illustration 5 | g00543779 |
Typical example (11) Pilot control valve (stick and swing) (12) Pilot control valve (boom and bucket) (13) Brake pilot pump (17) Pilot manifold | |
The pilot hydraulic system is driven by gear type brake/pilot and steering pump (13). Brake pilot pump (13) is mechanically connected to the engine timing gear.
The pilot circuit has the following functions:
- The pilot circuit operates main control valve (8) under the following conditions: Operation of pilot control valves (11) and (12), Operation of the travel pedal control valve and the blade pilot control valve and Operation of the travel pedal control valve or blade pilot control valve. Pilot oil flows to the main control valve through pilot control valves (11) and (12). This pilot oil flow shifts the stems in the main control valve. This allows the main pump oil to flow to the required circuits of cylinders (2), (3), and (4) and/or to the travel motor or to the cylinders for the blade/stabilizers.
- The pilot circuit also controls the main pump output. The main pump proportional reducing valve in pilot manifold (17) receives an electrical signal from the electronic controller in order to control the power shift pressure (PS) that is sent to the main pump regulator. The power shift pressure controls the output power of the main pump.
- The proportional reducing valve for the swing pump in pilot manifold (17) receives an electrical signal in order to control the power shift pressure (PS) to the swing pump regulator. This controls the swing pump output power.
- The pilot circuit also creates pilot pressure signals in the circuits for the automatic engine speed control (AEC) for the boom down, stick in and swing operations. This causes an automatic reduction of the engine speed when no hydraulic operation is required by the operator.
- The pilot pressure is also used to release the swing brake.
- The pilot pressure is used to upstroke the travel motor and the pilot pressure is used to shift to creeper speed.
- The pilot pressure is used to unlock the transmission. The pilot pressure is also used to shift to first gear or second gear through transmission manifold (29) .
Refer to Systems Operation, "Pilot Hydraulic System".