 | |
| Illustration 1 | g00543775 |
(1) Swing motor (2) Stick cylinder (3) Bucket cylinder (4) Boom cylinder (5) Bottom swivel (6) Boom drift reduction valve (7) Main relief valve (8) Travel makeup valve (9) Main control valve (10) Transmission manifold (11) Blade/Stabilizer control valve (12) AEC pressure switch (implement and travel) (13) Pilot control valve (stick and swing) (14) Pilot control valve (travel) (15) Pilot control valve (boom and bucket) (16) Governor actuator (17) Swing charge filter (18) Oil cooler (17) Pilot manifold (18) Pilot accumulator (19) Gear pump (pilot and brake) (20) Pilot manifold (21) Pilot accumulator (22) Main pump (23) Swing pump (24) Hydraulic tank (25) Return oil filter (26) Return oil manifold (27) Pressure switch for swing (AEC) (28) Pilot oil filter | |
Main Pump
 | |
| Illustration 2 | g00828614 |
Main hydraulic circuit (9) Main control valve (22) Main pump (23) Swing pump | |
The main hydraulic system is supplied by main pump (22). The main pump activates the following components:
- Stick cylinder (2)
- Bucket cylinder (3)
- Boom cylinders (4)
- Blade cylinders
- Travel motor
Main pump (22) is a variable displacement axial piston pump. Main pump (22) and swing pump (23) are mechanically connected in series through a flexible coupling.
 | |
| Illustration 3 | g00828511 |
Typical example (7) Main relief valve (8) Makeup valve (travel) (9) Main control valve (12) AEC pressure switch | |
The main pump delivers approximately 260 L/min (69 US gpm) of hydraulic oil at no load. The oil that is delivered from the main pump enters main control valve (9). The oil is then sent to the respective cylinders and/or the travel motor. If the hydraulic demand is low, the oil could be returned to the hydraulic tank.
The main hydraulic pump is load sensing. The pump receives signal pressures in order to regulate the pump flow. The three following signal pressures are possible:
- 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 are activated, the load sensing pressure increases and the pump flow is regulated in proportion to the amount of movement in the pilot control valve.
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
 | |
| Illustration 4 | g00828496 |
Typical example (1) Swing motor (17) Swing charge filter (22) Main pump (23) Swing pump (29) Swing charge pump (30) Inlet for the swing charge pump | |
The oil is supplied from swing pump (23). The oil activates swing motor (1). Swing pump (23) is a variable displacement axial piston pump that is mechanically connected to main pump (22). The swing pump is not self-charging. The pump is supplied oil by an attached charge pump. Swing pump (23) delivers approximately 112 L/min (30 US gpm) of hydraulic oil at no load.
Pilot Pump
 | |
| Illustration 5 | g00828406 |
Typical example (13) Pilot control valve (stick and swing) (15) Pilot control valve (boom and bucket) (19) Gear pump (pilot and brake) (20) Pilot manifold | |
The pilot hydraulic system is driven by gear pump (19). Gear pump (19) is mechanically connected to the engine timing gear.
The pilot circuit has the following functions:
- The pilot circuit operates main control valve (9) under the following conditions: operation of pilot control valves (13) and (15), 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 (13) and (15). 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 blade cylinder.
- The pilot circuit controls the pump output. The main pump proportional reducing valve in pilot manifold (20) receives an electrical signal in order to control the pilot system pressure (PS) that is sent to the main pump regulator. This controls the main pump output flow. The swing pump proportional reducing valve in pilot manifold (20) receives an electrical signal in order to control the pilot system pressure to the swing pump regulator. This controls the swing pump output flow.
- The pilot circuit creates pilot signal pressure in the pilot circuit so the following controls can be achieved. The pilot circuit activates the Automatic Engine Speed Control (AEC). This causes an automatic reduction in the engine speed when no hydraulic operation is necessary. The pilot circuit releases the swing motor brake. The pilot circuit changes the travel speed to the CREEPER speed. The pilot circuit changes the swing pump flow in order to change the swing motor direction.