Schematic of Main Hydraulic System
 | |
| Illustration 1 | g01270731 |
(1) Travel motor (Right) (2) Travel motor (Left) (3) Undercarriage cylinder (adjustable gauge) (4) Swing motor (5) Blade cylinder (6) Bucket cylinder (7) Boom cylinder (8) Swivel (9) Stick cylinder (10) Boom swing cylinder (11) Main control valve (12) Right travel spool (13) Left travel spool (14) Pilot control valve (Boom and Bucket) (15) Pilot control valve (Swing and Stick) (16) Main pump (17) Swing pump (18) Pilot pump (19) Oil cooler (20) Oil filter (21) Hydraulic tank (22) Pilot manifold | |
Pump Flow and Pressure Control System
 | |
| Illustration 2 | g01182652 |
Pump compartment (1) Pilot pump (2) Swing pump (3) Main pump | |
This machine is driven and controlled by the following systems:
- The main hydraulic system provides oil to the boom cylinders, the stick cylinder, and the bucket cylinder. The main hydraulic system also provides oil to the travel motors.
- The swing hydraulic system provides oil to the blade cylinder, the undercarriage cylinder (adjustable gauge), the boom swing cylinder, and the swing motor.
- The pilot hydraulic system provides oil to the control circuit.
Main pump (3) is directly connected to the engine through a coupling. The main pump is constructed as a single body, but the pump functions as a double pump. This is accomplished by splitting or separating the pump oil flow.
The main pump includes a right pump and a left pump. These pumps are variable displacement piston pumps. The pistons are arranged in a common cylinder block. Half of the pistons output oil to the right side of the main control valve, and half of the pistons output oil to the left side of the main control valve.
When an operation is being performed, the main control valve directs pump oil to the respective cylinders (boom, stick, and bucket) and/or motors (swing and travel). The main control valve contains numerous valve stems, passages, check valves, relief valves, and orifices in order to carry out a single operation or a combined operation. The maximum working pressure of the main hydraulic system is limited by the main relief valve.
ReferenceFor more information on the main control valve, see Systems Operation, "Main Control Valve".
The individual output flow of the right pump and the left pump is maximized at no load. As the load pressure increases during working conditions, the delivery pressure increases while the flow rate decreases. The maximum hydraulic horsepower remains constant even though the delivery pressure and the flow rates change. The hydraulic horsepower is approximately identical to the engine horsepower.
When there is no load on the machine, pump oil flows through the main control valve to the hydraulic tank. When a load is applied to the machine, pump oil is divided at the main control valve. The oil is sent to the travel motor, the swing motor, and the cylinders.
ReferenceFor more information on the main pump, see Systems Operation, "Main Hydraulic Pump".
The swing pump (2) is a gear type pump that is directly connected to the rear of the main pump.
The pilot pump (1) is also a gear type pump that is connected to the rear of the swing pump.