This module discusses the features and operation of the hydraulic and steering system. The following motor graders are covered in this module:
The hydraulic system is a proportional priority pressure compensated (PPPC) system. The PPPC system is a load sensing system. The PPPC system uses a load sensing hydraulic and steering pump in order to perform the pressure compensation function. The implement control valves have an internal flow compensator. This flow compensator performs the proportional priority function.
The hydraulic and steering system has the following main components:
- Hydraulic Tank and Filter
- Piston Pump (Hydraulic and Steering)
- Combination Valve
- Control Valve (Implement)
- Control Valve (Blade Lift)
- Centershift Lock
- Blade Cushion
- Metering Pump (Steering)
- Piston Pump (Hydraulic Fan)
The hydraulic tank supplies hydraulic oil to the hydraulic and steering system. The hydraulic tank is not vented. Pressure is relieved when the cap is loosened. The hydraulic tank contains a bypass valve. If the filter becomes full of debris, the bypass valve will open. Correct maintenance must be used in order to ensure that the hydraulic fluid flows through the filter.
Piston Pump (Hydraulic and Steering)
The hydraulic and steering pump is a variable displacement axial piston pump. When the engine is operating, the pump will produce flow in order to satisfy the following conditions:
- The demand of the steering system
- The pressure setting of the pressure compensator
- The demand of the hydraulic implements
- The internal lubrication of the pump components
- The margin pressure of the pump
The combination valve directs the oil from the hydraulic and steering pump to the steering circuit and to the implement circuit.
The implement control valve regulates the operation of each implement. Each implement control valve contains a compensator valve. The compensator valve distributes the oil flow that is available. The implement control valve may contain a relief valve. The relief valve will protect the rod end of the cylinders from high pressures.
The blade lift control valve regulates the operation of the blade lift cylinders. The blade lift control valve may contain a hydraulic detent. The blade lift control valve may contain a mechanical detent.
The centershift lock control sends a signal to the solenoid valve in order to engage the centershift lock pin. Transmission fluid is used in this circuit on all of the machines that are covered in this manual except the machines with all wheel drive. On the machines with all wheel drive, the fluid that is used in this circuit comes from the all wheel drive pump.
The blade cushion dampens the shocks that are made in the blade lift hydraulic circuit when the blade contacts an object that will not move. The blade cushion accumulators have a nitrogen precharge pressure that provides the cushion.
The steering metering pump is made up of two parts, the control section and the metering section. When the steering wheel is turned, the control section sends oil to the metering section. The metered oil is then directed by the control section to either the left steering cylinder or the right steering cylinder.
The piston pump for the hydraulic fan is a variable displacement axial piston pump. The piston pump for the hydraulic fan is used to supply oil to the fan motor. The piston pump for the hydraulic fan contains a pressure and flow compensator valve. The pressure and flow compensator valve regulates the fan circuit.