TM 5-3805-298-23-1
0004
STEERING HYDRAULIC SYSTEM
0004
Steering and Pilot Pump
0004
The steering and pilot pump is mounted to the implement pump, which is mounted to the back of the transmission
under the cab. The steering and pilot pump is a variable displacement piston pump with load sensing, compensa-
tion for pressure, and compensation for flow. The flow and pressure are dependent on the system demands that
are sensed by the pressure and flow compensator valves.
Steering System
0004
The hydraulic steering system changes the machine's angle of articulation. The four main components in the steer-
ing system are the steering and pilot pump, the hand metering pump, and the two steering cylinders. The steering
and pilot pump provides flow to the steering cylinders. The hand metering pump connects to the steering wheel
through a mechanical linkage. The hand metering pump controls the flow of hydraulic oil from the steering and pilot
pump to the steering cylinders. A hydraulic signal from the hand metering pump tells the steering and pilot pump
the amount of flow that is needed to the steering cylinders. The steering cylinders extend and retract to articulate
the machine left or right.
Secondary Steering System
0004
In the event of a primary steering system pressure loss, the secondary steering system is designed to provide tem-
porary steering control to maneuver the machine short distances. The secondary steering system consists of a
secondary steering pump and electric motor. The secondary steering pump is a gear pump which is driven by an
electric motor. The secondary steering pump and electric motor is located under the engine in front of the fuel tank.
The secondary steering pressure switch will detect a decrease in the steering system pressure. The pressure
switch will then send a signal to the transmission ECM in order to activate the secondary steering system.
IMPLEMENT HYDRAULIC SYSTEM
0004
Implement Pump
0004
The implement pump is mounted to the back of the transmission under the cab. The steering and pilot pump
mounts to the back of the implement pump. The implement pump is a variable displacement piston pump with load
sensing, compensation for pressure, and compensation for flow. The flow and pressure are dependent on the sys-
tem demands that are sensed by the pressure and flow compensator valves.
Implements System
0004
The implements hydraulic system features control valves that are pilot operated. The system only consumes
engine horsepower when the system requires increased pressure. Hydraulic oil flows from the implement pump
into the main control valve. The main control valve controls the flow of hydraulic oil from the pump to the lift and tilt
cylinders and the work tools. The main control valve sends signal oil back to the pressure and flow compensator
valves on the implement pump. The implement pump uses the signal oil to determine the amount of flow that is
required. If the pump flow is not sufficient for all of the functions, the flow of hydraulic oil to all functions is reduced
proportionally.
The implement hydraulic system uses a combination valve, which is a diverter valve and a relief valve. The combi-
nation valve is connected to each end of the tilt cylinder. When performing operations which force the bucket back-
ward, the diverter valve senses the difference in pressure between the head end and the rod end of the tilt cylinder.
If the difference in pressure exceeds 3,000 kPa (435 psi), the diverter valve opens and the oil from the head end of
the cylinder flows to the relief valve. If the pressure on the relief valve exceeds 12,300 kPa (1,784 psi), the relief
valve opens and the oil returns to the tank.
The combination valve relieves pressure from the head end of the tilt cylinder in certain dump operations. With the
lift arms level, the bucket in full dump, pressure will increase in the head end of the tilt cylinder until the tilt cylinder
collapses. When the hydraulic oil pressure exceeds 3,000 kPa (435 psi), the diverter valve opens. The oil from
the head end of the tilt cylinder flows to the relief valve. If the pressure on the relief valve exceeds 12,300 kPa
(1,784 psi), the relief valve opens and the oil returns to the tank. The diverter valve keeps the setting of the relief
valve low and the diverter valve maintains high pressures during the dump operation that are needed for normal
operation.
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