HYDRAULIC SYSTEM
SUBSECTION 5A
The boom hoist Interlock valve IS energized whenever the
SYSTEM DESCRIPTION
GENERAL. The descrrptron below covers the hydraulic con-
engaged to allow the boom to be lowered only when power
trol circuit of the machine it includes the optional third
IS available.
drum circuit as well as all basic items. The items described
When the master switch IS OFF the interlock valve is de-
are shown schematically in Figure 5A-1.
energized. In this position the interlock valve will block the
PUMPING CIRCUIT. The pumping circuit consists of the res-
flow of oil to the boom hoist lowering circuit, if the circuit
ervoir, suction filter, pump, high pressure filter, combina-
lever should be moved.
tion solenoid valve, and accumulator
SWING CIRCUIT. Swing operation IS performed by two
The pump is mounted on and driven by the engine. When
pressure regulating valves and the swing brake is released
the pump is driven, oil is drawn from the reservoir through
by hydraulic pressure. To release the swing brake, the op-
the tank suction filter and is forced out into the system. The
erator moves the swing lock switch to the left. In this posi-
oil leaving the pump flows through a high pressure filter,
tion, hydraulic oil passes from the accumulator through the
into the combination solenoid valve and then to the ac-
swing brake lock valve, to the swing brake cylinder. Oil flow-
cumulator. In the combination solenoid valve, the oil pres-
ing into the swing brake cylinder will cause the cylinder pis-
sure IS controlled by the built in relief valve.
ton to extend and release the swing brake.
If the diverting valve is in the "lower" position, hydraulic oil
To apply the swing brake, the swing lock switch is moved to
is available to the crawler extension circuit. Oil flows to the
the right. This allows oil to flow out of the swing brake cylin-
crawler control valves, but if they remain in neutral, oil is
der through the swing lock valve, to the reservoir. Oil flow-
returned to the reservoir.
ing out of the swing brake cylinder will cause the cylinder to
retract and allow springs to apply the swing brake.
If the diverting valve, which is part of the combination valve,
is in the "upper" position, oil flows to the accumulator. The
To swing the upper, either to the left or to the right, move the
oil will continue to fill the accumulator until maximum oper-
control lever forward or backward respectively. When the
ating pressure is reached. When the accumulator reaches
swing control lever is moved forward, oil from the accumu-
maximum operating pressure, the unloading valve will
lator passes through the left hand swing valve to the left
open and direct pump output back to the reservoir.
hand swing clutch cylinder. This pressure is regulated by
the swing valve, that is, the further forward the lever is
The oil will continue to circulate back to the reservoir as
pushed, the greater the pressure to the clutch cylinders.
long as the control valves are in the neutral (or off) position.
The upper will move towards the boom in this mode.
When the operator actuates the controls, oil will be drawn
from the accumulator causing accumulator pressure to
When the swing control lever IS pulled back, the same con-
drop to the low end of operating pressure. At this point the
dition as described above exists in the right hand circuit.
unloading valve will close and the pump will again re-
The upper will move away rom the boom in this mode.
charge the accumulator to maximum operating pressure.
HOIST CIRCUIT. The hoist circuit Includes the left and right
This charging and discharging of accumulator pressure will
drum brakes, planetary brakes, brake locks, drum pawls,
show up on the main pressure gauge as a gradual decrease
and clutch controls. To lift a load the operator pushes the
in pressure, followed by a rapid increase to maximum oper-
brake lock switch to the OFF posrtion. pushes the pawl
ating pressure.
switch to the OFF position and pulls the drum lever back. In
these positions, hydraulic oil passes from the accumulator,
BOOM HOIST CIRCUIT. To raise the boom, the operator
pulls the control lever back. In this position, hydraulic oil
through the brake lock valve, to the drum brake lock
cylinder. Oil also flows from the accumulator through the
passes from the accumulator, through the control valve,
boom hoist limit valve, shuttle valve and to the boom hoist
pawl valve to the pawl cylinder. Oil also flows through the
clutch and brake cylinders. Oil flow to the boom hoist brake
drum control valve, to the drum clutch cylinder. Oil flowing
cylinders causes the cylinder pistons to extend and release
into the drum brake lock cylinder will cause the cylinder
the boom hoist brake. Oil to the boom hoist clutch cylinder
piston to extend and release the drum brake. Oil flowing
causes the cylinder to extend and engage the clutch to lift
into the pawl cylinder will cause the cylinder piston to
the boom.
extend and release the drum pawl. Oil flowing into the drum
clutch cylinder will cause the cylinder piston to extend,
The boom hoist limit device is de-energized whenever the
apply the clutch and lift the load.
boom reaches maximum boom angle. At this point, oil is re-
turned to tank from the boom hoist brake and clutch cylin-
To stop drum rotation, depress the drum brake pedal and
ders, stopping the boom at the preset maximum angle.
move the drum control lever to neutral. In these positions,
hydraulic oil passes from the accumulator, through the
To lower the boom, the operator pushes the control lever
drum brake valve, to the drum brake cylinder. Oil will also
forward. In this position oil is fed through the boom hoist In-
flow out of the drum clutch cylinder, through the drum con-
terlock valve to the boom hoist planetary brake cylinder,
trol valve, to the reservoir. Oil flowing into the drum brake
boom hoist planetary pawl cylinder, and through a shuttle
cylinder will cause the cylinder piston to extend and apply
valve to the boom hoist brake cylinder. This action engages
the drum brake to stop rotation of the drum. Oil flowing out
the planetary brake, engages the boom hoist planetary
of the drum clutch cylinder will cause the cylinder piston to
pawl, disengages the boom hoist pawl, and releases the
retract and allow springs to release the drum clutch.
boom hoist brake to lower the boom.
5A-8
