Figure 67. Magnetic clutch brushholders and brushes, adjustment, removal and installation.
Section XVIII. HYDRAULIC SYSTEM
c. On the hoist brake and the digging brake
air/hydraulic (usually spoken of as "Air Over Hydraulic")
is used for additional ease of control. The use of
of the control stand levers
compressed air as a booster in the hydraulic system for
connected to the hydraulic compensators causes the
these two brakes provides these advantages.
compensator to move. Movement of this piston forces
hydraulic brake fluid through the tubes connecting the
(1) It enables the operator to apply more
compensators with the various brakes and clutches.
pressure to the brake than would be
The pressure of the hydraulic fluid in the connecting
possible with the hydraulic control alone.
tubes moves the piston in the brake or clutch cylinder.
(2) brake band travel is increased, making
This movement of the piston causes the clutch or brake
for easier and less critical adjustment.
to engage the drum and the force applied to the brake or
clutch varies with the force applied to the lever or pedal.
Springs in the compensators and cylinders return the
pistons to their normal positions as soon as the control
stand lever or pedal is released. The fluid reservoir
a. Fill the supply tank or reservoir with clean
makes allowance for the expansion and contraction of
hydraulic brake fluid and check the level frequently
the fluid and insures that the system is filled at all times.
during the bleeding operation to prevent air from
entering the supply line. Open the valve below the tank,
b. Smooth, uniform operation is a characteristic of
than bleed the air from the bleeder cap on each
the hydraulic system. Always check the adjustment of
compensator in the control stand (fig. 68). Start with the
the brake or clutch first, then check the adjustment of
lower compensators and work
the control stand linkage, if operation of the controls
appears faulty. Poor adjustment of the brakes or
clutches is usually the difficulty, rather than the