SUB-SECTION 4A
HYDRAULIC SYSTEM
The swing brake is used to lock the swing reducer so that
When the free-fall control lever is moved toward the opera-
the swing motor cannot turn, thus preventing the revolving
tor, the metered oil flow is restricted, creating pressure at
upper portion of the machine from turning.
the free-fall brake release port. As soon as the brake is
released sufficiently to allow the internal gear to rotate,
NOTE
the metering pump is driven by the internal gear and meters
part of the oil supply out of the circuit. This decreases the
The upper of the machine will swing freely if the
pressure in the free-fall brake circuit, which tends to apply
swing brake is not applied.
the brake; thereby regulating winch drum speed.
The swing brake pedal is shown in the released position. In
this position, oil is allowed to enter the brake chamber and
The speed at which the load is lowered is proportional to
release the brake. When the operator depresses the swing
the amount of control lever travel. As the travel of the
brake pedal, the oil in the brake chamber is allowed to
control lever is increased, the flow of oil through the con-
return to tank and the brake springs set the brake.
trol valve is restricted to a greater extent; an increase in
pressure releases the brake further, causing an increase in
The swing brake lock is shown in its normal operating posi-
speed. When the control valve lever is moved to its full
tion. When the machine is not working or is shut down, the
extent, all the oil is required to pass through the metering
swing brake lock should be placed in the locked position. In
pump and maximum uniform speed is obtained.
this position, the oil in the brake chamber is allowed to
return to tank and the brake springs set the brake.
MAIN WINCH CIRCUIT. The main winch control valve
directs hydraulic oil from the pump to the winch motor.
When a load is being lowered with the free-fall brake,
The direction in which the valve spool is shifted will deter-
the control valve lever must be moved gradually.
mine whether the winch will lift or lower a load. The speed
Sudden movement of the control lever will create a
of winch operation is determined by the amount of oil
pressure surge and cause the load to lower at an un-
metered through the control valve to the winch.
even speed. The control valve lever must also be
moved slowly to stop the load smoothly.
An optional free-fall feature is incorporated into the main
winch, and operates as follows:
AUXILIARY WINCH CIRCUIT. The auxiliary winch con-
trol valve directs hydraulic oil from the pump to the winch
A metered flow of hydraulic oil from the swing pump is
motor. The direction in which the valve spool is shifted
directed to the free-fall circuit by the priority valve. When
will determine whether the winch will lift or lower a load.
the free-fall control valve is in the released position, this
The speed of winch operation is determined by the amount
fluid passes through the valve and returns to the reservoir.
Under this condition, the free-fall feature is inoperative and
of oil metered through the control valve to the winch
the main winch operates as a non free-fall winch.
motor.
4A-14
