SUB-SECTION 4A
HYDRAULIC SYSTEM
The swing brake is used to lock the swing reducer so that
Under this condition, the free-fall feature is inoperative
the swing motor cannot turn, thus preventing the revolving
end the main winch operates as a non free-fall winch.
upper portion of the machine from turning.
When the free-fell control lever is moved toward the opera-
NOTE
tor, the metered oil flow is restricted, creating pressure at
the free-fell brake release port. As soon as the brake is
The upper of the machine will swing freely if the
released sufficiently to allow the internal gear to rotate,
swing brake is not applied.
the metering pump is driven by the internal gear and meters
pert of the oil supply out of the circuit. This decreases the
The swing brake pedal is shown in the released position. In
pressure in the free-fall brake circuit, which tends to apply
this position, oil is allowed to enter the brake chamber and
the brake; thereby quieting winch drum speed.
release the brake. When the operator depresses the swing
The speed at which the load is lowered is proportional to
brake pedal, the oil in the brake chamber is allowed to
the amount of control lever travel. As the travel of the con-
return to tank and the brake springs set the brake.
trol lever is increased, the flow of oil through the control
valve is restricted to a greater extent; and an increase in
The swing brake lock is shown in its normal operating posi-
pressure releases the brake further, causing an increase in
tion. When the machine is not working or is shut down, the
speed. When the control valve lever is moved to its full
swing brake lock should be placed in the locked position. In
extent, ail the oil is required to pass through the metering
this position, the oil in the brake chamber is allowed to
pump and maximum uniform speed is obtained.
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-fail 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 end cause the load to lower at an un-
metered through the control valve to the winch motor.
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 operation of the aux-
lliary winch circuit is identical to the operation of the main
A metered flow of hydraulic oil from the swing pump is
directed to the free-fall circuit by the priority valve. When
winch circuit, except that the metered flow of oil from the
the free-fall control valve is in the released position, this
swing pump is divided equally between the main end aux-
fluid passes through the valve end returns to the reservoir.
illary winch circuits after the oil leaves the priority valve.
4A-16
