SECTION 5 – SWING DRIVE
3120933 Rev. 0
USTC
5-1
GENERAL
The rotation capability of the crane is also referred to
as the swing. A hydraulically-driven gear motor
drives a speed reducer gearbox which outputs into a
large, internal-tooth ball bearing. The static brake,
mounted between the motor and gear reducer, pre-
vents rotation until the swing motor is pressurized.
The swing motor is driven by the end section of the
pump with a maximum of 8 gpm.
The swing drive may be removed as a unit from the
turntable or components may be removed as neces-
sary starting with the motor, brake, and gear reducer.
An optional swivel assembly provides full 360°
rotation of the turntable by allowing hoses and wires
to rotate. The top portion of the swivel is a slip ring.
The lower portion is a hydraulic swivel.
Recommended rotation speed is one revolution per
minute. To attain that speed, the PTO ratio is selected
to provide pump output at or near maximum engine
speed. If an incorrect PTO is installed, one rpm
rotation speed will not be attainable. Refer to the
Operating and Safety Manual for information on
PTO selection.
COUNTERBALANCE VALVE
A dual counterbalance valve mounted on the inside of
the turntable balances the pressure between left and
right swing. Without the counterbalance valve the
swing motor would drive the pump backwards until
the boom stopped rotating.
When one side is pressurized the “off” side recieves a
small amount of pressure to prevent cavitation. The
counterbalance cartridge maintains the offside pres-
sure at one-third of the pressure side.
If rotation of the crane is jerky or one direction of
rotation is faster than the other, the counterbalance
valve may be suspect.
WARNING: NEVER OPERATE BOOM
WITHOUT OUTRIGGERS SET ON A FIRM
SURFACE.
1. Park the machine in an open area and set the
outriggers.
2. Place a 4000 psi pressure gauge in each of the
hoses going into the counterbalance valve.
3. Using all applicable safety practices, operate the
boom and monitor the pressures on each gauge.
The higher pressure should be three times that of
the lower pressure.
4. If gauge readings are not properly set, replace
the counterbalance valve.
Figure 5-1. Swing Drive Components
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