2-23
SAFETY DEVICES
There are safety devices on the RT-300 to maintain control of a load in case of power or
hydraulic line failure. The operator should understand the function and operation of
these devices so that a continual check on their performance can be made.
OUTRIGGER CYLINDER CHECK VALVE:
A double-acting check valve is integrally mounted on each of the outrigger cylinders.
This valve holds the outrigger in the extended position should power or hydraulic line
failure occur. This valve has no adjustment. If an outrigger creeps up while supporting a
load, there is an internal leak in the valve or in the outrigger piston seal. In either case,
maintenance is required.
BOOM ELEVATION CYLINDER HOLDING VALVE:
A single-acting holding valve is integrally-mounted on each cylinder barrel. These valves
hold the boom in the elevated position should power or hydraulic pressure line failure
occur. These valves are adjustable to hold the desired load. If the boom creeps down
with loads to maximum capacity, these valves should be adjusted. If adjustment fails to
correct the problem, there is an internal leak in a holding valve or a hydraulic cylinder.
Refer to the maintenance instructions.
BOOM CROWD CYLINDER HOLDING VALVE:
A single-acting holding valve is flange mounted to the cylinder rod end. This valve holds
the cylinder in the extended position should power or hydraulic pressure line failure
occur. This valve is adjustable to hold the desired load. If the boom creeps in under
load, this valve should be adjusted. If adjustment fails to correct the problem, there is an
internal leak in the holding valve or the hydraulic cylinder. Refer to the maintenance
instructions.
ANTI-TWO-BLOCK DEVICE:
The anti-two-block device prevents damage to hoist rope or machine components from
accidentally pulling load hook against boom tip. There is a pivot arm at the boom tip that
is moved upward by the load hook as it approaches the boom tip. An electric switch
connected to a hydraulic solenoid valve dumps the HOIST RAISE, CROWD EXTEND,
and BOOM LOWER circuits. No other circuits are affected. These circuits are returned
to normal operation by operating the HOIST LOWER or CROWD RETRACT control.
An emergency override switch is provided so the boom can be operated in case of
system failure. This key-operated switch is located under the instrument panel.
W A R N I N G
We recommend the emergency override switch be used with discretion. Improper
or careless use of this switch can cause damage to the crane and endanger people
and property. The operator who uses this key in an emergency should use good
judgment.
SWING BRAKE AND HOLDING VALVE:
The boom swing position is held by a spring-applied, hydraulically released, parking
brake in the swing gearbox and by an overrunning load valve in line with the swing motor.
The valve relief cartridges, set at 2200 psi (152 bar), and the brake are designed to allow
smooth starts and stops of the boom swing. A shuttle valve is also built into this valve to
fully release the brake before swing begins.
Courtesy of Crane.Market
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