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12916 Parts & Specifications Manual #99905833
HOLDING VALVE INSPECTION
The cylinders are equipped with holding valves that prevent sudden movement of the cylinder
rods in the event of a hydraulic hose or other hydraulic component failure. The valve is checked
in the following manner:
1. With a full rated load, extend the cylinder in question and kill the engine.
2. Operate the control valve to retract the cylinder. If the cylinder “creeps”, replace the
holding valve. If the cylinder does not “creep”, the valve is serviceable.
TWO BLOCK PREVENTION DEVICE INSPECTION
(See Vol. 1, Operation, Maintenance and Repair for a complete description)
The two block prevention system halts
the “winch-up” and “extension-out” crane functions
before the block contacts the sheave.
The two block prevention system should be checked
daily as follows:
1. Examine flexible rod and weight to insure free unrestricted mechanical operation
2. Examine cord for damage, cuts or breaks. Grasp cord and pull to check operation of
cord reel. The cord should retract on reel when released.
3. Start vehicle, engage PT O and slowly winch loadline up until anti-two block weight
comes in contact with the hook end of the loadline cable. At the moment the weight is
fully supported by the hook end, the winch up function should become non-functioning,
because the two-block damage prevention switch will stop further movement.
If operation other than as described occurs, stop immediately and investigate. Failure to do
so will risk damage to the cable or the crane.
Then, extend the winch cable to relieve the two-block condition, and actuate the boom extend
function slowly. Again, once the weight is fully supported by the hook end, the boom extend
function should become non-functioning, because the two-block damage prevention switch will
stop further movement. If operation other than described occurs, stop immediately, reverse the
function, and check the system.
If the anti-two block function appears to be functioning normally, winch the cable down until the
sensing weight swings free.
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