Anti-Two Blocking System shuts
down crane functions when ATB
weight is freely suspended
Purge air from unloader
circuits. See procedure in
this manual
Disconnect drain line from
outlet end of unloader valve
Problem solved
Are all three functions
shut down?
Oil is passing through the
check valve in another
unloader
Install cap fitting to plug outlet
end of unloader valve
Functions operate correctly?
YES
NO
YES
NO
Flush to remove
contamination otherwise
replace unloader valve
The poppet in the unloader
is not seated. Remove
unloader and flush to
dislodge contamination
Cap each of other
unloaders in turn to identify
the unloader with the faulty
check valve
Reinstall, retest and replace
unloader if problem persists
NO
YES
Examine solenoid valve
for sticking spool
Work with individual
section that shut down
Operate function
Function operates correctly
9389
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