KB21 Service Manual Pub 09-14
54
Cylinder Control Systems
40-A. Bucher L.8S Manual Control/Cable
passage is blocked. This forces the oil to travel through the pressure passage by way of the inlet cap.
. The
opposite check valve is prevented from opening due to the closed passage at the spool.
Work Port Relief Operation
Most of the valve sections of the control valve utilize work port relief cartridges to protect the system
while the spool is in the neutral position. When the spool is in neutral, the work port relief precedes
breakaway protection of the circuit from over pressure due to inadvertent loading of the cylinder such
as from impact with a solid object.
As indicated, the pressurized oil is also present at the work port relief when the spool is shifted from
the neutral position to operate the cylinder. In this instance the oil will be relieved at the work port
relief set pressure rather than the higher main relief pressure.
The work port relief is actuated when the pressurized oil overcomes the work port piston spring
pressure and unseats the work port piston. The oil is then allowed to pass through the center of the
piston and relieve to the tank port.
The work port relief (shown below) pressure adjustment is set at the factory to provide the maximum
recommended.
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