EMERGENCY SHUT-OFF VALVE
EMERGENCY SHUT-OFF VALVE
This valve prevents the boom or arm being raised from fall-
ing. If the hydraulic hose breaks, the valve shuts off the
oil flow pushed back from the cylinder and prevent it from
further flowing.
When the boom or arm is raised, the pressure oil from the
hydraulic pump flows through the port V to push up the
check valve (1) and then through the port C into the boom
or arm cylinder.
When the boom or arm is lowered, the pilot pressure from
the pilot valve (2) is led to the port Pi. The pilot pressure
from the port Pi works on the spool (3) to push it up. The
return oil from the cylinder flows from the port C to the pas-
sage
through the spool (3) and the check valve (1), the port
V and into the tank passage.
The
boom or arm does not fall even if the hydraulic hose
breaks, because the oil flow leading to the head side of the
cylinder is blocked and isolated in the passage through the
check valve (1) and the spool (3).
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