Overload Relief Valve - Hitachi ZW180 Technical Manual

COMPONENT OPERATION / Ride Control Valve

OVERLOAD RELIEF VALVE

The overload relief valve is installed in order to prevent
the hoses and the ride control accumulator from being
damaged in case pressure in the bottom side circuit of
the lift arm cylinder is suddenly raised by an external
force or something during operation of the lift arm
cylinder.
Operation
1. Pressure at port HP acts on the pilot poppet via
orifice A of the main poppet and orifice B of the
seat.
2. When pressure at port HP reaches the set force
of spring B, the pilot poppet opens and pressure
oil flows to port LP, through passage A and the
periphery of the sleeve.
3. At this time, pressure difference arises between
port HP and the spring chamber by orifice A.
4. When this pressure difference reaches the set
force of spring A, the main poppet opens and
pressure oil at port HP flows to port LP.
5. Consequently, pressure in the actuator circuit
lowers.
6. If pressure in the actuator circuit is lower than the
set pressure, the main poppet is closed by the
force of spring A.
IMPORTANT: Do not disassemble or adjust the
overload relief valve. Replace the
overload relief valve as an assembly,
if necessary.
T3-8-8