Main Relief Valve - Hitachi ZW180 Technical Manual

MAIN RELIEF VALVE

The main relief valve prevents pressure inside the
main circuit from increasing over the set pressure
during operation of the cylinder.
This prevents oil leakage from the hoses and piping
fittings as well as cylinder breakage.
Relief Operation
1. Pressure at port HP (the main circuit) acts on the
pilot poppet through orifice A of the main poppet
and orifice B of the seat.
2. When the pressure at port HP reaches the set
force of spring B, the pilot poppet opens and
pressure oil flows to port LP (the hydraulic oil
tank) through passage A and the periphery of the
sleeve.
3. At this time, the pressure difference arises
between port HP and the spring chamber due to
orifice A.
4. When this pressure difference reaches the set
force of spring A, the main poppet opens, and
pressure oil in port HP flows to port LP.
5. Consequently, pressure in the main circuit
decreases.
6. If the main circuit pressure decreases to the set
pressure, the main poppet is closed by the force
of spring A.
COMPONENT OPERATION / Control Valve
T3-2-12