Hitachi ZW180, Technical Manual

Page: 289 / 374

COMPONENT OPERATION / Charging Block
T3-7-7
PILOT RELIEF VALVE
1. The pilot relief valve prevents pressure in the pilot
circuit from increasing over the set pressure dur-
ing operations of the actuators like the pilot valve.
2. When the pilot circuit pressure is more than the
set pressure, pressure oil acts on the poppet in
the pilot relief valve.
3. The poppet moves toward the spring and is con-
nected to port DR.
4. Pressure oil in the pilot circuit returns to the hy-
draulic oil tank through port DR.
5. When the pilot circuit pressure is below the spring
force, the poppet moves to the left and is not
connected to port DR.
During Normal Operation
T4GB-03-06-007
During Relief Operation
T4GB-03-06-008
Poppet
From Port P
(Section V-V)
Poppet
Spring
(Section V-V)
Port DR