Hitachi ZW180, Technical Manual

Page: 288 / 374

COMPONENT OPERATION / Charging Block
T3-7-6
PRIORITY VALVE (REFER TO THE PILOT
CURCUIT IN THE SYSTEM / HYDRAULIC
SYSTEM GROUP.)
1. Pressure oil from the pilot pump flows through
port P and acts on the both ends of the plunger in
the priority valve.
2. As same pressure acts on the both ends of the
plunger, the plunger does not move and a re-
stricted amount of pressure oil is supplied to other
pilot circuits.
3. When service brake accumulator pressure is ac-
cumulated and is more than the set pressure, the
piston of the relief valve pushes the needle valve.
4. Pressure oil in the spring chamber of the plunger
flows to the hydraulic oil tank through port DR.
5. The plunger is pushed toward the spring chamber
and is shifted as the spring chamber pressure is
reduced.
6. A larger amount of pressure oil from the pilot
pump is supplied to other pilot circuits through the
priority valve.
When service brake accumulator pressure is lower
than set pressure;
T4GB-03-06-005
When service brake accumulator pressure is more
than set pressure;
T4GB-03-06-006
Relief Valve
From Port P
(Section W-W)
To Service Brake Circuit
To Other
Pilot Circuits
Plunger
Needle Valve
From Port P
(Section W-W)
To Other Pilot Circuits
Piston
Service Brake
Accumulator
Pressure
To Port DR
Plunger
Spring Chamber