Maeda MK0003, Руководство по обслуживанию, Страница: 106 / 348

2-78
[4] Actuation of magnetic switching valve
(derricking, winching, extension/contraction and slewing)
1. When the solenoid is not excited
Spool (1) is maintained in the neutral position by return spring (2).
Pilot valve (3) is pushed up toward the solenoid side by the force of pilot valve spring (4).
In this state, while the pilot path is closed by pilot valve (3), pilot chambers (a) and (b) are connected together by
way of the drain path and socket (5). Consequently, the pressure of pilot chamber (a) becomes equal to that of
pilot chamber (b) (drain pressure), and no force that can move spool (1) is generated.
Further, since spool (1) employs the all port block type, in the neutral spool position, between parallel path (c),
actuator paths (d1) and (d2) as well as between actuator paths (d1) and (d2) and tank path (f) are closed.
Accordingly, since every path that leads to actuators is shut off, the actuators are stopped.
On the other hand, when every one of other switching valves is in the neutral position, the oil supplied from pump
passes the central bypass path (e) of each switching valve, and returns to the tank after passing the tank path (f)
via the U-turn cover.
Actuator
From pump
Pilot pressure
(via reducing valve)
Oil path when pilot is in neutral position
To drain path
1. Spool
2. Return spring
3. Pilot valve
4. Pilot valve spring
5. Socket