3-9
3
CONTROL VALVE
FUNCTION
Anti-cavitation valve
This valve is installed between the cylinder port and the
tank passage. If the cylinder is operated at a speed too fast
for the oil supply to keep up with, and thus the pressure of
the cylinder port becomes negative, the oil from the tank is
supplied to prevent cavitation.
Normally, the cylinder port (P) is under the pressure and
thus the poppet (1) is closed. If the negative pressure is
generated in the cylinder port (P) and its pressure becomes
lower than the tank passage (T), the oil pushes the poppet
(1) and flows through the tank passage (T) into the cylinder
port (P).
Anti-drift valve
This valve is installed in the head side of the cylinder cir-
cuit of the boom section, and it prevents oil leakage in the
cylinder head circuit and decrease the natural drop of the
boom.
When the spool is in the neutral position
The
pressure in the cylinder port is directed to the spring
chamber (5) via the passage (2), the hole on the spool (3)
and the passage (4). The spring force and the pressure dif-
fer
ence between the poppet areas pushes the seat surface
of the poppet (1) against the seat surface of the valve body.
Therefore, the oil flow is blocked in this section.
When the Boom Raise operation is performed
The oil supplied from the pump pushes open the poppet
(1), and then flows into the cylinder port.
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