Tadano TR-800XXL4, Service Manual

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7 W119-0212E
E - 3 . E - 3 .
Counterbalance Valve (Elevating)
2. Function
C
a
B
P.P
A
b
IW119-021003
This counterbalance valve prevents the actuator
from being driven by the load and its own weight
faster than the speed corresponding to the oil
supply rate.
2.1 When control valve is at the neutral position
The actuator holding pressure is sealed by seat
“a” of the main spool and seat “b” of the check
valve.
2.2 While actuator is being pushed up
1. The pressurized oil entering through port A of the
control valve enters chamber C, flows out through
port B by opening the check valve, and enters the
holding side of the actuator.
2. At this time, since port PP is connected to the tank
circuit, the main spool is kept forced to the valve
body by the spring, and remains inactive.
2.3 While actuator descends
1. The hydraulic oil directly flowing from the control
valve to the actuator also enters through port PP
to exert force to the main spool to move the main
spool.
2. Consequently, the holding hydraulic pressure in
port B is vented to port A.
3. At this time, the main spool motion is smoothened
by orifices.
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2
366-051-70000