Yanmar ViO12-2A, Service Manual

Page: 246 / 409

6. HYDRAULIC SYSTEM
6-
10
-3
2) Hydraulic Valve (Counterbalance Valve)
When pressure oil is fed from the port A, it presses and opens the check valve 3 and then flows into the port A' on
the inlet side of the hydraulic motor; while the pressure oil flows into the chamber D through the choke C and
exceeds the force of the spring
4 to slide the spool valve 2 to the right. This causes the oil on the return side of the
hydraulic motor to flow in from the port B' and return to the port B through the opening E in the valve body 1 and the
spool valve 2 , so that the hydraulic motor is rotated.
When pressure oil is fed from the port B, the above parts operate in the opposite way and the hydraulic motor is
rotated in reverse.
When the pressure oil from the port A is blocked, the spool valve
2 which has moved to the right starts to be returned
to the left by the force of the spring 4 . At this time, the oil in the chamber D starts to flow out to the port A through the
choke C. However, the throttling of the choke C controls the speed at which the spool valve 2 returns to the left.
The hydraulic motor keeps rotating due to inertial force even after the pressure oil from the port A is blocked. In this
condition, the controlled return speed and notched shape of the spool valve
2 allows smooth stop of the hydraulic
motor through gradual reduction of return oil.
E
2
3
1
4
A B
A’ B’
C
D