3 - 4
Section F
Transmission
9803/6400
Section F
3 - 4
Issue 1
Motor/Gearbox
Operation (continued)
Counterbalance Valve (continued)
Counterbalance Operation
Fig. 3 Counterbalance Valve (Counterbalance)
When hydraulic oil delivered from the hydraulic pump is guided to P1 port of the counterbalance valve through the control valve,
the hydraulic oil goes through the check valve and flows into the piston motor from M1 port and tries to rotate the motor.
On the other hand, the return oil from the piston motor can flow from M2 port to the counterbalance valve, but is prevented by
the check valve, so the pump delivery pressure rises. The boosted hydraulic oil at P1 port side goes past the orifice and works
on the flange face, and resisting the spring on the opposite side with a force proportional to the pressure, it tries to move the
plunger to the right side.
When a certain pressure is reached, the plunger moves towards the right and the hydraulic oil of M2 port passes through the
notch of the plunger outer perimeter and generates back pressure at M2 port while flowing to Ps port and returns to the tank
through the control valve. When the pump delivery pressure rises, the plunger opening enlarges and the M2 port back pressure
decreases. In this way, the opening of the plunger automatically adjusts the return side passageway area so the piston motor
will rotate at a speed suitable to P1 port side pressure, that is, the P1 port side flow rate.
P
2
P
1
M
2
M
1
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