jcb JS300 Service Manual page 988

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 that 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
F-11
A
P1
M2
Fig 6. Motor Rotating
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
diaphragm opening enlarges and the M2 port back
pressure decreases. In this way, the opening of the plunger
notch diaphragm automatically adjusts the return side
9813/5100-1
Section F - Transmission
Traction Motor / Reduction Gear
P2
M1
Operation
C076890
F-11