jcb JS300 Service Manual page 989

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.
Shuttle Function
The counterbalance valve has a shuttle function. When the
plunger moves from the state in the top illustration to that
in the lower illustration, the parking brake release port P3
is opened to guide the pressurised oil to the brake
releasing cylinder. This releases the parking brake. When
the motor stops, the counterbalance valve becomes as
shown in the top illustration and P3 port is blocked and the
drain port in the motor case is opened. The pressurised oil
in the brake releasing cylinder drains into the motor case
to activate the brake.
Fig 7.
Fig 8.
F-12
C076910
C076920
9813/5100-1
Section F - Transmission
Traction Motor / Reduction Gear
Operation
F-12