TM 5-3805-280-24-1
Theory of Operation
brake pressure reducing valve. The pressure reducing
Propel park brake is spring applied and hydraulically
valve operates to reduce the supply oil pressure.
released type brake. Brake is applied by a disk spring
Reduced pressure oil flows to the brake piston (C) to
(B) whenever the propel control valve spools are in
move it against the disk spring (B) force and releases
neutral. The plates in the brake pack (D) are
the park brake. Oil not used to release the park brake
connected to the motor housing. The disks are
flows through the orifice in the reducing valve spool
connected to and rotate with the drive shaft (E). The
and into the propel motor housing (F).
disk spring pushes against the piston to squeeze the
plates and disks together to keep the machine from
When propel pilot controllers are returned to neutral,
moving.
supply oil is blocked by the valve spools and the
propel motor work ports are open to the control valve
When the propel pilot controllers are actuated the
return passage. The counterbalance valve (G) returns
propel valve spools route supply oil to the bottom work
to its neutral position causing the machine to slow and
port of propel motor for forward travel or the top work
then stop (dynamic braking). The pressure reducing
port for reverse travel. The supply oil flows into the
valve (A) is shifted by its spring. The disk spring (B)
chamber (J) at the end of counterbalance valve (G). At
pushing against the brake piston (C) forces the oil to
the same time supply oil moves the park brake release
flow through the orifice in the reducing valve and into
shuttle valve (H) to route supply oil to the park brake
the propel motor housing (F). The delay caused by the
pressure reducing valve (A) but is blocked by the
oil flowing through the orifice is enough to slow
counterbalance valve. When supply oil pressure
engagement to ensure that park brake is only fully
increases enough to shift the counterbalance valve,
applied after the machine has stopped.
supply oil flows through the groove (I) to the park
TX,9025,GG2613 1920MAY982/2
9025
05
81
6-77
