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3 - 2
Brake Valve
During Travel - Brake Released
During travel, pressurised oil is fed into port
A
to open valve
127
and supply oil via port
C
to traction motor. The
pressurised oil also enters chamber
b
through drilling
a
of
spool
123
. The pressure build-up in chamber
b
causes spool
123
to move to the left to connect motor return port
D
to
port
B
.
The result is unrestricted oil flow and, therefore, rotation of
the motor. The movement of spool
123
also allows
pressurised oil to flow through port
P
into piston
112
of the
parking brake, overcoming the parking brake spring to
release the brake pressure.
The pressurised oil enters port
S
to chamber
t
and moves
the stopper
157
on the inner surface of the body
155
. This
prevents the spool
156
from moving and closes the
hydraulic motor port
C
. When the pressurised oil is delivered
from port
B
, the spool
123
and the valve
127
move and the
hydraulic motor initiates reverse rotation.
Travel Stopped - Brake Activated
When travel is de-selected, there is no pressure at port
A
.
Spool
123
is no longer under the influence of pressurised oil
(as described above) and returns to its neutral position under
the influence of the two springs
128 and 125
.
The oil from chamber
b
flows through passage
a
and out of
port
A
so that the back pressure is produced on passage
a
and the return speed of the spool is controlled. The inertia
of motor immediately following the de-selection of travel
produces a build up of pressurised oil at port
D
. The
pressurised oil flows from port
D
through the skim passage
between the spool and the rear flange and returns through
port
B
. When the spool returns to neutral status, the
hydraulic motor return passage is fully cut off by the spool
and the motor is gradually stopped.
Section F
Transmission
9803/6020
Section F
3 - 2
Issue 1
Operation
291130
291140
Summary of Contents for JS70
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