Terex TS14G, Maintenance Manual

Page: 276 / 376

Braking System - Treadle Valve
Section 250-0070
SM 1755 Rev1 04-04
2
circuit, the system is 'Lapped' with inlet valve (10) and
exhaust passage (32) closed.
This balance is maintained until the Treadle (1) is
depressed further or released.
When the operator releases the treadle, to reduce the
application of braking force. This causes piston (3) to
rise. With the valve (5) closed, the piston seat (4) will
open exhaust passage (32) causing the air in supply
port 1 to be exhausted till the pressure falls sufficiently
to balance the force on the piston (3).
At which time the piston (3) and its seat (4) will move
down, closing the exhaust passage (32). As the
pressure within the upper circuit falls, piston (8) will
rise. With valve (10) remaining closed and piston seat
(15) rising to uncover the exhaust passage (32) air
pressure from supply port 2 will fall to balance the
forces on the piston (8). At which time piston (8) and
its seat (15) will move down closing the exhaust
passage (32) once again.
The pressures within the upper and lower circuits are
thus maintained at levels proportionate to the degree of
mechanical force exerted by the driver on the treadle.
The self lapping action takes place whenever the brake
application force is increased or decreased.
adjust stop adjustment bolt to the correct setting.
3. Depress treadle (1) to several positions between
fully released position and fully depressed position and
check to be sure the delivered air pressure registered
by the test gauge varies in accordance with the
position in which the treadle (1) is held. The treadle
valve must control all delivery pressures between 0.34
bar (5 lbf/in
2 ) and upper limit of the air system.
4. With treadle (1) fully released, coat exhaust port 'J'
with soap suds to check for leakage. Leakage in
excess of a 25 mm (1 in) soap bubble in one second is
not permissible in either of these tests. If excessive
leakage is found, the treadle valve must be repaired or
replaced.
REMOVAL AND DISASSEMBLY
Numbers in parentheses refer to Fig. 1.
WARNING
To prevent personal injury and property
damage, be sure wheel blocks are properly
secured and of adequate capacity to do the job
safely.
spring seat (2) to the piston (3). Piston (3) moves down
its stem, which in turn moves its exhaust seat (4),
closing the exhaust passage through exhaust valve (5).
Continued movement of piston (3) contacts valve (5)
and moves valve (5) off inlet valve seat (6). Air
pressure from the rear primary reservoir enters supply
port 1, by inlet valve (5) and out of delivery port 1 to
the rear brake chambers via the rear relay valve.
As air flows to delivery port 1 , it also channels through
the transfer holes (7) to the piston (8). Prior to this, the
mechanical force exerted on the piston (8) by the
spring (9) will already have closed off the exhaust
passage in valve (10).
Thus air pressure through holes (7) moves piston (8)
further downward, contacting the valve (10) and moving
it down also, creating a passage between inlet valve
seat (11) and valve (10). Air pressure from the front
primary reservoir enters supply port 2 by inlet valve
(10) and out of delivery port 2 to the front brake
chambers.
Due to the small volume of air needed to pass through
holes (7) to move the piston (8), the action of the air
entering supply port 2 and out to the front brake
chambers can be thought of as instantaneous at the
same time as the air is directed to the Rear brake
chambers. The front brake circuit leads the rear circuit
with a maximum pressure differential of 0.2bar, at a
delivery pressure of 1bar. The differential diminishes
until perfect balance is achieved at about 5bar delivery
pressure.
Air continues to enter supply port 1 from the Rear
primary tanks, until the air pressure under piston (3)
combined with the upward forces of springs (12 & 13)
is greater than the brake application force exerted on
piston (3) which will cause the piston (3) to rise upward
allowing inlet valve (5) to close onto piston seat (4) ,
thus cutting off the air entering supply port 1 and
without letting piston seat (4) uncover the exhaust
passage (32).
This means that the upper circuit is 'Lapped' with both
inlet valve (5) and the exhaust passage (32) is closed.
In the lower circuit the air continues to enter until the
increased air pressure under piston (8) and the upward
force of spring (14) combine to overcome the downward
forces of Spring (9) and air pressure above piston (8).
This causes the piston (8) to rise allowing valve (10) to
close on the inlet seat (11), cutting off the supply of air
from supply port 1, without letting valve seat (15)
uncover the exhaust passage. Similarly to the upper
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