Terex TS14G, Maintenance Manual

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Section 250-0280
SM 1794 4-99
1
BRAKING SYSTEM - Relay Valve
Fig. 1 - Relay Valve Installation
1 - Relay Valve
2 - Bolt
3 - Lockwasher
4 - Adaptor
5 - Elbow - 90°
6 - Reducer
7 - Tee Piece
SM - 2238
DESCRIPTION
The relay valve can be identified as item 18 in
Section 250-0000, AIR BRAKING SYSTEM
SCHEMATIC.
Mounted off the rear fuel tank right hand mounting
bracket, the relay valve is located in the air lines
between the treadle valve and rear brake chambers.
The relay valve speeds the application and release of
air pressure to and from tractor and scraper brake
chambers.
OPERATION
Numbers in parenthesis refer to Fig. 2.
When a signal pressure is applied to port D air flows
into chamber C between the cover A and the top of the
piston B. A relatively small applied pressure reacts
quickly over the large area of piston B, which is forced
down. This movement of the piston closes the exhaust
passage as the valve seat N seals against the inlet/
exhaust valve G, which is also moved down against
the return spring K and opens the inlet at L. Air now
flows from the reservoir port F past the open valve
chamber M, and from there it passes out of one of the
delivery ports. This flow continues until the combined
forces of the piston and valve return springs and the
air pressure beneath the piston balance the force of
the applied air pressure above the piston. The piston
now lifts sufficiently to allow the valve to rise and close
the inlet at L. The valve is now in the 'lapped' condition
with both the inlet and the exhaust closed.
If the signal pressure is reduced at D, the forces below
the piston are now greater and the piston rises until
the valve seat N is lifted clear of the valve, allowing air
to exhaust through the hollow in the piston at J, and
out to atmosphere past the rubber flap at H.
The exhaustion continues until the force below the
piston is reduced to balance that above the piston and
the exhaust closes again, lapping the valve.
These procedures are repeated instantly the applied
pressure at port D is varied, either up or down, the
valve being self-lapping under all conditions.
Fig. 2 - Cutaway View of Relay Valve
SM - 2239
1
2
3
4
5
6
7
M N
L
K
J H G
A B C
D
F
Courtesy of Machine.Market