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OPERATION
The three push-pull control valves control all the required
functions of tractor spring brake control and trailer air
supply. The operating modes are detailed in Fig. 2 and in
the descriptive write-up which follows.
INITIAL CHARGE
Without air pressure in any part of the system, valve buttons
V-1, V-2, and V-3 are out. When system pressure reaches
60 psi, valve buttons V-1 and V-3 may be pushed in and air
will be delivered through valve V-3 charging the trailer
system. The trailer parking brakes (whether spring or air
applied) will release; however, the tractor spring brakes
remain applied. Pushing valve button V-2 in will release
tractor spring brakes.
NORMAL RUN POSITION
With valve buttons V-1, V-2, in and V-3 out, air is being
supplied to the trailer, all parking brakes are released and
the system is in the normal run position.
ACTUATION OF TRAILER BRAKES ONLY
To actuate only the trailer brakes, valve button V-1 is pulled
out. This action exhausts the air supply from the trailer
supply line, causing the tractor protection valve to close.
Typical use of this mode would be to apply trailer brakes
before uncoupling. This mode would be used during a tractor
"bob-tail" operation.
MANUAL SYSTEM PARK
To apply the parking brakes on both tractor and trailer, valve
button V-2 is pulled out.
NOTE: If the trailer is not equipped with spring brakes
(pre-121), it is desirable to release the trailer
emergency application and provide a "demonstrated
park" (proven holding ability via tractor spring brakes
only). This may be done by positioning valve button
V-1 "IN," V-2 button "OUT," and pushing button V-3
"IN." This action recharges the trailer supply line,
releases the trailer brakes and allows the tractor
spring brakes to demonstrate their ability to hold
both the tractor and trailer in a parked position.
AUTOMATIC SYSTEM PARK
If the supply or delivery pressure for the push-pull module
is reduced, either valve buttons, V-1 or V-2, or both will pop
out automatically when the supply pressure is between 35-45
psi. When button V-1 pops out, the trailer supply line will
vent to atmosphere, applying trailer brakes; should button
V-2 pop out, the tractor spring brakes will also apply as well
as the trailer.
OPERATING AND LEAKAGE TESTS
Prior to testing for leakage and function of the components
in either module, the knobs must first be removed from the
push-pull valves and then any panel cover plate or escutcheon
plates removed so that the top of the spool assemblies and
the retaining rings that hold the spools in place are visible.
For an operational test of the push-pull module, a test gauge
should be connected to a tractor spring brake line and one
to the trailer supply hose.
Function of the push-pull valves may then be checked per
the chart, Fig. 3.
PUSH-PULL MODULE OPERATIONAL TEST
VALVE
SUPPLY
POSITION
PRESSURE
V-1
V-2
V-3
100 PSI
I N
OUT OUT
IN
I N
OUT
IN
OUT IN
OUT IN*
OUT
100 PSI
I N
IN
OUT
REDUCING
TO
35-45 PSI
OUT OUT OUT
*When V-2 is pushed IN, V-3 should pop OUT.
FIGURE 3
PUSH-PULL MODULE LEAKAGE CHART
100 PSI SUPPLY PRESSURE FOR ALL TESTS
VALVE
POSITION
V-1 V-2
V-3
Leakage Symptoms Correction
OUT OUT OUT
Valve V-1 at S-1
(Around Stem)
Valve V-2 at S-2
(Around Stem)
OUT OUT OUT
Valve V-1 at S-3
Valve V-2 at S-4
Exhaust Port P-6
IN
OUT OUT
Valve V-3 at S-5
Valve V-3 at S-6
Exhaust Port P-6
OUT IN
OUT
Exhaust Port P-6
IN
OUT IN
Exhaust Port P-6
FIGURE 4
AIR DELIVERY AIR DELIVERY
TO TRACTOR
TO TRAILER
SPRING
SUPPLY
BRAKES
HOSE
ZERO
ZERO
100 PSI
100 PSI
ZERO
100 PSI
100 PSI
ZERO
100 PSI
100 PSI
ZERO
ZERO
Replace spool
assembly in V-1
Replace spool
assembly in V-2
Replace spool
assembly in V-1
Replace spool
assembly in V-2
Replace spool in
V-1 or V-2 as
required
Replace spool in
V-3
Replace spool in
V-3
Replace spool in
V-1
or V-3 as required
Replace spool in
V-2
or V-3 as required
Replace spool
assembly in V-1
or V-3
3
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