4
FIGURE 6 -
SERVICE BRAKE RELEASE
DIAPHRAGM
GUIDE
VALVE SPRING
TRAILER
CONTROL
TRAILER
SUPPLY
TRACTOR
SUPPLY
PLUNGER
STOP LIGHT
SWITCH
TRACTOR CONTROL
(SECONDARY)
TRACTOR CONTROL
(PRIMARY)
VALVE
AUXILIARY SUPPLY
DOUBLE CHECK
VALVE
FOOT VALVE
HAND VALVE
SERVICE BRAKE RELEASE
As shown in Figure 6, when a service brake application
is released, air from the trailer control line returns to the
trailer control port of the TP-3DC
™
valve and passes back
through the open inlet. It then forces the diaphragm to
move against its seat in the cover and fl ows out the tractor
control (secondary) port to be exhausted at either the foot
valve or the hand control valve.
TRACTOR PROTECTION
Figure 7 shows the tractor protection function of the
TP-3DC
™
valve. When the trailer supply valve is pulled
out, or if trailer supply line air pressure decreases to
approximately 20-30 psi, the valve spring forces the plunger
down and closes the inlet valve. Service air from the tractor
can no longer pass through the valve to the trailer.
ANTI-COMPOUNDING
The TP-3DC
™
valve has an internal single check valve
that prevents simultaneous spring brake and service brake
applications on the trailer. As shown in Figure 8, if a service
application is being made, and then the trailer supply valve
is pulled out to apply the trailer spring brakes, service air
passes back through the single check valve and exhausts
at the trailer supply valve. Future compounding is prevented
by the closed inlet valve.
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID PERSONAL
INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
engine be in operation, EXTREME CAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.
3. Do not attempt to install, remove, disassemble
or assemble a component until you have read
and thoroughly understand the recommended
procedures. Use only the proper tools and observe
all precautions pertaining to use of those tools.
