Service Brake Release; Tractor Protection; Anti-Compounding - BENDIX TP-3DC TRACTOR PROTECTION VALVE Manual

FOOT VALVE
DOUBLE CHECK
TRACTOR CONTROL
(SECONDARY)
HAND VALVE
FIGURE 6 - SERVICE BRAKE RELEASE

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
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.
4
TRACTOR CONTROL
(PRIMARY)
VALVE
STOP LIGHT
SWITCH
PLUNGER
TRACTOR
SUPPLY
™
valve and passes back
DIAPHRAGM
GUIDE
VALVE SPRING
VALVE
TRAILER
CONTROL
TRAILER
SUPPLY
AUXILIARY SUPPLY
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.