BENDIX SD-03-3656 User Manual
Bendix® TP-3DC™ Tractor Protection Valve with Double Check
TRACTOR CONTROL
(PRIMARY) 3/8"-18 NPT
LABEL WITH
™
VALVE
1/2"-14 NPT
TRACTOR
CONTROL
(SECONDARY)
3/8"-18 NPT
TP-3DC
O.E. PC. NO. HERE
DATE CODE
STAMPED HERE
SD-03-3656
1/2"-14 NPT
STOP LIGHT
SWITCH
1/4"-18 NPT
TRACTOR SUPPLY
1/4"-18 NPT
FIGURE 1 - TP-3DC™ TRACTOR PROTECTION VALVE WITH DOUBLE CHECK
AUXILIARY SUPPLY
1/4" -18 NPT
DESCRIPTION
The tractor protection valve system protects tractor air
brakes during trailer breakaway and/or when severe air
leakage develops in the tractor or trailer. This function is
required by law.
In normal use the tractor protection valve is used to shut off
the trailer control line before disconnecting the tractor from
the trailer. It is usually mounted at the rear of the tractor
cab, and it is used in conjunction with a dash-mounted
control valve.
The TP-3DC™ valve integrates tractor protection and double
check valve functions. It also has an integral single check
TRAILER CONTROL
1/2"-14 NPT
TRAILER SUPPLY
1/2"-14 NPT
Port Embossed I.D. Thread Size
Tractor Supply TRAC SUP 1/4"-18 NPT
Auxiliary Supply AUX SUP 1/4"-18 NPT
Tractor Control (Primary) TRACT CONT 3/8"-18 NPT
Tractor Control (Secondary) TRAC CONT 3/8"-18 NPT
Stop Light Switch STP LT SW 1/4"-18 NPT
Trailer Supply TRLR SUP 1/2"-14 NPT
Trailer Control TRLR CNTL 1/2"-14 NPT
Weight: 1.5 lbs.
Material: Die-cast aluminum
Operating pressure: 150 psi maximum
Operating temperature: -40° to 200° F
Figure 1 shows the TP-3DC™ valve with its port designations,
O.E. piece number, and date code identifi cations.
valve that prevents trapping of air in the trailer control line.
This prevents service and spring brake compounding, and
it avoids a trailer roll away situation if the trailer is parked
with the air applied.
Figure 2 is a sectional view of the TP-3DC™ valve, and
Figure 3 presents the TP-3DC™ valve in a partial air brake
system schematic.
™
QR-L
VALVE FACTORY
INSTALLED ON SOME
TP-3DC™ VALVE MODELS
A stoplight switch port allows direct stoplight installation,
and the auxiliary supply port, when connected to the
BP-R1™ control port, eliminates a tee in the tractor
supply line. Also, a QR-L™ valve can be factory installed
in the trailer control and/or supply port to meet timing
requirements.
1
TRACTOR CONTROL
(PRIMARY)
TRACTOR
CONTROL
(SECONDARY)
STOP LIGHT
SWITCH
PLUNGER
TRACTOR
SUPPLY
AUXILIARY SUPPLY
FIGURE 2 - TP-3DC™ TRACTOR PROTECTION VALVE WITH
DOUBLE CHECK SECTIONAL VIEW
DIAPHRAGM
GUIDE
VALVE SPRING
TRAILER
CONTROL
CHECK VALVE
CHECK VALVE
SPRING
TRAILER
SUPPLY
OPERATION
INITIAL CHARGE
As shown in Figure 4, during initial charge air pressure
enters the TP-3DC™ tractor supply port (TRAC SUP). In
addition to passing through the TP-3DC
the trailer and auxiliary supply lines, supply air moves the
plunger, against valve spring pressure, into contact with
the guide. With approximately 45 psi at the tractor supply
port, the inlet valve opens. The TP-3DC™ valve is now in the
normal “run” mode, ready to receive and deliver a service
brake application from the foot valve or hand valve.
SERVICE BRAKE APPLICATION
Figure 5 shows a normal service brake application. Supply
air holds the valve open, and the TP-3DC™ valve receives
service air from the primary and secondary service
circuits on the tractor. The greater pressure of the two (the
secondary service circuit double check valve delivers the
greater of foot valve secondary delivery and trailer hand
control valve delivery) will cause the TP-3DC™ valve's
internal check valve diaphragm to seal the port with the
lower pressure. The higher pressure will then fl ow out the
open inlet to the trailer control line. Figure 5 shows an
application with primary service air as the greater pressure.
Note that service air pressure also activates the stop light
switch, and it fl ows to the single check valve. However , with
supply pressure acting on the opposite side of the single
check valve, the valve remains closed.
™
valve to and out
TRAILER
SUPPLY VALVE
TRAILER
CONTROL VALVE
DOUBLE CHECK VALVE
(TO TRACTOR
SPRING BRAKES)
TRAC
CONT
STP LT
SW
TRACT
CONT
TRAC
SUP
TRLR CNTL
TRLR
AUX
SUP
Embossed I.D. Thread Size
TRAC SUP 1/4"-18 NPT
AUX SUP 1/4"-18 NPT
TRACT CONT 3/8"-18 NPT
TRAC CONT 3/8"-18 NPT
STP LT SW 1/4"-18 NPT
TRLR SUP 1/2"-14 NPT
TRLR CNTL 1/2"-14 NPT
SUP
FIGURE 3 - PARTIAL AIR BRAKE SYSTEM SCHEMATIC WITH TP-3DC™ TRACTOR PROTECTION VALVE WITH DOUBLE
CHECK
2
TRACTOR
CONTROL
(SECONDARY)
TRACTOR CONTROL
(PRIMARY)
STOP LIGHT
SWITCH
PLUNGER
DIAPHRAGM
GUIDE
VALVE SPRING
VALVE
TRAILER
CONTROL
FIGURE 4 - INITIAL CHARGE
FOOT VALVE
DOUBLE CHECK
VALVE
TRACTOR CONTROL
(SECONDARY)
HAND VALVE
TRACTOR
SUPPLY
TRACTOR CONTROL
(PRIMARY)
STOP LIGHT
SWITCH
PLUNGER
TRAILER
SUPPLY
AUXILIARY SUPPLY
DIAPHRAGM
GUIDE
VALVE SPRING
VALVE
TRAILER
CONTROL
FIGURE 5 - SERVICE BRAKE APPLICATION
TRACTOR
SUPPLY
TRAILER
SUPPLY
AUXILIARY SUPPLY
3
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