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SD-03-3656 |
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Bendix® TP-3DC™ Tractor Protection Valve with Double Check |
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TRACTOR CONTROL |
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(PRIMARY) 3/8"-18 NPT |
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LABEL WITH |
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TP-3DC™ VALVE |
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TRACTOR |
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O.E. PC. NO. HERE |
1/2"-14 NPT |
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CONTROL |
DATE CODE |
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(SECONDARY) |
1/2"-14 NPT |
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3/8"-18 NPT |
STAMPED HERE |
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STOP LIGHT |
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TRAILER CONTROL |
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SWITCH |
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1/2"-14 NPT |
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1/4"-18 NPT |
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TRAILER SUPPLY |
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1/2"-14 NPT |
QR-L™ VALVE FACTORY |
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TRACTOR SUPPLY |
AUXILIARY SUPPLY |
INSTALLED ON SOME |
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1/4"-18 NPT |
1/4" -18 NPT |
TP-3DC™ VALVE MODELS |
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FIGURE 1 - TP-3DC™ TRACTOR PROTECTION VALVE WITH DOUBLE CHECK
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 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.
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.
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. |
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Material: Die-cast aluminum |
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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 identifications.
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.
1
TRACTOR CONTROL |
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(PRIMARY) |
DIAPHRAGM |
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TRACTOR |
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CONTROL |
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(SECONDARY) |
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GUIDE |
STOP LIGHT |
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SWITCH |
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VALVE SPRING |
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TRAILER |
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CONTROL |
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CHECK VALVE
PLUNGER
CHECK VALVE
SPRING
TRACTOR
SUPPLY 
TRAILER SUPPLY
AUXILIARY SUPPLY
FIGURE 2 - TP-3DC™ TRACTOR PROTECTION VALVE WITH DOUBLE CHECK SECTIONAL VIEW
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™ valve to and out 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 flow 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 flows to the single check valve. However, with supply pressure acting on the opposite side of the single check valve, the valve remains closed.
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TRACT |
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CONT |
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TRLR CNTL |
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TRAILER |
TRAC |
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SUPPLY VALVE |
CONT |
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(TO TRACTOR |
STP LT |
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SPRING BRAKES) |
SW |
AUX |
TRLR |
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TRAC |
SUP |
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SUP |
SUP |
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TRAILER |
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CONTROL VALVE |
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Embossed I.D. |
Thread Size |
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TRAC SUP |
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1/4"-18 NPT |
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DOUBLE CHECK VALVE |
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AUX SUP |
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1/4"-18 NPT |
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TRACT CONT |
3/8"-18 NPT |
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TRAC CONT |
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3/8"-18 NPT |
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STP LT SW |
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1/4"-18 NPT |
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TRLR SUP |
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1/2"-14 NPT |
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TRLR CNTL |
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1/2"-14 NPT |
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FIGURE 3 - PARTIAL AIR BRAKE SYSTEM SCHEMATIC WITH TP-3DC™ TRACTOR PROTECTION VALVE WITH DOUBLE CHECK
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TRACTOR CONTROL |
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(PRIMARY) |
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DIAPHRAGM |
TRACTOR |
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CONTROL |
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(SECONDARY) |
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GUIDE |
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VALVE SPRING |
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VALVE |
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STOP LIGHT |
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SWITCH |
TRAILER |
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CONTROL |
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PLUNGER |
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TRACTOR |
TRAILER |
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SUPPLY |
SUPPLY |
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AUXILIARY SUPPLY |
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FIGURE 4 - INITIAL CHARGE |
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FOOT VALVE |
TRACTOR CONTROL |
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(PRIMARY) |
DIAPHRAGM |
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DOUBLE CHECK |
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VALVE |
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TRACTOR CONTROL |
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(SECONDARY) |
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GUIDE |
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VALVE SPRING |
HAND VALVE |
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VALVE |
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STOP LIGHT |
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SWITCH |
TRAILER |
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PLUNGER |
CONTROL |
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TRACTOR |
TRAILER |
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SUPPLY |
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SUPPLY |
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AUXILIARY SUPPLY |
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FIGURE 5 - SERVICE BRAKE APPLICATION |
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