2
FIGURE 3
- PARTIAL AIR BRAKE SYSTEM SCHEMATIC WITH TP-3DC
™
TRACTOR PROTECTION VALVE WITH DOUBLE
CHECK
TRACT
CONT
TRLR
SUP
TRAC
CONT
STP LT
SW
TRLR CNTL
FIGURE 2
- TP-3DC
™
TRACTOR PROTECTION VALVE WITH
DOUBLE CHECK SECTIONAL VIEW
TRACTOR CONTROL
(PRIMARY)
TRACTOR
CONTROL
(SECONDARY)
AUXILIARY SUPPLY
TRACTOR
SUPPLY
STOP LIGHT
SWITCH
PLUNGER
TRAILER
SUPPLY
CHECK VALVE
SPRING
CHECK VALVE
TRAILER
CONTROL
VALVE SPRING
GUIDE
DIAPHRAGM
TRAILER
SUPPLY VALVE
TRAILER
CONTROL VALVE
DOUBLE CHECK VALVE
(TO TRACTOR
SPRING BRAKES)
AUX
SUP
TRAC
SUP
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 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.
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
