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OPERATION
TRACTOR PROTECTION VALVE PORTION
Air from the delivery line of the PP-3
located within the cab enters the manifold at the tractor
protection control (delivery) port and passes through the
manifold, acts upon the plunger and moves the inlet valve
off its seat, opening the service line passage through the
manifold.
If the PP-3
™
trailer supply valve is manually or automatically
actuated, the trailer emergency line air pressure will exhaust
out the PP-3
™
trailer supply valve exhaust port, causing
an application of the trailer brakes. The piston spring will
move the piston allowing the inlet valve spring to close the
inlet valve, closing the service line passage through the
manifold, and protecting tractor air pressure.
DOUBLE CHECK VALVE PORTIONS
There are two double check valves in the TP-4
protection valve, and they work in combination with each
other to perform the following functions:
1. To permit the trailer hand control valve to be used for
applying trailer service brakes only.
2. To permit either the primary or secondary circuit from
the dual brake valve to apply trailer brakes if air is lost
in either one of the circuits.
DOUBLE CHECK
VALVE "A"
TO FRONT
BRAKE LIMITING
CONTROL VALVE
PRIMARY
CIRCUIT
(DELIVERY)
FROM DUAL
BRAKE VALVE
SECONDARY
CIRCUIT
(DELIVERY)
™
FIGURE 3 TP-4
TRACTOR PROTECTION VALVE
2
™
trailer supply valve
™
tractor
FROM
TRAILER
DOUBLE CHECK
CONTROL
VALVE "B"
VALVE
REAR FACE
B
A
FRONT FACE
STOP LIGHT
SWITCH
Each double check valve has two separate inlets and one
common outlet, and the passage of air can be traced by
referring to Schematic Figure 3.
Double check valve A inlets are connected to the trailer
hand control valve and the secondary delivery circuit of
the dual brake valve. If the hand control valve is applied,
the shuttle of the double check valve will move and seal
off the secondary delivery passage from the brake valve.
Air from the hand control valve will pass out the outlet port
of double check valve A. See Figure 4.
If a foot brake valve application is made, the shuttle of
double check valve A seals off the trailer hand control valve
air passage and application air will pass out the outlet port
of double check valve A.
Double check valve B inlets are connected to the primary
delivery circuit of the dual brake valve and the outlet of
double check valve A. The purpose of double check valve
B is to permit actuation of trailer brakes should a loss of
air occur in either the primary or secondary braking circuits
of the tractor.
When a foot brake application is made, air from the primary
delivery circuit enters one inlet of the double check valve
and air from the secondary circuit passes through double
check valve A and enters the other inlet valve of double
check valve B. Air passes out the outlet port and through
the tractor protection valve to the trailer actuating the trailer
brakes. See Figure 5.
FROM PP-3
™
SUPPLY VALVE TO TRAILER
EMERGENCY LINE
C
TE-1
™
TRAILER EMERGENCY
STOP LIGHT SWITCH
TO TRAILER SERVICE LINE
TRAILER
VENT
TRAILER
SERVICE LINE
SHUT-OFF
VALVE
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