BENDIX SD-03-3653 User Manual

Bendix® TP-4™ Tractor Protection Valve (Formerly VM-1)

PRIMARY CIRCUIT

DELIVERY PORT

(PCD)

SECONDARY

CIRCUIT

DELIVERY PORT

(SCD)

SERVICE STOP

LIGHT SWITCH

(SLS) PORT

SUPPLY PORT (TSS)

FIGURE 1 EXTERIOR VIEW

TRAILER EMERG. STOP

LIGHT SWITCH (TE-SLS)

PORT

TRAILER EMERG.

SUPPLY (TES) PORT

TRAILER SERVICE

SD-03-3653

MOUNTING

SURFACE

VENT

10

9

4

11

FIGURE 2 SECTIONAL

13

14

DESCRIPTION

The Bendix® TP-4™ tractor protection valve is used in the
dual air brake system and houses three valves that serve
the trailer and tractor braking system. The valves are:

1. The trailer service line shut off portion of tractor
protection system which operates in conjunction
with the dash-mounted PP-3™ trailer supply valve to
manually or automatically close and retain suffi cient air
pressure in the towing vehicle to stop it with its service
brakes.

2

8

3
VENT
12

6

7
PIPE PLUG

5

1

16

15

2. A double check valve which permits either primary or

secondary circuit air pressure from the dual brake valve
to actuate trailer brakes.

3. A double check valve which permits use of a trailer

control valve to control only the trailer brakes.

In addition to the ports necessary for the function of the
above described valves, the manifold also provides ports
for the installation of the service stop light switch, front
axle limiting control valve, and the TE-1™ trailer emergency
stop light switch.

Four 23/64" holes are provided for mounting.

1

OPERATION

TRACTOR PROTECTION VALVE PORTION

Air from the delivery line of the PP-3™ trailer supply valve
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
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™ tractor
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.

trailer supply valve is manually or automatically

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

TRAILER

CONTROL

VALVE

REAR FACE

TO FRONT

BRAKE LIMITING

CONTROL VALVE

PRIMARY

CIRCUIT

(DELIVERY)

FROM DUAL

BRAKE VALVE

DOUBLE CHECK

VALVE “A”

A

SECONDARY

CIRCUIT

(DELIVERY)

FRONT FACE

FIGURE 3 TP-4™ TRACTOR PROTECTION VALVE

DOUBLE CHECK

VALVE “B”

B

STOP LIGHT

SWITCH

FROM PP-3

SUPPLY VAL VE T O TRAILER

EMERGENCY LINE

™

C

™

TE-1

TRAILER EMERGENCY

STOP LIGHT SWITCH

TO TRAILER SERVICE LINE

TRAILER

VENT

TRAILER

SERVICE LINE

SHUT-OFF

VALVE

2