Bendix Commercial Vehicle Systems TP-2 User Manual

®

Bendix® TP-2™ Tractor Protection Valve

SD-03-3651

CONTROL CAP (13)

CONTROL PORT

CAP NUT

EXHAUST PORT

TRACTOR

SERVICE

PORT

TRACTOR

EMERGENCY

PORT

FIGURE 1 - TRACTOR PROTECTION SYSTEM

TRAILER
SERVICE

PORT

TRAILER
EMERGENCY
PORT

DESCRIPTION

The Bendix® TP-2™ tractor protection valve functions as a
set of remote controlled cut-out cocks, protecting the tractor
air supply should a loss of air occur in the trailer side
(delivery) of the valve. The TP-2™ valve is a three line system
as compared to the TP-3™ valve which is a two line system.

The valve is normally piped as shown in Figure 2. Lines
delivering service and supply (emergency) pressure to the
trailer are routed through the valve. A third control Iine comes
from the on-off control valve in the cab.

With the control valve in the “normal” (on) position and
reservoir pressure at approximately 50 psi, the valve will
open and service and emergency air is permitted to pass
through the valve. With the control valve in the emergency
position (off) position the vaIve is closed and service and
emergency lines on the trailer (delivery) side of the valve
are open to atmosphere through the vaIve’s exhaust port.

The valve will automatically close and vent delivery lines to
atmosphere should air pressure drop below a safe operating

EXHAUST VALVE PLUNGER AND
DIAPHRAGM ASS’Y (14)

CAP NUT (12)

EXHAUST PLUNGER

SPRING (15)

O-RING (16)

VALVE

RETAINER (7)

SPRING (8)

O-RING (10)

SERVICE AND EXHAUST

(11) O-RING

VALVE SEAT (5)

(1) CAP SCREW

(2) COVER

VALVE (6)

O-RING (9)

EMERGENCY

VALVE (3)

EMERGENCY VALVE

SPRING (9)

minimum pressure (approx. 40 psi), thus retaining and
protecting the tractor air brake system against complete
loss of air.

NOTE: With a TP-2™ valve system it should be noted that

the pneumatic logic for the legally required automatic
function is incorporated in the TP-2™ valve whereas
in the current TP-3™ valve system the logic is in the
supply valve in the cab. Consequently a TP-2™ valve
should never be replaced by a TP-3™ valve unless
the on-off control valve in the cab is replaced with
either a PP-3™ or PP-7™ trailer supply valve.

OPERATION - NORMAL POSITION

With air pressure at approximately 50 psi at the control
port, the diaphragm and plunger assembly is depressed
and the plunger contacts the service and exhaust valve
surface sealing the exhaust passage through the center of
the plunger. Continued travel of the plunger moves the service
valve off its seat, opening the service passage from the

1

CONTROL

VALVE

COMPRESSOR

BRAKE

VALVE

TRAILER

SERVICE LINE

TRAILER

EMERGENCY

LINE

TRACTOR

PROTECTION

VALVE

NO. 1

RESERVOIR

FIGURE 2 - TRACTOR PROTECTION SYSTEM

tractor service port to the trailer service port. The stem of
the service and exhaust valve contacts the emergency valve,
sealing the exhaust passage. Continued travel of the service
and exhaust valve plunger moves the emergency valve off its
seat and allows air to flow from the tractor emergency port
to the trailer emergency port.

EMERGENCY POSITION

If air pressure in the control port (and on top of the diaphragm
and plunger assembly) drops below approximately 40 psi,
the combined forces of the exhaust plunger spring, the
service and exhaust valve spring and the emergency valve
spring will return the diaphragm and plunger assembly
allowing the service and exhaust valve and the emergency
valve to close. Further flow of air through either the service
or emergency ports is stopped. The loss in air pressure
which would precede such action would be indicated to the
driver, either visually or audibly by the low pressure warning
device, before such action would occur.

PREVENTIVE MAINTENANCE

Important: Review the Bendix Warranty Policy before

performing any intrusive maintenance procedures. A warranty
may be voided if intrusive maintenance is performed during
the warranty period.

No two vehicles operate under identical conditions; as a
result, maintenance intervals may vary. Experience is a
valuable guide in determining the best maintenance interval
for air brake system components. At a minimum, the TP-2
valve should be inspected every 6 months or 1500 operating
hours, whichever comes first, for proper operation. Should
the TP-2™ valve not meet the elements of the operational

NO. 2

RESERVOIR

CHECK

VALVE

tests noted in this document, further investigation and service
of the valve may be required.

OPERA TING AND LEAKAGE CHECK

NOTE: To make the following operating and leakage

checks,an accurate test gauge installed in spare
hose coupling is required. The vehicle dash gauge
should be checked for accuracy against the test
gauge prior to making these tests.

1. Block and/or hold the vehicle by means other than air
brakes during these test.

2. Drain vehicle reservoirs. Then close drain cocks.

3. Disconnect vehicle emergency and service hose
couplings and connect assembled hose coupling and
test gauge in tractor emergency hose coupling.

4. Start engine and build up system pressure.

5. As pressure in system builds up there should be no
pressure reading on test gauge. When system pressure
reaches 30 psi on dash gauge, make and hold a foot or
hand valve application and observe that no air escapes
at the open service hose coupling.

6. When system pressure reaches 40 to 60 psi, valve should
open and pressure reading show on test gauge. Allow
system to build up to 100 psi and shut off engine.

7. With soap solution coat exhaust port of the Tractor
Protection V alve. Leakage of a 1" bubble in 3 seconds
is permissible (175 SCCM).

™

8. Place the tractor protection control valve in the
“Emergency” position and note that emergency line
pressure drops promptly to zero on test gauge.
Disconnect coupling and test gauge.

2