1
®
SD-03-3651
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
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
Bendix
®
TP-2
™
Tractor Protection Valve
FIGURE 1 - TRACTOR PROTECTION SYSTEM
TRAILER
EMERGENCY
PORT
CAP NUT
CONTROL PORT
TRAILER
SERVICE
PORT
EXHAUST PORT
TRACTOR
SERVICE
PORT
TRACTOR
EMERGENCY
PORT
(11) O-RING
(2) COVER
EXHAUST PLUNGER
SPRING (15)
CONTROL CAP (13)
O-RING (9)
VALVE SEAT (5)
SERVICE AND EXHAUST
VALVE (6)
O-RING (10)
SPRING (8)
VALVE
RETAINER (7)
O-RING (16)
CAP NUT (12)
EXHAUST VALVE PLUNGER AND
DIAPHRAGM ASS’Y (14)
EMERGENCY
VALVE (3)
EMERGENCY VALVE
SPRING (9)
(1) CAP SCREW
