Troubleshooting guide

33
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Parking and Emergency Systems: Tractor Protection Valves
Tractor Protection Valves
The primary function of tractor protection valves (e.g. the
Bendix
®
TP-3
®
tractor protection valve) is to protect
the tractor air brake system under trailer breakaway
conditions and/or conditions where severe air leakage
develops in the tractor or trailer. In addition, in everyday
use, the valve is used to shut off the trailer service and
supply lines before disconnecting the tractor from the
trailer. The valve is usually mounted at the rear of the
tractor cab and a dash mounted control valve.
The Bendix
®
TP-3DC
™
tractor protection valve
integrates the functions of the Bendix TP-3 valve and one
double check valve. A stop light switch port is provided
and is connected to the delivery of the internal double
check valve. It also has an internal single check valve
that prevents air pressure from being trapped in the
trailer service line, which prevents brake compounding
and minimizes roll away conditions.
The Bendix
®
TP-5
™
tractor protection valve is designed
to incorporate several pneumatic control functions within
a common housing, thereby eliminating considerable
interconnection piping.
It includes a combination of two double check valves and
a tractor protection valve. With this valve, either brake
circuit on the vehicle can be used to apply the trailer
Bendix
®
TP-5
™
Tractor
Protection Valve
Bendix
®
TP-3DC
™
Tractor
Protection
Valve
brakes. In addition, when used in conjunction with a
control valve, it opens and closes the trailer service and
supply lines in the same manner as a tractor protection
valve. The valve also incorporates porting for the
installation of the service stop lamp switch, and a quick
release valve for the trailer service line.
Bendix
®
TP-3
®
Tractor
Protection
Valve
Bendix
®
TP-5
™
Tractor
Protection
Valve
Service Hose to Trailer
Supply Hose to Trailer
Hose Couplings
Dummy Hose
Coupling
To the Tractor Spring Brakes
From Secondary Reservoir
From Primary Reservoir
From Rear Axle Service Reservoir
From Front Axle Service Reservoir
Bendix
®
SL-5
™
Stop Light
Switch
Bendix
®
MV-3
®
Dash Control Valve
Front Axle Delivery
Rear Axle
Delivery
Existing Brake Valve
Example of a Tractor Protection System