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To Park Tractor and Trailer Combination - With both controls pushed in (the normal
driving mode), pulling out the (YELLOW) Parking Brake control applies BOTH the trac-
tor and trailer spring/parking brakes. The Trailer Air Supply control (RED) will remain
pushed in and will not pop out. Both the tractor and the trailer should now be parked
with all spring/parking brakes applied.
To Apply Trailer Spring Brakes Only—The trailer spring brakes can be applied separately
from the tractor spring brakes. This is usually done when uncoupling the fifth wheel
from the trailer after the trailer has been moved. The trailer spring brakes can be
applied separately by pulling out the(RED) Trailer Air Supply control while the (YEL-
LOW) Parking Brake control is pressed in. This will not apply the tractor spring brakes.
NOTE: This is the position that the tractor will be in when it is not towing a trailer,
also know as the “bobtail” mode.
Tractor Protection Valve
The primary function of the Tractor Protection Valve (TP3) 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 operates in conjunction with the dash-mounted control valve.
Pressure Protection Valve
The pressure protection valve is normally a closed, pressure control valve which
can be referred to as a non-exhausting sequence valve. The air from the compressor
“reservoir” port connects to a tee connection at the inlet port of the pressure protec-
tion valve and the accessory reservoir. The delivery port of the protection valve runs to
the supply—or inlet—port of the 5th Wheel Unlatch air control valve.
This valve protects the brake reservoir pressurized air from a loss by the auxiliary air
circuit (5th wheel unlatch) by shutting off the auxiliary circuit’s air supply in the event of
a failure in that circuit.
Bobtail Proportioning Relay Valve (BP-R1)
The BP-R1 Bobtail Proportioning Relay valve is a combination of two individual valves
in a single housing. The lower portion, or body of the BP-R1, contains a “standard”
service brake relay valve which functions as a relay station to speed up brake applica-
tion and release. The upper portion, or cover, houses a brake proportioning valve,
which reduces normal service brake application pressure when the tractor is not tow-
ing a trailer.
Used in tractor air brake systems only, the BP-R1 is installed in place of a standard
relay valve. It functions as a standard service relay during operation of a tractor-trailer
combination. During bobtail operation, the BP-R1 is installed in place of a standard
relay valve. It functions as a standard service relay during operation of a tractor-trailer
combination. During bobtail operation, the BP-R1 improves controllability and reduces
stopping distances by reducing air pressure to the rear actuators/chambers, whose
axle load has been greatly reduced.
Air Brake System
Revised 11/15/99
(10 stránky)
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