Troubleshooting guide

18
For more information, visit www.bendix.com or www.foundationbrakes.com • 1-800-AIR-BRAKE (1-800-247-2725)
Section 3: The Control System
• Vehicle parking using push-pull hand-operated
valves and spring brakes;
• An anti-compounding system design to prevent
both the service brakes and the parking brakes from
being applied at the same time; and
• Proportioning valves to adjust braking when a
tractor is not pulling a trailer.
The control system typically consists of:
• A foot brake valve and, often, an additional hand-
operated trailer brake control valve;
• Brake actuators or rotochambers, to change the
applied air pressure into a push rod force which
operates the foundation brakes (air disc, foundation
drum brakes, etc.);
• Quick release valves to assist in releasing the brakes
quickly;
The Control System: Dual Circuit Brake Valves
Secondary
Delivery to
Trailer Brakes
Dual Circuit
Brake
Valve
Primary Reservoir
Secondary Reservoir
Delivery to
Rear Brakes
SECONDARY
PRIMARY
Modulator
(See the ABS
section for
more about
modulators)
Modulator
May Also Use
a Bendix
®
QR-1
®
Valve
Primary
Delivery to
Trailer Brakes
Delivery to
Front Brakes
Brake
Chamber
Brake
Chamber
See the fi nal
section of this
handbook for more
sample system
schematics in color.
Vehicle Maintenance
Optimal system braking requires a properly maintained air brake system, including:
• Low system air leakage, with a maintained air dryer, compressor and valve components
• Regularly maintained foundation brakes (drum, wide-drum, or air disc) which meet
appropriate safety standards and regulations
• A fully-functioning ABS system without any active ABS Diagnostic Trouble Codes (DTCs)
• Properly sized and infl ated tires, with a safe tread depth
Typical Foot Brake Application Delivery System