Air Brakes · Dual Air Brake Systems
Why do most heavy-duty vehicles use a dual air brake system instead of a single air system?
Explanation
Most heavy-duty vehicles use a dual air brake system so that if one of the two systems loses pressure, the vehicle still has at least partial braking from the other system, instead of losing all air braking at once. 49 CFR 383.111(b)(1) requires CDL applicants to know general air brake system nomenclature, the required-knowledge area a dual system's basic purpose falls under; the manual states the safety rationale directly, though no single CFR provision requires a "dual" design by that name for the purpose of redundancy. Fuel efficiency is wrong because a dual system's design goal is braking redundancy, not fuel savings. Letting a driver choose which axle to brake is wrong because both systems apply together under normal driving; the driver does not select between them. Reducing the purpose to manufacturing cost is wrong because a dual system is inherently more complex and expensive to build than a single system, the opposite of a cost-cutting measure.
Source: 49 CFR 383.111(b)(1)
Related Dual Air Brake Systems questions
- Structurally, how is a dual air brake system actually built?
- In a vehicle with a dual air brake system, which tank's pressure determines when the low air pressure warning activates?
- If one of the two systems in a dual air brake system loses most of its pressure while the vehicle is being driven, what happens?
- In a dual air brake system, how can a driver tell which of the two systems, the primary or the secondary, has lost pressure?