Air Brakes Section Review

Vocabulary-style flashcards covering the technical specifications, safety protocols, and operational components of heavy vehicle air brake systems based on CDL-style training materials.

Application pressure gauge

A gauge that shows how much air pressure you are applying to the brakes.

Spring brakes stop threshold

On a straight truck, these brakes will bring the vehicle to a stop when air pressure drops below $20\,psi$.

Alcohol evaporator

A component used to reduce the risk of ice forming in the air storage tank and valves during cold weather, which could cause brake failure.

Dual air brake system failure protocol

If a low air pressure warning comes on for only one system, the driver must bring the vehicle to a complete stop right away and park safely until fixed.

Water drainage

The process of removing water from compressed air tanks to prevent it from freezing in cold weather and causing brake failure.

Safety valve

A valve set to discharge automatically when air pressure reaches $150\,psi$.

Spring pressure

The mechanical force legally used to hold the parking or emergency brakes on trucks and buses.

Dual parking control valves

Valves that allow a driver to use pressure from a separate tank to release spring emergency/parking brakes to move the vehicle a short distance.

Air pressure build-up rate

In a properly functioning dual air brake system with minimum size tanks, pressure should build from $85$ to $100\,psi$ within $45\,\text{seconds}$.

Static air leakage rate

For a straight truck or bus with the engine off and brakes released, the rate should not be more than $2\,psi$ per minute.

Applied air leakage rate

For a straight truck or bus with the engine off and the brakes on, the rate should not be more than $3\,psi$ in one minute.

Air compressor cutoff

The pressure level at which the air compressor stops pumping air, which is $125\,psi$.

Low air pressure warning signal

A visible warning that must come on before air pressure in the service tanks falls below $60\,psi$.

Brake drum expansion

An effect caused by excessive use of service brakes leading to overheating.

S-cam drum

The most common type of foundation brake found on heavy vehicles.

Air brake lag distance

The distance added to stopping at $55\,mph$ on dry pavement, approximately $32\,feet$.

Brake leg distance

The factor that causes the total stopping distance for air brakes to be longer than that for hydraulic brakes.

Brake fade

The loss of braking power occurring when a driver must push harder on the brake pedal to control speed on a downgrade due to excessive heat.

Slack adjuster free play limit

The point at which free play needs adjustment, which is when it exceeds about $1\,inch$ when pulled hard.

S-cam function

The component that forces the brake shoes against the inside of the brake drum.

Supply pressure gauge

A gauge that indicates how much pressure is currently in the air tanks.

Emergency stab braking

A technique where the driver presses the brake pedal hard, releases when wheels lock, and reapplies when wheels start rolling.

Air compressor governor

The mechanism that controls when the compressor pumps air into the air tanks.

Storage tank manual drainage

If not automatic, oil and water must be drained from the storage tanks at the end of each day of driving.

Brake drum crack safety limit

A vehicle is unsafe if it has brake drum cracks longer than $\frac{1}{2}$ the width of the friction area.

Minimum drive-off pressure

The least amount of pressure needed in air storage tanks before driving off is $100\,psi$.