Alabama CDL Air Brakes flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Air compressor governor

A device that controls when the air compressor loads to build pressure and unloads to stop building, typically cutting out near 125 psi and cutting in near 100 psi.

Air dryer function

Removes moisture and oil vapor from compressed air before it enters the reservoirs; it purges collected contaminants during the compressor unload cycle.

Supply reservoir

The first tank after the compressor that collects moisture and feeds the primary and secondary circuits through one-way check valves in a dual system.

Dual foot valve

A brake valve with two independent delivery sections, one for each circuit, so a failure in one circuit still allows the other to deliver air.

Slack adjuster

A lever that converts the brake chamber pushrod's linear motion into rotary motion to apply the foundation brake; automatic types maintain pushrod stroke.

Spring brake chamber

A brake chamber using a heavy coil spring to apply the parking brake when air is released, and air pressure compresses the spring to release the brake.

Safety valve

A valve on the supply reservoir that vents air if pressure exceeds a set limit, typically about 150 psi, protecting the system from overpressure.

Primary circuit

One of two separate circuits in a dual air brake system, typically operating the rear brakes, with its own reservoir and check valve protection.

Secondary circuit

The second circuit in a dual air brake system, typically operating the front brakes, remaining functional if the primary circuit fails.

One-way check valve

A valve between reservoirs that allows air to flow in one direction only, preventing backflow from a charged circuit into a failed or leaking circuit.

Low-pressure warning switch

A pressure differential switch that activates a dash lamp and buzzer when pressure in either circuit drops below a set level, about 60 psi.

Dual system failure effect

A failure in one circuit reduces total braking capability but does not cause total brake loss because the other circuit remains functional.

Reservoir drain valves

Valves on each reservoir used to drain moisture and contamination; in a dual system each circuit's reservoir must be drained separately.

Pushrod stroke check

Measuring how far the brake chamber pushrod extends when brakes are applied; excessive stroke beyond the manufacturer's limit indicates adjustment or service is needed.

Brake chamber inspection

Checking brake chambers for cracks, dents, and damage, and verifying that clamp bands and mounting bolts are secure during a pre-trip inspection.

Air line inspection

Checking all air lines and hoses for cracks, chafing, and leaks, and confirming lines are secured and not rubbing against other components.

Reservoir drainage check

Draining all reservoirs and checking expelled air for water, oil, or excessive contamination, which indicates moisture or oil problems in the system.

Compressor build rate check

Verifying the compressor builds pressure at the required rate and that the governor cuts out and cuts in at the specified pressures.

Static leak test

With pressure at governor cut-out and engine off, a pressure drop of more than 3 psi per minute (single vehicle) or 4 psi (combination) indicates a leak.

Applied leak test

With brakes fully applied and engine off, pressure loss should not exceed about 3 psi per minute for a single vehicle or 4 psi for a combination.

Low-pressure warning test

With engine off, pump the brake pedal to reduce pressure; the warning lamp and buzzer must activate before pressure drops below about 60 psi.

Spring brake test

With pressure built and parking brake released the vehicle should not move; with air released, spring brakes should apply and hold the vehicle.

Compressor build-up test

With the engine at operating RPM, pressure should rise from about 85 to 100 psi within 45 seconds, a typical standard for build-up performance.

Governor cut-out pressure

The pressure at which the governor unloads the compressor to stop building air, commonly about 125 psi on most commercial vehicles.

Stopping distance with air brakes

Air brakes have longer stopping distances than hydraulic brakes due to system lag time, so following distance should be increased accordingly.

Brake fade from overheating

Continuous or excessive brake application overheats the brakes and reduces stopping power; use lower gears and engine braking on downgrades instead.

Downgrade brake technique

Select a low gear and use engine braking to control speed on long downgrades, applying brakes sparingly to avoid overheating and air loss.

Low-pressure response

If the low-pressure warning activates, stop as soon as safely possible; spring brakes apply automatically when pressure falls too low.

Parking with air brakes

Set the parking (spring) brakes and use wheel chocks; do not rely on air pressure alone to hold the vehicle when parked.

Automatic spring brake application

A rapid loss of air pressure causes the spring brakes to apply automatically, bringing the vehicle to a controlled stop.

Compressor failure symptom

A failed compressor or governor causes pressure to stop building; watch for slow pressure build-up or failure to reach governor cut-out.

Caging a spring brake

Mechanically compressing the spring with a caging bolt to release the brake for towing or repair; the caging bolt must be removed before returning to service.

Contamination freeze risk

Water or oil in the reservoirs can freeze or damage valves; drain reservoirs regularly and maintain the air dryer to prevent this.