Illinois CDL Air Brakes flashcards

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

Governor

A device on the compressor that controls air pressure by cutting the compressor out at about 125 psi and back in at about 100 psi, maintaining pressure in the system.

Safety valve

A valve on the supply tank that releases air at about 150 psi to prevent over-pressurization if the governor fails to cut off the compressor.

Air storage tanks

Tanks that hold compressed air for the brake system; manual drain cocks at the bottom remove accumulated water and oil.

Alcohol evaporator

A device that injects alcohol into the air system to prevent moisture from freezing in lines and valves during cold weather.

Foot valve

The brake pedal valve that applies air pressure to the brakes when depressed and exhausts the air to release the brakes when released.

Slack adjuster

A linkage component connecting the push rod to the brake chamber that allows adjustment of brake shoe travel to maintain proper braking.

Spring brake chamber

A brake chamber containing a strong spring that applies the brakes automatically when air pressure is lost, acting as an emergency and parking brake.

Low air pressure warning

A light and buzzer that must activate before air pressure drops below 60 psi, alerting the driver to a dangerous loss of pressure.

Tractor protection valve

A valve that closes automatically when trailer air pressure drops to about 20-45 psi, preventing loss of tractor air supply.

Primary circuit

One of two separate air circuits in a dual system, typically operating the rear drive axle brakes and having its own storage tank.

Secondary circuit

The second air circuit in a dual system, typically operating the front steering axle brakes and having its own storage tank.

Dual air system

A brake system with two independent circuits so that a failure in one circuit does not disable the other, allowing the vehicle to still stop.

Trailer air supply knob

The red knob that controls air to the trailer; pulling it out sets the trailer spring brakes and pushing it in charges and releases them.

Parking brake knob

The yellow knob that sets the tractor spring brakes when pulled out and releases them when pushed in, provided air pressure is sufficient.

Circuit isolation

The design feature of a dual air system that keeps a failure in one circuit from draining air from the other circuit.

Front brake limiting valve

A valve on some older vehicles that reduces front braking force in slippery conditions; modern systems use automatic limiting instead.

Leak test with engine off

With tanks full and engine off, release the parking brake and watch gauges; a drop of more than 3 psi in one minute indicates a leak.

Applied brake leak test

With the engine off, apply the brakes fully and hold for one minute; a pressure drop of more than 3 psi signals a leak in the applied system.

Governor cut-out check

With the engine running, build pressure until the compressor stops pumping at about 125 psi, confirming the governor cuts out properly.

Low pressure warning test

Turn the key on with pressure below 60 psi; the warning light and buzzer must activate, and they must turn off above 60 psi.

Spring brake test

With the engine off, release the parking brake and watch for the brakes to set automatically as pressure drops below about 45 psi.

Slack adjuster inspection

Check push rod travel and brake shoe thickness; excessive travel means the brakes need adjustment before driving.

Air tank draining

Open the drain cocks at the bottom of the air tanks daily to remove moisture and oil that can damage the brake system.

Safety valve test

Pull the ring on the safety valve; it should release air and reseat, confirming it is not stuck and will protect against over-pressurization.

Brake lag

The delay between pressing the brake pedal and the brakes actually applying, caused by the time air takes to travel through the lines.

Engine braking

Using a lower gear to let the engine slow the vehicle on downgrades, reducing reliance on the brakes and preventing overheating.

Fanning the brakes

Repeatedly pumping the brake pedal, which wastes air and reduces stopping ability; steady pressure should be used instead.

Riding the brakes

Keeping continuous pressure on the brake pedal, which overheats drums and linings and can cause brake fade on long downgrades.

Brake fade

Loss of stopping power caused by overheated drums and linings from continuous braking, reducing friction between the shoes and drums.

Runaway vehicle response

If brakes fail on a downgrade, downshift, use engine braking, and look for an escape ramp to slow and stop the vehicle safely.

Spring brake automatic application

When air pressure drops below about 45 psi, the spring brakes apply automatically, bringing the vehicle to a stop.

Emergency stop procedure

If the low pressure warning sounds, stop as soon as safely possible, investigate the leak, and do not drive until pressure is restored.