Michigan CDL Air Brakes flashcards

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

Governor cut-out pressure

The pressure at which the governor stops the compressor from pumping, typically about 100 to 110 psi on most heavy-duty air brake systems.

Governor cut-in pressure

The pressure at which the governor restarts the compressor after cut-out, typically about 85 psi, restoring system pressure before it drops too low.

Supply (wet) tank

The first tank after the compressor that collects moisture and oil, protecting downstream tanks and valves from contamination and corrosion.

Safety valve

A pressure-relief valve on the supply tank that opens at about 150 psi to prevent over-pressurization if the governor or compressor fails.

Foot valve

The self-lapping, graduated brake valve operated by the treadle that lets the driver apply and hold any desired brake pressure.

Brake chamber force

Force equals chamber effective area times air pressure; a Type 30 chamber at 100 psi produces about 3,000 pounds of force.

Spring brake operation

A heavy coil spring applies the parking brake when air pressure is lost; air pressure must be present to compress the spring and release the brake.

Low-pressure warning threshold

The warning buzzer or light must activate before system pressure falls below 60 psi, alerting the driver of an impending brake failure.

Static leak test limits

With the engine off and system charged, pressure loss must not exceed 3 psi per minute for a single vehicle or 4 psi for a combination.

Applied leak test limits

With the engine off and brakes held firmly, leakage must not exceed 4 psi per minute for a single vehicle or 6 psi for a combination.

Compressor build-up test

With the engine at operating rpm, pressure should rise from 85 to 100 psi within 45 seconds, showing the compressor works properly.

Slack adjuster free play

Normal push rod free play is about 3/8 to 1/2 inch; excessive free play means the brakes need adjustment or repair.

Push rod travel limit

Push rod travel beyond the adjustment limit, commonly about 2 inches for a Type 30 chamber, means the brakes are out of adjustment.

Tractor protection valve

A valve that closes and sets the trailer brakes automatically when system pressure drops to about 20 to 45 psi, preventing a runaway trailer.

Air tank draining

Draining tanks daily removes moisture and oil that can freeze in winter, corrode valves, and cause brake failure if left in the system.

Air dryer function

A desiccant dryer removes moisture from compressed air and purges automatically; a failed purge valve lets water reach the tanks.

Low-pressure warning response

If the warning sounds while driving, stop at the first safe place because brake pressure may be lost and total failure is possible.

Spring brake emergency application

When system pressure falls to about 20 to 45 psi, spring brakes apply automatically, stopping the vehicle even if the driver does nothing.

Burst line or chamber

A loud hiss with rapid pressure loss indicates a burst line or failed chamber; apply brakes firmly, stop, and secure the vehicle.

Compressor failure signs

Pressure that will not build or builds very slowly means the compressor has failed; stop driving before the remaining air supply is exhausted.

Brake fade

Overheated brakes from long downgrades lose stopping power; stop and let them cool, and do not set the parking brake on hot drums.

Trailer hand valve use

If the foot valve fails, the trailer hand valve, if equipped, can apply trailer brakes to slow and stop the vehicle.

Winter air dryer freeze

Frozen moisture in lines or the dryer can block air flow and cause brake drag or failure; drain tanks and use an alcohol evaporator.

Three-part air brake check

The check covers static leakage, low-pressure warning and compressor build-up, and applied leakage, performed before driving.

Low-pressure warning test

With the engine off, pump the brake pedal to reduce pressure; the warning buzzer or light must come on before pressure drops below 60 psi.

Parking brake holding test

With the system charged, set the parking brake and try to move; the vehicle must not move, confirming the spring brakes hold.

Downgrade gear selection

Select a gear low enough that brakes are not needed to hold speed; use the same gear that would be needed to climb the grade.

Pre-trip brake inspection order

Perform the walk-around inspection and air brake check in order: static leak check, warning device, build-up, and applied leak check.

Governor function

The governor senses system pressure and controls the compressor, cutting it out at high pressure and back in at low pressure.

Alcohol evaporator

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

Automatic drain valve

A valve that drains moisture from air tanks automatically; the supply tank should still be checked and manually drained periodically.

Air brake system failure

Loss of air pressure from leaks, compressor failure, or frozen lines; the vehicle must be stopped and repaired before continued driving.