Arkansas CDL Air Brakes Test 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 building more air, typically around 120-125 psi in a properly functioning system.

Governor cut-in pressure

The pressure at which the governor restarts the compressor to rebuild air, typically around 100 psi, after pressure has dropped from cut-out.

Safety valve function

A spring-loaded valve on the air reservoir that vents air at a set pressure, commonly about 150 psi, to prevent tank over-pressurization.

Alcohol evaporator purpose

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

Low air pressure warning

A light, buzzer, or both that must activate before reservoir pressure falls below 60 psi, warning the driver of insufficient air.

Supply versus application gauge

The supply gauge shows air pressure available in the reservoirs; the application gauge shows how much pressure is being applied to the brakes.

Compressor lubrication source

The air compressor is cooled and lubricated by the engine's cooling and oil systems, not by a separate oil supply of its own.

Brake chamber function

Converts air pressure into mechanical force; the pushrod moves the slack adjuster, which rotates the camshaft to apply the foundation brakes.

Dual air brake system

Two separate air circuits, primary and secondary, so a failure in one circuit still leaves the other able to stop the vehicle.

Primary and secondary circuits

In a dual system, the primary circuit typically operates the rear brakes and the secondary circuit typically operates the front brakes.

Check valve purpose

Allows air to flow in only one direction, preventing a loss of pressure in one reservoir from draining another reservoir.

Double check valve

A valve that admits air from whichever circuit has the higher pressure, allowing either circuit to supply a protected device.

Spring brake application range

Spring brakes apply automatically as air pressure falls into the 20-45 psi range, stopping the vehicle when air is lost.

Front brake limiting valve

A valve that reduces front brake force in slippery conditions; it must be returned to the normal position for full braking.

Reservoir draining

Opening the drain valves on the wet, primary, and secondary tanks removes moisture and oil; close them afterward.

Slack adjuster check

Inspect that slack adjusters move freely and pushrods have correct travel; excessive pushrod travel means the brakes are out of adjustment.

Compressor belt check

The compressor drive belt must be tight and not cracked, frayed, or glazed; a loose or broken belt prevents air pressure buildup.

Audible air leak

A leak that can be heard around hoses, fittings, or valves during inspection is a defect that must be repaired before driving.

Spring brake holding test

Apply the parking brakes and try to move the vehicle at low speed with the engine running; the vehicle must not move.

Static leak test

With the engine off and system charged, pressure should not drop more than about 3 psi in one minute for a single vehicle.

Applied brake leak test

With the engine off and brakes applied and held, pressure should not drop more than about 3 psi per minute; more indicates a leak.

Combination vehicle leak rate

For a combination vehicle, the static leak rate should not exceed about 4 psi per minute with the engine off and system charged.

Compressor build-up check

At fast idle, the compressor should build pressure from about 85 to 100 psi within 45 seconds in a properly functioning system.

Low pressure warning test

Pump the brake pedal to reduce pressure and confirm the warning device activates before the gauge falls below 60 psi.

Spring brake auto-apply test

Continue reducing pressure after the warning and confirm the spring brakes apply automatically in the 20-45 psi range.

Downgrade braking technique

Select a low gear before starting down a long steep grade and use brakes only to control speed, not to hold the vehicle.

Fanning the brakes

Repeatedly pumping the brake pedal can exhaust air pressure faster than the compressor rebuilds it, especially on long downgrades.

Falling supply gauge

A supply gauge that drops while driving indicates an air leak or compressor problem; stop and investigate before continuing.

Wet brake drying

Apply the brakes lightly while moving to heat and dry wet brakes, but avoid hard stops until braking returns to normal.

Loss of air pressure response

If air pressure is lost, the spring brakes apply automatically as pressure falls into the 20-45 psi range, bringing the vehicle to a stop.

Dual system circuit failure

If one circuit fails, the other circuit still provides braking; use it to stop safely and get the system repaired before driving again.

Parking brake control

Usually a yellow diamond-shaped knob that releases air from the spring brake chambers to apply the brakes and admits air to release them.