Minnesota CDL Air Brakes Test flashcards

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

Air compressor

Engine-driven pump that builds and maintains air pressure in the brake system; it is governed to cut out near 120-125 psi and cut in near 85-100 psi.

Governor

Valve that senses tank pressure and controls the compressor, stopping it at cut-out pressure and restarting it at cut-in pressure to keep pressure in the safe range.

Safety valve

Pressure relief valve on an air tank, usually set near 150 psi, that opens to release air if the governor fails and pressure rises too high.

Air dryer

Device that removes moisture and oil from compressed air before it enters the tanks, helping prevent corrosion and frozen or blocked valves and lines.

Treadle valve

The foot-operated brake valve; pressing the pedal meters air pressure from the tanks to the brake chambers in proportion to how far the pedal is pushed.

Brake chamber

Air cylinder that converts air pressure into mechanical force; a Type 30 chamber at 100 psi produces roughly 3,000 pounds of push rod force.

Slack adjuster

Link between the brake chamber push rod and the brake shoe; it takes up wear, and push rod travel beyond the limit means brakes are out of adjustment.

Dual air brake system

Two separate air circuits, primary and secondary, so that a loss of pressure in one circuit still leaves some braking ability in the other.

Low air pressure warning

Buzzer and light that must activate before system pressure drops below 60 psi, warning the driver that spring brakes are about to apply automatically.

Spring brakes

Brakes applied by a large coil spring when air pressure is lost or released; air pressure holds the spring compressed to keep the brakes off.

Parking brake control

Yellow diamond-shaped push-pull knob; pulling it releases air and applies the spring brakes, and pushing it in with pressure available releases them.

Trailer supply valve

Red octagon-shaped knob that controls air to the trailer; pulling it shuts off trailer supply and applies the trailer spring brakes.

Tractor protection valve

Valve that closes when trailer air pressure is lost or a line breaks, keeping tractor air from escaping and applying the trailer brakes.

Static leak test

With the engine off and system charged, release the parking brake, hold the foot brake, and check that pressure loss stays within 3 psi per minute (single) or 4 psi (combination).

Applied leak test

With the system charged and the engine off, press and hold the foot brake and confirm pressure loss does not exceed 4 psi in one minute.

Tank draining order

During the pre-trip air tank drain, empty the supply tank first, then the primary and secondary tanks, to remove moisture before driving.

Push rod stroke check

Measure push rod travel with the brakes applied; a stroke at or beyond the vehicle's adjustment limit means the brakes must be adjusted before driving.

Spring brake test

With pressure below 60 psi the spring brakes should be fully applied; as pressure builds after engine start they should release near 100 psi.

Compressor belt check

Inspect the compressor drive belt in the pre-trip; a loose, glazed, or broken belt prevents the compressor from building air pressure.

Total stopping distance

The sum of perception distance, reaction distance, brake lag distance, and effective braking distance; it grows with speed and with brake lag.

Brake lag distance

The distance traveled during the roughly 0.4 second between pressing the pedal and air pressure reaching the brake chambers, about 32 feet at 55 mph.

Perception and reaction distance

Distance covered while the driver sees a hazard and moves the foot to the brake, commonly estimated at about 1.75 seconds, roughly 142 feet at 55 mph.

Speed and braking distance

Braking distance grows with the square of speed, so doubling speed from 30 to 60 mph roughly quadruples the distance needed to stop.

Engine braking on downgrades

Using a lower gear and engine braking to control speed on long grades, avoiding continuous brake use that builds heat and causes fade.

Brake fade

Loss of stopping power caused by overheated brakes; the pedal may feel normal while braking force drops, so prevention through gears and safe speed matters.

Wet brakes

Water on the linings can make brakes grab or pull to one side; light application while moving heats and dries them, followed by a brake test.

Low air pressure response

When the warning sounds, stop safely at once; below about 60 psi the spring brakes apply automatically and the vehicle may not be able to continue.

Air line failure

A broken line or failed chamber lets the dual system's other circuit provide braking; stop as soon as it is safe and do not continue the trip.

Emergency brake application

With air brakes, apply firm steady pressure rather than pumping; a steady application delivers full air pressure to the chambers for maximum braking.

Parking with spring brakes

Always set the spring brakes when parked; they are the fail-safe parking brake and apply automatically if air pressure is lost.

Parking on a grade

Turn the front wheels toward the curb or road edge and chock the wheels when possible; never rely on the foot brake alone to hold the vehicle.

Cold weather parking

Drain the air tanks when parking in cold weather to remove moisture that could freeze in lines and valves and block the brake system.