California 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 unloads the compressor, typically about 125 psi, stopping further air delivery until pressure drops to the cut-in point near 100 psi.

Air dryer function

A device that removes moisture and oil vapor from compressed air before it enters the storage tanks, then purges collected water automatically when the compressor unloads.

Supply tank

The first storage tank after the compressor and dryer, also called the wet tank; it collects condensation and feeds the primary and secondary circuits through one-way check valves.

Foot valve

The treadle-operated brake valve that meters air from the reservoirs to the brake chambers in proportion to how far the driver pushes the pedal.

Brake chamber

An air cylinder containing a diaphragm and pushrod; air pressure pushes the diaphragm, moving the pushrod to apply the foundation brake, with force equal to pressure times area.

Slack adjuster

The lever connecting the brake chamber pushrod to the S-cam; it multiplies pushrod force and transfers it to the cam, and automatic types maintain correct pushrod stroke.

Relay valve

A valve that uses a small control signal from the foot valve to send reservoir air directly to the rear brake chambers, speeding application and release.

Low-pressure warning

A light and buzzer that must activate before system pressure drops below 60 psi, warning the driver that spring brakes will soon apply automatically.

Dual circuit layout

A system with two separate air circuits, usually primary for rear brakes and secondary for front brakes, each with its own reservoir, check valve, and warning lamp.

Check valve role

A one-way valve between tanks that allows air to flow in only one direction, preventing a leak in one circuit from draining the other circuit or the supply tank.

Tractor protection valve

A valve that closes when tractor air pressure falls to about 20 to 45 psi, sealing the tractor's air supply and causing the trailer air supply knob to pop out.

Safety valve

A pressure relief valve on the supply tank that opens at about 150 psi to release air and prevent tank rupture if the governor fails to unload the compressor.

Trailer air line colors

The supply or emergency line is red and the service line is blue; the electrical cable is separate, and mismatched connections can prevent proper trailer brake operation.

Alcohol evaporator

A device that injects alcohol vapor into the air system to lower the freezing point of moisture, helping prevent ice blockage in lines and valves during cold weather.

Leak test, brakes released

With the engine off and parking brakes released, a single vehicle should lose no more than 2 psi in one minute; a combination should lose no more than 3 psi.

Leak test, brakes applied

With the engine off and the brake pedal held down, a single vehicle should lose no more than 3 psi per minute; a combination should lose no more than 4 psi.

Spring brake pop-out test

With the engine running, pump the pedal until the red and yellow knobs pop out, which should happen between 20 and 45 psi, proving the emergency brakes work.

Compressor buildup test

With pressure at 85 psi and the engine idling, the gauge must rise to 100 psi within 45 seconds, showing the compressor and governor build air properly.

Chamber inspection

Check each brake chamber for cracks, dents, and a loose clamp ring, and confirm the pushrod and slack adjuster move freely without binding or misalignment.

Normal operating pressure

The air gauge should read roughly 100 to 125 psi while driving; pressure below 100 psi means the driver must find the cause before continuing.

Steady pedal braking

Apply the brake pedal firmly and hold it rather than pumping; each pump cycle releases and reapplies air, wasting stored pressure on long downgrades.

Downgrade gear selection

Before starting down a long or steep grade, select a low gear that limits speed, then use engine braking with short, firm brake applications to control descent.

Cold engine warm-up

Idle the engine briefly before driving so the compressor can build air pressure to operating level and the low-pressure warning goes out.

Wet brake drying

After driving through deep water, apply the brakes lightly while moving to heat and dry the linings, then test that normal stopping power has returned.

Trailer hand valve limit

The trailer hand valve applies only the trailer brakes, so it is used only to test trailer brakes and never for normal stopping or parking.

Rapid pressure loss response

Downshift, use engine braking, and brake gently to stop off the roadway; do not continue driving, because spring brakes will apply when air runs out.

Spring brake fail-safe

Mechanical springs apply the parking brakes automatically when air pressure falls to about 20 to 45 psi, so a major air loss still stops the vehicle.

Caging a spring brake

Inserting and tightening the caging bolt compresses the spring to release the brake for towing or repair, leaving that wheel with no parking or emergency braking.

Frozen air line

Moisture that freezes in a line or valve blocks air flow and can disable a circuit; daily tank draining and an air dryer or alcohol evaporator reduce the risk.

Parking brake knob

The yellow diamond-shaped knob controls the spring brakes; pulling it out applies them, and pushing it in releases them only when air pressure is sufficient.

Retarder use limits

A retarder helps control speed on downgrades and saves service brakes, but it does not replace them and must be turned off on wet, icy, or slippery roads.

ABS warning lamp

A lamp that stays on after startup means the antilock system is disabled; normal braking still works, but wheel lockup prevention is unavailable.