NJ 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 reservoirs; the governor loads it to build pressure and unloads it when the system reaches cut-out pressure.

Governor

Valve on the compressor that controls cut-out and cut-in pressure; it stops the compressor from building at about 120-135 psi and restarts it near 100 psi.

Air dryer

Device downstream of the compressor that removes moisture and oil from the air before it reaches the reservoirs, helping prevent freeze-ups and corrosion in valves and lines.

Wet tank

Reservoir closest to the compressor that collects the most moisture and oil; it is drained first and most frequently to keep contamination out of the rest of the system.

Foot valve

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

Slack adjuster

Lever that connects the brake chamber pushrod to the brake shoe mechanism; it converts pushrod stroke into shoe movement and must stay within the manufacturer's adjustment limit.

Relay valve

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

Spring brake chamber

Brake chamber containing a powerful coil spring that applies the brakes when air pressure is released; air pressure must be present to compress the spring and release the brakes.

Dual air brake system

System with two separate air circuits, each with its own reservoir, so a failure in one circuit still leaves the other able to stop the vehicle.

Primary circuit

In the standard split, the circuit that operates the rear brakes; the secondary circuit operates the front brakes, and each has its own reservoir.

Check valve

One-way valve between circuits that prevents air from a failed circuit from escaping into the good circuit, preserving pressure where it is still needed.

Low pressure warning

Buzzer and light that must activate at or before 60 psi in the service brake system, warning the driver that pressure is falling toward spring brake application.

Tractor protection valve

Valve that closes the tractor-to-trailer air lines when tractor pressure drops to about 20-45 psi, keeping enough air for the tractor's brakes and preventing trailer air loss.

Spring brake application point

Pressure range of roughly 20-45 psi at which the spring brakes apply automatically as system air is lost, bringing the vehicle to a stop.

Alcohol evaporator

Device that introduces alcohol vapor into the air system to prevent moisture from freezing in lines and valves during cold weather operation.

Static leak test

With the engine off, full pressure built, and brakes released, watch the gauge; a loss greater than 3 psi per minute on a single vehicle indicates a leak.

Applied leak test

With the engine off and the service brake treadle held fully applied, a pressure loss greater than 4 psi per minute on a single vehicle indicates a leak.

Low pressure warning test

With the engine off, pump the brake pedal to lower pressure; the warning light and buzzer must come on at or before 60 psi.

Spring brake test

Keep pumping below the warning point; the parking brake valve should pop out and the spring brakes should apply at roughly 20-45 psi.

Compressor build-up test

With the engine at operating rpm, pressure should rise from 85 to 100 psi within about 45 seconds; slower build-up indicates a compressor, belt, dryer, or leak problem.

Service brake test

At about 5 mph, apply the brakes firmly; the vehicle should stop smoothly without pulling, and the pedal should not feel spongy or go to the floor.

Pre-trip leak listen

With the engine off and brakes released, listen for hissing at hoses, fittings, chambers, and valves; any audible leak must be repaired before driving.

Reservoir draining

Open the drain cocks, wet tank first, and watch for water or oil; milky or oily discharge points to a failed air dryer or worn compressor.

Pushrod travel limit

With the brakes applied, pushrod stroke must stay within the manufacturer's or inspector's limit, commonly about 1 inch for a standard chamber; excessive travel means repair, not adjustment.

Brake chamber inspection

Check for dents, cracks, and a loose or broken clamp band; a damaged chamber or diaphragm is a defect that requires repair before the vehicle is used.

Stab braking

On a long downgrade, apply the brakes firmly enough to slow the vehicle, then release fully to let them cool, instead of holding light continuous pressure.

Brake fade

Loss of braking force caused by overheated drums and linings, usually from riding the brakes down a long grade; the cure is prevention with engine braking and stab braking.

Air brake lag

Slight delay between pedal movement and brake application because air must travel through lines and valves; it lengthens stopping distance, so allow extra following distance.

Downgrade gear selection

Before starting down a long or steep grade, select a low gear and use engine braking so the service brakes are not overheated and faded.

Low pressure response

If the warning sounds while driving, stop as soon as it is safe; continued driving drains remaining air and the spring brakes will apply automatically.

Service brake failure

If the service brakes fail, apply the parking brake gradually; a full application at speed can lock the wheels, so apply it progressively while steering to safety.

Trailer breakaway

If the trailer separates from the tractor, the trailer's emergency relay valve applies the trailer spring brakes automatically when the supply line separates.