Alberta Air Brake (Q) Knowledge Test flashcards

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

Wet tank

The reservoir that receives air directly from the compressor and air dryer, trapping moisture and oil before air moves on to the supply and primary/secondary tanks; it is drained first each day.

Relay valve

A valve mounted near the brake chambers that uses stored reservoir air to apply the brakes when it receives a control signal from the foot valve, cutting application lag on long lines.

Quick-release valve

A valve that speeds brake release by exhausting air from the brake chambers directly to atmosphere at the axle, instead of forcing it back through the foot valve.

Tractor protection valve

A valve that seals the tractor's supply and service lines when a trailer separates or the lines are disconnected, keeping enough tractor air to stop the unit.

Air compressor

An engine-driven pump that compresses atmospheric air and delivers it to the reservoirs; it is lubricated by engine oil and cooled by engine coolant.

Governor cut-out pressure

The reservoir pressure at which the governor stops the compressor from pumping, typically about 120 to 125 psi in a heavy truck air brake system.

Governor cut-in pressure

The pressure at which the governor allows the compressor to resume pumping, typically about 90 to 95 psi, producing a normal 20 to 25 psi range.

Air dryer

A device that removes moisture, oil and dirt from compressed air before it reaches the reservoirs, and purges the collected water automatically during each compressor unload cycle.

Reservoir safety valve

A spring-loaded valve on a reservoir that opens near 150 psi to release air if the governor fails and pressure climbs too high, preventing tank rupture.

Brake chamber

An air cylinder containing a diaphragm that converts air pressure into pushrod force, which the slack adjuster and S-cam turn into braking force at the shoes.

Slack adjuster

A lever linking the brake chamber pushrod to the S-cam shaft, converting pushrod travel into rotation and compensating for lining wear by adjusting clearance.

Pushrod stroke limit

The maximum pushrod travel allowed when the brake is fully applied, commonly about 1-3/4 to 2 inches depending on chamber type; exceeding it means the brake is out of adjustment.

Automatic slack adjuster

A slack adjuster that readjusts itself during brake applications; it should never be manually adjusted to hide a stroke that keeps going long, which signals a mechanical fault.

S-cam foundation brake

A drum brake in which a rotating S-shaped cam pushes the brake shoes outward against the drum; it is used with air chambers on most heavy truck axles.

Build-up test

With the engine at fast idle, air pressure should rise from 50 to 90 psi in 3 minutes or less; a slower rise indicates compressor or leakage problems.

Static leak test

With the system fully charged, the engine off and the brakes released, pressure loss must not exceed 2 psi per minute.

Applied leak test

With the brakes fully applied and the engine off, pressure loss must not exceed 3 psi per minute; a higher rate indicates an air leak.

Low-pressure warning device

A buzzer or light that must activate before reservoir pressure drops below 60 psi, warning the driver that braking performance is being lost.

Spring brake automatic application

Spring brakes begin to apply automatically when system pressure falls to roughly 20 to 45 psi, providing emergency braking after a severe loss of air.

Spring brake chamber

A chamber with two sections: the service section applies the brakes with air, while the spring section applies them by spring force when air is removed.

Parking brake control

A yellow diamond push-pull knob that exhausts air from the spring brake chambers to apply the parking brake, and admits air to release it.

Brake compounding

Applying the parking brake while the service brake is still applied, so spring force and air force act on the chamber together and can damage it.

Caging bolt

A mechanical bolt used to compress and hold the spring in a spring brake chamber so the brake stays released for towing or repair; never used for normal driving.

Inversion valve

A trailer valve that applies the trailer spring brakes when supply pressure from the tractor is lost, even if the trailer reservoirs still hold air.

Daily tank draining

Draining moisture from all reservoirs with the compressor off, starting with the wet tank, to prevent corrosion and cold-weather freeze-up in the air lines.

Pre-trip air brake test

A sequence checking compressor build-up, governor cut-in and cut-out, leakage with brakes released and applied, the low-pressure warning, and spring brake operation.

Slack adjuster stroke check

With the brakes applied and the engine off, measure pushrod travel; if the stroke exceeds the limit stamped on the chamber, the brake must be adjusted or repaired.

Gladhand inspection

Checking the trailer couplers for damaged seals, dirt and leaks, and confirming correct connection of the service (blue) and emergency/supply (red) lines.

Brake lag distance

The distance travelled while air moves through the lines and the brakes apply, about half a second; at 100 km/h this adds roughly 14 metres.

Snub braking

A downhill technique of applying the brakes firmly to cut speed by about 10 km/h, then releasing them to cool, repeated as needed instead of continuous light braking.

Brake fade

Loss of braking power caused by heat build-up in drums and linings from prolonged or repeated braking, which reduces friction and greatly increases stopping distance.

Downshift before descent

Selecting a lower gear and using engine braking before starting down a long grade, so the service brakes are used only for speed control, not for holding the load.