I85PREP
⌘ K
Alberta Air Brake (Q) Knowledge Test study materials
Alberta Air Brake (Q) Knowledge Test study resources

Alberta Air Brake (Q) Knowledge Test practice questions

One question at a time. Build your Alberta Air Brake (Q) Knowledge Test understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Air brake system fundamentals and component identification

Which component produces the compressed air used by an air brake system?

  1. The compressor Correct answer.
  2. The governor
  3. The foot valve
  4. The service reservoir

Explanation

The compressor is driven by the engine and pumps air into the brake system. The governor only controls the compressor, while reservoirs store air and the foot valve controls brake application.

Question 2Air brake system fundamentals and component identification

Which component controls whether the compressor is building air or running unloaded?

  1. The governor Correct answer.
  2. The safety valve
  3. The air dryer
  4. The relay valve

Explanation

The governor monitors reservoir pressure and signals the compressor to load at cut-in pressure and unload at cut-out pressure. This keeps system pressure within its normal operating range.

Question 3Air brake system fundamentals and component identification

What is the main purpose of the wet reservoir in an air brake system?

  1. To collect moisture and oil Correct answer.
  2. To reduce pressure for the trailer
  3. To store air for the parking brake only
  4. To supply air directly to brake chambers

Explanation

The wet reservoir is the first tank after the compressor, so moisture and oil tend to condense there. Air then passes to the dry reservoir for service use.

Question 4Air brake system fundamentals and component identification

Which valve prevents air from flowing back from the reservoir toward the compressor?

  1. The check valve Correct answer.
  2. The relay valve
  3. The safety valve
  4. The quick release valve

Explanation

A check valve allows air to flow in one direction only, protecting the compressor from backflow. The safety valve relieves overpressure, while relay and quick release valves affect brake timing.

Question 5Air brake system fundamentals and component identification

What is the function of the safety valve installed on an air reservoir?

  1. It warns of low pressure
  2. It drains moisture daily
  3. It sets cut-in pressure
  4. It releases excess pressure Correct answer.

Explanation

The safety valve is spring-loaded and opens if reservoir pressure rises above a safe limit, protecting the system from overpressure. It does not control normal compressor cycling or warn the driver.

Question 6Air brake system fundamentals and component identification

Which colour identifies the parking brake control knob in a typical air brake vehicle?

  1. Yellow Correct answer.
  2. Green
  3. Red
  4. Blue

Explanation

The parking brake control is normally a yellow diamond-shaped knob. The red knob is used for trailer air supply.

Question 7Air brake system fundamentals and component identification

What is the function of a brake chamber?

  1. It adjusts slack in the brake linkage
  2. It converts air pressure to force Correct answer.
  3. It controls compressor cut-out pressure
  4. It stores air for the service brakes

Explanation

Air pressure entering the brake chamber moves a diaphragm or piston, pushing the pushrod to apply the brake. Storage, slack adjustment, and compressor control are handled by other components.

Question 8Air brake system fundamentals and component identification

What does a slack adjuster do in an air brake system?

  1. It rotates the brake camshaft Correct answer.
  2. It releases chamber air quickly
  3. It limits reservoir pressure
  4. It removes moisture from air lines

Explanation

The slack adjuster is a lever that transfers pushrod travel into rotation of the brake camshaft. It also provides a way to adjust brake clearance.

Question 9Air brake system fundamentals and component identification

At what pressure does the compressor governor normally cut out on a typical heavy vehicle air brake system?

  1. About 125 psi Correct answer.
  2. About 100 psi
  3. About 150 psi
  4. About 80 psi

Explanation

The governor typically unloads the compressor at about 120 to 125 psi. It normally reloads the compressor at about 100 psi.

Question 10Air brake system fundamentals and component identification

Before air pressure falls to what value must the low air pressure warning activate?

  1. 20 psi
  2. 80 psi
  3. 60 psi Correct answer.
  4. 40 psi

Explanation

The low-pressure warning must operate before reservoir pressure drops below about 60 psi. This gives the driver time to stop safely before spring brakes apply automatically.

Question 11Air brake system fundamentals and component identification

When do spring brakes apply automatically?

  1. When the foot valve is fully applied
  2. When the compressor is unloading
  3. When reservoir pressure reaches cut-out
  4. When spring air is released Correct answer.

Explanation

Spring brakes are held off by air pressure. When that air is released or lost, the mechanical springs apply the brakes.

Question 12Air brake system fundamentals and component identification

What is the function of the tractor protection valve?

  1. It supplies trailer air only when parked
  2. It dries air before it reaches the trailer
  3. It adjusts trailer brake slack
  4. It limits tractor air loss on separation Correct answer.

Explanation

The tractor protection valve closes when trailer supply pressure drops sharply, such as during a breakaway. This keeps the tractor's air supply from being lost through the trailer lines.

Question 13Air brake system fundamentals and component identification

What is the main purpose of a relay valve?

  1. To warn the driver of low pressure
  2. To speed brake apply and release Correct answer.
  3. To remove moisture from the reservoir
  4. To prevent compressor overpressure

Explanation

A relay valve uses a small control signal to deliver reservoir air quickly to a remote brake circuit. This shortens the time needed to apply and release the brakes.

Question 14Air brake system fundamentals and component identification

What does an air dryer do in an air brake system?

  1. It dries compressed air Correct answer.
  2. It supplies air to spring chambers
  3. It increases pressure above cut-out
  4. It measures brake lining wear

Explanation

The air dryer removes moisture from compressed air before it reaches the reservoirs. This helps prevent corrosion and freezing in the air system.

Question 15Air brake system fundamentals and component identification

What is the function of a quick release valve?

  1. It limits pressure in the trailer circuit
  2. It allows air flow in one direction
  3. It drains the wet tank automatically
  4. It exhausts chamber air quickly Correct answer.

Explanation

A quick release valve is mounted near the brake chambers and exhausts their air rapidly when the brake control is released. This speeds up brake release.

Question 16Air brake system fundamentals and component identification

How does a dual-circuit foot valve improve safety?

  1. It prevents compressor pressure build-up
  2. The other circuit can still brake Correct answer.
  3. It automatically adjusts slack adjusters
  4. It drains moisture from both circuits

Explanation

A dual-circuit foot valve separates the service brake system into two circuits. If one circuit loses pressure, the other circuit can still deliver air to apply some brakes.

Question 17Air brake system fundamentals and component identification

What is the purpose of the trailer supply valve (red knob)?

  1. It adjusts trailer brake chamber stroke
  2. It controls air supply to the trailer Correct answer.
  3. It applies the trailer spring brakes only
  4. It drains the trailer reservoirs

Explanation

The red trailer supply valve controls air delivery to the trailer and works with the tractor protection valve. Pulling it out closes the supply and can cause the trailer spring brakes to apply.

Question 18Air brake system fundamentals and component identification

What is the function of an alcohol evaporator in an air brake system?

  1. It automatically drains reservoirs
  2. It increases compressor cut-out pressure
  3. It removes oil from compressed air
  4. It prevents line moisture from freezing Correct answer.

Explanation

An alcohol evaporator adds alcohol vapour to the air system to help prevent moisture from freezing in lines and valves. It does not change pressure settings or remove oil.

Question 19Air brake system fundamentals and component identification

What does the foot valve (brake valve) do?

  1. It protects the system from overpressure
  2. It controls compressor unloading
  3. It meters air to the service brakes Correct answer.
  4. It stores air for the parking brake

Explanation

The foot valve is operated by the brake pedal and controls how much air pressure is delivered to the service brakes. It provides graduated brake application.

Question 20Air brake system fundamentals and component identification

What is meant by a dual air brake system?

  1. Two separate service brake circuits Correct answer.
  2. A system using air and hydraulic fluid
  3. A system with two compressors
  4. A system with two foot pedals

Explanation

A dual air brake system has two separate air circuits for service braking. If one circuit fails, the other can still provide braking.

Question 21Air brake system fundamentals and component identification

At what pressure is a reservoir safety valve typically set to open?

  1. About 60 psi
  2. About 125 psi
  3. About 100 psi
  4. About 150 psi Correct answer.

Explanation

A typical reservoir safety valve is set to open at about 150 psi. This is above normal governor cut-out pressure but below the pressure at which system components could be damaged.

Question 22Air brake system fundamentals and component identification

What is the purpose of the compressor unloader mechanism?

  1. It drains moisture from the wet tank
  2. It releases spring brakes during parking
  3. It stops compressor pumping at cut-out Correct answer.
  4. It reduces pressure to the trailer brakes

Explanation

When the governor reaches cut-out pressure, it signals the unloader to hold the compressor inlet valves open. The compressor then stops pumping air even though it continues to turn.

Question 23Air brake system fundamentals and component identification

If the primary circuit in a dual air brake system fails, what remains available?

  1. No service brakes remain at all
  2. Only the parking brake remains
  3. The secondary circuit still brakes Correct answer.
  4. The trailer supply valve closes forever

Explanation

A dual air brake system is designed so that a failure in one circuit does not disable the other. The secondary circuit can still provide service braking, although braking performance may be reduced.

Question 24Air brake system fundamentals and component identification

What is the function of a pressure protection valve?

  1. It warns of low pressure
  2. It adjusts brake chamber stroke
  3. It drains the wet tank
  4. It isolates a leaking circuit Correct answer.

Explanation

A pressure protection valve closes when pressure falls below a set value, isolating one part of the system. This helps prevent a leak in an accessory or secondary circuit from draining air needed for essential braking.

Question 25Air brake system fundamentals and component identification

Which component retracts the pushrod and releases the service brake when air is exhausted from the brake chamber?

  1. Safety valve
  2. Governor
  3. Return spring Correct answer.
  4. Slack adjuster

Explanation

When air leaves the brake chamber, the return spring pushes the diaphragm or piston back. This retracts the pushrod and releases the service brake.

Question 26Air brake system fundamentals and component identification

Which component in an air brake system produces the compressed air that operates the brakes?

  1. The foot valve treadle
  2. The governor assembly
  3. The air dryer cartridge
  4. The compressor Correct answer.

Explanation

The compressor is driven by the engine and is the only component that generates compressed air. All other air-operated parts, such as valves and chambers, either control or consume the air the compressor supplies.

Question 27Air brake system fundamentals and component identification

On a tractor-trailer combination, the coupler for the emergency (supply) line is normally identified by which colour?

  1. Blue
  2. Yellow
  3. Green
  4. Red Correct answer.

Explanation

North American practice colour-codes the emergency or supply gladhand red and the service gladhand blue. Keeping the colours distinct helps prevent cross-coupling of the two lines during hook-up.

Question 28Air brake system fundamentals and component identification

What is the purpose of a check valve in an air brake system?

  1. It removes moisture from the air supply
  2. It reduces pressure supplied to the trailer
  3. It allows air to flow in one direction only Correct answer.
  4. It regulates compressor cut-out pressure

Explanation

A check valve is a one-way device that permits air to pass in the intended direction and blocks flow in the reverse direction. This protects charged reservoirs from losing air back through the supply side.

Question 29Air brake system fundamentals and component identification

In a typical three-reservoir arrangement, which tank receives air directly from the compressor first?

  1. The supply reservoir Correct answer.
  2. The secondary reservoir
  3. The primary reservoir
  4. The trailer reservoir

Explanation

Compressor discharge enters the supply or wet tank first, where most moisture and oil settle out. Air then passes through a check valve to the primary and secondary reservoirs that feed the brake circuits.

Question 30Air brake system fundamentals and component identification

What does a bobtail proportioning valve do on a tractor unit?

  1. It applies the trailer spring brakes automatically
  2. It limits compressor output with no trailer connected
  3. It increases trailer braking during a hard stop
  4. It reduces rear braking when no trailer is attached Correct answer.

Explanation

Without a trailer, a lightly loaded tractor can lock its rear wheels under full application pressure. The bobtail valve senses the absence of a trailer supply line and limits rear brake pressure to keep the unit stable.

Question 31Air brake system fundamentals and component identification

An anti-compounding valve prevents which of the following?

  1. Service air from adding to spring brake force Correct answer.
  2. Trailer brakes from releasing before tractor brakes
  3. The compressor from overcharging the wet tank
  4. Air escaping when a gladhand is uncoupled

Explanation

If a service brake application is made while the spring brakes are still applied, the two forces can add together and overload the chamber and foundation brake. The anti-compounding valve blocks service air from reaching a chamber whose spring brake is applied.

Question 32Air brake system fundamentals and component identification

A brake chamber marked as a Type 30 has what characteristic?

  1. 30 square inches of effective area Correct answer.
  2. 30 pounds per square inch of application pressure
  3. 30 inches of maximum pushrod stroke
  4. 30 millimetres of pushrod travel

Explanation

Brake chamber type numbers refer to the effective diaphragm area in square inches. A Type 30 chamber therefore delivers roughly 30 times the applied air pressure as force on the pushrod.

Question 33Air brake system fundamentals and component identification

Why would a driver mechanically cage a spring brake chamber?

  1. To test the warning buzzer
  2. To release it manually without air pressure Correct answer.
  3. To drain the supply reservoir
  4. To set the slack adjuster free play

Explanation

Caging compresses and locks the spring with a mechanical bolt so the brake is released even when no air pressure is available. This is done to move a vehicle with a disabled air system, such as during towing or recovery.

Question 34Air brake system fundamentals and component identification

What is the trailer hand valve, usually a blue control knob, used for?

  1. Supplying air to the trailer emergency line
  2. Applying the trailer service brakes for a test Correct answer.
  3. Draining the trailer reservoir
  4. Locking the trailer spring brakes for parking

Explanation

The trailer hand valve meters service air to the trailer brakes only, which lets the driver check that the trailer brakes apply and release correctly. It does not charge the trailer or hold it parked.

Question 35Air brake system fundamentals and component identification

In a dual-circuit air brake system, what does a two-way check valve allow?

  1. The compressor to feed both circuits equally
  2. Either circuit to supply the park control Correct answer.
  3. Both circuits to vent together
  4. Air to bypass the foot valve in a hard stop

Explanation

A two-way check valve accepts air from two sources and passes whichever pressure is higher. In the park and emergency control this means the spring brakes can be released from either the primary or the secondary circuit.

Question 36Air brake system fundamentals and component identification

What does a pressure differential switch do in a dual air brake system?

  1. It balances pressure between the two circuits
  2. It warns the driver of a circuit pressure loss Correct answer.
  3. It releases the spring brakes when pressure drops
  4. It stops the compressor charging a leaking circuit

Explanation

The switch compares the two service circuits and triggers a warning light or buzzer when one falls significantly below the other. This alerts the driver to a partial failure before the remaining circuit is drained.

Question 37Air brake system fundamentals and component identification

What typically operates the brake lights on an air brake vehicle?

  1. A switch inside the gladhand
  2. A pressure switch at the foot valve Correct answer.
  3. A contact in the governor
  4. A mechanical link on the pedal

Explanation

Brake lights on an air brake vehicle are switched by an air pressure sensor that closes the lamp circuit when application pressure reaches the foot valve. Light operation therefore tracks actual brake application rather than pedal position alone.

Question 38Air brake system fundamentals and component identification

How does an inversion valve assist a spring brake system after a primary circuit failure?

  1. It allows gradual spring brake application Correct answer.
  2. It reverses air flow to release spring brakes
  3. It prevents trailer rollaway when uncoupled
  4. It converts supply pressure to service pressure

Explanation

When the primary circuit is lost, the inversion valve lets the driver meter air through the park control so the spring brakes apply gradually instead of slamming on. This gives a controlled emergency stop rather than a sudden lock-up.

Question 39Air brake system fundamentals and component identification

What is the purpose of the manual drain valve at the bottom of an air reservoir?

  1. To release air from the spring chambers
  2. To test the safety valve setting
  3. To set the governor cut-in pressure
  4. To remove moisture and oil from the tank Correct answer.

Explanation

Water and oil collect at the lowest point of a reservoir, so a drain cock is fitted there to blow the contaminants out. Regular draining keeps moisture from travelling into valves and brake chambers.

Question 40Air brake system fundamentals and component identification

What is meant by brake lag in an air brake system?

  1. The air lost each time the brakes are released
  2. The pressure drop when the compressor unloads
  3. The time air takes to reach the brakes Correct answer.
  4. The distance covered while the brakes are applied

Explanation

Because air must travel through lines and valves, there is a brief interval between the pedal being pressed and pressure building at the chambers. Drivers must allow for this lag by leaving extra following distance.

Question 41Compressed air supply, compressor and governor operation

On a typical heavy truck, what drives the air compressor?

  1. The transmission output shaft
  2. An electric motor
  3. The engine, by gear or belt Correct answer.
  4. A separate air motor

Explanation

The compressor is mounted on the engine and driven by a gear or belt drive from the engine. It only operates while the engine is running. This is why an engine that is off cannot recharge the air system.

Question 42Compressed air supply, compressor and governor operation

What is the governor's main job in an air brake system?

  1. To warm air before it reaches the reservoirs
  2. To limit pressure in the brake chambers
  3. To drain moisture from the reservoirs
  4. To control compressor loading and unloading Correct answer.

Explanation

The governor senses reservoir pressure and tells the compressor when to pump (load) and when to stop pumping (unload). It does not drain the tanks or limit brake chamber pressure directly. Its action keeps system pressure within a designed range.

Question 43Compressed air supply, compressor and governor operation

At what pressure does the governor normally unload, or cut out, the compressor?

  1. 60 psi
  2. 90 psi
  3. 150 psi
  4. 120 psi Correct answer.

Explanation

The governor is normally set to unload the compressor at about 120 psi. At that point the compressor stops pumping and the system pressure stops rising. The safety valve is set higher so it does not release during normal governor operation.

Question 44Compressed air supply, compressor and governor operation

When reservoir pressure falls to about what value does the governor allow the compressor to pump again?

  1. 120 psi
  2. 75 psi
  3. 90 psi Correct answer.
  4. 60 psi

Explanation

The governor normally cuts the compressor back in at about 90 psi. This recharges the system before pressure drops to an unsafe level. The difference between cut-out and cut-in is the normal pressure range of the system.

Question 45Compressed air supply, compressor and governor operation

What is the purpose of the safety valve fitted to an air reservoir?

  1. To supply air to the trailer
  2. To release air when the governor cuts in
  3. To drain water from the supply reservoir
  4. To release air at a safe maximum pressure Correct answer.

Explanation

The safety valve protects the system if the governor fails and pressure rises too high. It opens at a preset pressure to release air and prevent reservoir damage. It is not a normal pressure regulator and should not open during routine operation.

Question 46Compressed air supply, compressor and governor operation

A reservoir safety valve is normally set to open at approximately:

  1. 120 psi
  2. 150 psi Correct answer.
  3. 200 psi
  4. 100 psi

Explanation

The safety valve is set above the governor cut-out pressure, commonly around 150 psi. This ensures it stays closed during normal cycling at about 120 psi. It then provides backup protection if the governor fails to unload the compressor.

Question 47Compressed air supply, compressor and governor operation

How does the compressor stop pumping air when the governor cuts out?

  1. The governor disengages the drive gear
  2. The governor stops the engine
  3. The inlet valves are held open Correct answer.
  4. The governor closes the discharge line

Explanation

When the governor signals cut-out, it allows pressure to hold the compressor inlet valves open. With the inlet valves open, the compressor cannot build pressure and simply idles. The drive gear remains engaged and the engine continues running.

Question 48Compressed air supply, compressor and governor operation

What does an air dryer do in a compressed air system?

  1. It increases compressor output pressure
  2. It lubricates the compressor
  3. It removes moisture and oil Correct answer.
  4. It cools the engine coolant

Explanation

An air dryer removes moisture and oil from the compressed air before it reaches the reservoirs. This helps prevent corrosion and freeze-ups in the air system. It does not increase pressure or lubricate the compressor.

Question 49Compressed air supply, compressor and governor operation

When should the manual drain cocks on the air reservoirs be opened?

  1. Only if the air dryer fails
  2. Only when the safety valve releases
  3. Once a year during inspection
  4. At the end of each day Correct answer.

Explanation

Reservoir drains should be opened at the end of each day of operation to remove accumulated moisture and oil. Regular draining prevents corrosion and freeze-ups. An air dryer reduces moisture but does not eliminate the need to drain.

Question 50Compressed air supply, compressor and governor operation

What does a one-way check valve do in an air brake system?

  1. It allows air to flow one way only Correct answer.
  2. It drains moisture automatically
  3. It reduces pressure to the trailer
  4. It sets the compressor cut-in pressure

Explanation

A check valve permits air to flow in one direction and blocks flow in the opposite direction. This prevents air from escaping back through the compressor or between reservoirs. It does not regulate pressure or drain moisture.