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NY CDL Air Brakes study materials
NY CDL Air Brakes study resources

NY CDL Air Brakes practice questions

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Question 1Air Brake System Components and Functions

On a CDL air brake system, which component stores compressed air for later use by the brakes?

  1. The slack adjuster
  2. The compressor governor
  3. The air reservoir tank Correct answer.
  4. The brake chamber diaphragm

Explanation

Reservoir tanks (supply and service tanks) hold compressed air produced by the compressor so that an adequate volume is always available for braking. The compressor only builds air; the tanks are what store it.

Question 2Air Brake System Components and Functions

What is the primary job of the air compressor in a CDL air brake system?

  1. To dry moisture out of the air after it leaves the tanks
  2. To release air pressure when the parking brake is set
  3. To pump air into the storage tanks until the governor cuts it out Correct answer.
  4. To regulate the pressure applied to each brake chamber

Explanation

The compressor is the source of compressed air; it runs loaded until tank pressure reaches the governor cut-out setting, then idles until pressure falls to cut-in. Pressure modulation at the wheels is done by valves, not the compressor.

Question 3Air Brake System Components and Functions

During a pre-trip inspection you drain the air tanks and find a large amount of water. What does this most likely indicate?

  1. The slack adjusters are out of adjustment
  2. The air dryer is not removing moisture properly Correct answer.
  3. The compressor is producing too much pressure
  4. The low-pressure warning buzzer is faulty

Explanation

Water in the tanks means moisture is passing through the system instead of being removed, which points to a saturated or failed air dryer (or a missing dryer). Excess water can freeze or corrode and cause brake failure, so it must be corrected.

Question 4Air Brake System Components and Functions

The governor on an air brake system is set to cut out at 120 psi and cut in at 100 psi. What does the governor actually control?

  1. The pressure at which the spring brakes automatically set
  2. The maximum stroke of each brake chamber pushrod
  3. The rate at which air escapes during a brake application
  4. Whether the compressor is loading or unloading air Correct answer.

Explanation

The governor senses reservoir pressure and signals the compressor to load (build air) at cut-in and unload (stop building) at cut-out. It is a compressor control device, not a brake application device.

Question 5Air Brake System Components and Functions

What is the function of the foot valve (treadle valve) in an air brake system?

  1. It divides supply air between the front and rear circuits
  2. It automatically applies the spring brakes when pressure drops
  3. It meters air pressure to the brakes in proportion to how far the pedal is pushed Correct answer.
  4. It releases air from the tanks during the compressor unload cycle

Explanation

The foot valve is the driver's primary control; depressing the treadle admits air from the supply circuit to the brake circuits in proportion to pedal travel. This gives the driver graduated control over braking force.

Question 6Air Brake System Components and Functions

A tractor is equipped with a dual air brake system. Why are there two separate circuits?

  1. So a failure in one circuit still leaves a separate circuit able to stop the vehicle Correct answer.
  2. So the compressor can run at two different pressures
  3. So the trailer can be supplied with air while the tractor tanks stay isolated
  4. So the parking brake can be released without building air pressure

Explanation

Dual circuits (typically front and rear) provide redundancy: if one circuit loses pressure, the other still has air and can apply its brakes. This is why a single leak does not necessarily leave the vehicle with no brakes.

Question 7Air Brake System Components and Functions

What is the purpose of the tractor protection valve?

  1. It closes the tractor-to-trailer air lines if tractor pressure drops or the lines separate Correct answer.
  2. It limits the maximum pressure the compressor can build
  3. It applies the trailer spring brakes whenever the foot valve is released
  4. It balances air pressure between the front and rear tractor circuits

Explanation

The tractor protection valve guards the tractor's air supply: when pressure falls too low or the trailer breaks away, it closes the supply and control lines so the tractor retains enough air to stop. This prevents a trailer leak from draining the whole system.

Question 8Air Brake System Components and Functions

The spring brakes on a vehicle have applied because system air pressure dropped below a safe level. What must happen before the vehicle can be moved?

  1. The air dryer must be drained of its desiccant
  2. Air pressure must be rebuilt to a level that compresses the spring brake chambers Correct answer.
  3. The foot valve must be held fully depressed
  4. The slack adjusters must be manually backed off

Explanation

Spring brakes are applied by heavy springs and released by air pressure; when pressure falls, the springs push the brakes on. Rebuilding air pressure and pushing the release control compresses the springs and frees the wheels.

Question 9Air Brake System Components and Functions

On a vehicle with spring brakes, what is the function of the inversion valve?

  1. It inverts the signal from the governor to the warning buzzer
  2. It converts hydraulic pressure into air pressure for the brakes
  3. It reverses the direction of airflow through the compressor
  4. It allows a modulated spring brake application when service air pressure is lost Correct answer.

Explanation

When service air is lost, the inversion valve permits a controlled, modulated application of the spring brakes rather than a sudden full lockup, improving control during an emergency stop. It is a safety valve found on many vehicles with spring brakes.

Question 10Air Brake System Components and Functions

What does a low-pressure warning device on an air brake vehicle do?

  1. It drains water from the reservoirs automatically
  2. It shuts off the compressor to protect it from overpressure
  3. It automatically applies the service brakes when pressure is low
  4. It alerts the driver with a buzzer or light before air pressure falls too low to brake safely Correct answer.

Explanation

The low-pressure warning (buzzer and/or light) must activate before pressure drops below a safe operating level so the driver can stop and build air. It warns only; it does not apply brakes or control the compressor.

Question 11Air Brake System Components and Functions

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

  1. It holds a reserve of air for the parking brake
  2. It opens to let air into the tank during the compressor load cycle
  3. It vents excess pressure to protect the tank if the governor fails Correct answer.
  4. It signals the driver when the tank is full

Explanation

The safety valve is a spring-loaded relief device that opens at a set pressure above governor cut-out, protecting the reservoir and system from overpressurization if the governor or compressor malfunctions.

Question 12Air Brake System Components and Functions

A brake chamber pushrod stroke is measured and found to exceed the adjustment limit. What does this indicate?

  1. The slack adjuster needs adjustment because the brakes are out of adjustment Correct answer.
  2. The air compressor is building too little pressure
  3. The reservoir is too small for the system
  4. The low-pressure warning light is burned out

Explanation

Excessive pushrod stroke means the brake shoes must travel too far to contact the drum, which is corrected by adjusting the slack adjuster. Out-of-adjustment brakes can reduce braking force and are a common cause of CDL out-of-service violations.

Question 13Air Brake System Components and Functions

Which component converts air pressure into the mechanical force that applies the brake shoes?

  1. The brake chamber and pushrod Correct answer.
  2. The governor
  3. The supply reservoir
  4. The air dryer

Explanation

Air entering the brake chamber pushes against a diaphragm or piston, moving the pushrod, which through the slack adjuster applies the brake shoes. The chamber is the point where air pressure becomes mechanical force.

Question 14Air Brake System Components and Functions

What is the function of the check valve located between the compressor and the supply reservoir?

  1. It balances pressure between the two halves of a dual circuit
  2. It prevents air from flowing back from the reservoir to the compressor Correct answer.
  3. It limits the pressure in the service circuit
  4. It releases air to the atmosphere when the pedal is released

Explanation

A check valve allows air to flow only one way, so compressed air entering the reservoir cannot bleed back through the compressor when it unloads. This keeps stored air available for braking.

Question 15Air Brake System Components and Functions

What is the purpose of the alcohol evaporator or air dryer in an air brake system?

  1. To reduce the noise of escaping air
  2. To increase the pressure delivered to the brake chambers
  3. To lubricate the compressor's internal parts
  4. To remove moisture from the air so it does not freeze or corrode the system Correct answer.

Explanation

Moisture in compressed air can freeze in valves and lines or cause corrosion, so an evaporator or dryer conditions the air before it reaches the reservoirs. This protects brake performance, especially in cold weather.

Question 16Air Brake System Components and Functions

During a test of the air system, pressure builds from 85 to 100 psi in about 45 seconds with the engine at operating rpm. What does this result suggest?

  1. The safety valve is stuck open
  2. The compressor is building air at an acceptable rate for the test standard Correct answer.
  3. The compressor is failing and must be replaced
  4. The governor cut-out is set too high

Explanation

The standard air brake test requires the system to build from 85 to 100 psi within about 45 seconds at normal engine speed; meeting that time indicates the compressor is keeping up. A much slower build would point to a compressor or leak problem.

Question 17Air Brake System Components and Functions

What is the function of a relay valve in an air brake system?

  1. It filters oil out of the compressed air
  2. It reduces pressure to the front brakes only
  3. It speeds up brake application and release by supplying air from a nearby reservoir Correct answer.
  4. It holds the parking brake applied until air pressure builds

Explanation

A relay valve uses a small control signal to open a large supply of air from a reservoir close to the brakes, shortening the time air takes to travel through long lines. This is why relay valves are common on rear axles and trailers.

Question 18Air Brake System Components and Functions

A driver releases the parking brake control and hears air exhausting, but the spring brakes do not release. Which condition best explains this?

  1. The low-pressure warning buzzer is disconnected
  2. Insufficient air pressure is reaching the spring brake chambers Correct answer.
  3. The air compressor is running too fast
  4. The safety valve is set too low

Explanation

Spring brakes release only when enough air pressure reaches the chambers to compress the springs; exhausting air alone does not guarantee release. Low pressure, a blocked line, or a faulty valve can prevent the chambers from receiving release air.

Question 19Air Brake System Components and Functions

What is the purpose of the supply reservoir in a dual air brake system?

  1. It collects water that is later drained through the foot valve
  2. It stores air that is available to both the front and rear brake circuits Correct answer.
  3. It supplies air only to the trailer brakes
  4. It holds air only for the parking brake release

Explanation

The supply (wet) reservoir receives air directly from the compressor and feeds the individual service reservoirs for both circuits through check valves. It is the common source of air for the whole system.

Question 20Air Brake System Components and Functions

Which statement best describes the function of automatic slack adjusters?

  1. They measure and display pushrod stroke to the driver
  2. They maintain correct brake adjustment as the brakes wear during normal use Correct answer.
  3. They apply the spring brakes when air pressure is lost
  4. They limit the maximum air pressure in the brake chambers

Explanation

Automatic slack adjusters take up clearance as linings wear, keeping pushrod stroke within limits without manual adjustment. They still require inspection, because they can fail and leave the brakes out of adjustment.

Question 21Air Brake System Components and Functions

What does the application pressure gauge on an air brake vehicle show?

  1. The compressor cut-out setting
  2. The pressure in the trailer supply line only
  3. The air pressure being delivered to the brake chambers during a brake application Correct answer.
  4. The pressure in the supply reservoir at all times

Explanation

The application gauge shows how much air pressure the driver's foot valve is sending to the brakes, which helps the driver judge braking force. It is separate from the reservoir pressure gauge, which shows stored air.

Question 22Air Brake System Components and Functions

A vehicle has a front-brake limiting valve. What is its purpose?

  1. To supply air to the trailer brakes first
  2. To cut off air to the front brakes permanently
  3. To reduce air pressure to the front brakes under light applications to help prevent wheel lockup Correct answer.
  4. To increase front braking force during hard stops

Explanation

A front-brake limiting valve reduces application pressure to the steer axle during light or normal braking, which helps maintain steering control and reduces the chance of front wheel lockup. It does not disable the front brakes.

Question 23Air Brake System Components and Functions

Why must the air compressor have a way to unload (stop pumping) once the reservoirs reach cut-out pressure?

  1. To allow the air dryer to reverse its airflow
  2. To prevent overpressurization and unnecessary wear while keeping stored air available Correct answer.
  3. To let the spring brakes release automatically
  4. To reduce the pressure shown on the application gauge

Explanation

Once the reservoirs reach the governor cut-out setting, the compressor unloads so pressure does not keep climbing and the compressor is not worked needlessly. The check valve keeps the stored air in the tanks while the compressor idles.

Question 24Air Brake System Components and Functions

In a dual air brake system, what is the role of the pressure protection valve?

  1. It isolates a circuit that has lost pressure so the other circuit can still receive air Correct answer.
  2. It drains the supply reservoir automatically
  3. It opens the safety valve when pressure is too high
  4. It controls the compressor cut-in pressure

Explanation

The pressure protection valve closes off a failed or leaking circuit once pressure drops below a set value, preserving air in the remaining circuit. This is part of how dual systems keep at least partial braking after a failure.

Question 25Air Brake System Components and Functions

A driver performs a static leak test: with the engine off and the brakes fully applied, pressure drops 4 psi in one minute on a dual-circuit vehicle. What is the correct interpretation?

  1. The gauge is faulty because any drop indicates a leak
  2. The spring brakes have applied automatically
  3. The leak rate is within the allowable limit for a fully applied brake test Correct answer.
  4. The leak rate is excessive and the vehicle must be placed out of service

Explanation

For a fully applied brake leak test, a loss of no more than about 3 psi per minute for a single vehicle (or 4 psi for a combination) is acceptable. A 4 psi drop in one minute on a combination vehicle is within limits, so no defect is indicated.

Question 26Air Brake System Components and Functions

Which component on a CDL air brake vehicle stores compressed air so that the system has a reserve for repeated brake applications?

  1. The brake chamber
  2. The slack adjuster
  3. The air reservoir Correct answer.
  4. The treadle valve

Explanation

Reservoirs are storage tanks that hold compressed air supplied by the compressor, giving the system a reserve for repeated stops and for releasing spring brakes. Brake chambers convert pressure into mechanical force rather than storing air, and the treadle valve only meters air.

Question 27Air Brake System Components and Functions

In an air brake system, what is the function of the compressor governor?

  1. It converts the compressor's rotary motion into air pressure in the chambers
  2. It controls when the compressor pumps and when it idles, based on reservoir pressure Correct answer.
  3. It automatically drains moisture from the supply reservoir each cycle
  4. It limits the maximum pressure delivered to the brake chambers during a hard stop

Explanation

The governor senses reservoir pressure and signals the compressor's unloading mechanism to stop pumping at cut-out pressure and to resume at cut-in pressure. This keeps system pressure within the designed operating range.

Question 28Air Brake System Components and Functions

What is the purpose of the drain cock or drain valve fitted to an air reservoir?

  1. To set the compressor cut-out pressure
  2. To bleed air from the brake chambers after each stop
  3. To release accumulated moisture and oil from the tank Correct answer.
  4. To supply air to the trailer emergency line

Explanation

Compressed air carries water vapor and oil carryover that condense inside the tank, so reservoirs are fitted with drains to remove this contamination. Draining tanks daily helps prevent corrosion and freeze-ups in the system.

Question 29Air Brake System Components and Functions

A driver applies the foot valve and the brakes engage, then releases the pedal and the brakes disengage. Which component is responsible for exhausting the air from the brake chambers when the pedal is released?

  1. The foot valve (treadle valve) Correct answer.
  2. The compressor
  3. The low-pressure warning buzzer
  4. The supply reservoir

Explanation

The foot valve both admits air to the brake chambers when depressed and exhausts that air when released, allowing the brakes to release. This dual admit-and-exhaust action is why it is often called the application valve.

Question 30Air Brake System Components and Functions

A driver notices that the low-pressure warning signal sounds and the spring brakes apply while the vehicle is moving. Which component group is intended to alert the driver before pressure falls far enough to cause this?

  1. The slack adjusters
  2. The relay valve
  3. The warning device and gauge system Correct answer.
  4. The trailer couplers

Explanation

The low-pressure warning device and the dash gauge give the driver early notice that system pressure is falling toward an unsafe level. Catching the warning in time lets the driver stop safely before spring brakes apply automatically.

Question 31Air Brake System Components and Functions

What is the purpose of the quick-release valve used in some air brake systems?

  1. To prevent air from flowing back into the compressor
  2. To automatically apply the spring brakes if pressure is lost
  3. To speed the exhaust of air from brake chambers so the brakes release faster Correct answer.
  4. To refill the supply reservoir more quickly after a stop

Explanation

A quick-release valve is mounted near the brake chambers and vents air locally when the control pressure drops, shortening the release time compared with exhausting all the air back through the foot valve. Faster release improves brake response, particularly on long wheelbases.

Question 32Air Brake System Components and Functions

A vehicle's compressor runs continuously and system pressure climbs well past the normal cut-out point. Which component should be inspected first?

  1. The slack adjusters
  2. The governor or its unloader mechanism Correct answer.
  3. The trailer emergency line couplers
  4. The brake chambers

Explanation

The governor signals the compressor to unload at cut-out pressure, so continuous pumping and overpressure point to a governor or unloader fault. If the unloader does not function, the safety valve becomes the last line of defense against overpressure.

Question 33Air Brake System Components and Functions

In a dual air brake system, the foot valve is designed so that a complete loss of pressure in one circuit still allows the other circuit to be applied. Which term describes this design feature?

  1. An inversion valve with a single control port
  2. A dual-circuit foot valve with separate supply and delivery sections Correct answer.
  3. A single-circuit foot valve with a shared delivery port
  4. A pressure protection valve with one outlet

Explanation

The dual foot valve has separate sections for each circuit, so loss of pressure in one section does not prevent the other from delivering air to its brakes. This preserves at least partial braking capability after a single circuit failure.

Question 34Air Brake System Components and Functions

What is the function of the tractor protection valve when the trailer air supply is lost or the trailer breaks away?

  1. It closes the tractor's trailer air lines to keep the tractor's air from escaping Correct answer.
  2. It releases the tractor's spring brakes automatically
  3. It opens the trailer supply line to atmosphere to speed refill
  4. It increases compressor output to compensate for the leak

Explanation

When trailer supply pressure drops, the tractor protection valve shuts off the tractor-to-trailer lines so the tractor retains enough air to brake itself. It also signals the trailer to apply its emergency or spring brakes.

Question 35Air Brake System Components and Functions

A driver is inspecting a brake chamber and notes the pushrod has very little travel when the brakes are applied. Which condition does this most likely indicate?

  1. The slack adjuster is badly out of adjustment in the loose direction
  2. The reservoir drain is stuck open
  3. The brakes are out of adjustment in the over-adjusted direction or the chamber is not receiving full pressure Correct answer.
  4. The compressor is failing to build pressure

Explanation

Excessively short pushrod stroke suggests the foundation brake is adjusted too tight or the chamber is not getting full application pressure, both of which can reduce braking force. Normal stroke should fall within the manufacturer's specified range.

Question 36Air Brake System Components and Functions

What is the purpose of the safety valve on an air reservoir?

  1. To supply air to the trailer emergency line
  2. To equalize pressure between the primary and secondary circuits
  3. To release air if pressure rises above a preset safe limit Correct answer.
  4. To release air whenever the compressor cycles off

Explanation

The safety valve is a pressure-relief device that opens if reservoir pressure exceeds a set limit, protecting tanks and components from overpressure. It is a backup defense, not a normal operating control.

Question 37Air Brake System Components and Functions

A driver applies the parking brake control and the spring brakes apply. Which component is responsible for releasing the air from the spring brake chambers so the springs can extend?

  1. The compressor
  2. The quick-release valve
  3. The spring brake control valve (parking brake valve) Correct answer.
  4. The supply reservoir

Explanation

The spring brake control valve controls air pressure to the spring brake chambers; when the driver sets the parking brake, it exhausts that control air so the springs extend and apply the brakes. Releasing the control admits air to compress the springs and release the brakes.

Question 38Air Brake System Components and Functions

During a pre-trip inspection, a driver finds that the air pressure gauge shows about 100 psi but the spring brakes will not release when the parking brake control is pushed in. Which component is the most likely cause?

  1. The slack adjusters are adjusted too tight
  2. The safety valve is stuck open
  3. The spring brake control valve is not admitting air to the spring brake chambers Correct answer.
  4. The compressor is over-pressurizing the system

Explanation

Spring brakes release only when air pressure is admitted to compress the springs, so a control valve that fails to admit air will leave them applied even with good reservoir pressure. Checking for air at the spring brake chambers helps confirm whether the valve or the chamber is at fault.

Question 39Air Brake System Components and Functions

A driver reports that the service brakes on the rear axle apply weakly while the front axle brakes work normally, and the rear relay valve seems to deliver air slowly. Which explanation best fits this symptom?

  1. The relay valve's control signal or supply is restricted, so delivery to the rear chambers is delayed Correct answer.
  2. The compressor is not building enough pressure for the whole system
  3. The front brake limiting valve is reducing front brake pressure
  4. The low-pressure warning device has failed

Explanation

A relay valve delivers air to the rear brake chambers in response to a control signal from the foot valve; if its control line or supply is restricted, rear brake application will be weak or slow. Front brakes working normally suggests the fault is downstream in the rear circuit rather than at the compressor.

Question 40Air Brake System Components and Functions

A driver performs a leak test and finds that pressure drops faster with the brakes applied than with them released. Which interpretation is most accurate?

  1. The reservoir drains are working correctly
  2. There is likely a leak in the service brake application side of the system Correct answer.
  3. The compressor is producing too much air
  4. The governor cut-in pressure is set too high

Explanation

A faster drop with the brakes applied points to leakage in the components that are pressurized only during application, such as chambers, hoses, or valves in the service circuit. Leaks present regardless of brake position would suggest a different part of the system.

Question 41Dual Air Brake Systems

On a dual air brake system, the two separate systems are commonly referred to as which pair?

  1. The wet and dry circuits
  2. The supply and delivery circuits
  3. The service and parking circuits
  4. The primary and secondary circuits Correct answer.

Explanation

A dual air brake system splits braking into two independent circuits, usually called the primary and secondary systems, so that a failure in one still leaves the other able to stop the vehicle. Each circuit has its own reservoir and check valve protection.

Question 42Dual Air Brake Systems

What is the purpose of a check valve installed between the supply reservoir and a primary or secondary reservoir?

  1. It prevents air from flowing back out of the reservoir Correct answer.
  2. It equalizes pressure between the two service circuits
  3. It drains moisture from the reservoir automatically
  4. It limits maximum pressure in the compressor discharge line

Explanation

A check valve allows air to flow into a reservoir but blocks it from flowing back toward the supply source. This keeps each circuit's stored air available even if the supply side or the other circuit loses pressure.

Question 43Dual Air Brake Systems

During a pre-trip test you build full pressure and shut off the engine. With the engine off and the service brakes released, how much air pressure loss is generally allowed in one minute for a single vehicle?

  1. No more than 20 psi
  2. No more than 3 psi Correct answer.
  3. No more than 1 psi
  4. No more than 10 psi

Explanation

For a single vehicle, a static leak test with the engine off and brakes released should show a loss of no more than 3 psi in one minute. A larger drop points to a leak that must be found and repaired before driving.

Question 44Dual Air Brake Systems

In a dual air brake system, which circuit typically supplies the rear service brakes on a tractor-trailer combination?

  1. The secondary circuit
  2. The parking brake circuit
  3. The trailer supply circuit
  4. The primary circuit Correct answer.

Explanation

The primary circuit normally operates the rear service brakes, while the secondary circuit operates the front service brakes. This split means a failure of one circuit still leaves a portion of service braking available.

Question 45Dual Air Brake Systems

What does the low air pressure warning device on a dual air brake vehicle signal to the driver?

  1. That the air dryer has completed its purge cycle
  2. That the parking brakes have fully released
  3. That pressure in a circuit has dropped below a safe operating level Correct answer.
  4. That the compressor is overcharging the system

Explanation

The warning device alerts the driver when air pressure falls to an unsafe level, typically around 60 psi or the manufacturer's setting. At that point the driver must stop safely because braking performance is compromised.

Question 46Dual Air Brake Systems

Which component in a dual air brake system compresses and supplies air to both circuits?

  1. The governor
  2. The quick release valve
  3. The relay valve
  4. The compressor Correct answer.

Explanation

The compressor is the source of compressed air for the entire system and feeds both the primary and secondary circuits. The governor only controls when the compressor loads and unloads.

Question 47Dual Air Brake Systems

What is the function of the governor in a dual air brake system?

  1. It applies the spring brakes when pressure is lost
  2. It regulates compressor loading and unloading based on reservoir pressure Correct answer.
  3. It divides air between the primary and secondary reservoirs
  4. It purges moisture from the air dryer

Explanation

The governor monitors system pressure and signals the compressor to load when pressure falls to the cut-in point and unload at the cut-out point. This keeps pressure within the designed operating range.

Question 48Dual Air Brake Systems

On a dual air brake system, a safety valve is normally installed on which reservoir?

  1. Only the secondary reservoir
  2. Each wheel-end chamber
  3. The supply (wet) reservoir Correct answer.
  4. Only the primary reservoir

Explanation

The safety valve is typically mounted on the supply or wet tank to protect the system from excessive pressure. It opens at a set pressure to vent air rather than allowing the system to overpressurize.

Question 49Dual Air Brake Systems

During a pre-trip inspection you press the brake pedal and hold it while watching the gauges. Air pressure drops and then continues to fall steadily. What does this most likely indicate?

  1. A properly functioning relay valve
  2. Normal operation of the compressor
  3. A leak in the service brake system Correct answer.
  4. A stuck governor cut-out setting

Explanation

When the brakes are applied, some pressure drop is normal, but a continued steady fall means air is escaping somewhere in the applied circuit. The driver should locate and repair the leak before operating the vehicle.

Question 50Dual Air Brake Systems

You are driving and notice the primary circuit gauge has dropped to zero while the secondary gauge still shows normal pressure. What is the correct response?

  1. Shift to a lower gear and drive to the nearest shop without braking
  2. Stop safely and have the system inspected before continuing Correct answer.
  3. Pump the brake pedal repeatedly to rebuild pressure
  4. Continue driving normally because one circuit still works

Explanation

A loss of the primary circuit means rear service braking is compromised even though the secondary circuit still functions. The safe action is to stop and get the system checked rather than continue relying on partial braking.