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FL CDL Air Brakes study materials
FL CDL Air Brakes study resources

FL CDL Air Brakes practice questions

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Question 1Air Brake System Components and Functions

On a Florida CDL air brake system, what is the primary job of the compressor?

  1. Releases excess pressure from the system
  2. Builds and maintains air pressure in the storage tanks Correct answer.
  3. Converts air pressure into mechanical braking force
  4. Stores pressurized air for later use

Explanation

The compressor is engine-driven and pumps air into the storage reservoirs until the governor cuts it out at the set pressure. It is the source of pressure, while tanks store and valves distribute it.

Question 2Air Brake System Components and Functions

What is the purpose of the governor in an air brake system?

  1. It limits the maximum pressure the brake chambers can receive
  2. It regulates compressor output by cutting the compressor in and out at set pressures Correct answer.
  3. It drains moisture from the reservoirs automatically
  4. It controls the rate at which brakes release

Explanation

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

Question 3Air Brake System Components and Functions

A driver notices the low air pressure warning activates at about 60 psi. What does this warning indicate?

  1. The compressor has failed permanently
  2. System pressure has dropped to a level where safe braking may be compromised Correct answer.
  3. The parking brake is fully released
  4. The air dryer is in its purge cycle

Explanation

The low pressure warning must activate before pressure falls below 60 psi so the driver has time to stop safely. It signals that reservoir pressure is approaching the minimum for reliable braking.

Question 4Air Brake System Components and Functions

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

  1. It releases air if system pressure exceeds a safe maximum Correct answer.
  2. It filters oil from the compressed air
  3. It maintains a minimum pressure in the tank
  4. It automatically applies the brakes on pressure loss

Explanation

The safety valve is a pressure relief device that opens if the governor fails and pressure climbs above a safe limit. This prevents tank or component rupture.

Question 5Air Brake System Components and Functions

What does the supply reservoir (wet tank) do in a typical air brake system?

  1. It receives air directly from the compressor and collects moisture and oil before air moves downstream Correct answer.
  2. It supplies air only to the trailer brakes
  3. It stores air solely for the horn and other accessories
  4. It regulates the pressure sent to the brake chambers

Explanation

The supply or wet tank is the first tank after the compressor, so it condenses and traps much of the moisture and oil. Downstream tanks then receive cleaner, drier air.

Question 6Air 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 lubricate the brake chambers
  3. To remove moisture from the compressed air before it reaches the reservoirs Correct answer.
  4. To increase the compressor's output pressure

Explanation

Moisture in compressed air can freeze in lines and corrode components, so an evaporator or dryer removes water vapor. This protects valves and brakes, especially in cold weather.

Question 7Air Brake System Components and Functions

In a dual air brake system, why are there separate circuits?

  1. To permit the compressor to run at two speeds
  2. To double the total air pressure available
  3. So a failure in one circuit still leaves a portion of the braking system operational Correct answer.
  4. To allow the trailer to brake independently of the tractor

Explanation

Dual circuits isolate the front and rear (or tractor and trailer) brakes so a leak or failure in one does not disable all braking. The intact circuit continues to provide stopping ability.

Question 8Air Brake System Components and Functions

What does the foot valve (brake valve) do when the driver presses the brake pedal?

  1. It stores air until the pedal is released
  2. It drains the reservoirs of condensation
  3. It sets the parking brake automatically
  4. It meters air pressure from the reservoirs to the brake chambers in proportion to pedal force Correct answer.

Explanation

The foot valve is the driver's primary control, delivering air from the reservoirs to the brake chambers based on how far the pedal is pushed. More pedal force yields more pressure and stronger braking.

Question 9Air Brake System Components and Functions

A driver releases the parking brake but hears a steady hiss of air from the rear of the tractor. What is the most likely concern?

  1. The compressor building pressure
  2. Normal operation of the air dryer purge
  3. The low pressure warning resetting
  4. An air leak in the brake system that should be located and repaired before driving Correct answer.

Explanation

A steady hiss after releasing the parking brake suggests air escaping from a chamber, line, or valve. Leaks reduce available pressure and should be found and fixed before operating.

Question 10Air Brake System Components and Functions

During a static leak test, the driver charges the system to governor cut-out, stops the engine, and watches the gauge. Pressure drops 3 psi in one minute with the brakes released. What does this indicate?

  1. The leak rate is within the acceptable limit for a single vehicle Correct answer.
  2. The compressor is still running
  3. The system has a serious leak requiring immediate repair
  4. The gauge is faulty

Explanation

A pressure loss of no more than 3 psi per minute with brakes released is generally acceptable for a single vehicle. A larger drop would indicate a leak that must be repaired.

Question 11Air Brake System Components and Functions

What is the function of the relay valve in a tractor-trailer air brake system?

  1. It controls the compressor cut-in pressure
  2. It reduces pressure to the trailer brakes permanently
  3. It drains the trailer reservoir
  4. It speeds up brake application and release at the trailer by supplying air from a nearby reservoir Correct answer.

Explanation

A relay valve uses a small control signal to open a larger supply of air close to the brakes, shortening response time. This is especially important on long vehicles with distant reservoirs.

Question 12Air Brake System Components and Functions

What is the purpose of the tractor protection valve?

  1. It closes the trailer air supply if pressure drops or the trailer breaks away, protecting the tractor's air Correct answer.
  2. It controls the trailer's spring brakes only during parking
  3. It increases pressure to the trailer brakes
  4. It filters moisture from the trailer line

Explanation

The tractor protection valve guards the tractor's air supply by shutting off the trailer lines when pressure falls too low or the trailer separates. This preserves enough air for the tractor to stop.

Question 13Air Brake System Components and Functions

How do spring brakes apply when air pressure is lost?

  1. Hydraulic fluid forces the springs to expand
  2. Air pressure pushes the springs to apply the brakes
  3. An electric motor engages the brakes
  4. Mechanical springs push the brake shoes into contact when air pressure is released Correct answer.

Explanation

Spring brakes are held off by air pressure; when pressure is lost, the springs expand and apply the brakes automatically. This provides a fail-safe parking and emergency brake.

Question 14Air Brake System Components and Functions

A driver must park a vehicle with air brakes on a grade. Which action best ensures the spring brakes are properly applied?

  1. Leave the transmission in neutral only
  2. Pull the parking brake control and confirm the trailer air supply is charged Correct answer.
  3. Drain all air from the system before exiting
  4. Rely on the foot valve to hold the vehicle

Explanation

The parking brake control releases air from the spring brake chambers so the springs apply, and the trailer must have air supply for its brakes to function. Confirming both ensures the vehicle is held.

Question 15Air Brake System Components and Functions

What does the quick release valve do in an air brake system?

  1. It closes the trailer line during a breakaway
  2. It exhausts air rapidly from the brake chambers to speed brake release Correct answer.
  3. It applies the brakes faster during a panic stop
  4. It regulates compressor cut-out pressure

Explanation

The quick release valve is located near the brake chambers and vents air quickly when the pedal is released. This shortens release time and reduces brake drag.

Question 16Air Brake System Components and Functions

An air gauge shows pressure building slowly and the compressor never cuts out. Which component is the most likely cause?

  1. A worn brake lining
  2. A misadjusted slack adjuster
  3. A clogged quick release valve
  4. A faulty governor or a major system leak Correct answer.

Explanation

If pressure keeps climbing without cut-out, the governor may be failing to signal the compressor to stop. A large leak elsewhere could also prevent normal cycling, so the governor and system integrity are the first checks.

Question 17Air Brake System Components and Functions

What is the function of the brake chamber and pushrod assembly?

  1. It stores compressed air for the service brakes
  2. It converts air pressure into mechanical force that moves the slack adjuster and brake shoes Correct answer.
  3. It regulates pressure from the foot valve
  4. It removes moisture from the air supply

Explanation

Air pressure entering the chamber pushes a diaphragm and pushrod, which transfers force to the slack adjuster and brake mechanism. This is where pneumatic pressure becomes mechanical braking force.

Question 18Air Brake System Components and Functions

A driver performs a brake check and finds the pushrod stroke exceeds the adjustment limit. What does this mean?

  1. The trailer is disconnected
  2. The brakes are properly adjusted
  3. The air pressure is too high
  4. The brakes are out of adjustment and must be adjusted before driving Correct answer.

Explanation

Excessive pushrod stroke indicates the foundation brakes are out of adjustment, reducing braking effectiveness. The brakes must be adjusted to bring stroke within limits before operation.

Question 19Air Brake System Components and Functions

What does the application pressure gauge on some air brake vehicles show?

  1. The compressor cut-in pressure
  2. The pressure in the supply reservoir only
  3. The pressure being applied to the brake chambers Correct answer.
  4. The trailer line pressure at the gladhands

Explanation

An application gauge displays the pressure delivered to the brakes, helping the driver judge braking effort. It differs from the reservoir gauge, which shows stored supply pressure.

Question 20Air Brake System Components and Functions

Why must a driver drain air tanks regularly?

  1. To test the safety valve
  2. To remove accumulated moisture and oil that can damage valves and freeze in cold weather Correct answer.
  3. To reset the governor
  4. To increase the compressor's output

Explanation

Condensation and oil collect in the lowest part of the reservoirs and can corrode or freeze in lines and valves. Regular draining keeps the air supply clean and the system reliable.

Question 21Air Brake System Components and Functions

In a dual circuit system, a driver notices the rear service brakes have failed but the front brakes still work. What is the best explanation?

  1. The air dryer has failed
  2. The parking brake is stuck on
  3. The compressor has stopped entirely
  4. One circuit has lost pressure, but the other circuit remains functional by design Correct answer.

Explanation

Dual circuits are designed so a failure in one circuit does not disable the other, preserving partial braking. The driver should still stop safely and have the system inspected.

Question 22Air Brake System Components and Functions

A driver hears a short burst of air from the air dryer every few minutes while driving. What is the correct interpretation?

  1. This means the brakes are dragging
  2. This is the normal purge cycle removing collected moisture Correct answer.
  3. This indicates a failed compressor
  4. This shows the low pressure warning is active

Explanation

Air dryers periodically purge moisture from the desiccant, producing a brief burst of air. This is a normal operating cycle, not a fault.

Question 23Air Brake System Components and Functions

A driver charges the system, shuts off the engine, and applies the brakes fully. Pressure drops 5 psi in one minute. How should this be interpreted?

  1. The leak rate is excessive and the vehicle should be taken out of service
  2. The leak rate is acceptable for a single vehicle when brakes are applied Correct answer.
  3. The gauge must be replaced
  4. The compressor is still supplying air

Explanation

With brakes applied, a pressure loss of up to 5 psi per minute is generally acceptable for a single vehicle. A larger drop indicates a leak that must be repaired.

Question 24Air Brake System Components and Functions

What is the purpose of the inversion valve in a spring brake system?

  1. It provides a modulated spring brake application when service brake pressure is lost Correct answer.
  2. It inverts the compressor output
  3. It switches the trailer supply from wet to dry tank
  4. It reverses the direction of the pushrod

Explanation

The inversion valve allows the spring brakes to apply in a controlled, modulated way when service air is lost, rather than slamming on. This improves control during an emergency.

Question 25Air Brake System Components and Functions

A vehicle with air brakes has a compressor that runs constantly but pressure stays below the cut-out point. Which combination best explains this?

  1. A dirty application gauge and a stuck drain valve
  2. A worn brake lining and a clogged quick release valve
  3. A significant system leak or a faulty governor/unloader preventing pressure buildup Correct answer.
  4. A misadjusted slack adjuster and a failed low pressure switch

Explanation

Continuous compressor operation without reaching cut-out points to a leak that outpaces supply or a governor/unloader fault. Either condition prevents normal pressure cycling.

Question 26Air Brake System Components and Functions

On a vehicle with air brakes, what determines the pressure at which the governor cuts the compressor out?

  1. The spring rate of the brake chamber return spring
  2. The setting of the safety valve on the wet tank
  3. The pressure protection valve opening point
  4. The preset cut-out pressure built into the governor Correct answer.

Explanation

The governor senses reservoir pressure and unloads the compressor at its preset cut-out point, then lets it build again at the cut-in point. Those two settings live in the governor itself, not in the safety valve or the brake chambers.

Question 27Air Brake System Components and Functions

Which component changes the driver's pedal force into a pneumatic signal that the rest of the system can use?

  1. The foot valve (brake valve) Correct answer.
  2. The low pressure warning switch
  3. The drain cock
  4. The slack adjuster

Explanation

The foot valve meters reservoir air into the service brake circuit in proportion to how far the pedal is pushed. The other listed parts either adjust linkage, warn of low pressure, or drain moisture; none of them create the control signal.

Question 28Air Brake System Components and Functions

What is the purpose of the supply reservoir (wet tank) in a typical air brake system?

  1. It stores air for the parking brake circuit only
  2. It meters air to the brake chambers when the pedal is pressed
  3. It collects air directly from the compressor and lets moisture and oil settle before the air moves on Correct answer.
  4. It releases air to the atmosphere when the spring brakes apply

Explanation

Air leaves the compressor hot and carries water vapor and oil, so it enters a supply reservoir first where contaminants condense and drop out. From there it feeds the other reservoirs through a check valve arrangement.

Question 29Air Brake System Components and Functions

A driver notices that the low pressure warning buzzer sounds and the light comes on while the engine is running and the vehicle is stationary. What pressure condition is the warning designed to announce?

  1. Pressure equal in both halves of a dual circuit
  2. Pressure below the minimum safe operating level, typically around 60 psi Correct answer.
  3. Pressure in the trailer circuit only
  4. Pressure above governor cut-out

Explanation

The warning device is set to activate before air pressure falls to a level where the spring brakes could apply unexpectedly, commonly about 60 psi. It gives the driver time to stop safely rather than being surprised by an automatic brake application.

Question 30Air Brake System Components and Functions

A driver wants to confirm the governor cut-in and cut-out pressures are within specification. Which observation gives that information directly?

  1. Watch the gauge fall while the brake pedal is held down
  2. Compare the application gauge reading with the reservoir gauge reading
  3. Watch the gauge rise until the compressor stops, then note the pressure where it restarts Correct answer.
  4. Listen for the air dryer purge cycle and note how often it repeats

Explanation

Cut-out is the pressure at which the compressor stops building and cut-in is where it resumes, so watching one full cycle on the gauge shows both values. Brake application tests and dryer purge cycling do not reveal those set points.

Question 31Air Brake System Components and Functions

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

  1. It prevents air from flowing backward from the secondary to the primary circuit
  2. It holds the spring brakes off until pressure reaches cut-out
  3. It automatically drains water from the tank each time the compressor unloads
  4. It vents air to the atmosphere if pressure rises above a preset maximum Correct answer.

Explanation

The safety valve is a spring-loaded relief device that opens at a pressure above normal governor cut-out to protect tanks and lines from overpressure. It is a backup for a failed governor, not a routine pressure regulator.

Question 32Air Brake System Components and Functions

A driver applies the brakes and releases them, and the pushrods return to the released position promptly. Which component is chiefly responsible for returning the pushrod and releasing the brake?

  1. The relay valve
  2. The pressure protection valve
  3. The alcohol evaporator
  4. The brake chamber return spring Correct answer.

Explanation

When the foot valve stops supplying air, the chamber return spring pushes the diaphragm and pushrod back, releasing the brake. The other parts listed handle air distribution, moisture control, or circuit protection rather than mechanical release.

Question 33Air Brake System Components and Functions

What does a check valve installed between the supply reservoir and a service reservoir accomplish?

  1. It allows air to flow only toward the service reservoir so pressure cannot bleed back to the supply tank Correct answer.
  2. It signals the low pressure warning switch when the service reservoir is full
  3. It meters air to the brake chambers in proportion to pedal travel
  4. It limits the maximum pressure in the service reservoir to the governor cut-in point

Explanation

A check valve permits one-way flow, so air entering a service reservoir cannot escape back toward the supply tank. This keeps each circuit charged independently and helps isolate a leak or failure.

Question 34Air Brake System Components and Functions

A driver notices that the trailer brakes apply later than the tractor brakes when the pedal is pushed. Which component most directly affects how quickly the trailer receives the control signal?

  1. The trailer supply line gladhand
  2. The tractor protection valve
  3. The relay valve on the trailer Correct answer.
  4. The compressor discharge line

Explanation

On a trailer, the relay valve uses a small control signal from the foot valve to admit reservoir air to the brake chambers quickly. A sluggish or restricted relay valve delays trailer brake application relative to the tractor.

Question 35Air Brake System Components and Functions

What is the purpose of the front brake limiting valve found on some older air brake vehicles?

  1. It reduces front brake application pressure to lessen the chance of front wheel lockup on slippery surfaces Correct answer.
  2. It prevents the front brakes from applying whenever the parking brake is set
  3. It balances pressure between the primary and secondary circuits
  4. It increases front brake force when the vehicle is loaded

Explanation

A limiting valve, often labeled with a slippery/dry setting, cuts the air pressure delivered to the front brakes to reduce lockup risk on low-traction surfaces. It does not add braking force or balance the two circuits.

Question 36Air Brake System Components and Functions

During a pre-trip inspection a driver finds the spring brake chambers on the rear axle have no visible clamp band and look different from the service chambers. What explains this?

  1. These are spring brake chambers, which contain a large stored-energy spring in addition to the service diaphragm Correct answer.
  2. The chambers are service chambers that were installed upside down
  3. The chambers are for the trailer supply line rather than the brakes
  4. The chambers are missing their diaphragms and must be replaced

Explanation

Spring brake chambers combine a service section with a spring section that applies the brakes when air pressure is lost. They are built with clamped or sealed construction that differs from a plain service chamber.

Question 37Air Brake System Components and Functions

A driver finds that the air compressor will not build pressure above about 85 psi and the safety valve on the wet tank has vented. What is the most likely explanation?

  1. The low pressure warning switch is stuck closed
  2. The trailer relay valve is leaking at the service port
  3. The governor cut-out setting is too low or the governor has failed, so the compressor keeps running past the intended cut-out Correct answer.
  4. The slack adjusters are out of adjustment

Explanation

If the compressor does not unload at the proper cut-out point, pressure keeps climbing until the safety valve relieves it, which fits a faulty governor or a misadjusted cut-out. The warning switch, relay valve, and slack adjusters do not control compressor unloading.

Question 38Air Brake System Components and Functions

A truck with air brakes has a slow pressure loss that stops when the trailer is disconnected but returns when it is reconnected. Which area should be inspected first?

  1. The tractor's front brake chambers and hoses
  2. The compressor discharge line and intercooler
  3. The governor and safety valve on the wet tank
  4. The trailer supply and service lines, gladhands, and trailer relay valve Correct answer.

Explanation

Because the leak disappears when the trailer is uncoupled, the fault lies in the trailer portion of the system or the couplings between them. The tractor's own components and the compressor are ruled out by that observation.

Question 39Air Brake System Components and Functions

What is the function of the inversion valve in a system with spring brakes and an emergency feature?

  1. It regulates the compressor output to maintain cut-out pressure
  2. It reverses the control signal so the spring brakes can be applied or released when normal control pressure is lost Correct answer.
  3. It converts hydraulic pressure to air pressure for the trailer brakes
  4. It drains moisture from the supply reservoir automatically

Explanation

The inversion valve takes a signal that is normally present and delivers the opposite action, which lets the spring brakes be controlled during an emergency or when normal control pressure is missing. It is not a compressor regulator, a moisture drain, or a hydraulic-to-air converter.

Question 40Air Brake System Components and Functions

A driver applies the parking brake control and hears air exhaust, but the vehicle does not hold on a slope. Which component should be checked first?

  1. The alcohol evaporator
  2. The spring brake chambers and their pushrods Correct answer.
  3. The safety valve on the wet tank
  4. The low pressure warning switch

Explanation

Exhausting air when the parking control is applied is normal, because the spring brakes apply as air is released. If the vehicle still rolls, the spring sections or their pushrods may not be delivering force to the brakes, so those are checked first.

Question 41Dual Air Brake System and Safety Features

On a dual air brake system, the two separate circuits are most commonly divided into which pair of systems?

  1. A primary circuit for the rear brakes and a secondary circuit for the front brakes Correct answer.
  2. A primary circuit for the front brakes and a secondary circuit for the trailer brakes
  3. A primary circuit for the compressor and a secondary circuit for the governor
  4. A primary circuit for the parking brake and a secondary circuit for the service brake

Explanation

In the standard dual service brake arrangement, one circuit operates the rear (primary) brakes and the other operates the front (secondary) brakes. This split keeps a single leak from disabling all service braking. Each circuit has its own reservoir, so the failure of one leaves the other able to stop the vehicle.

Question 42Dual Air Brake System and Safety Features

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

  1. It releases air to the atmosphere if reservoir pressure exceeds a preset limit Correct answer.
  2. It signals the driver when pressure drops below a warning level
  3. It prevents backflow of air from the tank to the compressor
  4. It drains accumulated moisture from the bottom of the tank

Explanation

The safety valve is a pressure-relief device that opens when tank pressure rises above its setting, protecting the reservoir and lines from over-pressurization. It is set above normal governor cut-out so it does not vent during routine operation. If it releases air steadily, the governor or unloader is likely malfunctioning.

Question 43Dual Air Brake System and Safety Features

At what pressure should the low air pressure warning device activate on a vehicle with a dual air brake system?

  1. Only after pressure falls below 20 psi
  2. Whenever the parking brake is released
  3. At the governor cut-out pressure of about 130 psi
  4. Before pressure drops below 60 psi Correct answer.

Explanation

Federal requirements call for a warning that activates before the air pressure in either service circuit falls below 60 psi. The warning must be a visible light and an audible buzzer or signal that the driver can see and hear. This gives the driver time to stop safely before braking ability is lost.

Question 44Dual Air Brake System and Safety Features

How can a driver check that the low air pressure warning signal is working?

  1. Release the parking brake and drive forward slowly
  2. Turn on the electrical power and repeatedly press the brake pedal while the engine is off to reduce pressure Correct answer.
  3. Open a reservoir drain cock while the engine is running at high idle
  4. Start the engine and let pressure build to governor cut-out

Explanation

With the engine off and electrical power on, fanning the brake pedal bleeds air until the warning light and buzzer come on. This confirms the warning device operates before pressure falls below 60 psi. The test should be done before driving so a failed warning is discovered on the ground.

Question 45Dual Air Brake System and Safety Features

What does the spring brake section of a parking brake chamber do when air pressure is released?

  1. It releases the brakes and holds them off
  2. It resets the governor to cut-in pressure
  3. It applies the brakes mechanically by spring force Correct answer.
  4. It sends air to the trailer supply line

Explanation

Spring brakes use a large coil spring to apply the brakes when air pressure is removed from the chamber. Air pressure compresses the spring to release the brakes during normal driving. If pressure is lost, the springs apply the brakes automatically as a fail-safe.

Question 46Dual Air Brake System and Safety Features

What is the function of the governor in an air brake system?

  1. It controls when the compressor loads and unloads to maintain reservoir pressure Correct answer.
  2. It limits the maximum braking force at the wheels
  3. It automatically drains water from the reservoirs
  4. It separates the primary and secondary circuits

Explanation

The governor senses reservoir pressure and signals the compressor to load (pump) at cut-in pressure and unload (stop pumping) at cut-out pressure. This keeps system pressure within the normal operating range. Typical cut-out is around 120 to 130 psi and cut-in around 100 psi.

Question 47Dual Air Brake System and Safety Features

In a dual air brake system, what does the tractor protection valve do when the trailer air supply pressure drops too low?

  1. It automatically applies the tractor parking brakes only
  2. It increases pressure to the trailer to help it stop
  3. It closes the trailer supply and service lines to protect the tractor's air supply Correct answer.
  4. It dumps all tractor reservoir air to the atmosphere

Explanation

The tractor protection valve senses trailer supply pressure and closes the lines to the trailer when pressure falls too low. This traps the tractor's remaining air so the tractor can still be braked and prevents a trailer breakaway from draining the tractor. It also causes the trailer spring brakes to apply.

Question 48Dual Air Brake System and Safety Features

After the air system reaches governor cut-out and the engine is shut off, what does a steady pressure drop indicate?

  1. A leak somewhere in the air system Correct answer.
  2. Normal cooling of compressed air
  3. That the compressor is still loaded
  4. That the safety valve is stuck open by design

Explanation

With the engine off and the system fully charged, pressure should hold with only a small drop allowed by regulation. A steady, continuing loss of pressure points to a leak in a line, fitting, valve, or chamber. The leak should be located and repaired before the vehicle is driven.

Question 49Dual Air Brake System and Safety Features

A driver applies the brakes and notices the low air pressure warning comes on and pressure keeps falling. What is the correct first response?

  1. Shift to neutral and coast to save air
  2. Pump the brake pedal rapidly to build pressure
  3. Downshift and continue to the nearest terminal
  4. Stop safely as soon as possible and investigate before continuing Correct answer.

Explanation

A continuing pressure loss with the warning active means braking ability may soon be lost, so the driver must stop in a safe place immediately. Continuing to drive risks a runaway or loss of service brakes. The system should be checked and the fault corrected before moving again.

Question 50Dual Air Brake System and Safety Features

During a static leak test on a dual air brake system, where is it acceptable to find a small pressure drop?

  1. Only when the parking brake is set
  2. Anywhere, because all air systems leak by design
  3. Within the manufacturer's or regulation's allowable loss over a set time with brakes released and applied Correct answer.
  4. Only at the compressor discharge line

Explanation

Regulations and manufacturers specify a maximum allowable pressure loss over a given time for both the applied and released conditions. A loss within that limit is acceptable; a larger or continuing loss indicates a leak that must be fixed. The test is done with the engine off and the system fully charged.