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Illinois CDL Air Brakes study materials
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Illinois CDL Air Brakes practice questions

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Question 1Air Brake System Components and Functions

On a typical air brake system, what is the function of the compressor governor?

  1. It measures the rate of air loss in the system and warns the driver of a leak.
  2. It limits the maximum pressure delivered to the trailer service line during a brake application.
  3. It controls when the compressor cuts in and cuts out to maintain system air pressure within a set range. Correct answer.
  4. It automatically drains moisture from the supply reservoir each time the compressor cycles.

Explanation

The governor senses supply-tank pressure and tells the compressor when to start and stop pumping, holding pressure between a cut-in and cut-out value. It does not meter air to the brakes or manage moisture; those are duties of other valves and drains.

Question 2Air Brake System Components and Functions

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

  1. To supply air directly to the trailer emergency line
  2. To boost brake shoe return spring tension after a release
  3. To remove moisture and contaminants before air reaches the reservoirs Correct answer.
  4. To raise system pressure above the governor cut-out point

Explanation

Moisture and oil in compressed air can freeze in lines and corrode valves, so an air dryer or evaporator conditions the air before storage. Clean, dry air protects the reservoirs and downstream brake components.

Question 3Air Brake System Components and Functions

The supply reservoir on a tractor is best described as which of the following?

  1. A gauge that displays application pressure at the treadle
  2. A valve that divides air between the front and rear service brakes
  3. A small chamber that only feeds the parking brake circuit
  4. A storage tank that holds compressed air for the brake system until it is used Correct answer.

Explanation

The supply (wet) reservoir stores compressed air from the compressor and feeds the other circuits. It is a storage device, not a control valve or gauge.

Question 4Air Brake System Components and Functions

What does the safety valve installed on the air system do?

  1. It holds the spring brakes applied until pressure builds.
  2. It releases air to the atmosphere if system pressure exceeds a preset maximum. Correct answer.
  3. It equalizes pressure between the primary and secondary circuits.
  4. It closes the trailer supply line whenever the trailer disconnects.

Explanation

The safety valve is a pressure-relief device that vents air if the governor or compressor fails and pressure climbs too high. This protects tanks and lines from over-pressurization.

Question 5Air Brake System Components and Functions

In a dual air brake system, what does the check valve between the two circuits accomplish?

  1. It allows air to flow one direction only, protecting a good circuit from losing air through a failed one. Correct answer.
  2. It lets air flow both ways so a failed circuit can be refilled from the other.
  3. It reduces pressure to the front brakes during hard stops.
  4. It vents excess air from the supply tank.

Explanation

Check valves permit flow in one direction, so a leak in one circuit cannot drain the other. This is what lets a dual system keep partial braking after a single-circuit failure.

Question 6Air Brake System Components and Functions

A driver notices the low air pressure warning buzzer does not sound as pressure drops. What component should be suspected?

  1. The relay valve
  2. The low pressure warning switch Correct answer.
  3. The quick release valve
  4. The slack adjuster

Explanation

The warning switch senses system pressure and triggers the buzzer and light when pressure falls into the warning range. If the alarm never activates, the switch or its circuit is the likely fault.

Question 7Air Brake System Components and Functions

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

  1. To store compressed air for the parking brake
  2. To control the amount of air pressure delivered to the service brakes as the pedal is pressed Correct answer.
  3. To release the spring brakes when the engine starts
  4. To drain water from the reservoirs automatically

Explanation

The foot valve is the driver's service brake control; pedal travel meters air pressure to the brake chambers. It is a modulating control, not a storage or drain device.

Question 8Air Brake System Components and Functions

Where is the quick release valve usually located, and what does it do?

  1. Near the brake chambers, where it exhausts air quickly to speed brake release Correct answer.
  2. At the dash, where it displays application pressure
  3. At the compressor, where it regulates cut-in pressure
  4. At the trailer gladhand, where it seals the emergency line

Explanation

The quick release valve is mounted close to the brake chambers so air can escape locally instead of traveling all the way back through the foot valve. This shortens release time and reduces brake drag.

Question 9Air Brake System Components and Functions

What is the role of the relay valve on a tractor or trailer?

  1. It reduces supply pressure to the trailer below 60 psi.
  2. It automatically applies the spring brakes during a service application.
  3. It senses control pressure and delivers reservoir air directly to the brake chambers, reducing lag. Correct answer.
  4. It filters oil from the compressed air before it reaches the tanks.

Explanation

The relay valve uses a small control signal to open a large local air supply to the chambers, so brakes apply and release faster. This shortens response time, especially on long trailers.

Question 10Air Brake System Components and Functions

What does the tractor protection valve do when the trailer air supply is lost or the trailer breaks away?

  1. It opens the trailer supply line fully to keep the trailer rolling.
  2. It closes off the tractor air supply and vents the trailer supply line, applying the trailer spring brakes. Correct answer.
  3. It disables the tractor's front brakes.
  4. It boosts pressure to the trailer service line.

Explanation

The tractor protection valve guards the tractor's air supply and, when pressure drops or the lines separate, it closes the supply and vents the trailer line. That causes the trailer emergency/spring brakes to set.

Question 11Air Brake System Components and Functions

In a spring brake chamber, what holds the parking brake applied when air pressure is released?

  1. A coil spring inside the chamber Correct answer.
  2. Air pressure trapped in the service chamber
  3. Hydraulic fluid from the master cylinder
  4. A mechanical linkage from the foot valve

Explanation

Spring brakes use a large compressed spring that pushes the pushrod out when air pressure is removed, applying the brake. Air pressure must be present to compress the spring and release the brake.

Question 12Air Brake System Components and Functions

What is a brake chamber's function in an air brake system?

  1. It converts air pressure into mechanical force that moves the slack adjuster and brake shoes. Correct answer.
  2. It stores reserve air for the parking brake.
  3. It cools the brake drums during long downgrades.
  4. It measures how much air the compressor has produced.

Explanation

Air pressure entering the chamber pushes a diaphragm and pushrod, converting pneumatic force into mechanical motion at the brake linkage. That mechanical force applies the foundation brakes.

Question 13Air Brake System Components and Functions

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

  1. It limits air pressure to the brake chambers during light applications.
  2. It releases air from the chamber when the pedal is released.
  3. It links the brake chamber pushrod to the brake camshaft and takes up wear so pushrod travel stays in range. Correct answer.
  4. It measures pushrod travel and sends it to the dash display.

Explanation

The slack adjuster is the lever that converts pushrod stroke into camshaft rotation, and its adjustment keeps pushrod travel within limits as linings wear. Proper adjustment is critical to braking performance.

Question 14Air Brake System Components and Functions

After a full brake application, the driver releases the pedal but the brakes stay applied on one wheel end. Which component is the most likely cause?

  1. A stuck or restricted return/exhaust path at that wheel's brake chamber or valve Correct answer.
  2. A governor cut-out set too low
  3. A low-pressure warning switch that has failed
  4. An air dryer cartridge that is saturated

Explanation

Brakes that stay applied on release point to air that cannot escape from that chamber, such as a blocked exhaust passage, a faulty quick release valve, or a sticking chamber. The governor, dryer, and warning switch do not hold a single wheel's brakes on.

Question 15Air Brake System Components and Functions

What does the application pressure gauge show the driver?

  1. The compressor's cut-out pressure setting
  2. The amount of air lost through the safety valve
  3. The pressure the driver is currently applying to the service brakes Correct answer.
  4. The pressure remaining in the trailer emergency line only

Explanation

The application gauge reflects the control pressure being sent to the brakes as the pedal is pressed. It differs from the reservoir gauge, which shows stored supply pressure.

Question 16Air Brake System Components and Functions

Which component prevents the trailer from rolling away if it separates from the tractor?

  1. The trailer spring brakes, which apply when the emergency line loses pressure Correct answer.
  2. The trailer relay valve, which locks the wheels by trapping service air
  3. The tractor safety valve, which vents the trailer tanks
  4. The trailer slack adjusters, which cam over when disconnected

Explanation

On breakaway, the emergency supply line loses pressure and the trailer's spring brakes apply automatically. This is the fail-safe feature that stops an uncoupled trailer.

Question 17Air Brake System Components and Functions

A dual air brake system is designed so that a failure in one circuit will do which of the following?

  1. Cause total loss of braking on all wheels
  2. Prevent the spring brakes from ever applying
  3. Allow the other circuit to continue providing braking, with a warning to the driver Correct answer.
  4. Automatically bypass the governor and overpressurize the good circuit

Explanation

Dual circuits are isolated by check valves so a single failure leaves the other circuit able to brake, though performance is reduced. The driver is warned by the low-pressure alarm and gauge.

Question 18Air Brake System Components and Functions

What is the function of the inversion (spring brake control) valve in some air brake systems?

  1. It swaps air between the primary and secondary reservoirs.
  2. It lets the spring brakes be modulated for service braking in an emergency. Correct answer.
  3. It reverses the direction of the compressor's rotation.
  4. It inverts the gauge reading from psi to kPa.

Explanation

An inversion valve allows controlled air to reach the spring brake chambers so they can be applied gradually for emergency stopping rather than only fully applied. This gives modulated braking when service air is lost.

Question 19Air Brake System Components and Functions

What does the front brake limiting (proportioning) valve do on some vehicles?

  1. It disables the front brakes whenever the trailer is connected.
  2. It increases front brake pressure to shorten stopping distance.
  3. It reduces air pressure to the front brakes during hard stops to help prevent wheel lockup. Correct answer.
  4. It holds front brake pressure after the pedal is released.

Explanation

The limiting valve caps pressure delivered to the front brakes under certain conditions to reduce the chance of front wheel lockup and loss of steering control. It does not boost pressure or disable the brakes.

Question 20Air Brake System Components and Functions

During a pre-trip inspection, the driver finds that pushrod travel on one brake chamber exceeds the adjustment limit. What does this indicate?

  1. The low-pressure warning switch is miswired.
  2. The chamber has too much air pressure and the governor must be reset.
  3. The air dryer needs a new desiccant cartridge.
  4. The brake is out of adjustment and braking force at that wheel is reduced, so it must be adjusted before driving. Correct answer.

Explanation

Excessive pushrod travel means the slack adjuster is out of adjustment, so the chamber stroke is used up before full braking force reaches the shoe. It reduces braking and must be corrected before the vehicle is operated.

Question 21Air Brake System Components and Functions

What is the purpose of the drain cocks (petcocks) on the air reservoirs?

  1. To release air to the brakes during a service application
  2. To connect the trailer emergency line
  3. To let the driver manually drain moisture and oil that collect in the tanks Correct answer.
  4. To set the compressor cut-in pressure

Explanation

Moisture and oil settle in the bottom of the reservoirs, and the drain cocks allow them to be blown out during inspection. Regular draining helps prevent corrosion and freeze-ups in the system.

Question 22Air Brake System Components and Functions

What does the compressor do in an air brake system?

  1. It pumps air into the reservoirs to build and maintain system pressure. Correct answer.
  2. It meters air to the brake chambers based on pedal position.
  3. It releases air from the chambers when the pedal is released.
  4. It applies the spring brakes when pressure is low.

Explanation

The compressor is the air source, driven by the engine, and it charges the reservoirs to the pressure range set by the governor. Metering, releasing, and spring brake application are handled by other components.

Question 23Air Brake System Components and Functions

A driver hears the compressor cycling more frequently than usual and the system pressure drops between cycles. Which explanation fits best?

  1. The low-pressure warning switch is drawing air from the tanks.
  2. The governor cut-out is set too high and the safety valve is stuck open.
  3. The slack adjusters are over-adjusted and using extra air.
  4. An air leak in the system is causing pressure to escape faster than normal. Correct answer.

Explanation

Frequent compressor cycling with pressure loss between cycles is the classic sign of a leak draining the system. The correct response is to find and repair the leak rather than adjust the governor.

Question 24Air Brake System Components and Functions

What is the function of the trailer supply (emergency) line in an air brake system?

  1. It carries the service brake application signal to the trailer chambers.
  2. It charges the trailer reservoirs and keeps the trailer spring brakes released while connected. Correct answer.
  3. It supplies air only to the trailer's front axle brakes.
  4. It exhausts trailer air to the atmosphere during a normal stop.

Explanation

The emergency/supply line delivers air to the trailer tanks and holds off the trailer spring brakes during normal operation. Loss of pressure in this line sets the trailer brakes.

Question 25Air Brake System Components and Functions

Why must a driver build full air pressure before releasing the parking brake and moving?

  1. The compressor will not run unless the vehicle is moving.
  2. Spring brakes release only when sufficient air pressure compresses their springs, and low pressure means weak or dragging brakes. Correct answer.
  3. The trailer supply line closes automatically below 120 psi.
  4. The foot valve is locked out until the tanks are full.

Explanation

Spring brakes need adequate air pressure to release fully, and the system needs reserve pressure for stopping. Moving with low pressure risks dragging brakes and insufficient braking capacity.

Question 26Air Brake System Components and Functions

Which component stores compressed air so the brake system has a reserve capacity for repeated applications?

  1. The low pressure warning switch
  2. The safety valve
  3. The alcohol evaporator
  4. The air reservoir (supply tank) Correct answer.

Explanation

Air reservoirs are storage tanks that hold compressed air delivered by the compressor, giving the system enough volume to make several brake applications before the compressor catches up. The other listed parts either protect, condition, or monitor the system rather than store air.

Question 27Air Brake System Components and Functions

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

  1. It releases air if system pressure rises above a safe preset level Correct answer.
  2. It drains moisture from the tank each time the compressor cycles
  3. It balances pressure between the primary and secondary circuits
  4. It closes the trailer supply line during a breakaway

Explanation

The safety valve is a pressure relief device that opens at a preset value to protect the reservoir and lines from over-pressurization, for example if the governor fails to unload the compressor. It vents excess air rather than controlling normal system functions.

Question 28Air Brake System Components and Functions

Which device controls when the compressor pumps air into the system and when it stops, based on reservoir pressure?

  1. The pressure relief valve
  2. The foot valve
  3. The governor Correct answer.
  4. The double check valve

Explanation

The governor senses reservoir pressure and signals the compressor to load (pump) at the cut-in pressure and unload (stop pumping) at the cut-out pressure. This cycling keeps system pressure within the designed operating range.

Question 29Air Brake System Components and Functions

In a dual-circuit air brake system, what separates the primary circuit from the secondary circuit so a leak in one does not drain the other?

  1. The compressor unloader
  2. The treadle valve spring
  3. The low pressure indicator
  4. The dual check valve arrangement inside the foot valve Correct answer.

Explanation

The foot valve in a dual system contains two separate delivery sections fed by separate reservoirs, and check valves keep the circuits isolated so a failure in one circuit does not bleed pressure from the other. This isolation is what allows a partial braking capability after a single-circuit failure.

Question 30Air Brake System Components and Functions

A driver applies the brakes and hears air escaping continuously near one wheel; the pushrod on that chamber does not extend. Which component has most likely failed?

  1. The brake chamber diaphragm or its housing Correct answer.
  2. The application pressure gauge
  3. The governor
  4. The alcohol evaporator

Explanation

A ruptured diaphragm or cracked chamber housing lets supply air escape to atmosphere instead of pushing the pushrod out, so that wheel end gets no braking force and a continuous leak is heard. The governor, evaporator, and gauge are not located at the wheel end and would not produce this symptom.

Question 31Air Brake System Components and Functions

What is the purpose of the supply (service) line running from the tractor to the trailer?

  1. It holds the trailer spring brakes released by maintaining constant pressure
  2. It delivers air pressure that the trailer relay valve uses to apply the trailer brakes Correct answer.
  3. It drains condensate from the trailer reservoir
  4. It carries the electrical signal for the trailer stop lamps

Explanation

The service line is the control line: air sent through it by the tractor's foot valve signals the trailer relay valve to deliver reservoir air to the trailer brake chambers. It is distinct from the emergency line, which supplies air and controls the trailer protection function.

Question 32Air Brake System Components and Functions

What does the compressor unloader mechanism do when the governor signals cut-out pressure?

  1. It applies the spring brakes automatically
  2. It routes air to the front brake limiting valve
  3. It holds the compressor valves open so it stops pumping air Correct answer.
  4. It opens the reservoir drains to purge moisture

Explanation

At cut-out pressure the governor sends an air signal that actuates the unloader, holding the compressor intake valves open so the compressor freewheels without building pressure. When pressure falls to cut-in, the signal is removed and pumping resumes.

Question 33Air Brake System Components and Functions

A driver observes that the application pressure gauge reads high but the vehicle decelerates weakly. Which explanation best fits?

  1. The low pressure warning buzzer is miswired
  2. Air is reaching the chambers but a mechanical brake adjustment or friction problem is limiting force Correct answer.
  3. The compressor is building too much pressure
  4. The governor cut-out setting is too low

Explanation

The application gauge shows control pressure delivered toward the brakes, so a high reading with poor stopping indicates the air is being delivered but the mechanical side, such as slack adjustment or lining condition, is not converting it into braking force. Pressure alone does not guarantee retardation.

Question 34Air Brake System Components and Functions

Why does an air brake system include a check valve between the compressor and the first reservoir?

  1. To prevent air from flowing back from the reservoir to the compressor when it unloads Correct answer.
  2. To sound the low pressure warning below 60 psi
  3. To automatically drain water from the compressor discharge
  4. To reduce the pressure sent to the trailer service line

Explanation

A check valve allows air to flow only toward the reservoir, so when the compressor unloads or stops, stored air cannot bleed back through the compressor. This protects system pressure and prevents the compressor from being cycled by reservoir backflow.

Question 35Air Brake System Components and Functions

A driver parks on a grade and hears a steady hiss from the dash area after setting the parking brake. Which component should be inspected first?

  1. The parking brake control valve Correct answer.
  2. The front brake limiting valve
  3. The trailer relay valve
  4. The quick release valve

Explanation

The parking brake control valve is mounted in the dash and controls air to the spring brake chambers; an internal leak there produces a hiss at the dash when the brake is set. The other valves are remote from the dash and would not typically be heard there.

Question 36Air Brake System Components and Functions

What is the purpose of the inversion valve in a system with spring brakes on a vehicle that has lost its primary circuit?

  1. It allows a modulated spring brake application for stopping when service air is unavailable Correct answer.
  2. It increases reservoir pressure above the governor cut-out
  3. It prevents the compressor from charging the wet tank
  4. It converts the spring brake chambers to service chambers permanently

Explanation

The inversion valve uses whatever control pressure remains to modulate spring brake application, giving the driver a controlled way to slow the vehicle when normal service air is lost. It does not make the spring brakes into service brakes or alter compressor output.

Question 37Air Brake System Components and Functions

Which statement best describes how a relay valve speeds up trailer brake response?

  1. It sends a small control signal from the tractor to release a large volume of trailer reservoir air close to the chambers Correct answer.
  2. It limits trailer reservoir pressure to the governor cut-in value
  3. It converts electrical brake signals into air pressure at the tractor dash
  4. It drains the trailer tanks whenever the service line is pressurized

Explanation

A relay valve is essentially a remote-controlled large valve: a small air signal from the tractor service line actuates it, and it delivers reservoir air from a nearby tank directly to the trailer chambers. This shortens the distance air must travel, reducing lag compared with routing all air from the tractor.

Question 38Air Brake System Components and Functions

During a walk-around inspection, a driver finds that a rear brake chamber's pushrod extends but does not return fully when the brake is released. Which component is the most likely cause?

  1. The safety valve
  2. The brake chamber return spring Correct answer.
  3. The governor
  4. The compressor discharge line

Explanation

The return spring inside the brake chamber pulls the pushrod back when air pressure is released; a broken or weak spring leaves the pushrod extended and can cause brake drag. Governor, safety valve, and discharge line problems affect system pressure, not pushrod return.

Question 39Air Brake System Components and Functions

What does the low air pressure warning device in an air brake system alert the driver to do?

  1. Stop safely because system pressure has fallen below a safe operating level Correct answer.
  2. Switch to the secondary circuit manually
  3. Release the parking brake to test the spring brakes
  4. Increase engine speed to charge the trailer reservoir

Explanation

The warning device, typically a buzzer and light, activates when pressure drops below the safe threshold so the driver knows braking capability is compromised and should stop. It does not instruct the driver to charge the trailer or perform brake tests.

Question 40Air Brake System Components and Functions

How does a front brake limiting valve affect braking on a vehicle equipped with one?

  1. It routes front brake air to the trailer service line
  2. It reduces front brake application pressure to help prevent wheel lockup on slippery surfaces Correct answer.
  3. It increases front brake force to shorten stopping distance
  4. It disables the front brakes entirely whenever the parking brake is set

Explanation

A front limiting valve, often called a proportioning or 'slippery road' valve, reduces the air pressure delivered to the front chambers so the front wheels are less likely to lock on low-traction surfaces. It does not boost front braking or redirect air to the trailer.

Question 41Dual Air Brake Systems

In a dual air brake system, how are the two circuits normally identified on a typical heavy truck?

  1. A high-pressure circuit and a low-pressure circuit
  2. A primary circuit and a secondary circuit Correct answer.
  3. A service circuit and a parking circuit
  4. A front circuit and a rear circuit

Explanation

Dual systems are described as primary and secondary circuits. The primary circuit typically supplies the rear brakes, while the secondary circuit supplies the front brakes, and each is charged independently so a failure in one does not empty the other.

Question 42Dual Air Brake Systems

What component on the supply side of a dual air brake system prevents air from one circuit from escaping through a failed circuit?

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

Explanation

The double check valve lets the two circuits share a common supply point, such as the compressor or a low-pressure warning switch, while isolating them from each other. If one circuit loses pressure, the check valve keeps the other circuit's air from bleeding out through the failure.

Question 43Dual Air Brake Systems

During a static leak test on a dual air brake system with the engine off and the system fully charged, which result indicates an acceptable condition?

  1. Pressure loss of no more than 2 psi in one minute with the service brakes released Correct answer.
  2. Pressure loss of no more than 3 psi in one minute with the service brakes applied
  3. Pressure loss of no more than 5 psi in one minute with the service brakes applied
  4. Pressure loss of no more than 4 psi in one minute with the service brakes released

Explanation

The standard static leak test allows no more than 2 psi loss in one minute with the brakes released and no more than 3 psi loss in one minute with the brakes fully applied. Losses greater than those limits indicate a leak that must be corrected before the vehicle is placed in service.

Question 44Dual Air Brake Systems

A dual air brake system's low-pressure warning device must activate before pressure in either circuit drops below what level?

  1. 80 psi
  2. 120 psi
  3. 60 psi Correct answer.
  4. 100 psi

Explanation

The warning device, usually a buzzer and light, must activate before either circuit falls below 60 psi. This gives the driver warning while enough pressure remains to stop the vehicle safely.

Question 45Dual Air Brake Systems

The governor on a dual air brake system is set to cut out at 130 psi. At approximately what pressure should the compressor cut back in to begin building pressure again?

  1. 125 psi
  2. 100 psi Correct answer.
  3. 130 psi
  4. 110 psi

Explanation

The governor typically has a cut-in pressure about 20 to 25 psi below cut-out, so with a 130 psi cut-out the compressor resumes near 100 to 110 psi. The cut-in point restores pressure after normal use without cycling the compressor too frequently.

Question 46Dual Air Brake Systems

If the primary circuit loses all pressure on a dual air brake system, what braking capability should remain available to the driver?

  1. No service braking at all
  2. Steering axle service brakes with reduced stopping power Correct answer.
  3. Spring brake application on the rear wheels only
  4. Full braking on all wheels

Explanation

A dual system is designed so that loss of the primary circuit leaves the secondary circuit, which typically operates the steering axle service brakes. The vehicle can still be stopped, but stopping distance increases and the driver should proceed cautiously to a safe location.

Question 47Dual Air Brake Systems

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

  1. To cool the compressed air before storage
  2. To remove moisture and contaminants from the air supply Correct answer.
  3. To increase system pressure
  4. To lubricate the compressor

Explanation

An alcohol evaporator or air dryer removes moisture from the compressed air before it reaches the reservoirs. Moisture in the system can freeze in cold weather and corrode components, so drying the air protects valves and brakes.

Question 48Dual Air Brake Systems

During the pre-trip inspection, how should a driver check that the dual air brake system's low-pressure warning works?

  1. Drain both reservoirs completely and restart the engine
  2. Apply the parking brake and release it repeatedly
  3. Pump the brake pedal until the warning activates, then rebuild pressure Correct answer.
  4. Open the draincocks and leave them open while idling

Explanation

The accepted check is to build normal pressure, then pump the brake pedal with the engine off until the low-pressure warning activates. This confirms the warning device works and shows the pressure level at which it triggers.

Question 49Dual Air Brake Systems

The supply reservoir in a dual air brake system is also known by which name?

  1. The dry tank
  2. The wet tank Correct answer.
  3. The secondary tank
  4. The application tank

Explanation

The supply reservoir is commonly called the wet tank because it receives air directly from the compressor and collects the most moisture. Air then passes through a check valve to the primary and secondary (dry) reservoirs.

Question 50Dual Air Brake Systems

A driver notices the air pressure gauge shows the primary circuit building pressure but the secondary circuit gauge stays at zero. What is the most likely cause?

  1. The low-pressure warning buzzer is disconnected
  2. The governor cut-out is set too high
  3. The compressor is worn out
  4. A check valve or line feeding the secondary circuit has failed Correct answer.

Explanation

If one circuit builds pressure while the other stays at zero, the problem is isolated to the supply path for the dead circuit, such as a failed check valve or a broken line. A compressor or governor fault would affect both circuits.