Montana CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

During a trip you find that the safety relief valve on the first air tank has been releasing air. How does the manual treat that?

Accepted Answer

As a sign that something is wrong and a mechanic should fix it — The safety valve keeps pressure in the first tank and everything downstream from climbing too high. Its usual opening point is 150 psi, well above the typical governor cut-out of around 125 psi. The manual says that if this valve lets air out there is a fault, and a mechanic should correct it.

Answer

As normal behavior whenever the governor cuts out

Answer

As a reminder that the tanks are overdue for draining

Answer

As proof that the spring brakes are about to apply

Question 2

You are checking that the low pressure warning works on a truck with a dual air system. Which tank's pressure does the manual's 55 psi standard apply to?

Accepted Answer

The tank with the lowest air pressure — The warning has to come on before pressure falls under 55 psi, and for dual systems the manual specifies the tank holding the least pressure. The test is done with the engine off and the electrical power on, pumping the brake pedal to bring the pressure down.

Answer

The tank with the highest air pressure

Answer

The average of all the tanks

Answer

Only the first tank the compressor fills

Question 3

A bus has lost its main air pressure and the spring brakes are on. The driver uses the spring-loaded control fed by a separate air tank to release them and move. Why does the manual say to plan that move carefully?

Accepted Answer

The separate tank holds only enough air to release the brakes a few times — On vehicles with dual parking control valves, pushing the spring-loaded control in sends air from a separate tank to release the spring brakes, and letting go brings them back on. The manual warns that this supply is good for only a few releases, so a poorly planned move could leave you stopped somewhere dangerous.

Answer

The separate tank refills only when the engine is switched off

Answer

Using the control disables the service brakes for the rest of the trip

Answer

The spring brakes will not reapply once they have been released this way

Question 4

Suppose the low pressure warning signal has failed and air is leaking away unnoticed. What does the manual say this could lead to in a single-circuit air system?

Accepted Answer

Sudden emergency braking — Without a working warning you could lose air and not know it. The manual says that in a single-circuit system the result can be sudden emergency braking, while in a dual system stopping distance grows and only limited braking is possible before the spring brakes apply.

Answer

A gradual, gentle stop

Answer

Automatic shutdown of the engine

Answer

Nothing until the tanks are refilled

Question 5

The manual describes air brakes as three braking systems in one. What does it say the emergency brake system is built from?

Accepted Answer

Parts of the service brake system and the parking brake system — The Air Brakes section says the emergency brake system draws on components of both the service brakes and the parking brakes so the vehicle can still be stopped after a brake system failure. It is not described as a separate hydraulic backup.

Answer

A separate set of brake shoes used only when the pedal fails

Answer

The trailer hand valve and the tractor protection valve

Answer

A hydraulic backup circuit that works without air

Question 6

Your air pressure builds more slowly than the manual's standard during the pre-trip check. What does the manual say could happen if you drive anyway?

Accepted Answer

Pressure may fall too low on the road and force an emergency stop — When pressure does not build fast enough, the manual warns that it can drop too low while you are driving and make an emergency stop necessary. It says not to drive until the problem has been fixed.

Answer

The governor will raise its cut-out pressure to compensate

Answer

The safety valve will open at 150 psi

Answer

The brakes will apply harder than normal

Question 7

Air pressure has leaked down until the spring brakes apply on a heavily loaded truck. Why does the manual say the stop will be a long one?

Accepted Answer

Not every axle has spring brakes working on it — The manual explains that spring brakes act on only some of the axles, so a heavy vehicle stopping on them alone needs a long distance. Stopping earlier, with air still available for the foot brake, is far safer.

Answer

Spring brakes apply only half of their force when the vehicle is loaded

Answer

The governor holds the spring brakes off until the engine stops

Answer

Heavy loads keep the brake drums too cool to grip

Question 8

In stab braking, you release the brakes when the wheels lock. What does the manual say happens if you put the brakes back on before the wheels are rolling again?

Accepted Answer

The vehicle will not straighten out — After you release locked brakes, the manual says the wheels can need as long as one second to begin rolling. Braking again before that happens keeps the vehicle from straightening out.

Answer

The spring brakes will apply

Answer

The ABS lamp will come on

Answer

The stop will be shorter

Question 9

One half of your dual air brake system has dropped very low on pressure while the other half is normal. What does the manual say this means for you?

Accepted Answer

The brakes at one end of the vehicle, front or rear, will not work fully, so stopping takes longer — With one system very low, the manual says the brakes at one end of the vehicle will not be working fully and you will need more distance to stop. Its instruction is to make a safe stop and get the air brake system repaired.

Answer

Nothing changes, because the good half runs every brake

Answer

The spring brakes release and cannot be reapplied

Answer

The trailer brakes lock at once

Question 10

The manual says the low air pressure warning must come on before tank pressure falls below 55 psi. What alternative figure does it give for older vehicles?

Accepted Answer

One half of the compressor governor's cutout pressure — For older vehicles the manual states the warning point as half the governor cutout pressure. The 80-85 psi figure is what it calls common on large buses, and 20 to 45 psi is the range in which spring brakes come fully on.

Answer

20 to 45 psi

Answer

80 to 85 psi

Answer

The governor's cut-in pressure

Question 11

Your low air warning light has just lit up and the buzzer is sounding. Why does the manual tell you to stop right then instead of waiting for the spring brakes to apply on their own?

Accepted Answer

Because at that point you can still control the brakes — Spring brakes on tractors and straight trucks come fully on somewhere between 20 and 45 psi. The manual says not to wait for that: make a safe stop as soon as the warning first appears, while braking is still under your control.

Answer

Because spring brakes cannot apply while the vehicle is moving

Answer

Because the compressor shuts down for good once the warning sounds

Answer

Because stopping later would damage the governor

Montana CDL — Air Brakes: Handling Emergencies practice test

Study questions with answers

1. During a trip you find that the safety relief valve on the first air tank has been releasing air. How does the manual treat that?

2. You are checking that the low pressure warning works on a truck with a dual air system. Which tank's pressure does the manual's 55 psi standard apply to?

3. A bus has lost its main air pressure and the spring brakes are on. The driver uses the spring-loaded control fed by a separate air tank to release them and move. Why does the manual say to plan that move carefully?

4. Suppose the low pressure warning signal has failed and air is leaking away unnoticed. What does the manual say this could lead to in a single-circuit air system?

5. The manual describes air brakes as three braking systems in one. What does it say the emergency brake system is built from?

6. Your air pressure builds more slowly than the manual's standard during the pre-trip check. What does the manual say could happen if you drive anyway?

7. Air pressure has leaked down until the spring brakes apply on a heavily loaded truck. Why does the manual say the stop will be a long one?

8. In stab braking, you release the brakes when the wheels lock. What does the manual say happens if you put the brakes back on before the wheels are rolling again?

9. One half of your dual air brake system has dropped very low on pressure while the other half is normal. What does the manual say this means for you?

10. The manual says the low air pressure warning must come on before tank pressure falls below 55 psi. What alternative figure does it give for older vehicles?

11. Your low air warning light has just lit up and the buzzer is sounding. Why does the manual tell you to stop right then instead of waiting for the spring brakes to apply on their own?

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