Minnesota CDL: Air Brakes Practice Test

Not quite. The answer is In the first tank to which the air compressor pumps air

A safety relief valve is installed in the first tank that the air compressor pumps air to. This tank is known as the supply or "wet" tank. The safety valve protects the tank and the rest of the system from too much pressure. The valve is usually set to open at 150 psi.

Not quite. The answer is At the end of each working day

Unless your vehicle automatically drains the air tanks, you should drain them at the end of each working day so that the moisture and oil will not freeze or coagulate and cause your brakes to fail.

Not quite. The answer is Yes, but only if the alcohol evaporator is located downstream from the air dryer.

The air dryer contains a desiccant pack. A desiccant is a chemical agent designed to remove moisture. However, alcohol vapor from the alcohol evaporator (injector) can damage the desiccant. Hence, if an alcohol evaporator is installed, it must be located downstream from the air dryer.

Not quite. The answer is brake drum.

In North America, the most common type of foundation brake is the S-cam drum brake. The brake shoes and linings press against the inside of the brake drum, which causes friction to slow the wheel.

Not quite. The answer is 3 psi for single vehicles and 4 psi for combination vehicles.

After the initial drop, the maximum acceptable leakage rates per minute are 3 psi for single vehicles and 4 psi for combination vehicles. If the leakage rate is higher, check for leaks and correct them.

Not quite. The answer is If the brakes are very hot

If the brakes are too hot, avoid using the parking brakes because the heat may warp and damage the brakes. Also avoid using the parking brakes if they are wet and at risk of freezing. If the parking brakes freeze, your vehicle will be immobilized. In both of these situations, use wheel chocks instead.

Not quite. The answer is a supply pressure gauge.

Every vehicle with air brakes has a supply pressure gauge, which shows how much air pressure is in the air tanks. Some vehicles also have an application pressure gauge, which shows how much air pressure you are applying to the brakes. Older vehicles also had a manual front brake limiting valve, which allowed the driver to cut front brake air pressure in half as a way of preventing front-wheel skids. However, tests have shown that full front-wheel braking is safe.

Not quite. The answer is 20 to 45 psi.

An air leak in your brake system can cause your air brakes to fail. If the air pressure drops to the manufacturer's specification (typically 20–45 psi), your spring brakes will come on automatically. You can avoid this by pulling over and checking the air brakes if the low pressure warning light ever comes on.

Not quite. The answer is Every time you leave your vehicle, with a few exceptions

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is service

Air brakes are really three braking systems in one: the emergency brake, the parking brake, and the service brake. As these names suggest, when you depress the brake pedal in normal driving, it's the service brake system that applies the brakes.

Not quite. The answer is Either the front or rear brakes will not be fully operational.

A dual air brake system has two separate air brake systems, each with its own air tanks, hoses, lines, etc. Typically, one system operates the brakes on the rear axle(s), and the other system operates the brakes on the front axle. If one of the systems loses air pressure, either the front or the rear brakes won't work properly. As a result, your vehicle's braking distance will increase. If this happens, stop your vehicle and get the system fixed. Continued braking would soon cause the spring brakes to come on.

Not quite. The answer is at all wheels.

Foundation brakes are found at each wheel. The most common type of foundation brake is the S-cam drum brake.

Not quite. The answer is 3,000 pounds.

The most common type of air brake chamber in trucks and trailers is the Type 30. The type number gives the area of the diaphragm. Thus, the diaphragm in a Type 30 brake chamber has an area of 30 square inches. If a force of 100 psi (pounds per square inch) is applied to the diaphragm, the resulting pushrod force will equal 100 × 30 = 3,000 pounds.

Not quite. The answer is Never

Never leave your vehicle unattended without first applying the parking brakes or chocking the wheels. Your vehicle might roll away and hit something – or someone.

Not quite. The answer is Otherwise, you will have to get a CDL with restrictions.

If you do not pass the air brake knowledge test, you will only be able to get a CDL with a restriction that limits you to driving vehicles without air brakes. So, good luck!

Not quite. The answer is spring brakes.

In some vehicles, a control handle on the dashboard may be used to apply the spring brakes gradually. This is called a modulating valve. It is spring-loaded so you have a feel for the braking action. The more you move the control lever, the harder the spring brakes come on. They work this way so you can control the spring brakes if the service brakes fail. When parking a vehicle with a modulating control valve, move the lever as far as it will go and hold it in place with the locking device.

Not quite. The answer is a supply tank.

An Integrated Solution Air Dryer (AD-IS®) and Reservoir System provides an integrated air dryer, purge reservoir, governor, and a number of the charging valve components in a module. The air dryer is so efficient that a supply ("wet") tank is not needed. Instead, the AD-IS sends air directly to the primary and secondary service ("dry") tanks.

Not quite. The answer is the air pressure may drop too low during driving.

The manufacturer's specifications should state how fast the air pressure should build up once the engine has reached normal operating speed. If the air pressure does not build up fast enough during your final air brake check, the air pressure may not replenish quickly enough during normal braking either. Don't drive the vehicle until the cause has been found and corrected.

Not quite. The answer is S-cam drum brake.

Foundation brakes are present on each wheel. In North America as of this writing, S-cam drum brakes are much more common than wedge or disc brakes.

Not quite. The answer is To show how much pressure is in the air tanks.

The air supply pressure gauge is connected to the air tank (or possibly to both tanks in a dual air tank system). It shows how much air pressure is in the air tanks.