Illinois CDL Practice Exam.

In an air brake system, the component used to hold compressed air and ensure braking functionality even in case of compressor failure is the Air Storage Tanks. These tanks store the compressed air necessary for braking, allowing the system to have reserve air in case the compressor fails. This ensures that the brakes can still be applied even if there is a problem with the compressor. The other options are not correct because: - Air Tank Drains are used to release excess moisture and contaminants from the air tanks but do not hold compressed air. - Safety Valve is designed to release air pressure from the system in case it exceeds a certain level to prevent damage, but it does not store compressed air. - Alcohol Evaporator is used to add alcohol to the air system to prevent freezing in cold weather conditions, but it is not responsible for holding compressed air for braking purposes.