What does an alcohol evaporator do?
- It lessens the chance that the air brake valves will freeze. ✓
- It removes alcohol from the air tanks.
- It acts like a supercharger.
- It eliminates the need to drain the air tanks.
Answer: A. It lessens the chance that the air brake valves will freeze.
An alcohol evaporator lessens the chance that the air brake valves will freeze.
Why this is the answer
The handbook says moisture in an air brake system can freeze in cold weather and cause brake failure, and that even tiny ice particles cause problems. The evaporator adds alcohol vapour to the air, which mixes with any moisture or ice and makes it less likely to freeze. That is why it protects the brake valves from icing rather than doing anything to boost engine power.
Why the other answers are wrong
- B. It removes alcohol from the air tanks. — It adds alcohol vapour to the air instead of taking alcohol out, and removing moisture from the system is the job of the air dryer, not the evaporator.
- C. It acts like a supercharger. — It has nothing to do with engine power or forced air intake; it only puts alcohol vapour into the air brake system to limit freezing.
- D. It eliminates the need to drain the air tanks. — The handbook still says the air tanks must be drained regularly to keep moisture and oil from collecting, so the evaporator does not remove that duty.
Remember it
Alcohol goes in to keep ice out, so think of the evaporator as the anti-freeze helper for your air brakes, not a tank cleaner.
Official handbook: Official MTO Air Brake Handbook, Air Supply Subsystem – Alcohol evaporator