What does an alcohol evaporator do?
- It eliminates the need to drain the air tanks.
- It lessens the chance that the air brake valves will freeze. ✓
- It acts like a supercharger.
- It removes alcohol from the air tanks.
Answer: B. 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 an alcohol evaporator introduces a small amount of alcohol vapor into the air system. That vapor mixes with moisture in the system, and the alcohol works like anti-freeze by lowering the freezing point of the collected moisture. Because the vapor is carried through the system, it helps keep that moisture from freezing in the air brake parts. It is an optional device, not a substitute for regular draining of the air reservoirs.
Why the other answers are wrong
- A. It eliminates the need to drain the air tanks. — The handbook says air reservoirs must still be drained regularly even with an evaporator, so it does not remove that job.
- C. It acts like a supercharger. — The passages describe alcohol being drawn in as vapor to mix with moisture, not a device that boosts or supercharges the engine.
- D. It removes alcohol from the air tanks. — The evaporator adds alcohol vapor to the air system to lower the freezing point; it does not take alcohol out of the air tanks.
Remember it
Think of the alcohol as anti-freeze for the air system: it lowers the freezing point of moisture, but you still drain the tanks.