During a leak test for an air brake system, the engine should be off and the brakes released. Which option describes this condition?

During a leak test for an air brake system, the engine should be off and the brakes released. Which option describes this condition?

• A. Engine on and brakes released
• B. Engine off and brakes released
• C. Engine off and brakes applied
• D. Engine on and brakes applied

Answer: (B)

In an air brake leak test you’re checking how much air is lost when the system isn’t being replenished. With the engine off, the compressor isn’t pushing air into the tanks, so any pressure drop comes from leaks in lines, fittings, valves, or components. Having the brakes released ensures the brake parts aren’t engaged and no air is being used to apply the brakes, which would distort the reading. This setup lets you gauge the true static leak rate of the system. If pressure remains stable during the test, the system isn’t leaking excessively. If the engine were running, the compressor would keep topping off the tanks and hide leaks; if the brakes were applied, air would be consumed by braking and again skew the results.

In an air brake leak test you’re checking how much air is lost when the system isn’t being replenished. With the engine off, the compressor isn’t pushing air into the tanks, so any pressure drop comes from leaks in lines, fittings, valves, or components. Having the brakes released ensures the brake parts aren’t engaged and no air is being used to apply the brakes, which would distort the reading. This setup lets you gauge the true static leak rate of the system. If pressure remains stable during the test, the system isn’t leaking excessively. If the engine were running, the compressor would keep topping off the tanks and hide leaks; if the brakes were applied, air would be consumed by braking and again skew the results.