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Heavy Duty Equipment Technician Red Seal Exam Prep · Question

A city bus with a full air brake system has a slow air pressure drop of 50 kPa over 5 minutes with the engine off and brakes applied, which exceeds the manufacturer's specification of 35 kPa. Which of the following is the most effective diagnostic step to pinpoint the leak?

When an air pressure drop is observed, the most effective method for locating the leak is to apply a soapy water solution to all potential leak points, such as

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Question: A city bus with a full air brake system has a slow air pressure drop of 50 kPa over 5 minutes with the engine off and brakes applied, which exceeds the manufacturer's specification of 35 kPa. Which of the following is the most effective diagnostic step to pinpoint the leak?

Answer options: ✅ Apply soapy water to all air lines, fittings, and chambers.

  • Check the air compressor's unloader valve operation.
  • Inspect the air dryer for proper desiccant saturation.
  • Drain all air tanks to check for residual moisture.

Correct answer: Apply soapy water to all air lines, fittings, and chambers.

Explanation: When an air pressure drop is observed, the most effective method for locating the leak is to apply a soapy water solution to all potential leak points, such as air lines, fittings, brake chambers, and valves. The formation of bubbles will indicate the exact location of the leak. Compressor unloader valve operation, air dryer saturation, and tank moisture do not directly diagnose a system leak.

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