While performing a leakage test using the Brake Pipe Leakage Method, why must the automatic brake valve be cut out?

While performing a leakage test using the Brake Pipe Leakage Method, why must the automatic brake valve be cut out?

• A. Cutting out the automatic brake valve also cuts out the Pressure Maintaining Feature, thus preventing it from maintaining against leakage in the brake pipe
• B. It prevents the brakes from applying fully
• C. It accelerates the test
• D. It eliminates the need to observe the brake pipe pressure

Answer: (A)

When testing brake pipe leakage, you want to see the true rate at which the brake pipe pressure drops due to leaks. The automatic brake valve includes a pressure maintaining feature that can compensate for small leaks and keep the brake pipe pressure from falling. If that feature is left in, the reading won’t reflect the actual leakage, making the test unreliable. Cutting out the valve disables that pressure maintaining function, so any observed pressure drop is due to leakage alone, giving an accurate measurement. The other ideas aren’t the main goal of this test: it’s not about preventing a full brake application, speeding up the test, or eliminating the need to observe brake pipe pressure. You still monitor the pressure to determine leakage.

When testing brake pipe leakage, you want to see the true rate at which the brake pipe pressure drops due to leaks. The automatic brake valve includes a pressure maintaining feature that can compensate for small leaks and keep the brake pipe pressure from falling. If that feature is left in, the reading won’t reflect the actual leakage, making the test unreliable. Cutting out the valve disables that pressure maintaining function, so any observed pressure drop is due to leakage alone, giving an accurate measurement. The other ideas aren’t the main goal of this test: it’s not about preventing a full brake application, speeding up the test, or eliminating the need to observe brake pipe pressure. You still monitor the pressure to determine leakage.