During an air brake test, what indicates brake application?

During an air brake test, what indicates brake application?

• A. 5 PSI brake pipe reduction.
• B. 5 PSI brake pipe increase.
• C. No change in brake pipe pressure.
• D. 10 PSI reduction.

Answer: (A)

In an air brake system, brakes apply when the brake pipe pressure is reduced. When the brake valve is actuated, air is vented from the brake pipe, which triggers the brake cylinders to press the shoes against the wheels through the connected brake mechanisms. A small, observable drop in brake pipe pressure—typically about 5 psi during a test—shows that the brakes have applied. If the pressure instead increases or stays the same, brakes are not applying. A larger drop is still an application, but the standard test uses a 5 psi change as the signal to confirm the brakes engage.

In an air brake system, brakes apply when the brake pipe pressure is reduced. When the brake valve is actuated, air is vented from the brake pipe, which triggers the brake cylinders to press the shoes against the wheels through the connected brake mechanisms. A small, observable drop in brake pipe pressure—typically about 5 psi during a test—shows that the brakes have applied. If the pressure instead increases or stays the same, brakes are not applying. A larger drop is still an application, but the standard test uses a 5 psi change as the signal to confirm the brakes engage.