For a pre-trip air brake inspection, which statement is correct about pop-out pressures?

For a pre-trip air brake inspection, which statement is correct about pop-out pressures?

• A. 50 psi for the air supply valve and 30 psi for the park control valve
• B. 35 psi for the air supply valve and 15 psi for the park control valve
• C. 70 psi for the air supply valve and 50 psi for the park control valve
• D. Any pressure that’s roughly equal for both valves

Answer: (A)

Pop-out pressures test how the air brake valves respond when the system pressure is rising. The idea is to verify that the valves will move to the released position at specific, low pressures, confirming they’re functioning and won’t trap the brakes or fail to release when you need them. For the air supply valve, the pop-out occurs around 50 psi. This means once the system reaches about 50 psi, the valve should pop out and allow normal operation to proceed. For the park (parking brake) control valve, the pop-out occurs around 30 psi. This lower pressure ensures the parking brakes will release reliably when there’s enough system pressure, while still allowing the brakes to engage if pressure drops toward zero to prevent rollaway. If the valves don’t pop out at these pressures, it can indicate a leak, a sticking valve, or other fault in the air brake system that needs service before driving.

Pop-out pressures test how the air brake valves respond when the system pressure is rising. The idea is to verify that the valves will move to the released position at specific, low pressures, confirming they’re functioning and won’t trap the brakes or fail to release when you need them.

For the air supply valve, the pop-out occurs around 50 psi. This means once the system reaches about 50 psi, the valve should pop out and allow normal operation to proceed. For the park (parking brake) control valve, the pop-out occurs around 30 psi. This lower pressure ensures the parking brakes will release reliably when there’s enough system pressure, while still allowing the brakes to engage if pressure drops toward zero to prevent rollaway.

If the valves don’t pop out at these pressures, it can indicate a leak, a sticking valve, or other fault in the air brake system that needs service before driving.