Brake button pop occurs at which pressure range?

• A. 20-40 psi
• B. 10-20 psi
• C. 30-50 psi
• D. 5-10 psi

Answer: (A)

Brake button popping is a low-pressure indication in an air-brake system. The control valve that holds the brake in the applied or released position relies on a certain pressure signal to stay engaged. When system pressure falls into roughly twenty to forty psi, there isn’t enough signal to keep the valve held, so the button pops out. This provides a warning that the air supply is dropping and action is needed to prevent brake failure. Pressures in the very low range (around five to ten psi) aren’t sufficient to produce reliable valve action, and at higher pressures (thirty to fifty psi) the valve would still be held and wouldn’t pop. So the pop occurs in the twenty to forty psi window.