The air compressor will stop pumping air to the air brakes at what pressure?

The air compressor will stop pumping air to the air brakes at what pressure?

• A. 125 psi
• B. 110 psi
• C. 135 psi
• D. 150 psi

Answer: (A)

Air brake systems use a governor to control when the compressor is allowed to pump. The compressor fills the reservoirs until the governor reaches its cut-out point, then it stops pumping to prevent over-pressurizing the system. When you use the brakes and the pressure drops enough, the governor opens again at the cut-in point and pumping resumes. This keeps the system within a safe, usable range, providing enough pressure for braking without pushing pressure higher than the system can safely handle. In most CDL training contexts, the cut-out value is the higher end of the operating range, which is why the correct choice reflects that maximum charging point. The other options would either be a lower threshold to start pumping again or an exaggerated value not matching how the governor controls charging.