At what psi pressure should air brake automatic activation occur during testing?

Air brake systems are critical for the safe and effective operation of vehicles, including those used in emergency services. The automatic activation of air brakes is a safety feature designed to engage when the pressure in the system drops below a certain threshold, ensuring that the vehicle can come to a stop safely.

Automatic activation typically occurs at a pressure level that allows for adequate braking force while still providing enough reserve air pressure for operation. The range of 21-40 psi is the most commonly recognized benchmark for when the air brake system should automatically engage. This range is selected to balance the need for vehicle operation with the need for safety, preventing the driver from losing braking ability due to a significant pressure drop.

Choosing this range ensures that the system provides adequate warning to the operator while still allowing for some operational capacity. Hence, recognizing this operational threshold is essential for ensuring a responsive and reliable air brake system.