How are emergency brakes on a bus with air brakes activated?

The emergency brakes on a bus equipped with air brakes are activated by a loss of air pressure. This is an important safety feature designed to ensure that the brakes engage automatically if the air pressure drops below a certain threshold. The use of air pressure is critical in air brake systems; when the pressure is lost, it triggers the emergency brakes to activate, helping to stop the vehicle safely.

Using this method ensures that the bus does not remain in an uncontrolled state if there is a failure in the air system. This is crucial for the safety of the driver, passengers, and other road users. In contrast, the other methods of brake activation do not directly relate to the operation of emergency brakes in an air brake system. For instance, pushing a knob or using the service brake pedal can be part of the normal brake operation but do not initiate the emergency system in case of air pressure loss. Hydraulic pressure, while relevant to other types of brake systems, is not applicable in the context of air brakes.