How can certain types of parking brakes be released without using air pressure?

The method by which certain types of parking brakes can be released without using air pressure often involves a mechanical mechanism. In this case, the correct answer highlights that some parking brakes can be disengaged mechanically by winding them off. This mechanical release typically involves a ratchet and pawl system, allowing the driver or operator to manually release the brake by turning a lever or winding a specific component.

This feature is particularly beneficial in situations where air pressure is not available, such as when a vehicle has experienced an air system failure or is parked without an air supply. In these scenarios, relying on a mechanical release ensures that the brake can still be disengaged safely.

The other possibilities involve various methods of brake release, but they do not reflect the mechanical aspect that is critical in ensuring that a parking brake can still function without air pressure. For example, simply turning a knob (as suggested by one option) implies a more straightforward action that may not encompass the mechanical intricacies involved in some systems. Similarly, automatic disengagement when the vehicle is off or the need for an electronic signal may pertain to modern braking technologies and systems but do not apply universally across all parking brake types.