What are "glad hands" used for in air brake systems?

Answer: B — Coupling devices

Glad hands are connectors used in air brake systems to facilitate the coupling of air supply lines between a tractor and its trailer. They are designed to create a secure connection that allows compressed air to flow from the tractor’s air system into the trailer's braking system. When the glad hands are connected properly, the brakes on both the tractor and the trailer can function together, ensuring safe and effective braking. This coupling mechanism is essential for the operation of the air brake system, as it ensures that the trailer receives the necessary air pressure to operate its own brakes in coordination with the tractor. The other choices refer to functions that are not typically associated with glad hands. Adjusting brake pressure is handled by other components in the air brake system, air tank levels are monitored by different gauges or sensors, and isolating emergency brakes is managed by dedicated valves within the system.