Every car in the train has its own compressed air reservoir, including the tender. The car or tender reservoir gets air from the locomotive and stores it separately from the rest of the air system. The brakes are then operated by this car-based air supply, after which the car's reservoir is refreshed from the engine. The car's reservoir is kept under pressure, it is isolated from the train's air, and the car's brakes are activated by a special "triple-valve" developed in the 1880s, which provides and controls the necessary three-way feed.