Steam locomotives consume large volumes of water. Traditionally, the engine water was replenished during station stops, but if the locomotive was running long distances on a tight timetable, the requirement to add water was a huge limitation.
To improve efficiency and speed up the schedule by reducing the number of times required for a steam locomotive to stop and refuel, a track pan or “water trough” was invented in the mid 19th century. A track pan is basically a device that enables a steam locomotive to replenish its water supply while in motion. It consists of a long trough filled with water lying between the rails. When a steam locomotive passes over the trough, a water scoop can be lowered, and the speed of forward motion forces water into the scoop, up the scoop pipe and into the tanks.
The track pan was first developed in Britain. Its initial purpose was to speed up the running time of the Irish Mail, an express train located in North Wales. The first example was placed into service on June 23, 1860. American lines implemented the invention about ten years later.
Taking water at speed results in considerable spray behind the scoop, potentially drenching passengers in the leading train car! In Great Britain it was customary for the conductor or other train crew to warn passengers in the first coach to keep the windows closed. The considerable water spray also made track maintenance difficult. In very cold weather the water would freeze, preventing water pick-up, unless a heating apparatus was installed.
Track pans normally took a while to fill up after being used, so they could not be used immediately by a close-following train. They were also expensive to maintain, generally requiring a pumping station, a lot of plumbing, and at least one employee to maintain. Track pans were only justified on a railroad with a high traffic volume.
The use of track pans naturally declined as steam locomotives were gradually replaced by electric and diesel locomotives in the early to mid-1900s. Some larger railroads in the United States continued using them in some form or fashion until the end of main line steam service in the 1950s.