Track pan

A track pan (American terminology) or water trough (British terminology) is a device to enable a steam railway 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 or locomotive tender.

Steam locomotives consume considerable volumes of water, and the tender or side tanks need to be replenished at intervals. Traditionally the engine water was replenished during station stops, but if it was desired to run long distances without stopping, the requirement to take water was a significant limitation. The Railway Magazine reported a development by John Ramsbottom:

In the year 1860 the London and North-Western Company having decided to accelerate the Irish mail [express train], Mr. Ramsbottom, then their chief mechanical engineer, was asked to make the run between Chester and Holyhead, 84¾ miles, in 2 hours 5 minutes... It was clear that if the usual stop on the road to take in water could be avoided, an important point would be gained; but there were no tenders of sufficient capacity to hold the quantity of water required to enable an engine to run through without stopping. In an ordinary way, from 1,800 to 1,900 gallons were consumed, but in the rough and stormy weather frequently experienced along the exposed coast of North Wales it was not unusual for the consumption to rise to 2,400 gallons; whilst the largest tenders only held 2,000 gallons.

Ramsbottom arranged some experiments and showed that the forward motion of a scoop in a trough of water would force water up a connected pipe and into a tank. He calculated the quasi-static head produced by the forward motion:

at a velocity of 15 miles an hour the water is lifted 7½ ft., this was exactly the result attained in practice by the apparatus; at this speed the water was raised to the top of the delivery pipe (7½ft.), and was there maintained without running over into the tender whilst the scoop was in action. Again, theoretically the maximum amount of water the pipe was capable of raising was 1,148 gallons—5 tons—and this was reached when the engine was moving at the rate of about 80 miles an hour. The result of experiments made at different speeds was that at 22 miles an hour the delivery was 1,060 gallons; 33, 1,080; 41, 1,150; and 50, 1,070; showing that the quantity delivered varies very little at speeds above 22 miles an hour, which is accounted for by the shorter times the scoop is passing through the water.

...
Wikipedia