Water column
Water column turns up in 2 fields: boilers, railroad. Here is what it means to the people in each one.
Water column in boilers
A vertical chamber piped to a steam boiler's steam and water spaces that carries the gauge glass and level controls.
Because the column connects above and below the waterline, water inside it stands at the same level as in the boiler, but with calmer surface and easy access. The gauge glass, try cocks and often the float-type low-water cutoff mount on it. A drain valve at the bottom lets the operator blow the column down to clear sludge from the connections, which keeps the level readings true.
"Blow down the water column and watch how fast the glass comes back, if it's lazy the lower connection is plugging."
Water column in railroad
A trackside standpipe used to fill the tender of a steam locomotive.
A vertical pipe with a swiveling horizontal spout used to deliver large volumes of water into the tender of a steam locomotive. Positioned alongside the mainline or at station platforms, it allowed crews to refill their water supply quickly without needing to spot the engine directly under a massive, fixed water tank.
"Spot the tender right on the mark so the fireman can swing the water column over without us having to move again."