My first thought was that you can’t make this stuff up:
That’s taken through one of the windows over Track 3 at the Poughkeepsie railroad station, so it’s a bit blurrier than usual.
It turns out a “Dry Water” pipe delivers ordinary water, but normally contains pressurized air to prevent freezing. An intricate valve in a heated room balances air pressure in the pipe against the supply water pressure; when the air pressure drops, water flows through the valve to the outlet.
Normally, you’d use a Dry Water pipe in a fire suppression system, but it makes perfect sense for an outdoor hose bib (or whatever you call that quick disconnect fitting) on the top level of the Poughkeepsie Railroad Station.
There’s (almost certainly) an automatic drain valve that removes water from the dry pipe: otherwise, it’d remain full after use and pop the pipe during the next freeze.
The Smell of Molten Projects in the Morning 
Comments
2 responses to “Dry Water”
Let me get an opinion here. One of my house bibs froze up last winter even though I shut down the inside valve and cracked open the outside one. What happened was this: the water froze in the outside valve, plugging it, and then it was so cold that the section further inside the house froze up and popped an elbow..
I fixed the elbow and moded it by replacing with a T and a short section of a blanked off pipe going up. The idea is that the stub should empty out when I shut off for winter, and provide a small expansion space should we have a serious freezing again. What do you think?
Sounds reasonable, but only if the bib valve opens enough to let air glug-glug-glug into the pipe and up the stub. No way to tell, I suppose, until the next freeze … [grin]
The classic long-stem freezeproof hose bibs on this place have worked perfectly for the last half century, but the new ones look like junk: hard to recommend using them.