Fire hydrant cutaway - photo

[Jon]

Fire hydrant cutaway.

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Previously:

Circuit breaker cutaway - photo
Reel-to-reel tape recorder cutaway - photo
Cutting torch cutaway - photo
Chiller compressor cutaway - photo
Golden Gate bridge cable cutaway - photo

[metric_taper]

I'm missing something, I thought these hydrants have a second valve that opens when the main pressure connection is made that lets the water drain down, so they don't freeze solid, and burst in the winter. At least this is the type I believe is used in the frost climes.

[jdurand]

I'm missing something, I thought these hydrants have a second valve that opens when the main pressure connection is made that lets the water drain down, so they don't freeze solid, and burst in the winter. At least this is the type I believe is used in the frost climes.

If you look at the bottom right of the cutaway you can see the drain. The main valve works like a spool valve to close off the drain while the poppet is opened.

[metric_taper]

If you look at the bottom right of the cutaway you can see the drain. The main valve works like a spool valve to close off the drain while the poppet is opened.

Thanks, I know these hydrants have to drain down. I did so some searching on this, and found the answer.
Where I grew up, there is over 800 feet of clay before bedrock. I recall as a kid watching the city workers fixing a water main break at a hydrant, but I don't remember them putting in any rock ballast for the hydrant to drain down in. I do remember how muddy the crew was, and the hole was more then 10 feet down. But the clay was always damp once you get below the 2 feet of black soil.
I'm guessing that the fire department has a procedure to use an auxiliary pump to pull the water out of the hydrant, at least in that area of clay subsoil.

[MeJasonT]

ah Jon you got me for a second. This one wont work its got a leak.

[MeJasonT]

Whats the pressure of these things 10 bar ? normal water main pressure. Looking at thickness of the casting its not as heavy as i would have expected.