Why doesn't water in a fire hydrant freeze?

[Wangel]

I got asked this today and didn't have a reason. We were up north a few weeks ago and the temperature was about -25. Since a car engine block will crack like an old womans face as soon as the temperature dips below 32 degrees (without antifreeze). Why doesn't the water in a fire hydrant also freeze and break the fire hydrant?

 

[Antisocial Virge]

The water is actually fairly far down. The actual valve that is opened is down in the ground a ways and not right up at ground level.

 

[vi edit]

Yup - keep the water deep down in the ground where the cold temps can't penetrate.

 

[geno]

frost layer?


EDIT - vi must've edited his post while I was posting this, nevermind 😕

 

[Wangel]

We thought this for a while, but after you opened the fire hydrant faucet, the water would fill up to the opening. Shutting off the valve should leave some water in the hydraunt, at least up to the hose connector.

 

[Antisocial Virge]

We actually used the hydrant where I used to work. The water drains back out after you shut the valve. Not sure where it goes but you can actually hear it draining.

 

[vi edit]

genocide - there is a frost layer - it's about 2-3 feet deep. It's for this reason that you can't dig foundations in the winter. The ground has the consistency of concrete. You have to way for that frost layer to thaw before you can dig.

 

[Zenmervolt]

Doesn't the high pressure help as well as the depth? I remember hearing or reading somewhere that water under high pressure doesn't freeze as easily.

Zenmervolt

 

[IBhacknU]

if me remembers correctly, the higher pressure will effect the temp at which H20 freezes