Holy vacuum batman

[Anonymous]

I did a short overnight trip this weekend, and it got fairly cold for the area–low of around 7 *F (not including windchill which was -1).

I filled up a large Hydroflask vacuum insulated thermos with near boiling tea, with a down sleeve over the top, and left it in my car.

When i got back to my car early afternoon the next day, and tried to open the Hydroflask bottle–i found a curious thing, as i unscrewed it and tried to pull off the lid, i couldn’t, and it would suck back down.  After trying this a few times, i gave up as the suction was too strong for me.

I’m guessing what happened is that hot, expanded air, cooled and contracted enough, to create a strong vacuum effect like in canning.

Never had this happen before.  Would screwing it less tightly help to prevent this?

[Mike Oxford]

Old post, but I’ll answer it for posterity …

The boiling water create a positive pressure system inside the thermos.  You cannot unscrew it – it’s not due to vacuum, but instead to the outward pressure on the threads being so high as to prevent unscrewing.

You can tell it’s a positive pressure system because if you DO get it open (such as opening it before the pressure builds up too much) it goes all over the place.  If it were a vacuum it would suck air in without exploding hot liquid all over your hands.

If it’s tight enough to keep the liquid in it’s airtight so “less or more” tightness won’t help.

Leave it cracked a bit or let it cool more before sealing it tight.

-mox

 

 

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