Weird issue with vacuum flask

bazzabear

bazzabear

bazzabear

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2 Nov 2013
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My daughter has one of these:

https://smile.amazon.co.uk/Pioneer-...06XGKFKVM/ref=cm_cr_arp_d_product_top?ie=UTF8

This lunch time, she had to be given a school lunch because neither she, nor any of the teachers, could get the top off.

Back home with it, and it seems that the food inside cooling has created such a strong negative pressure that as you unscrew it, it's sucking the lid back down across the thread - you can hear it banging across them.

So. Any theories on how to non-destructively get the lid off?
 
Sorry guys. I tried the heating, and it seemed to make a bit of difference. Problem is that it also makes the flask hard to handle, because it is both too hot to hold, and very slippy because it's wet.

So I'm ashamed to say I gave up. Basically, there was little point in getting it open at this point because we wouldn't trust it to not do the same again in future anyway.

It's a shame, because it had actually done a pretty good job of retaining temperature in the food so far - keeping it hot enough to eat by lunch time. But you can see in the pictures the design fault - the threads are just stamped in to the metal, and are very shallow so easily overcome.
 
Pawnless Endgame said:
Have you got anything like a vice clamp or a workmate? You could do with clamping the small plastic cap end of the flask so that it is upside down then try and muscle the main / body part of the flask.
Click to expand...

Tried using some G-clamps on each end of it to get a better grip. But they couldn't grip well enough without bending the flask wall.
 
I don't think it's worth the price of the gas to keep a pan of water at near boiling for an hour. :D

Given that even when we've opened it, we'll only be throwing it away anyway I guess.

But I do agree with your point and I did dry it off before trying to open, but it obviously hadn't been heated enough (and that was a good twenty minutes on the hob). I was about to put it back in the pan when my wife and I agreed there was no point.
 
Blackjack Davy said:
Um, dont' do it up so tight next time? In the meantime stick the cap in a vice and wrench the sucker off
Click to expand...

If you read the thread you'd see that:

1) It isn't done up too tight, that isn't the cause of it not coming off.
2) Putting it in grips hasn't worked. You certainly could grip it hard enough so it wouldn't slip - but you'd destroy it in the process.
 
theone8181 said:
Surely by now even the best thermos must have hit equilibrium so have you managed to just pop it apart?
Click to expand...
Equilibrium in temperature you mean? But the issue isn't a temperature differential, it's a pressure differential, caused by the interior cooling.

if I took it to space, it'd open really easily.
 
theone8181 said:
But there shouldn't be a pressure difference once it's cooled as the hot contents will not be hot anymore? Or is that the problem, in which case its not kept it warm till lunch so why bother with the flask?
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I'm not getting you.

When the flask was sealed, the pressure was equal with the outside. The contents have then cooled and therefore the pressure within the flask has reduced. It's the cooling which has caused the pressure differential - it doesn't get rid of it.
 
theone8181 said:
What I mean is that will a none compressible seal, I'm surprised it's sealed well enough to create a vacuum. My job involves building vacuum sealed lasers, so I know how hard is it to seal (I mean proper vaccums). I'd have thought the leak rate would mean it would have equalised by now.
Click to expand...

Oh right, I get you.

It hadn't equalised after 3 days. And it's gone in the bin now, so that's your last update. :D
 
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