3
$\begingroup$

Would the body of a normal round pot shaped pressure cooker (built to cook foods at 15 psi) be able to withstand being evacuated down to high-vacuum pressures?

Apparently it has been done before: i.e. this instructable but was this person just lucky it didn't implode?

Improve this question
$\endgroup$
8
  • $\begingroup$ I've designed pressure vessels to full vacuum. They're generally beefy. I'm assuming a 12" diameter by 20' tall vessel is your aim? $\endgroup$ – Mark Jul 10 '15 at 10:34
  • $\begingroup$ I suspect not. Structurally, it is easier to contain higher pressure inside a vessel than to resist higher pressure from outside the vessel; think about a balloon. $\endgroup$ – Chris Mueller Jul 10 '15 at 11:52
  • $\begingroup$ 12" by 20' is one mother of a pressure cooker! Was thinking more something you would see on a stove - say 20 litres maximum $\endgroup$ – norlesh Jul 10 '15 at 13:01
  • $\begingroup$ @norlesh Haha, I suspect that Mark meant 12" x 20" which is a more typical size for a pressure cooker. $\endgroup$ – Chris Mueller Jul 10 '15 at 13:50
  • $\begingroup$ I'd guess that YMMV as the shape is designed to place the body in tension throughout and no thought needs to be given to stresses which will occur in vacuum mode. ie it MAY work. An eg tin can that is pressurised to well above it's design rating will round out at the ends but if placed under partial vacuum will flatten. | Taking an extreme example - a PET 1.5 litre bottle can be pressurised to about 150 psi - at which point it will swell and may explode. BUT it will collapse partially under a few psi of vacuum and increasingly so with reducing pressure. $\endgroup$ – Russell McMahon Jul 10 '15 at 14:16
3
$\begingroup$

Going with this pressure cooker, made of aluminum, 15" diameter, 12" tall. I'm giving this a similar thickness throughout. At 8.4# weight, that leads to 0.094" thick.

Applying Roark's 7th edition, Table 15.2, Case 20, using the approximation listed, formula, the 0.094" thick shell can withstand 82 psi of external pressure without buckling. Even with comfortable safety factors in place, this seems plausible. Only when the shell gets really thin (I calculate 0.05", or anything lighter than 16 gauge for this particular pressure cooker) would the shell buckle.

Note that since the bottom is flat (i.e. shell with infinite radius), then if it can handle 15 psi from the inside, it can handle 15 psi from the outside. Also, the top is flat on this one as well, so it works the same. Only for some models with curved tops would I need to look at the top as well.

In short, it's definitely possible for full vacuum, but I can't legally recommend it.

Improve this answer
$\endgroup$
2
$\begingroup$

It MAY work, but there are no guarantees as a shape that is designed to place the body in tension throughout inder pressure will exhibit stresses under vacuum which there is no needs to design for in normal operation.
ie it MAY work.

Note that the lid will need to be adapted in many cases as it is usually made to seal under positive pressure.

A thin steel tin can that is pressurised to well above it's design rating will round out at the ends but if placed under partial vacuum will flatten.

Taking an extreme example - a PET 1.5 litre bottle can be pressurised to about 150 psi (ask me how I know :-) *) - at which point it will swell and may explode. Few will reach 200 psi. BUT the same will collapse partially under a few psi of vacuum and increasingly so with reducing pressure. You can flatten one with "breath suction". [*How I know: Water rockets!].

Testing:

If you have a larger pressure vessel rated to several atmospheres + you could place your target pressure cooker therein and subject it to multiple atmospheres of external pressure. That will show you what sort of safety margin you have , subject to the pressure capability of the external chamber.

Improve this answer
$\endgroup$
0
$\begingroup$

Round profiled vessels fail at vacuum collapse pressures far below those designed for internal pressures. If more vacuum resistance is required, corrugated designs are preferred. Thin bellows survive upto 30% of external pressure as vacuum.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.