I have a need to use more pressure differential than can be afforded by vacuum vs atmospheric pressure alone, and so I've come to consider using pressurised laboratory glassware for part of my setup.

I've made a little bit of research here on stack-exchange and on google and the general information I've gathered is that the physical shape of laboratory glassware and reaction vessel lends better to resisting external pressure (when we use them with internal vacuum), than to resisting internal pressure, though I'm left wondering what to expect to be doable in terms of pressurising glassware.

I have two pieces of glassware I'm considering using on the pressurised end of my setup: One is a 5,000mL flat bottom flask and the other is a 20,000mL flat bottom flask. Both are borosilicate glass, neither are perfect (they both have one or two tiny air bubbles in the glass at places) but both have shown very good resistance while being used with internal vacuum.

Is it realistic to expect them to be fine while adding an internal pressure up to 3 Bars? (I would put the glassware inside of a big metal cylinder for safety in case of "explosion")

What will be the best Resistance vs Glassware Shape / Glassware Volume / Temperature / etc. ?

Does anyone have any tips on the topic?

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    $\begingroup$ Glass in general is relatively bad at withstanding internal pressure, and glass joints in particular are even worse. $\endgroup$ Jul 27, 2019 at 21:35
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    $\begingroup$ No, I mean the part where two vessels meet. When you have vacuum inside, they are pressed together with great force, which is good. But internal pressure seeks to tear them apart. $\endgroup$ Jul 27, 2019 at 21:54
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    $\begingroup$ I am pretty sure you won’t find anyone stating their glassware will take anything greater than 1atm. That puts it into pressure vessel territory. $\endgroup$
    – Jon Custer
    Jul 27, 2019 at 22:18
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    $\begingroup$ Yes I thought of assemblies that disconnect without breaking. Metal clips are not strong enough to counter that. If they were made stronger, they themselves would break the glass when without pressure. $\endgroup$ Jul 28, 2019 at 15:28
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    $\begingroup$ Most chemists who need to do reactions at pressure use specialist vessels designed to do so not standard glassware which very much isn't designed to do so. Large volume pressure vessels will usually be made of metal (which is far better under pressure than glass). Or, perhaps, internally glass coated metal vessels). There are some specialist thick-walled glass vessels designed to cope with some modest pressure, but they will usually be fitted with specialist pressure seals: standard glass joints don't work under internal pressure. $\endgroup$
    – matt_black
    Jul 29, 2019 at 23:51

1 Answer 1


Put the flask in a metal container, with a large (at least three times the volume of the flask, for 3 atm pressure) bladder or sylphon (metal bellows) in the supply to the inner flask. Pressurize the outer metal container with air or inert gas.

The absolute pressure in the reaction vessel should be the same as the outer vessel (unless the reactants outgas rapidly), but there would be no differential pressure difference, ergo, no additional stress on the glass.

Or just conduct the whole experiment in a hyperbaric chamber... not a wimpy 0.1 atm plastic bubble, but something like this 10 atm unit, with margin for error. ;-)

  • $\begingroup$ This sounds like the way to go. I'll just have to find the equipment (not the hyperbaric chamber though, I can't afford that). Do you know of something affordable with connections going out of the chamber or do I have to be able to put my entire setup inside of it? (part of my setup will be under vacuum, so the chamber would put additional stress on it, though it seems glass resists better that way around) $\endgroup$
    – Hans
    Jul 28, 2019 at 22:58
  • $\begingroup$ The chamber looks really cool ^^ I want one! I can't afford it, but just out of curiosity do you have any idea of the order of pricing of such a chamber? Makes carrying out pressurised stuff so much more simple. $\endgroup$
    – Hans
    Jul 28, 2019 at 23:05
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    $\begingroup$ Sorry... the atmosphere in marketing is toxic, and they're under pressure not to release that info ;-) $\endgroup$ Jul 29, 2019 at 0:48
  • $\begingroup$ :D You made me laugh $\endgroup$
    – Hans
    Jul 29, 2019 at 13:47

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