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I am intending to construct a small pressure vessel. It needs to be around 7 centimeters in length and width and around 1-2 centimeters in depth. It must be capable of being pressurised to 300 psi with sufficient space to contain a small amount of liquid (say 5cc)

Constraints

  • The body of the vessel must be made out of nickel-plated annealed brass.

  • The vessel will have a brass cap, held in place with silver solder.

  • The cap must be sufficiently thin to be pierced when it is inserted into a receptacle.

Is this design feasible?

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  • $\begingroup$ For bonus points, what is the minimum possible weight of such an object? $\endgroup$
    – Richard
    Commented Sep 24, 2015 at 15:12
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    $\begingroup$ you are thinking about a 7x7x2 cm box? $\endgroup$
    – mart
    Commented Sep 24, 2015 at 15:26
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    $\begingroup$ A solder connection may not be strong enough to withstand 300 psi, but I'm not an expert. The big red flag is the word "thin." How thin is thin? 300 psi means a 1 in diameter cap would have about 270 pounds exerted on the rim. If the wall is 1/64 in then the stress is on the order of 10000 psi, or 70 MPa. Brasses have yield strengths between 50 and 200 MPa, depending on composition and processing. What kind of brass does your application require? Why choose brass at all? Edit: goofed up units, but this is intended to give a ballpark idea of stresses $\endgroup$
    – do-the-thing-please
    Commented Sep 26, 2015 at 20:57
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    $\begingroup$ This question is less a design, and more a collection of requirements. To answer the question as is would require generation of a design. As noted by Wasabi and Algo, it would be helpful to see your design first. $\endgroup$
    – do-the-thing-please
    Commented Sep 26, 2015 at 21:06
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    $\begingroup$ Well, here's a start, which might be enough to show you whether your idea is feasible or not. 7 cm = about 2.75 in. A 2.75 in square has area about 7.5 sq in so the pressure force on it will be about 2250 pounds, near enough 1 ton. So, you need to make your little box strong enough to drive one wheel of a 4-ton truck over it without breaking it, and also make it "thin enough to be pierced". Good luck! $\endgroup$
    – alephzero
    Commented Sep 27, 2015 at 21:51

1 Answer 1

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Sure. CO2 cartridges are made of steel and hold 850 psi. You want to use brass, which has 80% of the yield strength of steel (200MPa vs 250MPa) to hold 35% of that pressure. Not to mention the fact that you specify a 7x7x"1-2"cm vessel, which is 49-98cc, to hold 5cc of liquid, so you're left with up to 93cc of brass to use as the wall thickness, where again, the same dimensions as a CO2 cartridge should suffice due to the difference between yield strength and desired pressure limits. The use of silver solder won't matter because you can use whatever surface area you need to provide enough contact area to provide a solid joint - see the comment above about having plenty of excess volume.

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  • $\begingroup$ Have you seen a CO2 cartridge anywhere near the dimensions specified? Most pressure vessels are cylindrical for a reason. If you pressurized a vessel of the dimensions given, you would soon have the large sides bowing out. $\endgroup$
    – hazzey ♦
    Commented Oct 2, 2015 at 23:42
  • $\begingroup$ @hazzey - As I understood the question, the only container volume required was "sufficient space for 5cc of liquid". As I mentioned in my answer, if you have a cylindrical void in the container for 5cc of liquid, you're left with a lot of material that can be used for wall thickness. Think mosquito in amber. Little void, big walls. Just because the external dimensions are large doesn't mean the interior needs to be that large or the wall thickness needs to be uniform. $\endgroup$
    – Chuck
    Commented Oct 2, 2015 at 23:56

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