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Making a pressure cooker from scratch - need help with equations

  1. May 3, 2014 #1
    Hi all.

    I'm new here. My name is Tobias and I'm a danish resident.

    For a long time it has been on my mind to make a pressure cooker, since that I will be needing one in the near future for an agricultural project (a small mushroom farm in my apartment, which i plan on selling to customers.)

    My question is this: How do i go about calculating the necessary strength and thickness, of the metal cylinder which is going to encapsulate the water steam.

    If you know of any inspirational/instructional video's, links, books etc. feel very free to post, I would be glad for some inspiration. I've tried to surf the net, and couldn't find anyone engaging in a similar project.

    Would appreciate any help very much, thanks! :-)
  2. jcsd
  3. May 3, 2014 #2


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    Hi TobiasA1990. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    Why not use a commercial pressure-cooker? It would be a cheaper and a lot safer and much more reliable. Steam burns are dreadful!

    Are you wanting to cook the fungi, or to sterilize the growth medium?
    Last edited by a moderator: May 6, 2017
  4. May 5, 2014 #3
    Hi and thx :)

    A commercial pressure cooker gets rather expensive as i live in Europe and we have a high taxation on import. It rounds up to about 600-800$ for a 40liter, for which i imagine i could build one that's bigger at around the same price, maybe cheaper.

    I saw a video once on Youtube where a guy build a pressure cooker with metal barrels, racks other stuff, unfortunately I haven't been able to find the video again, I think it was taken down for some reason.
    The way he had it set up, was so that he had 2 barrels arranged vertically, and in the lower barrel he had steam generated which rose to the top (through some metal tube of a sort) and in the top one, he had the growth medium.

    The cooker is for sterilizing the growth medium.
  5. May 5, 2014 #4


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  6. May 5, 2014 #5


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    You'd think so. Do you feel the same way about other manufactured items, as well? Like building your own car from scratch, or a stove, for instance?

    Anyway, building a pressure vessel is more involved than picking up some pieces of steel and throwing a few formulas at it. In most places, the law discourages novices from building their own pressure vessels unless they have proven to be skillful and knowledgeable in the mysteries of such activities. I mean, the authorities want to inspect such devices to make sure they don't blow up, or some such nonsense, typical bureaucratic busywork.

    Maybe you have heard of the Boston Marathon bombing in April 2013? I recall pressure cookers came up in that, somehow. Anyhoo, after that, the bloom was off pressure cookers, especially those falling into the hands of foreign students.

    Are you sure maybe his estate didn't have the video taken down? Have you tried surplus autoclaves from a hospital or a laboratory?
  7. May 6, 2014 #6


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    It is not clear whether you are planning to grow mushrooms in your apartment, or whether you are thinking of manufacturing and selling D-I-Y boxes in which buyers can grow their own mushrooms. If the former, then I think you will run into moisture problems that will see mould and mildew growing on your apartment walls. Your landlord will not be happy. http://physicsforums.bernhardtmediall.netdna-cdn.com/images/icons/icon11.gif [Broken]
    Last edited by a moderator: May 6, 2017
  8. May 6, 2014 #7

    You have chosen a question that is not likely to get answered by anyone who knows better, since no one would want to see you kill yourself or others. Bottom line, pressure vessel design is not for amateurs (and is guaranteed to cost more than a commercial device, even for someone who knows what they are doing). If you truly want to sterilize some growth medium, I don’t really see the point of doing so at an elevated pressure (though I’ve never grown mushrooms). If there is truly a reason for this step, I would strongly suggest you buy whatever size commercial unit you can afford and do multiple batches. Never defeat the safety features in the commercial device, keep the seals clean, and make sure the relief port can’t be plugged up accidentally.
  9. May 6, 2014 #8

    What you said: 'and couldn't find anyone engaging in a similar project.', should be a major clue for you... I'd recommend you Google 'Darwin awards', a group you don't wish to join...
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