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Homework Help: A box Under Air Pressure -- will it blow?

  1. Oct 4, 2016 #1
    1. The problem statement, all variables and given/known data
    I'm doing a personal project to keep me busy for the winter. I grow Bonsai and I'm making a hospital for sick trees or recently collected ones from the wild that need to recover. I have constructed a 40x40 inch plywood box, 5/8 inch thick walls, air tight. The lid will be made of an Acrylic sheet (not purchased yet) to let light in from the outside. It will be a sealed controlled environment inside. Co2, O2, humidity temp levels etc will be controlled and measured.

    I am considering putting the box under pressure for an experiment so see if it effects growth and healing. I am no physicist, I spent 7 years as a machinist so I can build. However, advanced calculations are not my thing :) I do not want to pressurize anything without knowing if its safe, and I don't want to spend too much money. So if materials are to much cost to put it under 15 PSI I wont bother and just stick with controlled co2 etc... I was thinking 15 PSI just to double atmospheric pressure (AP) and see the results...

    My logic

    if AP is 14.7 PSI at sea level to double the air available to the surface level of the foliage of a plant I woudl have to put my box at 14.7 PSI (or 15 to round up...) How much pressure can a 40x40" 5/8 plywood box with an acrylic lid actually hold... maybe I could try 7PSI and just up it by 50%...

    My Math
    My attempt at a math solution was 40"x40"= 1600 square inches 1600 x 15PSI= 24,000 lb or 12 tons... That seems like to much for my construction. But maybe those numbers are relative to something I'm not thinking about...

    Should I even bother with this idea and stick to simply producing greater amounts of CO2 and o2 without pressure as a factor? When I worked in a shop 15 PSI was not much at all, if I didn't have a wife and kid I would just do it and see if it blows up (from far away ;) ). But now its best I do the responsible thing and ask someone and save a trip to the dog house hehe.

    Thanks in advance.
  2. jcsd
  3. Oct 4, 2016 #2


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    I think your math is correct. 15 PSI will blow it apart. 1-2 PSI is probably all it will be able to stand.
  4. Oct 5, 2016 #3


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  5. Oct 6, 2016 #4
    Thanks guys, Haruspex, I have seen only a few studies on plant growth under pressure as the article says, its not something many people have looked at. I have developed methods for increasing the C02 organically and that certainly has a major impact. Mixing that with higher pressure is something I will try just not with this set up. I will move the idea to a 55 gallon drum reinforced and start with 5 psi and see the results and if its worth it to move to more expensive set up. So far any study I have seen that puts living organisms under pressure has had some positive effects. I can only hope it increases the survival rate of my trees :)
  6. Oct 6, 2016 #5


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    So the area of a side is 1600 sq inches. At 1 atmosphere the force on that side would be 1600 * 15 = 24,000 lbs !

    Plywood is frequently used as shuttering when casting concrete. Google found a table of recommended maximum pressures for that application. See Table 3 here..


    Assuming I have interpreted that table correctly then it recommends limiting the pressure to below about 110lbs/sqf (5/8th ply with bracing every 16-20 inches not 40 inches). That's equivalent to a PSI of only about 0.7 psi. This limit might be to might be based on limiting distortion rather than burst strength.

    I think I would use an open ended tube filled with water tube as a combined pressure gauge/safety valve. (eg over pressure pushes the water out of the tube reducing the pressure).
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