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Pressurized Box Engineering Help
4

Pressurized Box Engineering Help

Pressurized Box Engineering Help

(OP)
thread794-92440: Pressurized box: Pressurized box

Hi, I'm looking to create a pressurized box that is very similar to the one listed in the forum above. It will be about 25 inches x 14 inches x 16 inches and will need to hold about 18 psi. I want to a lightweight material and the box have thin walls to have the most possible space inside the box. What type of material does anyone think I should use?

I was thinking a plastic, with a plastic lid... Is that possible to create and hold that much pressure?

RE: Pressurized Box Engineering Help

If you're above 15 psi, then you're in ASME code space (if you're in the US). You need to find a copy of the Code and read up on what is required. If you're in some other country, then you need to find the applicable code for that country and follow those codes.

Patricia Lougheed

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RE: Pressurized Box Engineering Help

Pressurized "box" ??? A boxy shape (which implies a rectangular shape, 6 sided, with rectangualr wall and square corners) is the least efficient shape you can imagine for a pressurized contain. But, it also implies a removeable "cover" of some kind - probably also at least the same size as a the "bottom" as if you were going to "insert" something inside the "box" replace the cover, then pressurize the container.

Why a box shape? What kind of cover?

Operations: How often are you loading this "load" How heavy is it? Are you going to manually insert it? Move it in automatically? Is it on rails of some kind? By crane or What is your "load" and what is its shape? on a sling?

Sure, anything can be built, but you have not provided enough information to discuss your problem.

RE: Pressurized Box Engineering Help

Plastic may not be rigid enough to prevent leak from the lid. Plastic can deteriorate and become brittle, not a good choice. You need the lips of the lid to be rigid enough and you most likely need gasket.
Steel is the most economic choice due to its strength. Other materials, such as light weight fiber glass or fiber composite material (used in aircraft) may do the work, but I believe the cost will be high.
FEA is the best tool since you may need to modify the design many times.
You can put stiffener bars around the outside to brace it, especially the corner areas which are the weakest, that way you can reduce the wall thickness. Everything can work out well by FEA and easily adjust and optmise the shape. but to prevent leak from the lid is the major issue you need to concentrate. Clamp all around or by bolting ?
Build a model after verified by FEA, and water test it, then you are good to go.



RE: Pressurized Box Engineering Help

Consider a revised shape.... the rectangular shape is very poor when pressure loaded

As stated above, a cylinder or sphere is much better

How about an inexpensive short section of Sched 40 PVC or GRP pipe with end caps ?

The 18 psig should be no problem....... the small volume means it will fly under the code regulations

RE: Pressurized Box Engineering Help

(OP)
I can lower it to between 14 and 15 psi. Sorry for the shortage of information. I know a box shape like that is really one of the most difficult shapes there is, but it has to be that shape. I was thinking that the ends could be curved and made out of a mold to insure that there would be no leak. The lid ideally should be at least 16 inches long and 12 inches wide. And it would have to be easily opened, with maybe 1 or 2 quick fastening screws. The weight that is going in is very low, not more than 10 lbs.

So my main problems are which material would be strong enough to withhold 15 psi in a box shape? And what is the best type of lid and gasket combination that could seal the box completely, but being very quickly and easily opened and closed.

RE: Pressurized Box Engineering Help

Modify the plastic cooler sold in Walmart or outdoor store such as Academic, and put more hinge ( normally it has only 2 hinges) and clamps ( normally it has only 2), and add rubber gasket. Contact Igloo, their engineer shall be able to make one for you.
http://www.igloo-store.com/?trk_src_ss=IGLPAYPCWEB...

RE: Pressurized Box Engineering Help

No, your problem is NOT the "box" shape to withstand 15 psig (don't let it go over 14.7 psig if you wish to stay in the non-Code -regulated range.

The problem will be sealing that 14 psig for the duration needed for your process - and THAT job of sealing a gas cannot readily be done (particularly with any form of "box" pressure vessel pressure vessel) - simply and easily with "one or two" hand-twisted screws.

Round pipe with a rotating cover plate and lugs? Maybe - if the cover plate were stiff enough to hold firmly all the way around the sealing surface so only two lugs would clamp evenly around the periphery of the lid.

What is the pressurized gas? Hoqw much does it cost poer cycle? How flammable, toxic, corrosive? How will you vent it, refill it, where will the released fumes go when you vent it?

RE: Pressurized Box Engineering Help

(OP)
Great that helps me a lot. This post has helped me a lot, thank you to everyone that has commented. I have a much clearer image of what and how I want to create this now.

It's very simple. It's just air going into the unit. It will have an automatic pressure valve with a compressor to always maintain the pressure. It's not for me, otherwise I wouldn't mind it have a few more bolts to really secure the top, but it is for people that won't use it unless it is very easy to use. So the easier it is to open it and securely close it the better it will be. The pressure and everything else will be taken care of by just plugging it in.

The weight of the whole unit should be light enough to pick up and move to wherever you would want. So I was thinking of the whole thing being aluminum, with the lid having a gasket (thanks to jtseng123)? Anyone see any problems with this or recommend something else?

RE: Pressurized Box Engineering Help

pressure vessel engineers always think about "code", "non-code" when facing a challenging problem such as this, circling around chnaging "pressure" or changing "shape", trying to make it fit to the "code". Sometimes, we have to open our eyes with imagination beyond "code". For example, a steel wire tire can hold more than 50 psig, why not mold it to a box shape, and a special lid design with steel frame for rigidity so it can be sealed tightly, water test it and that's it, forget about 'code". The other material is engineered plastic. Google it if it fits. Even you can mold a PVC to the box shape, no need to be just like a pipe which may not be the desired shape. I believe there are nmany ways to make it workable with the shape you want and light weight, as long as you can water test it without leak. Just need several trials and errors.

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