11751Views15Replies

# How much pressure can the average milk crate withstand? Answered

Can the average milk crate (actual milk crates, not the cheapie wallmart 'back to school' crates) withstand at least 20PSI on all sides? I'm intending to use one as the support structure of a vacuum chamber.

Tags:

The forums are retiring in 2021 and are now closed for new topics and comments.

Perhaps I dont understand PSI. You mean like bike tire PSI, Pounds per square inch, is that the same thing? Because 20 PSI is like a flat mountain bike tire.

I 'm thinking yes. Those things or strong. Stand on one. I dont know about the sides. Theyre made to support weight vertically. The sides are still pretty strong though. If you can build a vacuum strong enough to cave that in then Wow! Get a bathroom scale, set the crate on its side and put the scale on put weight on it to get some estimates. Im thinking if I stood on the sideof one it would just bend if i put weight near the open side. Maybe get two milk crates and cut the bottom of one to make a top for the other. Or put wood on top. Or build a box out of wood. Good luck. Sounds interesting.

As a suggestion. Try a small cube made of your plexi first. Make sure it is a decently thick piece. Come to that, you should be able to find some engineering data about your specific material and its pressure properties. Take your cube, use a chemical bonder (chemical welding, think PVC glue) on every joint, and use screws to pull it together. Now the fun part. Tap and die two 1/4" holes into the cube. Buy a cheap vacuum gauge (1/4") and put it in the first 1/4" hole w/ teflon taped threads. The second hole needs a 1/4" M x M coupler. Teflon tape the cube side well and screw it in. Remember, tight enough is TIGHT ENOUGH. Don't over tighten and fracture your material. More torque, a better seal does not make. Buy a cheap 4 cfm small appliance vacuum pump (sub \$100 / ebay) and a 1/4" refrigeration hose (800 PSI Burst, 400 PSI sustained rating should do it). Vaccuum! (*Note: The top of the box with connections can also be made to have a decent foam seal and bolts so that it can be removed)

It also depends on whether your pressure is quick or slow.

Some plastics fracture under quick, intense pressure while a slow pressure would not break the crate.

Why not get a spare crate and test it for your conditions?

I'm betting the answer is "no". I realize that isn't the answer you want, but think it through:

Atmospheric pressure adds up. 20PSI on 144 square inches (assuming a 1 foot cubic milk crate) means almost a ton and a half on each face. (2880 pounds). I've broken the bottom of a milk crate by standing on it. Admittedly my weight was concentrated on just a few square inches, but ... well, you're talking about the weight of a car; even when spread out, that's nontrivial.

If the crate's face is larger, the force is too.

Feel free to try it, but I agree with Guardian Fox that sudden catastrophic failure is a plausible scenario and two layers of denim (a) may not be enough and (b) will do nothing to protect your face/head/neck in any case. You're dealing with an implosion risk here, which means the possibility of throwing shards at high speed if anything is sufficiently fragile to fracture rather than simply crumple, or if it simply recoils strongly when the vacuum breaks.

That's all assuming you can actually make a seal which will withstand a 20PSI difference. I'd expect your joints will shred themselves before the crate does --- but I wouldn't bet my safety on it either way. I second the suggestion to assume this is dangerous until proven otherwise, and to build in a serious safety buffer.

Sorry... but that's the best answer I can give you. I seriously doubt that there is such a thing as an "average milk crate", or that any of them have been tested for this usage, so you either need to find out a lot more about how yours is constructed and do some serious engineering calculations, or assume the experiment is dangerous until proven otherwise -- and even then, progressive failure remains a risk.

So... Doesn't the atmosphere naturally put about 14 psi on our bodies? How many cars is that (for a husky boy)?

Remember that this is about a pressure difference, you're pumped up to ~14 PSI on the inside.

L

I ALWAYS KNEW I WAS PUMPED UP!!!

Normally, that's balanced by internal air/hydraulic pressure. (What, you've never done the "watch air pressure crush a metal can" experiment?)

Valid point about 14 rather than 20. The rest of my comments, I think, remain valid, just scale appropriately. It's still over a ton on each side.

You'd be better with something round. But I'm struggling to think of an alternative that isn't a steel cylinder...

L