15" Pressure pot for resin casting: anybody build one?

You'll do what you'll do, but when you consider the potential for catastrophic self-disassembly, the paint pots may not be all that expensive. My quick calculation says that a 15 inch diameter lid at 100 psi is holding 17,671 pounds. Might hurt just a tad.

I won't advise you on the general construction/gauge/metal types, but I can on the lid; it's pretty simple.

You build an oval lid which seals to the _inside_ of an oval lip. It can be held by simple dogs, or just a cross-bar like the clamp on the bottom of, say, a tailstock or steady-rest. Pressure makes it seal more tightly.

That's a pretty conventional pressure vessel hatch.

LLoyd

Thought of one of those stainless pressure kegs (oval lids) for homebrew beermaking after reading Lloyd's post. I think they're only good for ~15 PSI though.

You might want to check with a local company that hydraulically tests scuba/oxygen/whatever tanks. Last time I was in one of those places, they had all kinds of scary looking pressure vessels in the shop.

I've used PVC piping with a pressure gage and air connection at one end and a screw in clean out plug at the other end. Worked OK, but the screw plug leaked. Also took a bit longer to screw in the plug.

NOTE: PVC pipe at 73 degrees F is rated for 280PSI. Make sure all glued joints are dry before putting it under pressure. So that means let it set for 24 hours or more before putting any pressure in it.

On the safety side, the less air this thing holds, the better.

Dave

Please let me recommend against that, even though the ratings are valid. I once made a cyclonic (coalescing) water remover/buffer tank from 4" PVC for an air system. It worked just fine until it failed one day with no provocation.

The joints didn't fail, the pipe did (at 125psi). It made a _big_ explosion, and did substantial damage to the wall to which it was affixed. Luckily, nobody was in the area when it failed, because we found shrapnel fifty feet away.

A viable alternative might be to wrap such a vessel in many layers of fabric as a fail-safe guard.

LLoyd

That rating is for liquids, and is dependent on the size of the pipe. Ordinary PVC pipe is not rated for use with compressed gases.

Ned Simmons

That rating is for water, not air. Pressure is pressure. BUT the failure mode for an incompressible fluid, (water) is spilt water whereas for a compressible fluid (air) the failure mode is an explosion. Further, when a PVC pipe fails it shatters into sharp pieces. People who have had accidents of that sort report finding shards embedded into drywall despite their low density.

There are plastic pipes that do not shatter and fragment when they fail--I _think_ ABS is OK. If you google for "compressed air line" and PVC you will find this discussed.

So gas pressure is different from water pressure? How so? Please explain.

I thought you can't get water pressure unless there was a gas behind it pushing, unless you are doing a hydro test.

Ah yes ABS. Perhaps a steel pipe or maybe copper would work better for this application then?

I've gotten some very good answers to the PVC question. Looks like I'll be looking for something in copper or maybe better yet steel gas line. Any recomendations since I also do resin casting for model railroading apllications?

I hope OP got some good advice here. I know I did.

There's no difference in the stress induced in the pipe, so one's just as likely as the other to cause a failure. The difference is in the consequence of the failure. A bursting pressurized gas vessel releases a bunch of stored energy in an instant; the vessel filled with water under the same pressure stores a tiny amount of energy relative to the gas-filled container.

Ned Simmons

Where are you located I have a couple of 5 Gal paint pots but the shipping would be prohibitive if you live far. I am in southern Minnesota.

I have a nice piece of steel pipe, ~3' long, 6" ID, 7" OD, out behind the shed that is free for pick up. Gerry :-)} London, Canada

Thanks Gerry. Might have a bit of trouble trying to get it over the boarder though. :-)

"> There's no difference in the stress induced in the pipe, so one's just as

Thanks for explanation Ned. If I'd of checked the next poster, "fredfighter" I would have got the same answer.

Bernd

It rolls quite nicely once you get it up to speed - lots of momentum! Gerry :-)} London, Canada