I'm bouncing another idea off you guys. How about an old hydraulic cylinder tube for a steam engine cylinder? Machine a recess into some 3/4 plate, copper gaskets, and clamp a plate on either end of the cut to length tube and clamp together with four pieces of 3/4 or 1" all-thread. Surely a tube designed for 2k or 3k psi could handle the 2 or 3 hundred or so steam. May have problems with rust being steel and not iron? Any thoughts?

Been thinking about this for years and have just never gotten near the thing. You would even need copper as leather was what was used. Same for the piston rings.Might wanna check some local regulations and insurance companies about the high pressure though.

Yep, the boilers are well regulated and inspected. Have seen first hand what a boiler explosion can do when I was in Turkey. This is one place that I agree with the system.
Terry

I think the idea is sound, however I would test the completed contruction maybe 3 times the max pressure you will be using. I was thinking that heat may be a factor here causing the cylinder to expand and can contract when cooled. I guss the leather piston seals are used to deal with that. It sounds plasable given the pressures that hyd cylinders operate at. Not to mention that in some cases the hydraulic tempures get quite high as well. However that being said taking on that risk for one self is one thing exposing the risk to others is another. I'm not sure what the end goal is. But I think it would pass muster with regulations. But can't say for sure.

Wear might be an issue as well. Cast iron is much more abrasion resistant than steel, hence cast iron engine blocks or liners.

Well, I was thinking teflon piston ring, I have seen them used before. Its supposed to be good for up to 500F and its definately nonsticky What I've seen people do for pressure testing is fill the boiler with water, then pump it with a high pressure hand pump up to 3x and let it set for a while, with water there wouldnt be a boom, just a spray from the leak.

A pressure failure is a pressure failure,but cold water wouldn't burn.

Iv'e had the pleasure of machining a lot of teflon. Yes it is SLICK. The cutting tools even slide good on it.Maybe even use it for the piston. Check with a local plastics company and see if you can get some samples. I can't get to any of my engineering books right now but maybe someone here can check them out and post them. Please be VERY careful. I don't want to read about you in the newspaper.
Terry

You might check out Delrin as a seriously tough but easily machinable plastic. Have used it before for small bearing races (like under a phonograph turntable). Still going strong some 15 years later.
Doc

Point taken bob, I've always heard that a pressure vessel wouldn't explode if filled with water, just leak. It certainly wouldn't be the first time I was wrong. I'll look into the derlin but I don't know about the max working temperature. Another thought - How about cylinder liners from a big diesel truck? They're cast iron and the detroits I've looked at are about 6" bore. Completely worn out they still look about 3/8's thick. Hm, 6" bore 6" stroke double acting twin should have some "oompf". I just need to find some time to work on things instead of just thinking. Working second shift is tough, hard to go to bed right when I get home at midnight. Maybe I should start back up drinking, anyone got some 'shine?

(PS: terry, next time you try machining teflon - if using a single point tool, give it a bit steeper than normal top rake, the plastic wont break it as easily as metal. Then hone it till razor sharp. Makes a world of difference on plastics.)

I like the cylinder liner idea. Tie bolts could hold it between the head and the frame work.
A hydrostatic test won't cause explosive failure if a leak or rupture occurs. Water is effectively incompressible, once a leak occurs the pressure is gone, nitrogen pressure tests are another story, pieces move a long way before the gas stops expanding. We regularly did hydrostatic pressure tests on oilfield wellhead equipment to 2 1/2 times working pressure in the shop but never went above well head pressure with gas. For a proper test with anything that has o-rings you bring the pressure up, bleed it off then re-pressure and hold it. The first cycle will show if an o-ring is going to cut on a sharp mating surface. Probably more than you ever wanted to know about pressure tests

Delrin spec sheet: http://plastics.dupont.com/plastics/pdflit/americas/delrin/H76836.pdf Melts @ 178 C (352 F)

Doc

Thanks Doc, all my books and stuff are still packed up from where I retired last August.

Yes, pressure test your rig filled with water, but contain it safely anyway, since a jet of high pressure fluid can also be dangerous--as in high pressure washers. A fluid leak does tend to dissipate with distance though, as you can tell using a pressure washer.

Pressures in the range used in hydraulic cylinders can be deadly, however, since the fluid is oil--more viscous, tends to stay in a stream for greater distances, and can cut you like a blade. I've seen some ugly industrial accidents.I'd want a piece of steel plate between me and a pressure test, even using water. Thick Lexan is good, too.

Edit to Add: For teflon cylinder packings, check out Baum Hydraulics at: www.baumhydraulics.com Just click on "printable catalog", and then section G. They have quite a variety and in some large sizes for heavy equipment. Possibly you could find a suitable cylinder with the right seals, or reseal an existing one to suit you.