Lubrication free condensing?

[Mike Rometer]

The wear pattern in an IC engine bore is as much to do with the angular thrust of the con-rod as the extra pressure of the rings at the top of the bore. Steam would apply much less rear pressure to the inside of the ring as the pressures in the bore are much lower to start with.

Point taken from Greg about the 'O' ring maybe not getting lubed with the water when running at speed, but then all liquids have a meniscus.

There is another option available, that will work even better than a plain piston, and that is one with labyrinth grooves. They are much ignored in modern times, but are very effective.

I have seen and used 'O' rings used on slide valve spindles very sucessfully though of course that is only short stroke and run with oil.

A further option is PTFE. I have also used that to seal piston rod glands, it could possibly be another option for rings.

Just because the basic steam engine is a hundred plus years old doesn't mean there is no benefit to be had from applying some modern technology.

[Lopez Mike]

Actually it turns out that the side thrust on a trunk type piston is at a maximum somewhere around mid stroke. I have graphed the wear of several cylinders over the years and the wear follows the declining pressure quite accurately. By mid stroke the pressure on a non-supercharged I.C. engine has dropped dramatically. I have no idea what the pressure v.s stroke graph on a uniflow engine might look like.

Enough about horrid I.C. engines!

I've tried Teflon for rings. I never could get a good enough cylinder surface. The rings went away very rapidly. Like in an hour or tow of running. I honed and then lapped and it looked great but apparently not as good as a broken in cylinder with metallic rings.

I really want a plastic piston ring that will last under non-lubicated air operation. I have customers who want Stuart engines for mantle pieces and would prefer to run them on air. I haven't tried acetal (Delrin) or UHMW yet. Teflon has worked well for piston rod packings but perhaps the factory finish on the rods is better. I dunno how they do that.

[barts]

I really want a plastic piston ring that will last under non-lubicated air operation. I have customers who want Stuart engines for mantle pieces and would prefer to run them on air. I haven't tried acetal (Delrin) or UHMW yet. Teflon has worked well for piston rod packings but perhaps the factory finish on the rods is better. I dunno how they do that.

Hard chromed rods are 8 rms or so... hard to do that in a cylinder bore .

- Bart

[Oilking]

I wish to dispel a commonly circulated belief about the Liberty ship engine. The boilers had super heaters and the engine had a pressure injector run off the HP crosshead that provided oil to the throttle, HP and IP valve boxes, and the HP metallic packing. Loofa sponges were floated in the baffled hotwell, and a diatomaceous earth filter/"degreaser" in the feed line prevented oil from returning to the boiler.

The Navy had an enduring fear of oil ever getting to the boiler. To this end all the piston driven pumps on the two ships I served on ran on 150 psi saturated steam. Cold iron on the 1200 pounder the bilge stripping pump would be run on compressed air. A practice that lead to a premature need to replace the cylinder liner.

Some where I have heard a story of a mechanic at the Olympia brewery in the 60's that solved problems he was having with compressors by using teflon piston rings that he made on a lathe. As an avid steamer he instituted the practice on his boat with apparent success. I don't know what grade of teflon was used. I believe that this appeared as a letter in "Steamboats & Modern steam Launches", but I can't give you chapter and verse.

For what it's worth.

Dave

[DetroiTug]

I think the solution for this is graphite impregnated PEEK. And stainless or bronze cylinder liners. Peek is sold in bars and it is very hard - just make the whole piston out of it with about ,001" clearance. For an engine to operate on air, I'd go with UHMW. It is much tougher than Delrin or Teflon. Peek can withstand 500° F

-Ron

[TahoeSteam]

I know Joe Sweeney, former owner of the Leviathan swore by teflon rings... Asked John York about them and he had nothing but bad things to say about them, and that they were just snake oil.

Perhaps a method of getting a suitable bore would be to break the engine in with cast rings, then switch over after a suitable finish has been reached.. as soon as any rust forms from sitting or lack of lubrication though you're back to square one.

It's not just the bores that need lube. In our engines it's the valves, most of which have unbalanced d-slide valves, arguably the highest loading anywhere in the engine. Here is a valve face of a Scripps compound that went through a couple season period of attempting to run saturated steam without lubrication

[Lopez Mike]

Impressive picture Wes. Startled that it was still running.

The guy at the Oly Brewery was Al Giles and my dad made the rings for the brewery compressor. I believe, however, that he used ordinary cast iron rings on his boat, the Crest, but used Teflon for packings and had very good service. I will check on that the next time I look the engine over. It's out of the boat in Olympia.

I machined the Stuart 4A generator engine for the Crest and used Teflon packings but used the supplied iron rings for the piston. I was a whole lot younger then! That's been over fifty years ago. Sigh.

Reminds me of a bumper sticker I saw recently that said, "Remember Dementia in your Will!"

[RGSP]

I have used PTFE for seals of all sorts on things other than steam engines over the years, and a few comments might be useful.

1. You CAN machine it like a metal as long as you cool it down. Dry ice gets cold enough, but I've had liquid nitrogen available, and you can machine for 10 minutes or so before PTFE warms up too much and starts to "smear".

2. If you haven't got any cooling fluids etc., making up special knife-like tools works pretty well at room temperature. You need two different knifes for cutting piston rings, but once you've made them up, the procedure is easy, if different from the standard machining most of us do. Works pretty well for cutting rubber washers etc. as well.

3. PTFE will withstand high temperatures, but it does go soft and floppy when hot, and so piston rings of pure PTFE really need a sprung metal backing ring to keep them in good contact with the cylinder wall. Packing glands are fine without of course.

4. Lots of PTFE does have glass or other ceramic fillers in it, which make it much more resistant to wear, and sometimes easier to machine. I suspect people's different experiences may be linked to using PTFE with different proportions and grades of filler.

5. A major problem with the purer and softer grades of PTFE is that any metal particulates get stuck into it (e.g. off a machined, not polished, cylinder bore) which are impossible to remove, and eventually coat rubbing surfaces so that they become solid-ish metal shims backed by PTFE, and they then don't seal all that well in vacuum systems, and probably not in steam engines either.

6. This story has been around for at least 40 years and may never have been true, but do be careful with any PTFE swarf. Someone did manage to get a few shreds of it into his roll-up cigarette, and it killed him, so the story goes. Flourine gas compounds produced by burning temperatures on PTFE are not nice, and that's also definitely true!

BTW I worked effective for Du Pont for some years, and met the guy in the Wilmington labs (I forget his name) who discovered PTFE: it had nothing whatsoever to do with the Space Programme. He had a cylinder of what was supposed to be ethylene gas, and when it was turned on after a weekend nothing came out. At this point most of us would have just gone and got a fresh cylinder, but the clever bit was that he took a hacksaw to the nominally ethylene cylinder (which had got contaminated with flourine, with hindsight) and found this hardish white slippery plastic lining the cylinder walls. And the rest is history, as they say.

[Lopez Mike]

I knew that someone lurking on here would have the info. Thanks!

I was mildly poisoned once by brazing a Teflon insulated electrical connector in an oceanographic application. I had this sudden onset of severe allergy/flu symptoms and it was so strongly connected with what I was doing that I sought medical care immediately.

The doctor looked me over and treated me with Atropine which is used for dealing with things like nerve gas and pesticide poisoning. Got better right away.

I wonder if wildly overheating a Teflon frying pan would do this? Guess it wouldn't be a good idea to melt some aluminum in such a vessel!

Think I'll stay with iron on iron with water. I like primitive African Queen stuff.

[barts]

Think I'll stay with iron on iron with water. I like primitive African Queen stuff.

Well, it does make wonderful packing, so I'll keep using that. And it might do really well
as a piston in a Bailey air pump, running in a brass cylinder with just water grooves for sealing.

I do like plastics as bearing materials for valve linkages, etc; a bit of Delrin for a bushing is quiet and
really needs no oil save what it gets accidentally.

- Bart