Steel cylinders and piston rings?

[Bill Shields]

stay away from stainless no matter what.

the RINGS do not support the piston...the guide bushing / packing and crosshead do.

.010" is a minimum for me. I have models running with 0.015"...you have to allow for wear in the guide bushing / crosshead

[Harold_V]

While I don't have any experience with what I'm about to say, I suspect you could get away with using stainless, assuming one chose the proper grade. I'd suggest the use of 416, which can be heat treated and is exceptional in machining ability. I suspect it would serve perfectly well, especially if non-metallic rings were applied (for the bore). Once heat treated, the bore could be honed to size. As metallic rings would likely be required for the valve, an iron liner could be pressed in.

Bill's comments make perfect sense for the vast majority of stainless grades, which tend to gall easily, although corrosion would not be an issue.

H

[rkcarguy]

400 series stainless would be preferred. I honestly think with Viton rings 316 stainless would also serve well if it was finished properly. 303 and 304 are too gummy.
I do have a question regarding lube though, how much lube is typically injected with the steam?

[Harold_V]

There's not enough difference (chemically) between 303/304 and 316 to make a significant difference in the problem of galling. The differences in the three alloys relates more to easy machining (303 has either sulfur or selenium included, along with phosphorus, for that reason), while 316 has a small percentage of molybdenum included to enhance corrosion resistance, which, in truth, isn't an issue for the application in question.

In reality, any of the stainless alloys could work, but it's the luck of the draw if one has issues, or not. Good fortune would be drastically enhanced if proper lubrication was guaranteed.

Bottom line---it's risky choosing pretty much any stainless if a bearing surface is part of the mix. That's why I suggested 416---it can be heat treated to limit problems, but I expect no one is willing to go that route when iron serves the purpose perfectly well, and solves pretty much all issues one might face.

H

[darjeeling]

As per the threads on this subject of piston rings, there are many ways to make them together with different materials, as we all know.
Many years ago I was shown a cast iron CLUPIT made piston ring. They look like a key ring with no gaps open to leakage and in most cases will take up to a 1mm of wear without any leakage problems. I have used these in the 4" scale Darjeeling locomotive as seen in the US 'Live Steam' magazine some years back. I have continued to use them in two further locomotives with great results. They give a perfect seal and should last the life of the engine working in cast iron cylinders, with good lubrication. I also understand many vintage cars are being fitted with them.


Safe steaming------------ John Heald, New Zealand