Taking off from the boring, sleeving thread I'm hoping to get some real data here on how do redesign all the above with a view towards not wasting steam through blowby and reliability / robustness. There's a lot reported on sort of generic descriptions of what was done, without getting into the formulas and understandings that led to the design.

One thing mentioned is "diesel quality" rings - see Martyn Bane's excellent pages on the Rio turbio for that along with pictures, etc. So, hyaving no formula available for steam rings that aren't the traditonal design, I went over to the dark side and found, in a 1936 book on diesel mechanics, formulae for one piece compression ring design:

Calclating tension of a ring - T=KCG B3/A3 (cubed, not times three).
T = diametrical tension (tension between both widths equidistant from end gap edges)
K is a constant dependent on the material and thickness of the ring
C=face width
G=free end gap
B=ring thickness
A=ring diameter

About K - for standard cast iron rings values for K are:
1/8" - 3,150,000
3/16" - 3,100,000
1/4" - 3,000,000
5/16 to 1.25" - 2,800,000

Tangential tension (between end gap edges) is about one third T.

So, PSI of the ring against the cylinder wall is:
P=0.968T / DC

P=Lbs.
T= diametrical tension in lbs.
D= ring diameter in inches
C= face width in inches

Not sure just how helpful this is without knowing just what the useful compression rate PSI is, however, the value in diesel practice is given as between 5 and 20 PSI - which is a pretty wide berth if you ask me. I guess it sort of depends on whether Martyn's "diesel quality" refers to all characteristics or just what kind of metal.

This is followed by a table of standard ring dimension for rings between 5" and 15.5" diameter. I'lls can it and post it when I can.

Anybody want to compare traditional compression values for steam with what is above?

dave

Dave,

I'm pretty sure Porta came up with the concept of using "diesel quality" rings on steam locomotives. The first reference I saw to this was in 1980 in some of the publicity info on the ACE 3000. From what I've read in Porta's published work and in David Wardale's book, "the Red Devil..." the main features that were desirable from diesel practice were narrow width, materials, and precision of manufacture. I checked through the list of Porta's technical papers on my website (http://www.trainweb.org/tusp/porta_biblio.html) and there are several papers (mostly unpublished) regarding rings and a few about tribology (the study of friction, lubrication, wear, etc.) which probably contain relevant info.

Wardale talks about improved piston rings quite a bit in his book and I believe he does go into some detail about materials. One thing I remember is that he used alternating hard (chrome plated cast iron or something equivalent) rings and soft rings made of bronze for both the pistons and valves on the Red Devil. Apparently some metal-to-metal contact is inevitable, and the bronze coats the cylinder or valve cage walls, which provides a slipperier surface for the hard rings to ride on, reducing wear.

One other thing I picked up from Wardale is that ring and cylinder wear is generally less at the center of the stroke than at the ends. Wear is minimized under conditions of hydrodynamic lubrication, when the ring is moving fast enough that it "floats" on a cushion of oil with no metal-to-metal contact. Apparently narrow rings achieve this condition more readily and that's one of their advantages over wide rings. The other apparent advantage is that a narrow ring seals just as well as a wide one, and several narrow rings will fit in the space required for one wide ring allowing greatly improved sealing.

I'd think that the design and manufacture of piston rings are specialized enough that it'd be well worthwhile to go to a piston ring manufacturer for their recommendations. Here are a some links to manufacturers I found:

http://www.precisionrings.com/

http://www.epm.com/lg_pistons.htm

http://www.grovercorp.com/applications/ ... ngine.html

Another source worth checking would be Bill Petitjean. I'd imagine whatever they used for rings in Skinner Unaflow engines would be a good starting point for better rings for locomotives. Bill also offers some old sales literature for sale which may have relevant info.

Regards,
Hugh

Dave

Valves, rings, tribology and all that stuff is far from my area of expertise I'm afraid. However this drawing has very recently come my way. It shows a Porta type lightweight, articulated mutli ringed piston valve. It doesn't necessarily relate to the very latest thinking on valves; I am uncertain of the date of the drawing but it is advanced compared to just about everything else. It also doesn't provide all the info you are after but it may be a start?

Martyn! Welcome......and thanks. Thanks also for your web posting of a lot of very interesting international information.

Looks maybe like a refrigerant compressor valve but my limited Spanish is mostly obsceneties in Cuban dialect picked up in the '60's in Miami. I'm sure others can translate much better.

The bronze lands and narrow grooves do look a lot like what Porta and Wardale were suggesting and using in their experimentation.

Has Shaun or anybody actually published the design work and results of the retrofits to the locomotive used for blowby leak testing in the Porta Papers book?

dave

Dave,

I think that is simply "Cooling Steam" because an auxiliary passage sweeps cool exhaust steam over the back of the rings. It is interesting that admission is not a ring controlled event. It is my recollection that Mr. Porta advocated for admission to be ring controlled and exhaust piston controlled (softer.)

Some of the larger bore stationary steam engines I work on have fairly narrow rings for their size. A 1" x 1 1/4" x 45+" OD ring can barely put tension on a cylinder wall.

There is always an issue of practicality, too. Very small narrow rings are easily damaged from corrosion due to poor layup or loss of lubrication, The smallest engines I work on often have labyrinth groove valves for this reason.

I think the basic lesson from Mr. Porta is to use a plurality of rings (redundancy) for a purpose with the minimum number of joints (leak paths), and make sure they are flexible enough to seal despite cylinder irregularities.

My experience so far is that a suitable grade of cast iron is the way to go and success depends a lot depends on how the ring was made.

Sincerely,

Matt J.

Thanks Hugh, I finally looked all the way down on your list of papers and found one on just what I'm pondering - modernizing steam for the rest of us. The same paper is linked twice as there are two entries in if from Porta. I would certainly encourage anybody interested to link to Hugh's papers list page, scroll all the way down, and check it out.

I see in Hugh's ring makers links that Double Seal is now a part of Grover. Double Seal has furnished steam locomotive rings before. I have no fiscal interest in either firm, just saying.....

I'm having some discussion on the steam tech list about this as well (although steam tractors have now taken precidence). I'm amazed at the amount of political / mercenary static it is causing due to some projects that were perhaps oversold and undermaintained and have not yielded expected results immediately, with fingerpointing and great secrecy imposed.

People, we know that some modernizations have been proven, such as Lempor front end designs, although there may be some disagreement between exerienced people on the details. We also know that experimental modernizations of locomotives in power pools in such places as South Africa and China suffered from just plain apathy in the operating and maintenance departments and didn't have a chance to prove their longevity in hard service as a result. The US sponsored programs died economically or politically, generally both. None of this changes the experimental nature of it for our purposes, and we have to anticipate if we are going to work on it that we will have substantial debugging, sharing freely of what works and doesn't, and open unembarrassed agreement to try and fail without repercussions. Pretty much eliminates the commercial mercenaries and posturing experts who may or may not really know what they claim to know.

If you think about it, we baby and care for our loocmotives and treat them better than the commercial railroads ever did, so we are probably better able to experiment and follow through than they were.

I have no access to a test bed, but will continue to share what information I can find and hope others will do so as well. Perhaps somebody with a small locomotive to overhaul might be willing to try - in which case, I hope we will all provide what supportive discussion we can.

dave

You are correct, Matt - if you look at the valves in Red Devil, you will see the outermost lands on either side of the distal admission and exhaust rings are very narrow, stop just inside of the rings circumference, and gracefully widen in a sweeping aerodynamic curve down to the hollow valve body on the admission sides, and widen but less gracefully at the exhaust sides. The edge of the ring controls the opening.

Wardale also makes a point of the lubrication happening in the valve liners in a location that will be swept by the rings but not ever open to the exhaust passage. This practically means two oil feeds, one for each end. I think he stayed with one for the cylinder........I'm rereading Red Devil now, and it is densely packed with information and makes for a slow go.

For our purposes, I'd want to make the valve and piston rings sacrificial to preserve the integrity of the bores. Rings are easy to change; boring and sleeving not so much as indicated on the other thread about it.

I'm very interested in Kelly's lube recommendation and just how much it has reduced wear.

dave

OK, here's the table of stock ring sizes specifications by diameter of bore I promised.

I've read it cover-to-cover at least 4 times and I pick up something new EVERY time I read it.

My deepest respect to Matt Janssen, he knows that!

Matt has personally applied the theory of reading things FIVE times so that he can fully understand the intention of the author. This includes at least five full readings of "Red Devil"......something I will not even finish twice in my entire life time!

Matt is truly dedicated to the study of and best application of technology!

I have personally witnessed his approach!

Always,

New information from a contributor to the SteamTech list: Frisco 1522 had grooves for 3 sets of rings, each 1" wide. The outer two used common style segmented rings, and when the center ring was replaced with a stack of 3 rings, each .332" wide, they claim they got a 10% increase in cylinder pressure and significant water savings.

So, if we build up the OD of our pistons with something like silicon bronze or aluminum bronze wire weld, turn to within maybe 25-30 thousandths of the bore, and retrofit a similar set of stacked rings in a central groove, maybe we can gain some serious efficiency.

Welding experts please advise if the products I mentioned would be unsuitable - I've only used them in bearing resurfacing so far.

dave

Do you mean three rings set "on end" next to each other? The ring gaps would be staggered 1/3 apart, with some means to hold them in place? Dave, are you suggesting that all the old-style rings on a piston be replaced with this sort of edge ring to gain that efficiency?

Howard P.

There were a bunch of small interlocking rings in the Skinner inventory. Two narrow rings sitting next to each other (stacked) with an inner wide ring that both rode on. I believe they went to one of the two new stationary steam engine projects they were working on in the 80's. I can tell you that a downside is that they are much more fragile than a ring of a larger cross-section. These were a "little bit" corroded from a steam engine standpoint from storage an it basically ruined them- they were all seized together and it took months and lots or Kroil to get a few apart. All and all not dissimilar to Total Seal Gapless piston rings in fad with diesel geeks now.

One can reduce the lands down a bit on most designs and add a ring or two. Its nice to have good sealing and robust and meat to touch-up the grooves a few times.

Not sure I understand the question, Howard but:

Think of taking the one inch wide ring and slicing it into three one third inch wide rings.

Then, pin them with loose indexing pins such that each is free to move a bit but the gaps are held 120 degrees apart so they will not align.

Then, set that whole assembly into the one inch wide groove in the center of the piston.

I'm not sure just which standard segmented design the outer rings were, check in the Cyclopedias. Maybe Ron or somebody who knows 1522's innards well can provide the exact spec. It really doesn't matter - if the outer rings were even standard solid split rings, adding the stacked narrow bundle to the center will provide a gain.

So, what happens if we stack every groove? Maybe we just need the usual two? Tribologists pitch in here please.

dave