Hello All,
I am looking for thoughts/experience/advice on rings for a locomotive piston. To get them back to round the cylinders were bored enough that we are making new bull rings for the pistons. The rings that came out were segmented rings. There was a pair of rings in each groove and 2 grooves per bull ring. The bore is around 22". We have at least one supplier who will be happy to supply us with either solid or segmented rings.
What is the reasoning for/against each type of ring?

I thank you in advance for time & thought put into this thread.......mld

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Out of curiosity, why would a piston be made in two pieces and riveted together? It isn't a complicated shape, certainly a straight forward casting shape. Is the bull ring a different material that the body? If so what logic drives that design?

I would appreciate any insight anyone would have.

CCdW

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What is meant by "bull ring"? I see a two rings the same...?

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It was found that bronze on a piston/valve running surface helped burnish the cylinder and reduce wear. One approach is to apply the bronze to the running surface of the piston or valve - particularly as a repair practice, however, this was a construction feature of the SNCF 141R valve. Another approach is to have the bronze as an easily replaceable ring and/or rider band. The sectional design allows the rider band to be retained, and when called to act as a ring, spring out against the cylinder wall to effect a seal. The Skinner Engine Company used both Koppers and American Hammered "TU" sectional locomotive piston rings in their vertical Unaflow steam engine in stationary and marine service.

I have a lot of experience on stationary steam engine-driven compressors running in continuous service at a piston speed of about 400 FPM using commercial cylinder oils with and without bronze running surfaces. In this application, I find the bronze primarily acts to take the majority of the wear, and the total wear rate (piston + cylinder) of bronze vs. all cast iron running surfaces is about the same. However, I would expect in locomotive applications with more varying conditions and higher piston speeds the situation favors the bronze/iron sectional design. I believe that to be the findings of the 614T valve design, which is a snap ring design and constantly failed, however, I do not know the details of the design, only the service experience and incredibly demanding service conditions. The 141R's do very well with their bronze running surface and snap rings.

From a preservation point of view, it seems like incorporating a bronze running surface or rider band would be advantageous to reduce cylinder wear and perhaps burnish the cylinder better to reduce rusting during layup.

I have new-old-stock American Hammered and Koppers rings which I am happy to provide details of if needed. There are still two Skinners using them, however, the ring OEM supplies the rings directly. The rest use gray iron snap rings which I have a vendor for. A number of "superpower" locomotive groups as well as a couple of contractors associated with those locomotives have mastered sectional ring manufacturing, so there are lots of resources out there. If you choose to apply bronze to the pistons, you can do so manually, however thermal spraying aluminum bronze or "Navy brass" does work, but with higher porosity and less adhesion.

Sincerely,

Matt Janssen
Vapor Locomotive Company

THANKS! Very much for the replies. That whole paying job thing has kept me from replying earlier.
As a side note the pistons we're dealing with are not contoured like the Baldwin and actually use a front and rear plate to capture and seal around the bull ring. Here's a shot of the disassembled piston.

More detail can be seen here: https://www.midcontinent.org/category/cnw-1385/page/2/ .......mld

Ah..... a built up piston. When I was in Australia many years ago, a 3800 class was in test runs in primer and developed a blow across the piston - turns out a rivet holding the piston assembly together had broken and was blown out through the valve and out the stack without fouling anything on the way, and landed on the running board. I stopped in and helped pull the piston the next day - beautiful machine, welded saddle, everything done first class. Very lucky, too...…..

Double check your rivets and don't drive them cold. Not everybody will be that lucky.

The outfit I work for a few years back made our own piston valve rings for one of our engines after ones ordered from an outside firm didn't fit properly. A big chuck of cast iron and a big hole saw is a good place to start

There might be something to be said for late South African practice, which used both bronze and cast-iron rings in the same bore.

As I recall, the specific application was sectional rings, backed with springing rather than steam passages, and the section joints staggered between the two (contiguous) rings. That allowed for what I presume to be equal effective ring pressure against the bore at 'worst case' (probably highest achieved superheat?) operating conditions. This might argue, if you're using gapless rings installed at piston assembly time, for a sandwich construction of two bronze rings of slightly smaller gap flanking cast iron, or vice-versa...

Personally, I'd machine the bronze so the tribology acted ever so slightly to 'float' the piston on the bronze at peak output or highest machinery speeds, keeping the cast iron ever so slightly away from any asperities in the bore.

As Mr. Janssen says, operators of super-power locomotives have mastered production of Hunt-Spiller sectional rings with bronze and "gun iron" rings in the same groove with an expander underneath. We made piston and valve rings for PM 1225. However, when one of ours broke recently at the rivet holding the two rings together, I believe we just ordered replacements at a good price from a ring supplier and put them right in. The name was something like American Piston Ring Company.

Aarne H. Frobom
Steam Railroading Institute
Owosso, Michigan

Aarne - Are you thinking of these guys: American Hammered Piston Rings: http://www.americanhammered.com/products/piston-rings.html

While surfing, this outfit popped up: AD Piston Rings https://adpistonring.com/. Website says that make them up to 30" for steam.

Thanks again for all the thoughts & suggestions freely given. I will comment that I don't believe the C&NW R-1 class qualifies as "superpower" but we'll see what we can put into her......mld