Piston rings

[Chickens]

Now you have me thinking. The design calls for 2 piston rings. I have one ring installed. Maybe there has to be two rings. There's no flywheel. Steam just pushes piston back and forth. I assume it incorporates steam pressure to cushion the piston so as to not slam the piston into the head. I agree with you when you say you can't see how it can even work. It's an entirely different animal. The piston movement on one side activates the valve movement on the opposite side.

[rkcarguy]

What is your piston/bore clearance? Because you say you have no motion when on steam(?), the heat of the steam may be causing the piston or ring to expand and get tight in the bore.

[Chickens]

I am starting to believe there has to be 2 rings on each piston to seal properly. Piston and cylinder are both bronze. Can't remember the clearence bur it is as per specified on the print. I don't think that is the issue. McMasters Carr lists 16 different styles/shapes/hardnesses of O rings. Which one is the best for this application. Thare is an animation of a duplex steam pump on utube that kind of shows it's operation. A bit hard to understand. I slowed the animation way down. The center part is the exhaust.

[NP317]

If the pistons are locking up when run on steam, that implies thermal expansion might be producing an interference fit between the piston and the cylinder.
Try a decreased diameter piston.
RussN

[Chickens]

Pistons are not locking up. Steam is simply bypassing the cylinder/valve somehow and piston is not moving.

[Bill Shields]

there are thousands of locos out there with one piston ring..not as good as 2 -> but they will run.

cast iron works well...would not use bronze...the synthetics are good...

PTFE rings require a lot of experience and fiddling to get to work...

quick and dirty is a standard o-ring...have such in a loco with 100's of hours of operation on it..yes...every winter I take the engine apart and put new rings in it...

[Builder01]

If you could post an image of perhaps a cross section of your pump, that would be helpful for everyone. You don't have to post all the drawings, just the ones that might make it more clear for those of us trying to help you figure out what is going on. I assume you are building to a published design?

[tetramachine]

What is the clearance of the ring within the piston groove. I have lapped the rings to get a .001_2". Do you have a groove for 2 rings, but only one installed?

[Chickens]

I don't think I can come up with a sketch/drawing to get accross what I am dealing with. This is not a steam engine in the traditional sense. It is a steam pump. Best I can do is suggest an animation on utube. If you do a utube search for (horizontal duplex steam pump animation) you can get a better idea of what is going on. From what I see on those videos 2 piston rings are essential. Again this all bronze construction. I hesitate putting cast iron piston rings in it. I may be wrong but that doesn't seem like a good idea. Lots of excellent advice here. I had 2 bronze rings I installed that were lapped. They failed after a short run on air. I replaced them with (one) one piece teflon backed with a vitron 0 ring as described in a previous post.

[Builder01]

Vitron?? You have used this word several times, do you mean Viton??

[Chickens]

You are correct. I have been spelling it wrong all my life.

[Builder01]

Since you have no drawing, when you say the Teflon ring is backed by a Viton ring, do you mean under the Teflon ring, or side by side to the Teflon ring. Is the Teflon ring circular in cross section, or square? Or, are the two rings in separate grooves? A drawing would be really helpful.