Steam Engine - Piston Ring materials

In message , Steve W writes

45mm is probably near enough to 1.75" for you to try nominal 1.75" o.d. Viton 'O' rings. These can be obtained from many of the usual Model Engineering suppliers. Those same suppliers will be able to quote suitable width and depth for the groove(s) in the piston.

He said he did not want to use PTFE.

Iron would be the normal choice for a metal ring in an iron bore, but I am not so sure about using it for either piston or rings in a non-ferrous cylinder. It would be an 'unusual' combination. A non-metalic seal of some kind would be more 'normal'. In restoring an old engine, packing fairly large grooves with graphited yarn might be more authentic.

Iron or steel running in a copper alloy cylinder is what you get with a cylinder head valve and guide and that's a very normal combination. The basic rule about tribology is always run different metals against each other where possible. Copper alloys are very tolerant about what will run against them. A steel valve stem needs to be chrome plated to run in a cast iron guide but works fine unplated in a bronze one. I can't imagine a steam engine piston ring being any different although chrome plating always reduces friction and increases life.

Thanks Charles. I'll put it on the list for Harrogate.

Steve

Just curiosity, can you get away with a Viton 0-ring even in a low pressure steam engine? I would worry that the pressure-speed product might be a bit high.

In message , Newshound writes

'O' rings seem to be the norm for both piston ring and piston rod glands. I guess that in comparison with the likes of graphited yarn they are the bees' knees. I believe that there are people who use off the shelf automotive rings. It is my understanding that DIY production of rings requires heat treatment skills and equipment way beyond the average home workshop.

Hope not - next round of construction on a little IC engine is to make the piston AND cast iron rings!

Steve