Dave- I'm glad you're gradually pulling together some info on this.

I noticed on the 5AT Project site they have a list of a few of Porta's papers that have "circulated in the steam community". Among those is this one:

Steam Engine Cylinder Tribology - Pt 2 Piston Rings (hand written)

I imagine this would be a great one to have. I'll see if I can find someone with a copy and let you know if I do.

Got it, Dave, that's just what I envisioned from your description.

Howard P.

Another missing piece of information: Wardale also mentions he based his design for piston valves on the AAR Rules for Lightweight Dished Pistons. So, there's an AAR recipe for piston design out there somewhere.........which might be very useful when pistons need to be replaced, as during a bore and sleeve, or if yours, like some I've found, were lying in the bottom of the bore with a half inch of clearance at the top and the radial thickness of the rings was 7/16. Anybody have a link to this AAR spec or can post it?

Also, thinking about piston and valve rods and packings, a never ending source of amusement. There are some very good comppressor packing designs using stacks of indexed elements with girdle springs holding them tight, which are then stacked again in a steam-tight gland. So, their durability is probably a function of the quality of the lube and the rod surface. We can oil the gland, or set graphited or sintered elements into the stacks of packings for the lube thing, but what about the rod surface? Is ground steel enough, or would hard chroming be better? Can we inspect for cracks through hard chrome?

dave