Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hi Tony, I can only share what I know about using O-rings in a gas engine.

The ring groove is a couple thousandths wider and deeper than the o-ring used. This allows pressure from the combustion to force the o-ring down against the bottom of the groove and out against the cylinder wall thus allowing the ring to "shrink" back to a size that allows near frictionless movement. In other words the o-ring remains loose when no pressure is applied.

I am not certain how this would work with steam but it would be an interesting experiment.

Gil