Hi Gary

I have used square section PTFE impregnated yarn packing on all my engines with very successful outcome. Unlike an 'o ring' which needs to be just the right fit to avoid friction or be just too loose the packing can be fitted to a piston with a good two thou annular gap undersize and still provide superb compression.

If an engine is to be run on steam pure PTFE can swell and grip and sometimes seize but the yarn does not appear to have quite the same result. I ran a twin Victoria on steam for many years as such without any such effect.

Personally I like it because of the relaxation of tolerances on piston and liner and in the piston groove itself plus the fact that its virtually friction free which makes for a good slow speed on low pressure. Its ability to fit any slight discrepancy in concentricity is a bonus as well.

Unless I was making something that was going to work hard on steam – and all engines made so far now just run air – I wouldn't use anything else because of these reasons.

There is some very nice looking pure PTFE braided square yarn – it's not a suitable alternative as it frays easily and does not compress very well. Bought some for the last build but quickly reverted to the impregnated yarn

Hopes that 's of use to you

Tug

Another vote for Viton.

Re, Viton O-Rings,

I have a vague recollection of reading somewhere. That Viton after being exposed to steam can have an adverse effect on Human Skin. I think it was something to do with "burns", and not those caused from handling hot objects.

If anyone knows more about this issue then I for one would like to know more about it. As I have fitted Viton O-rings to my Steam Wagon.

Regards

Gray,

Thanks for that bit of info,

Regards

Gray,

I notice the link above does not work so here's another go

**LINK**

If that's not working either the company name was 'Bearingboys'

If it's more than you want I'm happy to share mine when it arrives – but not by the inch

Tug

Thank you Ramon.

Thanks, Ramon. I would like to take up your offer.

Ron

It's quite safe – this explains everything

HSE – Fluoroelastomers in Motor Vehicles

Thank you for taking time out to get the facts, my memory does not serve me well these days and having some hard data means I can file this away for future reference.

Regards

Gray,