Piston Packing Choices

[Clive Brown 1Participant @clivebrown1]

What are views/opinions on the choice of either O-rings or woven PTFE square packing for model steam loco cylinders?

Is silicone rubber the best choice for O-rng material?

I'm currently machining the pistons for my Princess of Wales, 1.5" dia.

The cylinder and pistons are gunmetal, as supplied by Reeves.

TIA,

Clive

[Clive Brown 1Participant @clivebrown1]

[Simon CollierParticipant @simoncollier74340]

Friends are using Viton O-rings with success but you have to get the squeeze right. Not too much.

[Fowlers FuryParticipant @fowlersfury]

"What are views/opinions on the choice of either O-rings or woven PTFE square packing for model steam loco cylinders?"

Clive ~ your very reasonable question must represent one the most contentious issues in model engineering when you've added "The cylinder and pistons are gunmetal".
One of the problems with PTFE is its expansion at steam temps.There are many articles as you might know in the M.E. and elsewhere suggesting other high performance polymers are preferable.
After a lot of research I used PEEK-CA30 [rather than PTFE with graphite or mica] with this method:-
**LINK**

on David Carpenter's website. It's not easy to follow or do, so if you decide to go that route and need guidance, post again.

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