PTFE film for Brake Valve wafer / disc

[05hwy28]

Nelson mentions on his site that he used PTFE from Mc Master that is .015" thick for his redesigned/2nd shay brake valve. A 6" x 12" x .015" sheet from them costs ~10 and with shipping it'll be around ~20 bucks to my door.

I found a 16" x 60" .0138" (.35mm) thick roll of PTFE film on am-a-zon for 18. Does anyone see any problems (durability?) with a slightly thinner thickness?

-Mike

[Asteamhead]

Hello Mike,
No problem, as long as the support of the disc by a (complex) curved disc is made carefully. That is recommended to avoid stress to the diaphragma, anyway.
Years ago I built a similar brake reduction valve which is still in use.
Best regards
Asteamhead

[Harold_V]

The one caution is that it should be etched, so it can be applied by some means (like contact cement). Etched PTFE typically has one side colored a light brown. Not all PTFE film is etched.

H

[shayloco]

Plain PTFE is fine for that brake valve. .0138" should also be fine, too. The PTFE disc is held in position with a post inside the brake valve so that it does not rotate with the valve. I know because I just replaced that disc in Nelson's brake valve. I now own that Shay. The original PTFE disc was worn by 'stuff' coming in through the steam feed. I would guess it should be changed every few years. I made an extra disc while I was at it. Seals very well now. Brakes work very well with steam apply and steam release, which is typical for Shays.

[05hwy28]

Thank you all for your replies. I ended up ordering the 60" roll from amazon and now have enough to last several lifetimes. Guess I will have to find other uses for it.