Graphite string or O rings

[Firebird]

Hi

I'm looking into my next project, going through a few plans etc. Some of these plans for steam engines date back to the 50's and 60's.

I would like to incorporate as many "modern" ideas and materials as possible. The use of stainless steel and stainless steel fixings is an obvious example.

I have been wondering about the use of O rings instead of graphite yarn that most of the plans specify for pistons and glands etc.

This sort of thing



Doe's anyone have any experience using O rings on pistons. Mostly bronze cylinders and bronze pistons. The engines will run on steam

Cheers

Rich

[Jasonb]

I use Viton rings a lot on my IC and steam engines giving plenty of compression with minimal drag.

Should say I don't run mine on steam only air but have seen my designs running on steam and they go well.

[steamer]

Viton works, so does a teflon ring as long as you don't superheat more than about 100F

That's based on the performance of the engine in my boat which has pushed my 25' boat around the lake for a couple of weeks on end   160 psi saturated.

Runs on air well as well.     but you need an overlapping ring joint with plenty of room for expansion.   Easier to machine than you might think.

Dave

[Firebird]

Hi

Thanks Jason and Dave

Could I trouble you both for a little more info. What size groove do you machine etc

Cheers

Rich

[Jasonb]

What size is that bore 1.5" ?

[Firebird]

Hi Jason

Its 1 1/4''

Cheers

Rich

[Jasonb]

I'd go with a BS121, which is 3/32" nominal cross section but actually 0.103"

Groove width of 0.125"

Groove depth of 0.098"

[steamer]

1.5 inch bore.    Ramsbottom style    1/4 inch wide on the HP.     The LP was 3" OD...and also 1/4 inch thick

Dave

[steam guy willy]

I make my own  'graphite yarn'. using cotton yarn charged with graphite by pulling it back and forth over a carpenters pencil   this works for me ....I have tried bought yarn but find it quite difficult to wrap it round the recesses...with my own yarn I can just wind it on and add as much as is needed...

willy

[john mills]

I use standard  plated or woven graphited yarn for bronze cylinders use the size for the groove it packs in firmly  a tapered lead in to the cylinder can help to get it in the bore . cut the join at an angle so the ends but together and it will give good long service .
    John   

[Bobsmodels]

Hi

Somewhere there was a discussion on o-rings for steam engines, and one suggestion was an Aflas O-Ring, can handle 450 degrees F.    Here is McMaster  link https://www.mcmaster.com/catalog/126/3729.
I am currently fitting one of these to a 2" Case Traction Engine.

Bob

[crueby]

Hi

Somewhere there was a discussion on o-rings for steam engines, and one suggestion was an Aflas O-Ring, can handle 450 degrees F.    Here is McMaster  link https://www.mcmaster.com/catalog/126/3729.
I am currently fitting one of these to a 2" Case Traction Engine.

Bob

Thats an interesting material - being hard it wont squish in like viton or buna, is it more critical of the groove depth because of that? Being slippery is a plus.  They will still stretch a bit to go over the piston though?

[10KPete]

That's Teflon. It's much like HDPE in hardness and machining. No, it won't stretch and recover. And the bore would need to have a very polished finish.

Used a lot of teflon in the last 50 years. Machined, stamped, molded, bla. I love the stuff.

I think it would make a great ring with the proper seal configuration at the join. Skive 2:1 and a good snug fit when assembled.

Or a two piece piston....

Neat stuff.

Pete

[paul gough]

Hello all, 'RULON', a ptfe with various fillers can be used successfully. The black graphite filler one seems to be satisfactory, but there are others. I seem to remember being told Aster models of Japan used it in there model steam loco piston valves and pistons. Think it was brown or gold in colour. I am pretty sure 'Saint-Gobain', <saintgobainseals>,is a supplier in the US and Europe. They have a comprehensive website. Might seem a bit exotic, but there are Aster locos with this material that have been running for more than ten years. Needs a very sharp lathe tool to machine it. Paul.

[10KPete]

Yes, there a quite a few 'plastics' out there that could easily work. I used Rulon for some stuff back in the late '80s for stationary seals/thermal barriers. Assuming a gland and assembly method could be worked out give plastics a try. At worst make a 2 piece piston and try different materials.

Says the guy with more  projects on the bench than he'll ever get close to finishing........

Cheers,
Pete