Viton rings

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Viton rings

This topic has 12 replies, 3 voices, and was last updated 21 February 2010 at 16:44 by calder percival 1.

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16 February 2010 at 22:35 #48738
mgj
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@mgj
Been running the LS (1 1/2″ bore) on Viton rings. They seem to have worked well, but they have worn very quickly.

I admit that I made the bores for iron rings, so perhaps the wear was to be expected. However, the bores haven’t glazed yet , so every time you put the engine away you get rust in the cylinder and that, it seems to me is an irredeemable pain. Despite which I’m certainly not going to polish the bore personally when Mr Steam will do it for me!!!

So its back to iron rings I think, but I wonder how others have got on with Viton in these sizes.
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16 February 2010 at 22:35 #2682
mgj
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@mgj
17 February 2010 at 01:05 #48744
Windy
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@windy30762
Hi Meyrick, I haven’t had much to do with Viton O rings of that size as alternatives to metal piston rings but would PTFE ones be any better there is also Kalrez it has the same advantages as Viton but it has greater chemical and temperature resistance. However Kalrez is considerably more expensive than Viton.

Windy

Edited By Windy on 17/02/2010 01:06:41
17 February 2010 at 20:34 #48767
mgj
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@mgj
Windy – I don’t know. PTFE is very slippery certainly but not that elastic as I have seen it – though people are using Fluorosint which is mica loaded ptfe. Nor have I ever met Kalrez. I have no experience at all in this area.

The rings have arrived from Stuart – too idle to make them! – and they look rather good. Not too thick, so friction should be fine, so with apologies, but the Chinaman calls – time to munch a chunk of cast iron.
20 February 2010 at 23:07 #48951
calder percival 1
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@calderpercival1
for viton rings to work correctly they need room to “roll” otherwise you will scuff them everytime also the lubricatione needs to be very good.
20 February 2010 at 23:28 #48955
mgj
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@mgj
Well they were 1/8 rings, in .132 wide grooves, and depth was .132. See Model Engineers Handbook page 11.3. and also, you may trust me – the lubrication was fine. I wouldn’t have run the machine if it wasn’t.

These rings from Stuart should be good. If you go to page 11.7 of the ME Handbook, the recommended wall pressure for the rings is about 8-12 psi. If you solve equation 5 , which is a touch awkward you get a ring thickness of .053″. These rings are .050, so they are pretty well perfect for an installed gap of 2 thou.

For those who don’t fancy solving the equation, it was in graphical form in ME a little while ago, and its then very basic rithmetic to derive the ideal ring thickness for your engine. (For those who don’t want to use metallurgical formulae/terms – but its worth doing it with a calculator just once because then one understands what the terms are and what the ring is doing)

But I’m impressed – they have these rings dead right.
21 February 2010 at 09:23 #48966
calder percival 1
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@calderpercival1
i take it that your cylinders are iron and if so why are you not using piston rings anyway?
21 February 2010 at 09:30 #48967
mgj
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@mgj
Yes its iron.

No reason why you cannot use Viton, or ptfe, or lip seals on iron. What matters is less the material of the bore, but the surface finish. See original post.
21 February 2010 at 13:03 #48975
calder percival 1
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@calderpercival1
oh i beg to differ but it does matter and yes while the surface finish does matter the only choice for iron is a true piston ring, if it were not the case then industry would change its methods
21 February 2010 at 13:06 #48976
mgj
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@mgj
I’m sure you are right. Which industry?

Edited By meyrick griffith-jones on 21/02/2010 13:07:06
21 February 2010 at 13:16 #48977
calder percival 1
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@calderpercival1
all industry as you mentioned it is the glaze you lack, the surface finish which in gunmetal becomes burnished over use is what the viton ring is required for the viton rings main use in industry is in the hot melt glue application where the cylinders in the pump are exposed to very high temperatures . You will also no doubt be aware of the dangers of a burnt or tainted viton ring hold.
21 February 2010 at 14:32 #48981
mgj
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@mgj
Thanks for that – that was useful about the burnish on bronze.

We will have to disagree slightly about other uses of iron bores, but I agree, proper rings in this instance will be better, and those I now have. The new piston has been made, and the rings fit fine. It was a bit of laziness not using rings. To make and set rings is a bit of palaver, and I just wanted to get the thing steamed up after several years of building.

Anyway – it worked well enough for the purpose, but I wouldn’t do it again. It passed hydraulic 1 with no problems, so now its in bits having the cladding put on, and then we shall be ready for the steam test, i hope in 2 or 3 weeks. (If I don’t steam it some more first!)
21 February 2010 at 16:44 #48983
calder percival 1
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@calderpercival1
good luck with that i hope it goes well. and there are no shortcuts in engineering only the proper way will do the Victorians should us that and now we through everything away because we can!
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