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Post by Deleted on Feb 26, 2015 12:18:38 GMT
In truth if I wanted to make something like a piston valve for a real world engineering application I would just use all metal construction and labyrinth grooves or metal rings for sealing .
That's not the point though - tossing ideas around by oneself or with friends is stimulating of itself . 99% of ideas will be discarded but just every now and then a real design gem will drop out .
Actually going back to my first line - if I wanted best efficiency I wouldn't use piston valves anyway . Come to think of it I wouldn't use a steam locomotive either !
Was it Eddison who when asked why he was so driven to invent said 'prevents ennui' ?
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Post by Roger on Feb 26, 2015 12:28:42 GMT
I felt sure there was little original in my design, just me bringing together some existing ones in one place. I'm not sure if concentric rings is new but I somehow doubt it. It's only the overlap that needed to be created between the two slits and I couldn't think of a way to do that other than by using two rings. Anyway, it's not important, if it works well I'll be delighted.
I know someone who used individual springs radially pushing out piston rings but I'm not sure what the other elements of that design were or why that method was chosen.
When it comes to the main piston rings, I'll try the same design, but this time I'll make the rings much narrower so that there is less friction. The 'O' rings underneath can determine the width of the rings, they can almost touch each other. Again, I'll probably use two rings side by side but it could be more of course.
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Post by Deleted on Feb 26, 2015 12:32:09 GMT
Was it Eddison who when asked why he was so driven to invent said 'prevents ennui' ? I've had too much of that lately being laid up in bed....need to get back down the workshop for some much needed therapy....  Pete |
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Post by joanlluch on Mar 30, 2015 13:07:11 GMT
Despite this thread being a month old, I thought it would be useful to add some additional data to it. This is from the Polymax UK site: Kalrez up to 260 C  Kalrez-260 by joan.lluch, on Flickr Viton up to 260 C  Viton-260 by joan.lluch, on Flickr Viton up to 150 C  Viton-150 by joan.lluch, on Flickr Silicone up to 150 C  Silicone-150 by joan.lluch, on Flickr Silicone up to 260 C  Silicone-260 by joan.lluch, on Flickr According to the site: (1) Kalrez is the King. (2) Viton is not suitable for steam according to the site (3) Silicone may be suitable up to 150 C |
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Post by Roger on Mar 30, 2015 15:00:33 GMT
This may well be true, but the problem is that Kalrez appears to only be available to special order and that makes it prohibitively expensive. If you can find a stockist for them then that would be brilliant but I don't know of any at the moment. Maybe it's worth contacting the supplier so see if anyone stocks a range of them.
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Post by joanlluch on Mar 30, 2015 15:17:35 GMT
This may well be true, but the problem is that Kalrez appears to only be available to special order and that makes it prohibitively expensive. If you can find a stockist for them then that would be brilliant but I don't know of any at the moment. Maybe it's worth contacting the supplier so see if anyone stocks a range of them. Hi Roger, Well, actually I have been searching about it AGAIN on the internet after talking with my supplier. Indeed Kalrez is very expensive, although imperial sizes seem to be readily available (at such a extremely high prices of course). Not such availability for metric sizes unfortunately. However, my point was mostly about Viton vs. Silicone -we already knew Kalrez was the best :-) There have been a number of posts in the past suggesting that Viton is a better choice than Silicone, which appears to contradict the claim from the site above. Unless there are special grades of Viton that do it. That's something that my supplier is now investigating from his sources. Joan |
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Post by timjenkins31 on Mar 30, 2015 16:47:47 GMT
But that is only the suitability for steam itself, not for use as a piston ring, silicon is much softer and less resistant to wear, which in a piston ring is quite important, I use viton and change them about every 12-18 months, only takes a couple of hours, and they are very cheap rings, the amount of hours most engines are in steam in a year is very few when compared to industry, when they would expect to be in use all day every day
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Post by alanstepney on Mar 30, 2015 18:39:52 GMT
I wish there was a way I could edit the thread title as I feel it is misleadiing. But I cant.
As for rings, I use CI in cast iron cylinders, and in gunmetal ones, I use the "traditional" soft packing.
I have never felt the need to change over to O rings, (although I have used them on shafts etc) so havent investigated the various types.
For many models, that work at less than 90 C, 150 degrees is enough. In those cases, silicon would seem to be suitable.
Some months ago there was a discussion on one of the American boards, and mention was made of a material for O rings that would handle 220C (from memory).
If ever I decide to use O rings on pistons etc, I may have to find out what it was.
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Post by joanlluch on Mar 30, 2015 20:33:47 GMT
I wish there was a way I could edit the thread title as I feel it is misleadiing. But I cant. As for rings, I use CI in cast iron cylinders, and in gunmetal ones, I use the "traditional" soft packing. I have never felt the need to change over to O rings, (although I have used them on shafts etc) so havent investigated the various types. For many models, that work at less than 90 C, 150 degrees is enough. In those cases, silicon would seem to be suitable. Some months ago there was a discussion on one of the American boards, and mention was made of a material for O rings that would handle 220C (from memory). If ever I decide to use O rings on pistons etc, I may have to find out what it was. Alan, I have a general interest because I want to use static o-rings as well in places such as a joint between the main cylinder and the cylinder valve as they are split in my loco. I can change the title (I think) because I started the thread. Any suggestions?. |
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jma1009
Elder Statesman
Posts: 5,917
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Post by jma1009 on Mar 30, 2015 21:37:27 GMT
tim,
i pity you having to change your rings every 12-18 months! this suggests to me what you are using is totally unsuitable!
i fitted the graphite asbestos braided square section packing to my GWR 0-6-0 in 2005 and it hasnt needed any attention to the chassis since then so 20 years use many years of which were of quite an arduous nature with long regular hours passenger hauling - so alan stepney's advice is very pertinent.
on an inside cyliner loco it is quite a big job to change the rings/packing and i wouldnt want to do it every 12 months!
i never understood why the Polly locos with cast iron cylinders werent fitted with cast iron rings in the cast iron pistons! they were fitted with viton 'O' rings which wore out very quickly as a friend of mine found out to his displeasure and annoyance!
cheers,
julian
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Post by timjenkins31 on Mar 30, 2015 23:19:03 GMT
I don't change them because I need to, I've just changed a set for the start of the season, they weren't too bad really, but I'd rather change them now and know they will be okay for another 12 months, I have a bag of 50 so why not, better than waiting until they have completely worn out and risk scoring the piston and bores, such a quick job on a polly, disconnect little end, two bolts for the slide bar, and whip the back cover off, but I agree, I wouldn't want to use them only anything else, my 5" jubilee has them currently but probably going to look into ptfe, it already has ptfe piston valves
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Post by alanstepney on Mar 31, 2015 5:57:49 GMT
I wish there was a way I could edit the thread title as I feel it is misleadiing. But I cant. As for rings, I use CI in cast iron cylinders, and in gunmetal ones, I use the "traditional" soft packing. I have never felt the need to change over to O rings, (although I have used them on shafts etc) so havent investigated the various types. For many models, that work at less than 90 C, 150 degrees is enough. In those cases, silicon would seem to be suitable. Some months ago there was a discussion on one of the American boards, and mention was made of a material for O rings that would handle 220C (from memory). If ever I decide to use O rings on pistons etc, I may have to find out what it was. Alan, I have a general interest because I want to use static o-rings as well in places such as a joint between the main cylinder and the cylinder valve as they are split in my loco. I can change the title (I think) because I started the thread. Any suggestions?. You nmay be right about the thread-starter being able to edit the title. If so, I suggest either removing the word "shocking" or changing the title to "Discussion on O ring materials", for example. |
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Post by Roger on Mar 31, 2015 6:17:22 GMT
I've just emailed this company to see if they can supply small quantities of 5mm and 8mm ID 'O' rings in Kalrez. The google search for them suggests they can do this so let's see. |
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Post by joanlluch on Mar 31, 2015 9:12:42 GMT
You nmay be right about the thread-starter being able to edit the title. If so, I suggest either removing the word "shocking" or changing the title to "Discussion on O ring materials", for example. Done ! |
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Post by joanlluch on Mar 31, 2015 9:15:19 GMT
I've just emailed this company to see if they can supply small quantities of 5mm and 8mm ID 'O' rings in Kalrez. The google search for them suggests they can do this so let's see. It's a pity they are that expensive though. I would happily use imperial sizes for them if the material was cheaper !!. |
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Post by Deleted on Mar 31, 2015 10:50:48 GMT
Just put my professional hat on .
O rings are not ideal for reciprocating steam applications . Full stop .
Various people in model engineering have reported good results and bad results over many years . Problem is that very few people have ever run their engines long enough to get a definitive answer .
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Post by joanlluch on Mar 31, 2015 11:41:18 GMT
Just put my professional hat on . O rings are not ideal for reciprocating steam applications . Full stop . Various people in model engineering have reported good results and bad results over many years . Problem is that very few people have ever run their engines long enough to get a definitive answer . Hi Michael, I fully agree with that. For the piston and valve rings I intend to use PTFE in one of the proven designs, so that's NOT my intended use for the o-rings. However. I intend to use o-rings to join and seal parts that are subjected to steam pressure, such as: (1) The valve sleeves in their bore. (2) The cylinder block and the piston valve block; They are two parts in my design and I need to join/seal the steam passages between them. (3) O-ring placed underneath PTFE rectangular section split rings for pistons (4) The glands Both (1) and (2) are static joints, so maybe I may just use PTFE o-rings there. This is used in the industry for static sealing applications. This should last and work fine, with the only constraint that PTFE joints must be replaced every time the parts are dismantled because PTFE is not an elastomer. Case (3) is the one that worries me more. It is a semi dynamic one. The o-ring in this case is essentially static but it must keep elastomeric features to slightly push the PTFE ring that is on top. Case (4) is dynamic (reciprocating) but it can be replaced by something like (3) if the o-ring is not able to stand the friction. That's my intended use of the o-rings. Ideas? |
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Post by Deleted on Mar 31, 2015 20:39:01 GMT
Cancelled/
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