miken
Part of the e-furniture
Posts: 481
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Post by miken on Jul 18, 2022 21:10:00 GMT
Hi Mike, apologies for the slight diversion. I notice that your super heaters appear to be stainless and are silver soldered into the header. I am intending to use the same approach on my Jubilee build, I already have the radiant end welded. Can I please ask what type of solder and flux you used at the header end. The people who welded the spears recommend Tenacity 5 flux powder. Regards Paul. Paul, Yes I used tenacity 5 flux and JM easyflow no. 3 which is (or was, it's probably banned now because it contains cadmium) recommended for stainless steel. Also, I was given a large tube of it for free when they were having a sort out at work. No. 3 isn't as runny? (Thats probably not the correct term) as, say no.2 which means you can build up fillets which add a bit of strength.
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miken
Part of the e-furniture
Posts: 481
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Post by miken on Jul 18, 2022 21:17:12 GMT
Hello Mike, Now that I've seen what you're doing, I think you may better sticking with your original choice - PTFE rings. They should handle the heat and will expand to close the joint at the right time. I don't see any advantage looking for an alternative, you already (probably) have the best solution. Regards, Steve
Steve, I've also been coming around to that line of thinking as today has progressed. As mentioned, I have run the loco a couple of times with the ptfe rings and they didn't leak. When I dismantled the pipework the rings looked the same as when I built it a few years ago. Maybe I will just stick with what I know works.
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Post by chris vine on Jul 18, 2022 21:38:32 GMT
I wonder if fluorsint might be a bit more stable at high temperature.
Looking at the plastics shop website and data sheets, it doesn't go much higher than ptfe, but it might be less likely to deform as it gets hot in your application...
Alternatively, can you make up a sort of stuffing box with graphited yarn in it??
Chris.
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O- rings
Jul 18, 2022 22:27:09 GMT
via mobile
Post by GWR 101 on Jul 18, 2022 22:27:09 GMT
Mike, many thanks for confirming that, good luck with your build. Regards Paul.
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Post by Roger on Jul 19, 2022 6:49:20 GMT
I wonder if fluorsint might be a bit more stable at high temperature. Looking at the plastics shop website and data sheets, it doesn't go much higher than ptfe, but it might be less likely to deform as it gets hot in your application... Alternatively, can you make up a sort of stuffing box with graphited yarn in it?? Chris. Hi Chris, You're right, it's definitely more stable. However, any PTFE based seals will almost certainly suffer from creep. I can see why they're used because they may be the only thing that survives long enough to be useful.
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Jul 19, 2022 8:43:01 GMT
Guys, years back was a discussion here about Viton "O" rings used at very high temperatures. Seems very high temperatures can cause them to degrade and produce hydrofluric acid which on contact with humans just keeps going.
Yes there is an antidote other amputation above the site but it is expensive and had limited shelf life.
You also need to be very careful with PTFE at high temperatures. Would favour annealed copper washers.
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miken
Part of the e-furniture
Posts: 481
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Post by miken on Jul 19, 2022 11:48:30 GMT
O rings delivered today. Although I don't think I'm going to use them now. I chose the "free" dellivery option and they arrived 18 hours later!! Excellent service. If I had paid for a faster service I think they would have had to teleport them.
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Post by doubletop on Jul 23, 2022 5:32:49 GMT
Hello Mike, Now that I've seen what you're doing, I think you may better sticking with your original choice - PTFE rings. They should handle the heat and will expand to close the joint at the right time. I don't see any advantage looking for an alternative, you already (probably) have the best solution. Regards, Steve
Steve, I've also been coming around to that line of thinking as today has progressed. As mentioned, I have run the loco a couple of times with the ptfe rings and they didn't leak. When I dismantled the pipework the rings looked the same as when I built it a few years ago. Maybe I will just stick with what I know works. My vote would be to stick with the PTFE for all the reasons Steve gave. The builder of my boiler suggested that's what I should do to join the superheater assembly to the wet header bush. It has been fault free since the build. The PTFE absorbs water and seals the joint but still allows easy dissassembly. Pete
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Jul 23, 2022 10:23:05 GMT
Guys, years back was a discussion here about Viton "O" rings used at very high temperatures. Seems very high temperatures can cause them to degrade and produce hydrofluric acid which on contact with humans just keeps going. Yes there is an antidote other amputation above the site but it is expensive and had limited shelf life. You also need to be very careful with PTFE at high temperatures. Would favour annealed copper washers. Question is, what constitutes a high temperature? The dangers of (say) burning viton have been known about for some time, but superheat on the average steam model must be a rather lower temperature than that. So at what temperature does the hazard start?? Same question with ptfe, but it seems rather less well known about. Gary
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Jul 23, 2022 20:00:14 GMT
Yes the PTFE question ...
Years back a mate of mine told me a story about a machinist at his works machining PTFE while also smoking a fag. Apparently some sort of airborne residue ended up of the hot end of his fag resulting in 6 months off work having had a near death experience.
I recall the discussion on Viton rings described the ring degrading in to a mystery goo which contained the acid. Basically, if disassembling something with Viton rings and it has degraded in some way into goo best be very cautious.
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Post by John Baguley on Jul 23, 2022 20:37:20 GMT
I seem to recall that the temperature at which Viton decomposes is something like 400°C.
John
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,912
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Post by JonL on Jul 23, 2022 20:45:11 GMT
Hi Mike, apologies for the slight diversion. I notice that your super heaters appear to be stainless and are silver soldered into the header. I am intending to use the same approach on my Jubilee build, I already have the radiant end welded. Can I please ask what type of solder and flux you used at the header end. The people who welded the spears recommend Tenacity 5 flux powder. Regards Paul. I know I'm not who the question was directed at, but my answer for doing exactly that (swapped out copper superheaters for longer stainless tig welder darts without the big U-casting at the end to make them radiant) was that I used my normal silver solder with HT5 flux. I think I used 455 silver solder. Whatever I used its been fine so far with lots of hours under its belt.
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Jul 25, 2022 8:51:03 GMT
There is useful information on superheated steam seals here: www.sealseastern.com/Steam-Resistant-Seals.htmIt indicates that Viton (FKM) should last for >1000hrs at 175deg C, enough for a decent lifetime. For much longer term resistance "AFLAS" rubber is best, though maybe difficult to get in the right size.
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Jul 25, 2022 21:43:51 GMT
There is useful information on superheated steam seals here: www.sealseastern.com/Steam-Resistant-Seals.htmIt indicates that Viton (FKM) should last for >1000hrs at 175deg C, enough for a decent lifetime. For much longer term resistance "AFLAS" rubber is best, though maybe difficult to get in the right size. They don’t though (AFAICT) include silicon rubber in their comparison. Although mechanically quite weak, I understand it is better at resisting heat than nitrile at least, and some comparisons rank it close to Viton. Not that Viton is ideal either, but the comparisons I have seen are less than clear; not least because they often use different names from the ones we are used to. (and it appears that there may be different grades of “viton” to add to the confusion) Gary
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