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Post by Deleted on Jun 17, 2010 11:42:23 GMT
Hello folks,
Just an easy question about veracity of fuseable plugs. I wondered if a 3/32" dia x 7/16" copper rivet soft soldered in a No.40 x 13/32" bronze bush is going to work when called on.
Thanks, Dave
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jasonb
Elder Statesman
Posts: 1,209
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Post by jasonb on Jun 17, 2010 15:13:24 GMT
why not just fill the bush with lead or even solder? Any build up of scale on the end of teh rivit may stop it comming out of the bush when required or the heat may make it expand in the bush.
Jason
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Post by alanstepney on Jun 17, 2010 19:35:33 GMT
The official rules (mainly catering to big stuff) call for plugs to be filled with pure lead.
I disagree.
Lead melts at 621F., which equates to a water/steam pressure of around 2,000 psi.
60/40 electrical solder (correctly, 63/37) melts at 361F, which = aproximately 200psi.
For "our" models which usually operate at 100psi or less, I reckon that a plug that drops at double the working pressure, gives an added measure of safety.
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Post by AndrewP on Jun 17, 2010 22:35:06 GMT
I know naff all about fuseable plugs (not much call for one on a Rob Roy) but saw a really good description recently, after digging around a bit I found it again here near the bottom of the page. Warrants some serious thought methinks. Andy |
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jasonb
Elder Statesman
Posts: 1,209
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Post by jasonb on Jun 18, 2010 6:32:01 GMT
Alan surely the plug when exposed will be subject to the heat of the fire not the heat of any water/steam around it as the whole idea is that the plug melts when the water drops below the crown?
Jason
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Post by alanstepney on Jun 18, 2010 7:46:09 GMT
Andy, An "interesting" experience, but they did say it was working at 120psi, whereas I said "for 100psi or less" which does make a diference.
Jason. That is correct, but it can take time for the lead/whatever to melt, and an alloy gives a lesser margin between normal operation and blowing.
On the GWR, they used to use tin-lead alloys of varying proportions, according to the class of engine and hence working pressure involved.
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Post by drjohn on Jun 18, 2010 9:05:59 GMT
Gotta say I also wondered about fusible plugs.
To my mind they're a complete and utter waste of time - why blow out the little remaining water and allow the fire to melt the silver solder - sounds totally daft to me.
DJ
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kwil
Part of the e-furniture
Posts: 383
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Post by kwil on Jun 18, 2010 9:48:53 GMT
It does remind you that something has gone wrong and you have not been watching the water level, better dump the fire quickly or whats left of it!
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Post by havoc on Jun 18, 2010 10:18:17 GMT
I know I'm coming into the Alzy range but didn't we have a quite heated debate about this not that long ago?
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Post by AndrewP on Jun 18, 2010 10:37:28 GMT
Alan, no criticism intended of your input, far from it. I think the relevant points of the Station Road Steam event were that the solder had not wetted the plug bore and the assertion that the large bore caused the dramatic effect. It presumably failed with a full boiler since it was undergoing steam test at the time, and that is quite a sizeable boiler.
Andy
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Post by alanstepney on Jun 18, 2010 11:14:11 GMT
Andy, as I am sure you know, to be effective any soldering etc must be done properly and ensuring the surface is wetted properly is part of that.
I did once see suggested bore sizes for plugs, but dont recall what they are.
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Post by havoc on Jun 18, 2010 19:16:30 GMT
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Post by Deleted on Jun 18, 2010 22:07:04 GMT
Well, that was an interesting (animated?) read! I apologise for not doing a search before posting my question as it may have answered my query. I normally do so. On balance, it would seem that for 3/4" and 1" scales, fuseable plugs are not necessary, but may be useful as an additional low water reminder if Full scale eyes have some difficulty in always seeing miniaturised guage glasses . Nick Feast in writing about his 3/4" Q1 in M.E. is convinced that a fuseable plug is a good idea. The same applied to Martin Evans if a locomotive boiler has any soft solder... I note that the solid core plug is mentioned in the 2009 thread (as a "Nathan Drop Plug") except with a G.M. core and lead film outer (c.f. copper rivet and S.S film). Scale causing failure could be a problem but inspecting the plug occasionally or using a fuseable core may get round this issue. If it does fail to operate it is no worse than a non-fuseable plug boiler. One other thought, surely in the explosive release of pressure from a dry topped firebox, whilst no liquid water would pour directly out, in the blast that occurs, perhaps water from lower down the boiler may be included in the steam.
Thanks all,
Dave
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Post by havoc on Jun 18, 2010 22:11:02 GMT
That's about it. But as soft soldered boilers are "not done" these days I wouldn't bother. Even in full scale they were problematic at best and called for frequent inspections/replacement.
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Post by Shawki Shlemon on Jun 19, 2010 8:28:18 GMT
AMBSC code does NOT require to fit a fuseable plug on model boilers (optional) .If the plug drops while the fire door is open , I wouldn't want to be behind that boiler as some of that hot stuff will end up in driver's lap or face . Soft soldered rivet joint may deteriorate over time and fail prematurely . The main problem with them is maintenance or lack of it due to hard access . I personally will never fit one to my engines . On our engines , the safety valves should handle high pressure , to melt the silver solder one must be firing the engine without water for long time , I mean dry . Just think how much heat is required to perform final steps of silver soldering . In my opinion they are waste of time for our size of boilers and another thing that can go wrong . ;D
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