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Post by ayesha2 on Sept 20, 2009 16:53:55 GMT
Hi All Has anyone got a design or the best way of making a fusible plug for a 2 and 1/2inch boiler i.e. [whats best solder etc or lead]. i have about 1/16th to 1/8th clearance has the super heater tube goes over the top on its centre. this was not on the drawing and i was not consulted about it, ;D same has the 2 bushes on last post yours Tony
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Post by mutley on Sept 20, 2009 17:05:39 GMT
do you have a bush in the centre of the firebox crown? Your post doesnt make sense.
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Post by alanstepney on Sept 20, 2009 17:55:05 GMT
Very few people fit fusible plugs in the smaller boilers, certainly they are rare in 2.5" and 3.5" gauges. I wouldnt bother with one in those sizes.
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Post by baggo on Sept 20, 2009 18:28:41 GMT
I agree with Alan, just blank it off with a plain screwed plug. There is no need for a fusible plug in such a small boiler and no requirement for one in the boiler testing code.
John
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Post by ayesha2 on Sept 20, 2009 20:49:05 GMT
Hi mutley
sorry about lack of info i should have realised not all members downloaded the photos.
the bush is central, directly in line with the super heater which goes over the top of it,
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Post by mutley on Sept 21, 2009 8:35:53 GMT
okay, now I understand.
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Post by Shawki Shlemon on Sept 21, 2009 9:17:20 GMT
If you fit a fusible plug , you must regularly inspect it and if required replace it because in that hot area I believe that sooner or later the soft solder will deteriorate . I have never fitted one in my boilers and I will not fit one as they are not required in our code, only recommended for large engines ( not required ) . One more thing to cause problems and has no benefit for small engines .
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Post by fostergp6nhp on Jan 4, 2010 17:11:59 GMT
Fusible plugs are not even required in a 4" scale Fowler ploughing engine boiler and that is approx 12" diameter x 4' long.
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Post by maunsell on Jan 5, 2010 19:39:47 GMT
I would not recommend the fitting of a fusible plug in any smaller boilers. They do have a tendency to scale up over the top surface and therefore may not perform as designed. As has already be said if a fusible plug is fitted it falls within the Blue Book inspection code and the inspector may require a fusible plug where fitted to be removed, inspected or replaced at the periodic test intervals. (page 18)
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Post by havoc on Jan 5, 2010 20:45:50 GMT
Are you sure this is for a fusible plug? If there are radiant superheaters, then it might be a thread to hold a support for the superheater tubes to give them some support at the hot end.
Like the others I'm not convinced of the usefullness of fusible plugs in our engines.
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Post by drainblocker on Jan 5, 2010 21:07:34 GMT
How many Model engineers does it take to blank up a bush hole..................... Option 1. Make a grub screw out of good hard bronze screw into bush until flush. Option 2. Fusible or blank it , make you body out of good hard bronze, screw it into the bush if it is tight to the superheater run a marker pen along the face of the blank. Remove blank, place it in the mill and run a ball nose cutter along the pen mark to give clearance for the tube. If blanking nothing further needed, if you want a fusible dill a suitable hole and soft solder in a copper blank, re-machine clearance if needed. Simples!!!!!!! Drainblocker
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Post by GWRdriver on Jan 6, 2010 15:45:59 GMT
This is an interesting referendum . . . a few years ago, being an occasional boiler builder, I got caught up in a debate (in the USA) over the necessity or advisability of fusible plugs. My position was similar to the majority of yours, possibly a useful thing but the drawbacks outweight the benefits. There was one particular individual (a supplier of 3.5" gauge locos) who lead the pro-fusible plug attack and no matter the quantity, weight, and reasonableness of evidence he incontrovertably clung to an insistance that every loco no matter what size must have them. No agreement was reached.
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Post by havoc on Jan 6, 2010 17:22:57 GMT
Well, it isn't very clear either if there is a benefit. I see some issues. Due to the small size, any buildup of scale is going to more important in scale engines than in real engines. And in full size engines, fusible plugs were looked at very well because of reliability issues. It was standard practice to change them each inspection regardless of condition. We seldom use fire doors that open to the inside of the firebox. This means that a fusible plug that blows might force open the door and blow the content of the grate to the driver.
During a discussion at the club about boiler testing it was mentioned that whatever size, if you let your boiler test (in Belgium) by the same instances that tests real boilers, then a fusible plug must be present. I guess this is because they use the same test script as for real boilers and doesn't say much about usefullness.
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Post by maunsell on Jan 6, 2010 23:03:15 GMT
Re: Havoc reply #12. A fusible plug is a signal of low water level over the firebox crown and the possibility of it blowing the firebox door open is extremely unlikely. The real nub of the comment is "the same test script as for real boilers" I suggest that this is where our hobby has been taken over by the "What if brigade" who have lost sight that we are not dealing with full size boilers, but miniature versions with a legendary safety record over the last 70 years.
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Post by havoc on Jan 7, 2010 9:04:49 GMT
It isn't a signal of low water, it is a rather drastic safety device that indicates there is no water at all above the crown. If there would be any water then the lead wouldn't melt. It just blows the complete steam content of the boiler in the firebox. And I haven't seen any model firebox door that opens inside like in real size. Quite a lot are held close by nothing more than a light spring.
Nothing to do with the "what if brigade" at all. Simply if your boiler is over the 300 liter-bar limit it isn't tested by the club inspectors. If you fall into that category then you have to seek a professional boiler tester and they have no exceptions for model boilers, they only test "real" boilers. Mind you, this is only the largest 7.25" boilers that fall into that category so it isn't very common either.
I tought this would be clear from my post as I wrote:
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Post by GeorgeRay on Jan 7, 2010 20:07:45 GMT
Havoc Do you mean in your country firehole doors on full size locomotives are inside the firebox. Certainly I dont know of any standard guage locomotive in the UK where the doors are inside. They are all mounted outside and some swing into the firebox from the top when opened, most but not all slide sideways outside the firebox. Just curious. George
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Post by havoc on Jan 7, 2010 21:34:54 GMT
No, like yours they were mounted on the outside but opened to the inside. Can't find back the type used.
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Tony K
Elder Statesman
Posts: 1,573
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Post by Tony K on Jan 8, 2010 8:31:38 GMT
Havoc, I have seen one of these blow - the steam just puts out the fire and dampens everything down. The hole in the plug is small. It is only Michael cane who "Blows the bloody doors off!" ;D Most responses so far have said it is not worthwhile for small boilers. Do you mean all model boilers or 3½" and below?
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kwil
Part of the e-furniture
Posts: 383
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Post by kwil on Jan 8, 2010 9:45:24 GMT
Is it really worth loosing the boiler due to low water rather than fit a fusible plug? Please do not tell me you never run low on water, it must happen to most people at some time. Full scale eyes have some difficulty in always seeing miniaturised guage glasses.
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Post by maunsell on Jan 8, 2010 10:52:38 GMT
Havoc as an apprentice trained steam locomotive Fitter & Turner in a main Works during the 1950's I can assure you that fusible plugs are not a drastic safety device but were always referred to as a "signal or warning device to alert the enginemen of a serious situation" There were two types of plug both of which protruded well into the water space above the firebox crown, and normally two plugs, one near the firebox tubeplate, and the other adjacent to the firebox doorplate. The older version of plug was a simple one with a low melting point core, while the more modern version known as a drop plug. This was I believe an Anglicised version of the American "Nathan Drop Plug" which had a small gunmetal button with a thin film of lead around it. Discussions about the dubious efficiency of fusible plugs date back to the 1800's and even in 1936 E A Phillipson said that they were still controversial question and that a strict inspection regime had to be in place. I have never fitted a fusible plug in any boiler I have built, but having said that mine have always been copper and from 2.5" to 5" gauge.
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