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Post by havoc on Jan 8, 2010 11:40:40 GMT
Fine, but this is not what I read in manual for railway men (Lamalle et Legein: "La Locomotive, description raisonnée de ses organes à l'usage des ouvriers" 3th ed) Can be it was classified different in UK than in Belgium.
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Tony K
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Post by Tony K on Jan 8, 2010 12:23:13 GMT
Fine, but this is not what I read in manual for railway men (Lamalle et Legein: "La Locomotive, description raisonnée de ses organes à l'usage des ouvriers" 3th ed) In the absence of Doctor John, I feel someone should say something like - I must read that one day    ;D |
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JDEng
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Post by JDEng on Jan 8, 2010 12:40:57 GMT
Page 53, British Transport Commission "Handbook for Railway Steam Locomotive Enginemen".
Fusible Plugs:
".............If the water level in the boiler drops too low and uncovers the plugs, the lead melts and allows steam to escape into the firebox, which acts as a warning to the Enginemen. Should this occur both injectors should be immediately put on and steps taken to remove or deaden the fire."
I've never seen a plug go but I've made a few for full sized locos, I can't remember the bore off hand but it's only about 5/16" or so. It certainly wouldn't pass enough steam to douse a fire in a full sized loco and the inference above backs that up.
John.
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ewal
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Happiness is a good wife & a steam engine.
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Post by ewal on Jan 8, 2010 17:16:41 GMT
I was driving the first Tinkerbell I built in 1999 when the plug blew. I managed to drive to the shed but I was covered in ash. I think I used very soft solder which was exposed when climbing the 1 in 10 grade. I dispenced with the plug after as I only use steel boilers.
E.W.
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Post by baggo on Jan 8, 2010 17:56:47 GMT
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JDEng
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Post by JDEng on Jan 9, 2010 11:56:54 GMT
Interesting what they have to say. It appears the bore on the plug was way too big. Since my earlier post I've had a look at the drawings I have for a BR Standard fusible plug and also the LNER standard. I was a bit wide of the mark on the bore size, the BR having a 5/8" hole and the LNER 1/2"; threaded in both cases presumably to provide an increased "key" for the lead. The water side of the plug protrudes between 5/8" and 7/8" beyond the end of the threads; I presume this is to allow the plug to melt whilst there is still some water over the crown in an attempt to limit damage. I appreciate that this might not be the case where a loco is not standing on the level but you can't have everything! As I've said before I have a full sized loco and our boiler inspector is very particular about plugs being filled with pure lead rather than a lead alloy such as solder. Apparently alloys can react differently and this can affect their ability to melt (or not) at the critical moment. John. |
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Post by havoc on Jan 9, 2010 12:43:57 GMT
Similar construction and size here, the hole is only threaded in the center section and sticks 10mm out at the water side. Reason given is to minimise scale on the lead which could block the plug. Metal to be used is given as lead or alloy melting at about 350°C.
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russell
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Post by russell on Jan 9, 2010 22:04:26 GMT
Here in France the CAV recommend fitting a fusible plug and the insurance cover may depend on the boiler conforming to this regulation.
The bore of the plug in mm is calculated as 10 x Grate area (dm2) / Pressure (bar). It should have a 15 to 30 deg entry cone and a 90 deg exit cone. It should stand proud of the firebox roof by the thickness of the roof and be filled with lead after tinning it with solder.
For Simplex the bore works out at 2 mm. I doubt if steam escaping from this could blow the firebox doors off!
Regards,
Russell.
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steam4ian
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One good turn deserves another
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Post by steam4ian on Jan 10, 2010 4:00:35 GMT
G'day all
I think I have shared this before. A few years back a 12" to 1' 4-8-4 literally dropped a plug. The result was two burned engine men and one dead cab rider. The loco was a relatively modern streamliner with fully enclosed cab and the blast came straight back at the cab rider (official).
At the time the loco was an coal/oil burner with over fire oil jets through openings in the back of the firebox. A coal fire was maintained in the grate with supplementary oir firing at times of high load. The firedoor was of the butteryfly type and closed at the time. The blast came out the openings for the burners.
It turned out the the complete plug assembly came out of the hole tapped in the crown sheet discharging water and steam onto the coal fire. There had been an ample glass.
Inspection of records showed that the plug had been periodically leaking so the solution had been to slog it up tighter. Ultimately the thread gave way.
It is one thing for a plug to go with no water behind it with only steam released; another when there is a good covering of water.
Regards
Ian
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russell
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Post by russell on Jan 10, 2010 9:22:47 GMT
In other words poor maintenance. Could this kind of accident not have happened if any boiler bush was overtightened in an attempt to stop leaks? It is not really an argument against fusible plugs.
The French recommendation is for a bush with 1/4 in gas thread for a bore of up to 3 mm with a 1 mm thick annealed copper washer with graphite grease for sealing. I have not managed to find any reports of failures here.
Regards,
Russell.
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Post by ayesha2 on Jan 28, 2010 17:13:21 GMT
hi drainblocker
why should a professional boiler maker !! put one in a 2 and half inch boiler in the first place,
beggars the question, really, and a total lack of experience on such matters,
or he was,nt trained right, an then to put it in the place it is, shows total lack of common sense, just like the bush [not on drawing], right below the water gauge bush. tut, tut
yours tony
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Post by Shawki Shlemon on Feb 1, 2010 9:53:54 GMT
I have only heard this ,I have not seen the report personally , a fusible plug on 7.25" G let go while water level was OK and at that moment the driver had opened the door to feed the fire , the contents of fire box ended up in the lap of the drive who suffered sever burns . I am let to believe it happened in WA . Fusible plugs here are optional in large engines and I would not fit one on my engines . Just keep the water above the crown and if not possible one should kill the fire and end the run . Fusible plugs require regular maintenance and because of its position , that task get neglected .
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kwil
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Post by kwil on Feb 2, 2010 9:23:28 GMT
If fusible plugs are dangerous as implied surely they would be banned by regulation or guidance?
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Post by Shawki Shlemon on Feb 6, 2010 9:05:23 GMT
As I mentioned if they are regularly checked and maintained , they should be OK but because of their location they tend to be neglected and for what they do for a model boiler , in my opinion they are not worth putting in .
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russell
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Post by russell on Feb 6, 2010 10:35:39 GMT
Shawki,
I agree about the maintenance aspect. The recommendations here include details to make them easily accessible. However, I'm inclined to agree that, if they were not required for insurance purposes here I wouldn't fit one.
Russell.
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;D
