Fuseable plugs

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Fuseable plugs

Post  Steve Traill on Sat 01 Apr 2017, 10:45 pm

Just got back from a boiler inspectors seminar at Taunton, very well organised day, it was put together by the Northern Association of Model Engineers (NAME) and the Southern Federation of Model Engineering Societies. The expert on steel boilers advised that the best thing we could do with our fusible plugs on miniature engines with steel boilers is throw them away and fit a steel bolt! We were all stunned, apparently there have been incidences where the fusible plug has gone and the rush of steam has caused serious injury. Also the dissimilar metals can cause corrosion of the threads and they can come loose or blow out that way. They are of limited value in hard water areas anyway due to scaling over.

He's not saying don't worry about keeping water over the top of the firebox but in reality, because of the thickness of steel and the size of the fire grate very little damage is likely to occur compared to full size. By fitting a steel bolt you have eliminated the dissimilar metal corrosion and reduced the risk to nil of being scorched with boiling water from the fusible plug.

This is only advice on miniature steel boilers not copper boilers.

I'm still thinking about this one, what do others think?
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Re: Fuseable plugs

Post  Mark the spark on Sun 02 Apr 2017, 8:49 am

Hi Steve
I don't think I will follow that advice however the use of brass as boiler fittings has been a problem for sum time and I will be fitting bronze or gunmetal fuse plug and the same for the washouts
The fuseable plug is your last line of safety and I would rather get burnt if it blows than sitting behind it with my legs spread when the crown gives up
I have seen a plug go on a 4"and it was quite a sight it blow off the ash pan and spread the fire in a perfect circle of about 10feet round
I should point out I am a tester for my local club and this is just my own two pence worth
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Re: Fuseable plugs

Post  Kevster on Sun 02 Apr 2017, 9:24 am

The plugs supplied by STW should be bronze or gunmetal surely ?
I always thought brass should not be used.

Kev
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Re: Fuseable plugs

Post  lynnr on Sun 02 Apr 2017, 10:42 am

My commercial inspector wants the plug out every year for inspection. Plug and flange both in excellent condition. No wastage what so ever.
I have been present when a 4" plowing engine dropped its plug. The fire went out and we got a whistle but no sudden release. No scalding steam every where and the fire stayed on the grate but out.

As others said. I would rather suffer a bit of discomfort for a while with a slight possibility of scalding. Than a boiler crown cutting by legs off on its way past.
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Re: Fuseable plugs

Post  Kevster on Sun 02 Apr 2017, 4:45 pm

Im inclined to agree with Lynn,afterall how many years have we had fusible plugs in steel boilers then all of a sudden they are no good.
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Re: Fuseable plugs

Post  Steve Traill on Sun 02 Apr 2017, 11:11 pm

Pretty much all the other 72 delegates (boiler testers) were thinking the same but these guys are in charge of the NAME & Southern Fed who also arrange the insurance we all need. The green book we all read at night is being revised later this year in a bid to streamline some of the anomalies between the North & South and also make it a bit clearer. I have to say the guys 'oop north' are leading the way in my opinion.

Using a steel bolt instead of a fusible plug would take the worry out of the short steep bit we all find on a rally field and fear being left at the bottom, half a mile from your caravan. On the other hand no-one wants to see damage to the structure of the boiler. I think what they were saying is that the steel is not to scale on a miniature, it is almost full size thickness and because of that it would not be possible to do damage to it if it was dry for a few minutes due to the size of fire in the firebox. Obviously no-one is saying run around with no water, you still have to keep water in sight on the gauge glass, just that it's not quite so critical as we all thought and the risk of personal injury from a plug going is a higher risk than the possibility of damage to the firebox crown.

I'm still sitting 50:50 on this one at the moment. I think I would like to see real evidence that not having a fusible plug doesn't hurt the firebox crown with a good fire going & no water over the top. Cue a U tube video, any volunteers?!!!
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Re: Fuseable plugs

Post  Mark the spark on Mon 03 Apr 2017, 8:05 am

Hi Steve
I would like one of them to prove it on one of there boilers first then I might take my fuse plug out

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Re: Fuseable plugs

Post  lynnr on Mon 03 Apr 2017, 10:20 am

Well.

I feel an experiment is in order. I have some steel bar the same thickness as the boiler. I think if I bend it to shape so it fits in the top tube hole and sits at the crown above the fire. Leave for 5 minutes with Crystal on the belt. I bet the bar will be slagging and drooping without any pressure behind it.

5 minutes "uncovered" event would be a fair test. What do you all think?
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Re: Fuseable plugs

Post  Mark the spark on Mon 03 Apr 2017, 1:28 pm

Hi Lynn
good idea and I think it will bend in 2 or 3 mins

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Re: Fuseable plugs

Post  Steve Traill on Mon 03 Apr 2017, 8:05 pm

I know what you are saying but I feel if such a major change to a safety system is to be recommended then NAME or the Southern Fed should do there own experiments and sacrifice a boiler in a true real world test. The problem with smaller unsupported pieces of steel is that they probably would buckle. I guess if someone recreated a fire box ( not in a boiler) and then got a good fire going inside it that would be a pretty reasonable test as one could see & film any distortion. Would STW let us have a fire box that the apprentice made!!
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Re: Fuseable plugs

Post  LiveSteam on Mon 03 Apr 2017, 9:05 pm

I've heard rumours of this last year at a couple of shows and thought it sounded like a April fool, in all honesty and in my relaitvely newbie stance theres no way I'll be replacing mine especially the fact I run copper tubes. As for scale build up .......well you should be using water treatment shouldnt you ?
Over the last couple of years the amount of scale build up on the top of the plug could be virtually wiped off with your fingers (this year it had some descaler so cant say how much was on it) so I'm not sure what the scale issue is ?

lynnr wrote:My commercial inspector wants the plug out every year for inspection. Plug and flange both in excellent condition. No wastage what so ever.


Likewise Lynn, plug out every test, checked for wastage, cleaned and refitted, last year it was decided a new one was required due to wastage and threads being pulled slightly, it was 10yrs old after all.

So if we are using a commercial inspector are they likely to follow this daftness or is this only for the club folks who do their own ?

I would far rather think about traversing a hill or even reversing down it (done that before) than change the plug for a solid one Neutral


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Professional inspectors / NTET?

Post  Tim Watson on Mon 03 Apr 2017, 11:51 pm

I have just undertaken my own hydraulic test on Frederick prior to the proper test next weekend.  The plug had been replaced and was dripping very minimally under pressure.  It had been OK when I fired up the engine a couple of weeks ago.  Anyway, water drained, plug removed and new tape applied, replaced, and pulled up tight.  All OK under hydraulic pressure second time round.  Life would have been much simpler with a permanent steel plug in place!

However, I had discussed this with my (club) boiler inspector a few weeks ago.  We both thought that this was a flawed idea.  Whilst people talk of model boilers having steel plate as thick as full size engines when new - that's fine.  But what about the older boiler when there is wastage of the crown due to corrosion?  At that point, I think the fusible plug comes into its own. Having a fusible plug encourages correct engine driving practice.  The plug failed on my previous engine 'Madeline' a few times, originally due to my incompetence, then down to others who were 'in charge' and finally from a couple of mishaps. At no point did it blow, just weeped and stopped the fire from working.  Testing bits of steel in a firebox is easily done: look at your firebars if you don't clear the ash away from under them - they soon buckle.

The ME Federations /Associations risk a major loss of confidence from rally organisers and possibly the NTET if the professional boiler inspectors do not agree with this steel bolt suggestion.  There is already a deal of scepticism in some quarters about amateur club boiler inspectors and I don't see this idea improving their image.  Boiler explosions are terminal events.

I will continue to use a fusible plug.

Tim
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Re: Fuseable plugs

Post  LiveSteam on Tue 04 Apr 2017, 8:09 pm

Tim Watson wrote:I have just undertaken my own hydraulic test on Frederick prior to the proper test next weekend.  The plug had been replaced and was dripping very minimally under pressure.  It had been OK when I fired up the engine a couple of weeks ago.  Anyway, water drained, plug removed and new tape applied, replaced, and pulled up tight.  

Word of caution if you are talking about PTFE tape, my current thoughts, and that of my boiler inspector, is stay away from PTFE tape, it shouldnt be needed really and it seems it slowly builds up in the threads flattening them out, unless you run a tap through it everytime.

Must admit I havent been using PTFE tape on any of my plugs (inc the fusible one) for the past year. Just a smear of copper slip round the threads and wind it in. Todate no leaks and they wind in and out with ease.

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Re: Fuseable plugs

Post  Tim Watson on Tue 04 Apr 2017, 10:30 pm

I run a tap through the threads to clean up and always remove old PTFE tape from the bolt thread.

Tim
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Re: Fuseable plugs

Post  Capricorn1 on Wed 05 Apr 2017, 12:14 pm

Removal of the fusible plug and running without it is a dangerous line to cross, as has already been said it would only encourage poor engine management. The plug is a warning device to alert the driver that the crown sheet has become overheated by low water level. If an owner dropped the plug which then resulted in blowing off the ash pan then clearly the plug was of the wrong design - the hole containing the loose bronze insert / lead was too large. The plug should be taken out at every boiler examination to inspect the threads and to see if there is any creep - partial melting of the lead. There are alternatives to PTFE tape if your particular boiler inspection has some aversion to it... There may be times when the water level will disappear below the bottom nut on the water gauge if going over a crest of a hill but if you simply shut the damper, close the regulator and put on the injector on you should be in no danger of dropping the plug, you can slow the engine down by easing back on the reversing lever then putting it forward again - this will cause the water to slosh back and forth so wetting the crown sheet.
The main point is to be in control of the engine and that includes boiler management.
Locomotive boilers fitted with fusible plugs have been around for a long time, there's no need to try to justify their use by backyard experiments.

"The modern manual for drivers of road steam vehicles" by W. Michael Salmon is recommended even for the owners of miniature engines.

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Re: Fuseable plugs

Post  Mike King on Wed 05 Apr 2017, 3:57 pm

I'm not experienced in these things like you guys, but wouldnt there be some kind of insurance implications if a boiler did explode in the public domain, and someone was hurt through the fitting of a non certified fuseable plug! Just wondering.
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Re: Fuseable plugs

Post  Steve Traill on Wed 05 Apr 2017, 4:02 pm

I have written to Peter Squires of N.A.M.E. to confirm in writing this advice and the reasons for it.

When I get a reply I'll let everyone know. 

Also the reason for not using PTFE tape is that when in contact with boiling water any loose material turns into little PTFE balls which can get stuck in the injector/gauge glass etc.  I think this is more of a problem with the railway engines as they are a lot smaller generally.  I've used it for 10 years and am not aware of it causing any problems.
The 2" Burrells might want to consider this.

Regarding Insurance, Royal Sun Alliance operate the insurance and are guided by NAME & Southern Fed.  I don't think it would be an issue if we are following advice from NAME & SF as they are all linked together.

According too NAME the last record of a miniature steam boiler exploding/failing was in the 1960's, it was a rolled steel barrel and it split along the welding at the bottom, no-one was hurt.
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Re: Fuseable plugs

Post  Mike King on Wed 05 Apr 2017, 4:15 pm

It looks like ill have to remove my plug from my 2"and remove the tape then, before it gets its first steaming this year.
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Re: Fuseable plugs

Post  LiveSteam on Wed 05 Apr 2017, 7:37 pm

Tim Watson wrote:I run a tap through the threads to clean up and always remove old PTFE tape from the bolt thread.  

Tim

Thats good to hear although do you really feel the need for it, as I've mentioned I've been running PTFE free for a good year and so far no problems (famous last words) Laughing I've definately found the plugs all come out so much easier now.

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Re: Fuseable plugs

Post  chrisnchrisroberts on Wed 05 Apr 2017, 9:47 pm

If PTFE is a problem, what was used before it was developed? I can remember years ago using hemp rope wrapped around the thread and then a bar of soap was used to push the hemp into the threads. This was on industrial fire sprinkler systems. They never leaked if done properly. So, again, what else was used?

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Re: Fuseable plugs

Post  Mark the spark on Wed 05 Apr 2017, 10:14 pm

Hemp and boss white but Mr H+S does not like boss white any more so you cant get it

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Re: Fuseable plugs

Post  Capricorn1 on Wed 05 Apr 2017, 10:42 pm

The date of the start of this thread is .... ?

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Re: Fuseable plugs

Post  Capricorn1 on Wed 05 Apr 2017, 10:44 pm

Mark the spark wrote:Hemp and boss white but Mr H+S does not like boss white any more so you cant get it

You can get Boss Jointing Compound from screw fix = other suppliers are available.

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Re: Fuseable plugs

Post  Mark the spark on Thu 06 Apr 2017, 7:58 am

its not quite the same stuff as I remember they taken something out

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Re: Fuseable plugs

Post  LiveSteam on Thu 06 Apr 2017, 7:58 pm

chrisnchrisroberts wrote:If PTFE is a problem, what was used before it was developed? I can remember years ago using hemp rope wrapped around the thread and then a bar of soap was used to push the hemp into the threads. This was on industrial fire sprinkler systems. They never leaked if done properly. So, again, what else was used?

I wouldnt say PTFE is a major problem, I know many who swear by it, just if used excessively and not properly cleaned out could and appears to cause problems, I think its because it doesnt compress and eventually builds up flattening the threads, hemp I suspect doesnt.
I think the issue is when folks wrap half a roll of PTFE around every joint in the vain attempt to stop leaks, which it might do, but my understanding of PTFE tape is it should be used as a dry lubricator for the thread rather than a leak supression system Laughing
In truth if a thread is good and the surfaces are good I dont see the need for anything other than a little lubrication which copper slip seems to take care of very well.

I can only really go on my few years of experiences on steam but since swapping to copper slip everything come undone far easier than when it had PTFE tape round it everytime and the threads maintain a healthy look. My commercial inspector seems to be of the same opinion.

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