Fusible plug in a 5" gauge copper boiler?

What are the pros and cons for putting a fusible plug in the copper boiler of my Claud, under construction?

I have never really found it necessary in my 5" Manor and I am minded to omit it unless there are good reasons not to.

Kind regards

John B

I suppose its like any insurance policy, a waste of time/money until you need to claim! Phil

The current UK regs don't insist on it. Can you actually get to it when the loco is fully assembled and running to change it? I haven't come across one yet and I wouldn't fit one myself unless I had to.

When my boiler was made by Paul Tompkins (Southern Boiler works LTD) 2 years ago he included a fusible plug as that was the legislation for the CE mark, it was a recently added requirement at the time. Now that we have left the EU perhaps things have changed?

Pete

[This posting has been removed]

I’m with bill why would you not have one?

Can anyone reference the "recently added requirement" for CE marking? I can think of a few reasons why there is not much point in a 5" gauge boiler. One being where would you get a plug of known composition / quality in that size that you would be confident of fusing? Do those of you that have them fitted remove them on an annual basis for inspection? If you drop a plug you are supposed to have a re-inspection of the boiler. I suspect the requirement has been added by the certifying body that underpins the CE process rather than any actual change in standards but happy to be proved wrong.

Paul.

I think Nigel covered this in stating how hard it would be to replace if it failed. I'm still open minded as to whether I will fit one or not, again as Nigel rightly stated it is not a requirement for the UK. However, I do like the idea of fitting a fuseable plug, after all the boiler is the most expensive part on the model, whether home made or professional. Fuseable plugs in models have been known to fail prematurely and thus it may be prudent to fit a blank?

My own firebox will be fitted with an arch which should reduce the direct heat to the plug, as I say, the jury is still out as to whst I'll actually do when I get there.

We shall see...

Pete

Hi Paul, I can only say what I was told, I'm sure that professional boiler makers wouldn't fit one unless forced too to have the then all important CE stamp. As for the plug, you make this yourself, make a blanking plug to fit, drill a suitable hole through the centre and soft solder a copper rivet to it with the head inside the firebox. The idea being that the rivet head will protect the solder for normal running but if too hot the solder will melt thus extinguising the fire. If the plug drops you'll need to remove the boiler anyway and thus it will need testing.

Pete

Our model code for boilers in Australia stated that boilers less than 273mm dia should be fitted with at least one fusible plug. (should, not shall. So not mandatory). BUT if you have the option, why would you choose not to have one. It is a safety feature to prevent damage if the crown overheats because of low water level. Could save a lot of money for a new boiler.

Paul.

In the many, many years of model loco operation within the ME hobby, how many instances of boiler damage due to low water level have there been? I've not heard of one.

I find it hard to visualise a small fire, say 0.5kg of coal, releasing around a maximum of 1-2kW or so of heat, significantly damaging a typical silver soldered copper boiler, which will contain at least, some water. When I've soldered a boiler I might use heating of up to 20kW with plenty of firebrick insulation and, even then, it's a stuggle.

I agree, and my boiler tester has mentioned this to me more than once.

In normal operation most 5" and smaller boilers have very little water over the firebox crown, this is after all where most of the steam is made. It is quite likely that parts of the crown will be uncovered momentarily while running, as the water must be sloshing around, to use a technical term. In that situation a fusible plug would be quite likely to melt when in fact there is no danger. What usually happens if you let the water get too low is that the steam pressure will drop, and then the blower will not be effective in maintaining the fire, so the system fails safe.

In addition I understand that it is quite difficult to design fusible plugs that will behave consistently as you want them to. So it is not such a simple matter as it seems.

Just looked at the current version of AMBSC, para 5.7 which states that a fusible plug SHALL be fitted and makes no concession for diameter, which means it is mandatory on all boilers. It also states the fusible material shall be commercially pure tin, I read this meaning solder with at least 99% tin (eg lead free solder) and leaded solder if you still have some not being allowed.

This week I had to repair a small leak around a Bush on my 5 inch gauge boiler. I hit it with a very large propane blowtorch, which sounded like a jet engine, to warm it up and then moved onto oxy acetylene and I was still struggling to get the area hot enough to melt the silver solder. So my question is how much hotter could a fire be? The copper is very good at dispersing heat, would it actually damage anything in the short term if it was dry?

Lets face it a train is unlikely to encounter a hill sufficent to uncover the crown for long enough to do damage or wake up the plug.

Road steam is another matter and over 3" models might be long enough to expose the crown on a hill, no doubt priming like crazy at the same time making the issue even worse.

All that said on a train it's fit and forget.

hmm... I'm not sure that I would agree with some of the comments here regarding how difficult it would be for a boiler to fail. Model boilers have failed in the past, IIRC one brand new boiler at my club was ruined due to the crown being exposed. The melting point of copper is just over 1000C, models have recorded higher temps than this in their firebox when measured properly. How often do you look into a well-fired model firebox and see how bright the colour is, this alone will give some idea of how hot it is in there, it can be hotter than the melting point of copper.

There are articles out there where model engineers have measured the heat in their firebox, I recall one where the firebox dimensions weren't that far off the size of my 5" pacific, this was fitted with an arch, temp taken from the arch was 2000-2300F which is easily above the copper melting point.

have a look at this chart next time you look inside a model firebox...it gives a good visual idea of how hot it is in our fireboxes. I'm sure that an 'orange' or even 'lemon' is not that unusual to see...

Pete

With respect Peter, it is not about melting copper, but melting the silver soldered joints the boiler is made with, around 700C should do the trick if held for a little time.

That said, I prefer not to have a fusible plug fitted, preferring to blank off the bush, since I have in the past had several plugs fail for no good reason.

Also in larger locos with fitted ashpans, the boiler has to be removed to replace the plug, bit annoying if the plug fails for no good reason.

Regards

Brian B

Sorry Brian, you are of course correct...I was getting a little carried away in trying to show how hot these things can get...

Pete

Forgot to add, thanks for sharing your own experience with fuseable plugs, Brian. Paul Tompkins did say to me that he wouldn't advise fitting a blank for the reasons you give.

Regards

Pete

Meant to say..'advise fitting a blank'...can't find edit?