Superheaters in the Firebox

Hi Chaps.

I'm part way through getting a boiler built for my 5" GWR KIng and intend to have superheaters made to run in the firebox. The question is how far to extend them. On a King the firebox is narrow but rather long (firebars are 3" x 10" approx).

Clearly there needs to be a degree of intrusion into the firespace but to make them run almost to the firedoor would be a rather long unsupported length. Could any of you voice an opinion on this please. I'm sure there are many more expirienced heads than mine on this particular question.

Best regards Martin

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If firebox is about 10 inches long why not make them protrude about 5 inches?

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I've seen some designs with a shelf silver soldered to the inside of the firebox backplate so the superheater block bend can sit on it. As long as it doesn't stick out too far it shouldn't get too hot, copper is a very good conductor, especially if you made it a square lump rather than angle

That's one idea Duncan. Thanks.

I'd still like to hear what others have done.

regards Martin

Some pictures of the progress in my Album. Here is a sample.

The 5/16 stainless 316 elements in my Springbok go to the back of the firebox. They have TIG welded spear point joins. I'm pretty sure taking them to the back is standard. No need for support.

Simon is quite correct with stainless radiant elements. Though you provide no mention of cylinder and piston valve material, and design.

Seems to me your 5"g GWR King boiler is of rather novel construction. I hope your club boiler inspector is happy with it all. It is a very complicated boiler to make.

Cheers,

Julian

Julian Atkins - I know you are very knowledgeable about steam models. However it would do you credit to dispense with the passive aggressive overtones ie "novel construction" and "I hope your club boiler inspector is happy with it".

That's Mr Kyte's business, isn't it?

If the TIG welding on the firebox is what you are having issues with, TIG welded copper boilers have been well proven and are here to stay. Get used to it.

Gosh, English is wonderful confusing! I didn't read Julian's comment as passive aggressive at all. I only picked up a gentle reminder that club Boiler Inspectors are famously nervous of new designs. (This because their job is about getting insurance for public running rather than encouraging innovation.)

Always hard to get new ideas accepted, and it's worth being aware of the extra bother before putting effort into a big job like a boiler.

Dave

Hi Chaps.

The boiler is being constructed by Steam Technology down in Kent. They have been at the previous 2 Doncaster shows. Talking to Ryan last week they started building copper welded boilers well over 10 years ago and it is true that initially at least some club boiler inspectors didn't quite know what to make of them. As a commercial build it comes certificated.

As to cylinder and piston material they are in Cast Iron.

On the Perrier design the centre of the superheater tubes is level with the top of the firehole ring so going right to the back would obscure the firehole to some extent so the superheaters are going to have to stop at least an inch shy of the end.

There must come a point where any additional length of superheater tube in the firebox ceases to add to the degree of superheat so I was wondering if people had a feel for that.

As mentioned the firebox is 10 inches long so even if they stopped 2 inches short of the back would give an out and return length of 16 inches which is a fair lenth of tube to acheive reasonable thermal equilibrium but maybe someone has done some sums.

regards Martin

you could experiment with a couple of bits of tube to see if you could have a slight bend to lift the superheater pipes above the firedoor.

I very much doubt that there is some sensible limit to length which does not result in more superheat. Martin Johnson's series of articles in ME were most enlightening, perhaps contact him? If you think about it, all 5"g narrow firebox locos have about the same width, so doubling the grate area means doubling the length, It also means doubling the steam production, so doubling the length of the superheaters seems sensible

Don't suppose you know what issues that series were in (approx). I'll have a read.

regards Martin

started 13 april 2018, 6 parts up to 14 sept 2018. If you can't lay hands on paper copy send me a pm with your email and I'll send scans

Hi Martin,

You deserve a fuller reply from me in response to Jeff Dayman's post.

My own 3.5"g GWR King to the Jackson design required new superheaters, and the LBSC type will be replaced with stainless elements extending the full length of the firebox. It will also have a redesigned smokebox draughting kindly done for me by Jos Koopmans.

(If the Perrier drawings follow the GWR drawings for the original single chimney design they will be deficient, or at least not ideal).

The GWR King boiler is an elegant thing and very nuanced and complicated.

A simple butt welded joint to the throatplate and barrel will IMHO reduce water circulation at quite a vital point, and the butt welded joints elsewhere will rob the boiler of it's external appearance, unless well covered up by the cleading.

I am assuming the tubes, being TIG welded on your boiler, are thicker than normal? A recent Commercial boiler on the modeleng proboards site (for Don Young's 'Doncaster' ) has some TIG welded joints but the tubes are silver soldered in. It looks the part, and is clearly extremely well made.

If you have cast iron cylinders etc and piston valve liners and piston valves with cast iron rings, you won't have any problem with full length radiant superheaters in the firebox, and I have no hesitation in fitting them as such to my own 3.5"g example with cast gunmetal cylinders and slide valves.

Quite a few club boiler inspectors haven't a clue how to deal with a TIG welded copper boiler, or for that matter steel welded boilers. Quite a few haven't a clue how to deal with all silver soldered copper boilers.

Cheers,

Julian

Edited By julian atkins on 25/06/2019 23:29:15

Edited By julian atkins on 25/06/2019 23:29:54

Thanks Duncan. Down loaded the articles from the archive.

My gut feeling so far is 2 inches shy of the back of the firebox in order to preseve clearance for the firehole.

The original design called for non radiant superheater elements so this has to be an improvement not least beacause it will improve gas flow into the superheater tubes by not having the end blocks clogging up the space just the two tubes of the elements.

regards Martin

Whilst I could be the first to say that Julian Atkins is a far more experienced Model Engineer than myself, I still think I am experienced enough to spot a criticism that is not worth noting. After all, I didn't start the hobby until 1972. I note that what he says has many valid points but why does he have to either finish what he says or within his words, by "slanging someone off.". In his last write up he starts on the Boiler Testers. I think this is wrong. None of our Societies would function without these people that give their time up to help the rest of the Societies members. I have heard him call LBSC, MARTIN EVANS, DON YOUNG and many more, including an esteemed deceased friend of mine GORDON SMITH. Where would the hobby be without these sort of people in the past.Would the hobby be in the same place as it is know with all the knowledge that has been written down in our many books an magazines etc.The person that has not made a mistake yet has not been born yet but why call people like these down so that the rest of the world knows about it. I know its helpful to point a mistake out but lets do it via some other means, other than this forum. Back to the Boiler Testers. I have a lot of friends within the hobby of witch a lot are boiler testers. I WOULD TRUST ANY BOILER THAT'S BEEN MADE BY MEMBERS OR PROFESSIONALLY IN THEIR HANDS. Indeed our Societies inspectors are". very on top of the job" whether it be hydraulic, steam test or checking the silver soldering during the construction stage. If as he says" Some havn't got a clue", surely that is up to the Societies governing body,who must have agreed to them filling the position, to find someone else that can do the job.. I do not think that our Societies fill the boiler testers positions with idiots or people that don't know what to do. The boiler test code books are mainly easy to follow and in for our Society, Allan Reid of the NAME is always easy to get hold of.

So to finish off, is it right to call people down within this forum?.

Keith,

Of course you are right but I like to see Julian's contributions. Yes they can be a bit blunt at times but it is absolutely clear that he has more than a rough idea how to build and operate live steam locomotives. I have not yet completed 1 steam locomotive and I would be more than happy to receive comments from him.

As for the designers you have listed, I know myself (as an ex designer) that any designer who can't take a bit of criticism isn't worth much. They would probably agree with half the comments made against their designs.

Phil H

Keith,

Is this really contentious? Perhaps you and Julian aren't quite on the same page:

Julian said: 'Quite a few club boiler inspectors haven't a clue how to deal with a TIG welded copper boiler, or for that matter steel welded boilers. Quite a few haven't a clue how to deal with all silver soldered copper boilers.'

And you said: 'I do not think that our Societies fill the boiler testers positions with idiots or people that don't know what to do. The boiler test code books are mainly easy to follow and in for our Society, Allan Reid of the NAME is always easy to get hold of.'

Surely both statements are true? My understanding is that Club Inspectors are limited by experience and boiler codes to a take a conservative stance on boilers. Copper boilers made to a proven design are relatively straightforward to make and inspect, so few problems with them.

A steel-welded boiler is a very different proposition. Probably not something a semi-skilled amateur should tackle, and difficult to assess without suitable equipment and suitable welding qualifications and experience.

It's when someone develops a boiler of unusual design, materials, or construction, that trouble starts. Whatever the boiler's merits, and they could be substantial, it's likely that the boiler is outside Code and the Inspectors experience. This undoubtedly makes life difficult for innovators, and perhaps societies should be doing more for adventurous builders. As it is, anyone wanting a certificated modern boiler has to go the professional route. Not because Boiler Inspectors are idiots - they can only do what they know.

I don't think Julian's comments on loco-designers are misjudged either. They all dropped the ball at least once! LBSC deservedly has many fans but he was a living breathing human being with all the usual faults. I find over a long career his work ranged from brilliant to half-baked. I'm sure everybody who has ever made anything is more-or-less flawed, and the basis of progress can only be criticism.

Dave