The Home Machinist!

Here's the superheater assembly for my 1 inch scale loco. This is a very typical setup. The fittings are all made from copper and stainless steel, nothing is purchsed ready made. Everything is silver soldered together. The elements themselves are stainless steel and are tig welded at the fire box end. The tig welding is the only thing I did not do myself, I had this done professionally. Since installation, I have had to make a stainless steel shroud for the hot header to protect it from being blasted from the draft. You might benefit from purchasing the drawings for a similar size loco to see how a miniature copper boiler is built.
David

Conventional, . . not standard.
"Conventional" would be a fabricated manifold from which pairs of superheater tubes (in and back) would be connected. There would be a different manifold/superheater tube arrangement for every different locomotive design. There would be many superheater assemblies which would be typical, or similar, in detail (ie, conventional) but between different loco designs and builders virtually none would be identical.

I wrote this before seeing David's post and his photos describe the process very well. As he mentions, the inside of a smokebox can be a brutal environment. Things have to be very well made in order to survive there.

Hi Builder01, gwrdrive,

Thanks, this is what I envisaged more or less, did wonder whether the superheater pipes were in series or parallel. I do have drawings, but I wonder about the superheaters being in parallel, now I have had a chance to think about it and see your pictures I understand parallel will be fine.

I do like to do things to the best I can, so I will always think about making it that way.

Pictures say a 1000 words! Thanks.

Ian

Hi,

Below is a picture of the proposed tubes for my boiler. The tubes maybe slightly smaller than some night recommend.
The small tubes are 7/16 OD and the superheater flues are 7/8 OD, the boiler barrel is 5 1/2 inch. I have considered a few different designs form different plans. These tube sizes are used on an almost identical boiler size to mine. Also maybe some tubes are to close to the bottom of the boiler.
There is at least 1/8 space between tubes. Since I have no practical experience in running a steam locomotive, I do wonder what is practical.

Ian

Ian,
The 7/8" tubes should be adequate.
What is your flue length, measure from inside head to head?

Under the heading of "Making More Work for Myself" . . . I've considered trying concentric superheater elements, that is, where the supply line runs inside the return line. The elements would be relatively easy to do, but this would require a manifold design which would collect steam off the perimeters of the return tubes. Doable, I think, with a clever design and deft silver-soldering.

Do you have a source of 7/16" tube? I don't recall ever seeing it. Even if you can find it, 1/2" OD is probably going to be less expensive.

To make more work..... I removed the out and return shtr assembly on my Nigel and for fun made a concentric one. After about 5 or 6 weekends, passenger hauling over about 80 miles I took it out and refitted the original shtr. No empirical data to prove that it wasn't as good but just didn't feel as good when you needed that little bit extra.
Only thing in favour of a concentric is that it's dead easy to make.

Hi,

Thanks for the feedback

gwrdriver: The flue length is approx 15 1/2".

Marty: yes 7/16 is available, not locally probably, but then not much is available locally, I can by it internationally. Supply of any material will be a challenge because of the small quantities. I will probably try scrounging at a local machine shops my work place uses.

super7b: you are running a Nigel Gresely? This is so similar to the BR55 in almost every way, how she run? strong runner? what gauge is she (5")?

Took me a little while to understand the concentric superheater, but I get it now after reading it a few times.

Ian

datman wrote: ↑Thu Feb 27, 2020 2:45 pm gwrdriver: The flue length is approx 15 1/2".

Ian,
Using the formula for flue length to diameter, your flues will be optimized at .488" ID.

gwrdriver wrote: ↑Thu Feb 27, 2020 3:34 pm

datman wrote: ↑Thu Feb 27, 2020 2:45 pm gwrdriver: The flue length is approx 15 1/2".

Ian,
Using the formula for flue length to diameter, your flues will be optimized at .488" ID.

gwrdriver,

Thanks, I had considered 1/2 tubes but at this size I cannot get such a good nest of tubes.

Ian

Understood.
For a reference, an ID of .455" would put you at the lower limit of the "optimal" range but still workable.
I'm using the formula for optimal flue diameter to length ratio D²=L/50-75, where D=tube ID, L=heated length, and 50-75 is a numerical range between which you will optimize the balance between gas flow and heat absorption. The problem (if you can call it a problem) is your flue length is proportionately over-long relative to barrel diameter and that asks for larger flue diameter with no increase in nest area.

Check your NET area to see if you get the necessary flue to grate area ratio. I'm not so familiar with that relationship as I am the flue L&D, but that ratio needs to be considered.

super7b: you are running a Nigel Gresley? This is so similar to the BR55 in almost every way, how she run? strong runner? what gauge is she (5")?

I've run it for years on ground level continuous tracks and a portable track as well. Normally do 3 to 4 hours at a weekend on a 1.2 km track. Portable track 150mtrs long, up and down for around 7 hours, my back gives up before the loco.

It is 5" gauge, reliable, ultra reliable, very forgiving and yes, she feels strong. Had odd occasional problems with suddenly becoming shy of steam, found that the bottom row of tubes had blocked, rodded out and carried on. After a couple of times, fitted a stainless front to the grate to deflect the fire up and over and get a better spread of gases through all the tubes. never blocked since.
Boiler was built to Martin Evans' except I reduced the number of tubes to 14.

Not much more that I can say.