Belpaire Throatplate

[Deleted]

Hello folks,
Does anyone know of a Belpaire boiler design where the throatplate flange into the boiler is inside the barrel. This could potentially make the outer width of the boiler the same, or very close to, the width of the firebox wrapper. I can see various potential weaknesses of this, but wondered if any built examples existed, or at least drawings.
Many thanks, Dave

[Shawki Shlemon]

There is no problem with this idea except that the flange has to be wider as the tube ( barrel ) will not go over the radius of the flange . However it is possible to have the tube inside the flange as long as the belpaire fire box is larger than the dia of the barrel by 2x plate thickness of the wrapper , I have done that , I can't remember the engine . All it needs is to be patient when forming the throat plate and do as many annealing as required .Leave extra material on the sides as it shrinks , don't ask me why ? I don't know . don't ask me how I know !!!.

[Deleted]

Thanks for that Shawki.
I suppose as long as the throatplate flange is a bit longer to allow for the root of the bend and silver solder/brazing spelter is able to get a good penetration, this is going to provide the same support to the barrel from inside as it would if it was if the flange was around the tube.
Dave

[baggo]

Bryan (Brozier) did this for the throatplate on his Spencer boiler and it made a nice neat job.

homepage.ntlworld.com/bryan.rozier/Spencer/boiler_making/Boiler_Making3.html

The original design uses a plain throatplate with just a hole in it. The barrel has a joining strip in the end which passes through the throatplate and is then peened over inside, effectively forming an inside flange. It might actually be a bit easier to do it this way.

One thing you have to watch with the inside flange is clearance between the inside of the flange and the lowest tubes. In some designs the bottom tubes are quite close to the bottom of the barrel.

John

[GWRdriver]

I made such a throat plate for my current 2X Tich build. This boiler has a 6" diam barrel and by far the most time-consuming chore was the making of the flanging plates. I disagree that anything on a model is best because that's what full size has, but I agree that an inside fllange can be a bit more of a problem to solder than and outside flange. All one has to do though is provide additional entrance points for the solder.

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[Deleted]

That looks very tidy. Will the final finished level of the boiler and firebox wrapper be flush and will therefore also the finished level of the cleading, will that be flush from barrel to firebox?
Thanks
Dave

[GWRdriver]

Dave,
Yes. You may be able to see that the turned out ring becomes tangent and flush to the firebox flange at the top (nearest in the photo) and sides. The wrapper and barrel gauge are essentially the same resulting in a continuous outside surface (or very close to it.) I'm away from my home computer at the moment and I'll post more photos later.

[GWRdriver]

Former materials vary a bit from builder to builder, I have a local source for scrap steel plate which I prefer, but for this particular forming job everyone seems to use a similar approach. (I don't seem to be able to post more than one photo per measssage.)

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