5"Britannia brick arch

[peterdanastas]

I am building a 5" britannia to Doug Hewsen design and he has the superheater tubes going back into the fire box which will probably need a brick arch in fire box . If the superheater tubes where only inside the fire tubes [not sticking into fire box]will there be any need for a brick arch in fire box

[oldnorton]

Superheaters only really work if they are exposed to the radiant heat above the fire. Evidence is that there are no failure problems if they are welded stainless. Even better are Doug's design of small tubes bent at the end for a return.

A brick fire arch would be super realistic! but possibly more trouble than it is worth. I think that in full size the arch was for more efficient combustion of the volatiles. Might pay off if you wanted to win IMLEC I guess :-)

Norm

[jo479]

I always thought that Superheaters that didn't go through into the firebox, were just blocking the tubes and maybe drying the steam a bit (only my opinion, before everybody jumps on me)

[flyingfox]

greetings jo479,

You will learn that one of the biggest discussions in Miniature locomotive building are Superheaters V no superheaters and radiant type v non radiant type.

Volumes have been written about the merits of each type, and their effectiveness.

regards
Brian B

[jo479]

I have built 4 engines complete, and bought 2 engines which I reboilered and overhauled one of which was a 5"G 4-6-0, which when I bought it had 4 superheaters that were knackered, the new boiler I made had the flue tubes etc, but I never fitted Superheaters, steams like a witch with the firehole door half open. I used Martin Evans B1 design only 3" longer and 1/2" narrower, all the "experts said I couldn't increase the length of the tubes without increasing the diameter, but I did and it steams very well, the 4 flue tubes are still there without the superheaters fitted in case I decided to fit them, but no need. I do realise that to enter the likes of IMLEC, superheaters would probably be an asset, but most of the time we're only shunting 1 lap with passengers, stop at station, repeat etc, my other engines have superheaters, probably needed on the 3 1/2" G engines more the the bigger engines, cat amongst the pigeons time.

[lesstoneuk]

Not trying to put the cat amongst the pigeons but would a thermic syphon be more efficient than protruding superheaters.

[miken]

The 4x homemade 316L welded stainless steel radiant superheaters that go all the way to the back of the firebox on one of my locos have been in regular use for about 30 years now with no problems.
However,
Ironically, they failed at the smoke box, header end after a mere 27 years. When the silver soldering gave up.
This is probably because I used the wrong flux. I made the mistake of using ordinary easy flow flux with no.3 solder.
I didn't know at the time that you are supposed to use a different flux when soldering stainless steel which accounts for the premature failure.
I have now rebuilt the superheater assembly using the same old superheater units but using the correct flux, so hopefully they will be good for a few more years.

[uuu]

Feb 14, 2023 5:57:14 GMT lesstoneuk said:

Not trying to put the cat amongst the pigeons but would a thermic syphon be more efficient than protruding superheaters.

This could certainly improve the boiler, but won't achieve the result we're looking for. We could get more steam from them - but still at the same pressure and temperature determined by the setting of the safety valves. So each cylinder-full of steam will be the same as before.

The superheater will take that steam and raise it's temperature (so you get more energy in a cylinder-full), which it can only do once it's out of contact with the mass of boiling water. This will also expand the steam, so it goes further.

Wilf

[dhamblin]

Thinking about this further the LBSC boiler design of combustion chamber with water tubes is probably great for producing lots of saturated steam, but in efficiency terms relatively poor as the superheater elements don't extend past the firebox tubeplate. A standard combustion chamber or none at all would provide more flexibility for experimenting with ways to improve efficiency.

Regards,

Dan

[Jim]

Feb 14, 2023 5:57:14 GMT lesstoneuk said:

Not trying to put the cat amongst the pigeons but would a thermic syphon be more efficient than protruding superheaters.

A thermic syphon is a requirement out here if using a Briggs Steel Boiler such as the one I have on my Burrell. The purpose is to ensure the circulation of water over the top of the crown as the sides are solid with no water space hence the need for fire bricks to protect the sides of the fire box. The syphons are not superheaters.

Regards Jim

[stevep]

Feb 14, 2023 5:57:14 GMT lesstoneuk said:

Not trying to put the cat amongst the pigeons but would a thermic syphon be more efficient than protruding superheaters.

They do completely different functions.

A thermic syphon increases water movement in the boiler.

A superheater makes the steam hotter so that the engine can use the expansive properties of steam more efficiently.

[ejparrott]

Superheaters all the way to the door plate is the correct way to do it. In 5" a brick arch is an unnecessary complication

[JonL]

I know I sound like a broken record but the difference between my copper non-radiant superheaters and my stainless superheaters was nothing short of astonishing. I can be more efficient with my use of the reverser and as a result steaming has become easier. For my Britannia (a 3.5" gauge, almost complete) I've got four stainless darts all the way to the firebox door. I'll let you know how that goes, although I don't have a benchmark to test it against.