A SCOTCH MARINE BOILER FOR MY TRIPLE EXPANSION ENGINE

[simplyloco]

A SCOTCH MARINE BOILER FOR MY TRIPLE EXPANSION ENGINE #1

I constructed this boiler several years ago, intending it for a large model steam launch. On shell testing it at the time it held 100 psi but not more due to two tiny stay end leaks. I wanted at least 150, so I discarded it and got on with something else!
However, circumstances have changed, i.e. I'm too lazy to make another boiler, so I dragged this one out of retirement and fixed the little leaks by the judicial application of Loctite 648 drawn into the warmed boiler by my trusty workshop vacuum cleaner! It now holds nearly 200 psi so it's quite safe to run at 125 psi. I'll put a big superheater coil at the rear. You will note that this boiler has thicker tubes...😉

[crueby]

Never would have thought to try the 648, but it says its operating  temperature  range is up to 355F so as long as its not in the way of direct flame from the burner thats okay. Have you run a boiler with that before?

[simplyloco]

Never would have thought to try the 648, but it says its operating  temperature  range is up to 355F so as long as its not in the way of direct flame from the burner thats okay. Have you run a boiler with that before?

Not personally, but I know of one case where the 648 was applied to a superheated 5" loco and it is still running several years later!
John

[baz]

I can confirm the efficacy of Loctite 648 on a boiler, I know of a 2 inch traction engine that had a leak around the fire hole, an application of 648 cured it and has never given any trouble in the last twenty years.

[simplyloco]

End Cap and Smoke Box.

I've been busy today...😍

End cap from 1/4" alloy plate. It was rebated to a snug fit. I'll use the hole for a 3mm stay. It will hold the two ends together.

I just have to clad the sides of the box and the thing is finished apart from the water gauge and super heater.😍

[Vixen]

End Cap and Smoke Box.

I've been busy today...😍

End cap from 1/4" alloy plate. It was rebated to a snug fit. I'll use the hole for a 3mm stay. It will hold the two ends together.

I just have to clad the sides of the box and the thing is finished apart from the water gauge and super heater.😍

Would that be a alloy steel or an aluminium alloy? Aluminium alloys have a melting point between 500*c  and 600*C which is roughly 1/3 the temperature of a propane burner flame. So I assume you are using an alloy steel for the end cap and smoke box. I would have thought copper or mild steel would have been adequate.

[simplyloco]

End Cap and Smoke Box.

I've been busy today...😍

End cap from 1/4" alloy plate. It was rebated to a snug fit. I'll use the hole for a 3mm stay. It will hold the two ends together.

I just have to clad the sides of the box and the thing is finished apart from the water gauge and super heater.😍

Would that be a steel alloy or an aluminium alloy? Aluminium alloys have a melting point between 500*c  and 600*C which is roughly 1/3 the temperature of a propane burner flame. So I assume you are using an alloy steel for the end cap and smoke box. I would have thought copper or mild steel would have been adequate.

Hi Mike
Thanks for that. It didn't even cross my mind. I just had the material lying around and it would be easier to hang the cladding on the plate edges.
I could clad them with the foil backed 6mm ceramic fibre I have and see what happens!

[crueby]

Mixing metals on the boiler shell? Not sure thats a good idea, differnt coefficients  of expansion, electrolysis  effects, etc.

[Jasonb]

Plenty of model traction engines running around with aluminium chimneys that would see hot flue gasses

Would the gas burners flame even reach as far as the blanking plate on the return end?

If you are running off a propane/butane mix then the flame could be  cooler than pure propane

[crueby]

Plenty of model traction engines running around with aluminium chimneys that would see hot flue gasses

Would the gas burners flame even reach as far as the blanking plate on the return end?

If you are running off a propane/butane mix then the flame will be a lot cooler than pure propane

The first picture appeared to show a steel or aluminum (I couldnt tell) end plate on the end of the shell itself, not on the end of the smokebox? That doesn't seem like a good idea to me since it would be taking direct pressure from the boiler, expanding/contracting differently than the copper shell and tube.

[Jasonb]

Yes I took it a sAluminium at both ends, and agree that too snug a fit may cause problems with expansion and depending on the amount of use  galvanic attack could be an issue.

But regarding heat the plates are a bit like the 648 will they see direct heat ?and if so what flame temperature and more importantly material temp, a typical air/propane torch may only give 750degC temp in the components and that is with the flame directly applied

[crueby]

Yes I took it a sAluminium at both ends, and agree that too snug a fit may cause problems with expansion and depending on the amount of use  galvanic attack could be an issue.

But regarding heat the plates are a bit like the 648 will they see direct heat ?and if so what flame temperature and more importantly material temp, a typical air/propane torch may only give 750degC temp in the components and that is with the flame directly applied

I'm not as concerned about melting as much as cracking around the solder from the different expansions as it heats/cools. I'm no expert on it, just never seen those metals mixed in a boiler before. Usually see all copper, or all steel, that sort of thing. Would it meet code anywhere? Just passing a single static test would not convince me. As I say, I'm no expert on this, just concerned!

[Jasonb]

As it's not part of the pressure vessel I don't think it would come under code.

It is also a fair way from the tube plate so unlikely to affect the joint

[crueby]

But thats my point, in the first picture in Reply 5 it sure looks like its the end cap at the burner end, part of the pressure vessel, NOT the smokebox end where its just a cover. If I'm wrong on that, ignore the concern since the smokebox door is not structural. But, if its the other end, then it most defintely is pressurized. 

[Jasonb]

Flame goes in the end where the tube plate is nearest the end of the main tube, the deeper "void" at the other end being closed with the plate is where it changes direction and returns through the smaller tubes and is collected in the angled smoke box and up the brass chimney

The copper endplates form the pressure vessle the aluminium is not under any pressure just stopping the flue gasses going straight out the opposite end to the burner and then directing the returned gas up the chimney