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

[crueby]

Ooooohhhhh, okay!  I had not looked close enough at the plan cross section in the very first post, sorry!  Never seen that arrangement before, so I assumed it was the usual  burner-at-one-end-chimney-at-the-other style. So, as you say, not part of the pressure vessel, though it will take a direct hit from the burner flame coming through the lower pipe.   

 

[Jasonb]

regarding expansion, if we said the metals could get upto 500deg C which they are unlikely to then the difference in expansion across the diameter will be 0.21mm or 8thou. ( 0.83mm - 0.62mm ) so provided the "snug fit was eased a bit to sat 5thou all round then the aluminium won't apply any force to the boiler shell

copper boilers used to be caulked withsoft solder and that never melted out at 200deg C or less and is why 648 is OK and aluminium unlikely to melt.

[Vixen]

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

You need to be careful how you interpret that graph. That graph shows the flame temperature of propane/ air to be 1950*C and that has only recently been demonstrated to be hot enough to melt pure copper down tubes. It appears that the flame tube (if that is what it's called) is 2.25" diameter, so will do little to cool the flame. Therefore, I would be very concerned at the flame playing directly on the return end plate. The return path through the smaller boiler tubes will remove most of the heat and so reduce the flue gas temperature, so I am less concerned about the smoke box end.

Why make-do with what's in the scrap box? Why not work to MIL TBD41 standards?
For those who are not familiar with that standard, it stands for "Make It Like The Bl**dy Drawing For Once"

[Jasonb]

I can melt steel with my propane torch, just depends on how thin it is and the output of the burner and where you hold it in the flame.

Do we actually know what John is going to fire it with, Harris suggests the Stuart paraffin blowlamp, Flame temp of paraffin 1100degC

There are other variations from the drawing so would really need to start from scratch if sticking to them.

[simplyloco]

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

You need to be careful how you interpret that graph. That graph shows the flame temperature of propane/ air to be 1950*C and that has only recently been demonstrated to be hot enough to melt pure copper down tubes. It appears that the flame tube (if that is what it's called) is 2.25" diameter, so will do little to cool the flame. Therefore, I would be very concerned at the flame playing directly on the return end plate. The return path through the smaller boiler tubes will remove most of the heat and so reduce the flue gas temperature, so I am less concerned about the smoke box end.

Why make-do with what's in the scrap box? Why not work to MIL TBD41 standards?
For those who are not familiar with that standard, it stands for "Make It Like The Bl**dy Drawing For Once"

Hi Mike.
If there was a drawing available I would have probably attempted to make it to that.
However, in it's absence I did my own thing, as most competent model engineers would do. I will leave it as it is and see what happens in practice.
John

[Laurentic]

On a full size Scotch boiler the 'flame tube' is usually called the furnace, or furnace tube.  Originally Scotch boiler were coal fired so would have had a grate longitudinally ecxtending about 1/2 to 2/3rd down the furnace tube with a brick wall at the end, the hot gasses would then go over the wall to the end, which is called the reversal chamber, as the flue gasses then reverse direction and come back down to the front of the boiler to the smoke box and then up the chimney. 

When they were coal fired there was a sacificial fusible plug on the top of the furnace tube over coals.  If the water level was lost then the plug overheated, melted and the boiler water then poured through, put the fire out and prevented the furnace overheating from the coals, sagging down, fracturing and causing a boiler explosion, which would (and did) have killed anyone nearby and the boiler might well have ended up about 100 yards down the road, or a couple of fields away.  If you ever get to see a photo of a boiler explosion, it is quite horrifying, the energy released so suddeny is horrific, people were killed and the damage done to buildings exceedingly extensive, and, as I said, the boilers used to end up down the end of the street.  It was partly due to those occurances that 'proper' boilers in the UK are subject to statutory cold thorough inspections internally and externally every 14 months, or within that period, followed by a working inspection upon return to service when the safety valves were checked for blow-off at the correct pressure under steam and at full firing.  Why 14 months?  The statutory inspections all started when there were plenty of factories and mills in the UK, and they all used to shut down at Easter, and Easter being a movable feast 14 months covered it!

Later Scotch boilers were oil fired, a pressure jet flame being projected down the furnace tube.  Sometimes the brick wall in the furnace was retained, to slow the gasses down, sometimes not.  If the oil burners were changed to gas fired at a later date - and at one time when gas was a lot cheaper than oil a lot of various boilers were changed to gas firing, it was found that the gas flame burned with a far longer envelope than the oil flame, giving rise to the tube ends on the rear tubeplate burning away.  A solution, to avoid endless requirements for tube end repairs by welding each year and possible tube leaks before the year was up, was to fit ceramic protective rings in the tube ends.

In their day Scotch were a renowned, reliable and very respected boiler used extensively both on land and at sea

None of the above applies to the Scotch boiler in this thread thankfully, but just saying!  Provides a bit of background info to the model.   

Chris

[Laurentic]

Standard MIL TBD41 - Make It Like The Bloody Drawing For Once, - bit revolutionary that Mike, for us model engineers! 

Chris

[Jasonb]

I suppose if there was a bit of a worry about the flame heating the plate at the far end it would not be difficult to add a circular disc mounted on a central stand off to act as a baffle, something you see on model and full size firebox doors

I see that PM Research vertical boilers have a cast aluminum cone on the top to collect the flue gasses and direct them to the central chimney and that mounts very close to the top tube plate. Anyone read of reported problems with this arrangement?

[Jasonb]

Touching on the flame temperature again, I quite often see those new to silver soldering wanting to know what to use or why they end up with  a blob of solder rather than a nicely flowed joint. Many think that a MAP gas torch should do the job as they have read that MAP gas burns hotter than propane at 2700degC

Well it does but they miss the point that it is not the temp of the flame but the actual output of the burner that matters be that in watts or BTU. So their Map torch with maybe a 12 to 15mm burner dia will actually only be putting out 2 or 3 KW where as the usually suggested Sievert 28mm nozzle puts out about 7KW and therefore gets the job hot enough even though the flame temp is less.

[simplyloco]

Taking Jason's point about a baffle, it will be quite easy to mount a thin steel plate on the 3 mm stay that holds the two ends on. I'll just use a nut as a spacer between the plates. I'm confident that the alloy smoke box won't pose a problem, after all, it is 300 mm away from the burner and also 5 mm thick.
Potential problem solved!
John

[Jasonb]

I was thinking central to the furnace tube but a bigger disc central to the barrel would also work. Less than 3mm would do, I think my Fowler has 1mm thick or whatever that is in SWG. but depends what you have to hand, could always flatten that yarrow boiler top tube and cut one from that

EDIT that flattening of a tube made me think you could make the baffle slightly curved and then that would help return the gasses

[simplyloco]

SNIP

EDIT that flattening of a tube made me think you could make the baffle slightly curved and then that would help return the gasses

Agreed on the curve. I have plenty of alternative material.

[simplyloco]

Following some good advice I've fitted a stainless steel baffle plate to the big end cap, sandwiching some ceramic fibre insulation for good measure! It ain't gonna melt..
I've also done one side of the smoke box cladding. I'm torn between cap screws and slotted csk ones. I prefer the former...
The box is now so snug I'll have to relieve the outer tube to relax the chimney to get it vertical!
 
Fiddly stuff!

[simplyloco]

Cladding attached and up to steam in less than ten minutes!
It held 85psi without trouble. I'll take it further when I fit a proper water gauge.

[Vixen]

 

Congratulations!!!   Well done!!!  It's a steamer!!!

That's an impressive blow lamp firing it. Just as well you protected the far end plate.

Cheers   

Mike

 

[crueby]

Terrific!!

[steamer]

When they were working on reboilering "Sabino" some time back, The Almy boiler had tube headers that were 1 into 4 back into 1      It involved right and left hand pipe threads and was a real PITA to put together!

They built some test headers and could never get the tubes to seal....I can see why.........eventually they welded the headers in another configuration, Which didn't work so well.. and I'll avoid that conversation......

Later, we found out that Almy would build these headers, and hang them in the brackish salt water next to their factory so that they would "take up" with a bit of rust to seal them   

Now the boiler they took out was sched 80 through sched 120 construction. A real beast, and was built in 1942 IIRC.    So it lasted a good while......

How rust as a sealer compares to Loctite....well.   I'll let you decide on that.... 

[crueby]

That 1:4:1 arrangement is quite complex, but gave them a lot of surface area for heating. The relatively small top drum must have meant keeping a close eye on the water level and the feed pump?


for models, I'll stick with loctite and solder for sealing!

[steamer]

That 1:4:1 arrangement is quite complex, but gave them a lot of surface area for heating. The relatively small top drum must have meant keeping a close eye on the water level and the feed pump?


for models, I'll stick with loctite and solder for sealing!

Main drum was 14" sched 120   about 1.25 thick.....or there abouts....      55 gallons of water.....so a VERY fast steamer...

Dave

[simplyloco]

The water gauge has to 'hang out' the side, and as drawn it looks vulnerable. I made a rigid brass column and mounted the 5mm gauge on that. I used some salvaged pipe as I'd run out of nipples...
It will look better (and vertical) when I redo the pipes with new fittings!

[cnr6400]

 

[simplyloco]

A simple double coil superheater.

It's not pretty, as I got the handing wrong on drilling the shell holes and had to recoil it!
However, it won't be seen and it will do the job required of it!

I started planking the boiler shell today, the planks have a 7 degree bevel each side to close the gaps.  Great fun!

[simplyloco]

More planking!

This is the result of two hours concentration, getting the planks to fit each other and the various bushes. Not perfect, but it's only an old boiler...

[crueby]

Nice!  How are they held on? Glue, metal straps, ?

[simplyloco]

Nice!  How are they held on? Glue, metal straps, ?

Medium/high viscosity superglue in the first instance, but close fitting boiler bands will be fitted later.

[simplyloco]

Finished Planking the Boiler Shell.

I'm still waiting for the 150 psi pressure gauge and a globe valve for the steam fountain, and I need to tidy up the water gauge connections, and find some black high temp paint, but it looks nice enough and hopefully will pass muster alongside the Triple!
Well pleased.

[Laurentic]

Very good, nearly there!

The problem here, with me, is, you've now got me reading up K Harris's Model Boiler & BolierMaking book, and I have too much to do on IC engines stuff with not enough time at the moment as it is.

Chris

[Vixen]

John,
Your new boiler looks very smart. I love the contrast between the dark timber cladding and the brass bands. Waiting for the sights sounds and smells of it driving the triple

Mike

[Michael S.]

I congratulate. You quickly managed to create a beautiful boiler. The wood paneling looks very good.

Michael

[Kim]

You have really made short work of this project!  You must be taking a page from Chris's book and using some of those extra days, or living in his alternate time dimension or something.  It looks great! 

Kim

[cnr6400]

 

[simplyloco]

Pressure gauge and globe valves received, so it's ready and waiting for the Triple! Apart from a little soldering that is...

We are off to Spain in ten days time: we've rented an apartment in L'Albir, north of Benidorm, and we won't be back until mid May, so the Triple will have to wait. Goodness I need a break from this damned workshop!😱😇

Some pics.

[crueby]

Its all turned out beautiful!   Enjoy your trip!

[Kim]

Your boiler is simply gorgeous!   

Have fun on your vacation!

Kim

[simplyloco]

Testing for fittings and level of superheat. I haven't gone on holiday yet...😍

The boiler shell test is one thing, but they often leak at the fittings connections. This one was no exception, as one of the banjos wasn't seating squarely on the bush. The boiler now holds 75psi quite happily on the small propane burner and the safety valve works OK. Steam at this pressure is at a temperature of around 160 degrees C. Quite hot! However, once it is superheated...

Steam exit temperature was 274C settling to 217C after going through the double coil superheater. That's pretty dry steam! However, to sustain the output at this temperature I'll probably have to use the big burner and a very good boiler feed pump!
Well pleased.

[Laurentic]

The way that reads, the superheater took nearly 60 degC out of the steam - not sure its supposed to work like that!!  It never used to!!

Chris

[simplyloco]

The way that reads, the superheater took nearly 60 degC out of the steam - not sure its supposed to work like that!!  It never used to!!

Chris

Let me explain. When I first opened the steam valve the initial rush of steam was at 274C. Not surprising given the temp in the end space and no movement of steam. Then the constant stream was at the lower temperature, which was to be expected. Still 60 degrees above the wet steam temp so I read that as OK. Or am I being a numpty...?

[MJM460]

Hi John,
you are correct about the reason for the temperature dropping when the steam flow starts.

Of course, it is worth thinking about how to set a tiny flow to warm things up as the boiler heats, at the same time ensuring there is a small flow through the superheater to avoid that temperature extreme.  You don’t want to melt anything during warmup.

The scotch boiler looks great.

MJM460

[Laurentic]

Are, so, now I understand what you were saying!!!!

Chris