scotch marine boiler

[Russell FurzerParticipant @russellfurzer50760]

I am drawing a 4" scotch boiler for gas firing. (1.25 furnace flue, no Galloway tubes, dryback, single return). Probably a "poker" burner vs a blowlamp with a "v" of stainless mesh.

I am trying to work out the best number and size of tubes.

KN Harris has 28 5/16 tubes in his 5" boiler.

When I draw sketches using a 4mm "ligament", I can fit 15 3/8 tubes or 22 5/16 tubes, leaving the top 1/3 of the boiler without tubes.

The factors that I am interested in include:-

1. How much difference does the area of the tubes actually make? I can see plenty of internet-land builds with a couple of large return flues. Also "they" say that in locos 80% of the heat transfer happens in the firebox.

2. How much space should be left above the top row?

3. will loads of tubes make assembly a bridge-too-far?

As for the engine, I have a stuart Sirius that will take all the steam that I can give it – certainly more than this boiler will make. Nice to see it going tho (school project from 1985), I also have a 10V underway (to get my hand back in), and a set of OBB triple castings for later.

I already have a length of 4" 14G tube so that sets the dia and the pressure (85psi).

[Russell FurzerParticipant @russellfurzer50760]

[Ady1Participant @ady1]

ET Westbury has a couple of articles in 2510 2512 and 2514

[Russell FurzerParticipant @russellfurzer50760]

Ok thanks

Ill try to dig those ones up from the library. Pity that all of them aren't on the archive!

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Hi, i has Scotch boiler. Then i can tell you: With large diameter in flue tubes will have larger heat surface. With calloway pipe in furnace will improve the effect of boiler.

To example the boiler 100 mm diameter and 160 mm length and the boiler is fired with blow lamp:

Boiler #1

Furnace: 35 mm diameter x 1 furnace

calloway: 10 mm x 7 tubes

Flue tube: 10 mm x 12 tubes

Total heat of surface: 0,856 m2

Boiler #2

Furnace: 35 mm diameter x 1 furnace

Calloway: 10 mm x 7 tubes

Flue tubes: 15 mm x 8 tubes

Total heat of surface: 0,856 m2

In case: flue tube: 15 mm x 12 tubes will give total heat of surface at 1158 m2

Best to calculate the heat of surface first before you are planning to make the boiler. Also larger heat of surface will give more steam and short boiling time from cold water to full steam pressure. Prevent to use too thick wall tickness in flue pipe and furnace due loss of heat. I am using 1 mm wall tickness in flue and furnace while the boiler 2,5 mm thick. Insulate the boiler to keep boiler heat enough to produce more steam.

I will recommend you to buy the book "Model boilers and boiler making" by K. N. Harris, there is a lot of information about boiler and how to design and make the boiler.

[Russell FurzerParticipant @russellfurzer50760]

Thanks Jens.

ive got KNH's book . I am comparing his design, for a 127mm dia boiler with 28x 8mm tubes.

for my 100mm design, I can fit 15 x 10mm tubes or 17x 8mm tubes up to 65% of the height. I could fit another 7x 8mm or 5x 10mm if I went another row but then the steam space would be less and the soldering more!

i plan to use a 32mm furnace because that suits the local rules better.

what about 2x 25 mm furnaces? Is there a downside?

[Ady1Participant @ady1]

Flash boiler details aren't that common, even in ME. There's a chap called Windy who drops in here from time to time who does some serious flash boiler hydroplane work

He still seems to be about

 

 

Edited By Ady1 on 01/04/2014 11:11:28

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Posted by Russell Furzer on 01/04/2014 09:17:33:

Thanks Jens.

ive got KNH's book . I am comparing his design, for a 127mm dia boiler with 28x 8mm tubes.

for my 100mm design, I can fit 15 x 10mm tubes or 17x 8mm tubes up to 65% of the height. I could fit another 7x 8mm or 5x 10mm if I went another row but then the steam space would be less and the soldering more!

i plan to use a 32mm furnace because that suits the local rules better.

what about 2x 25 mm furnaces? Is there a downside?

Russel..

You can use waterpump to keep water level in the boiler if you has not much water in the boiler.

I has a boiler with 2 furnaces 35 mm with 10 mm 7 calloway. Really fast steamer!

25 mm double furnaces is too little for a boiler with 127 mm diameter . Better 37 mm dia. furnace + a lot of calloway tubes without flue tubes or 32 mm dia. furnace + a lot of calloway tubes + flue tube.

Edited By Jens Eirik Skogstad on 01/04/2014 17:56:30

[Russell FurzerParticipant @russellfurzer50760]

Thanks again Jens.

my boiler is 100mm not 127- that is the design in KNH's book. Mine is smaller.

are your burners blow-lamp type? I plan to use "poker" type.

furthermore, there seems to be no consensus about acceptable water levels and steam space. KNH's scotch has the WL one tube row above half-way but his 'inglis' has two more rows and the WL about 75%.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

My scotch boiler is fired with blow lamp. My bolier 105 mm x 190 mm long dia. has double furnace 35 mm and 10 mm x 10 calloway in each furnace + flue tubes 12 mm x 12 tubes. Boiler is a "dry back" type due practical to repair if leakage is occured.  When the boiler got heated by blow lamps and it came weak heat out of chimney without burning my hand when i hold the hand over chimney. Mostly of heat is taken up though flue tubes. It means the boiler is effective to produce steam. The steam engine is a Stuart triple steam engine.

There is two alternatives: "Poke" type burner or ceramic burner.

And my vertical multi tubular boiler has ceramic burner, works very well.

Are your scotch boiler wet or dry back boiler?

 

Edited By Jens Eirik Skogstad on 02/04/2014 06:06:50

[Russell FurzerParticipant @russellfurzer50760]

Great Jens,

similar size to my plan. I have 100mm tube and imagined 200mm long.

my sketches can't seem to fit as many 12mm tubes over a 32mm furnace as you have managed.

What is the spacing between tubes and how much space is there above the tubes?

would you be prepared to let me see your sketches (perhaps by a private message if you don't want to post them?)

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

I used the Turbocad when i measured and placed the tubes before i maked the boiler. It is practical to use Turbocad or Autocad when you are planning to make the boiler where you can try and fail to place the tubes in the boiler in case it is possible or impossible to have a lot of flue tube/furnaces.

Edited By Jens Eirik Skogstad on 02/04/2014 19:15:03

[Russell FurzerParticipant @russellfurzer50760]

Thanks for the pic Jens.

I see that you have your WL about 75% of the way up.

How much do think the galloways help?- I am worried that they will limit me to a blow-torch burner and will add to the complexity of the build (especially if they leak!)

And- what was your order of assembly – obviously the galloways go in the furnaces first (and then did you test them?). Did you then solder in the flue tubes and furnaces to the endplates, then solder that assembly; or solder on one endplate, then the tubes to that end, then the other end; or solder in both end plates then the flues?

Did you use just one type of solder, or different melting points for different steps?

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

No problem with leakage in calloways if you are careful to silversolder the calloways in the furnace. First expanding the calloway tube if the calloway tube is too loose in the hole in the furnace before silversoldering. After soldering is tone, take leakage test with waterpressure to be sure it is tight around calloways/furnace before assembly with the parts of scotch boiler and then silversoldering + boiler test with pressure of water. Best to use difference melting points to be sure the solder is not melting in the calloways when soldering the boiler.

I did with calloways placed as a spiral form inside the furnace to distibute the heat oveall in the calloways. Works very well.

[Russell FurzerParticipant @russellfurzer50760]

Thanks Jens

I now have a better understanding of some of the issues!

Russ

Edited By Russell Furzer on 04/04/2014 00:58:02

[JAParticipant @ja]

Russell

Have you seen the recent publication "Building Small Boilers for Gas Firing" by Alex Weiss? Although his horizontal boilers are smaller than your boiler he does go into the construction sequence with good photographs.

I am about to start making a 4" vertical boiler to his design and although the details he gives are very comprehensive I still have a few questions (all part of the learning process).

JA

[Russell FurzerParticipant @russellfurzer50760]

Thanks JA

ive googled that- a bit exxy to get to australia. I'll put the dosh toward a 3525 cyclone burner!

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