Galloway Tubes

This topic has 23 replies, 10 voices, and was last updated 6 February 2026 at 08:54 by matthewwatts.

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27 January 2026 at 10:54 #834463
Colin Teasdale
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@colinteasdale
Thinking of building a small vertical boiler that would have Galloway Tubes in the central flue tube. I think the Galloways would be angled upward, from firebox to smoke box, but what kind of angle – would 5 degrees do?
Advert

27 January 2026 at 11:36 #834471
bernard towers
Participant
@bernardtowers37738
Are they what are commonly known as cross tubes? if so they need an angle to promote thermal flow.
27 January 2026 at 13:54 #834522
Colin Teasdale
Participant
@colinteasdale
Cross tubes? Quite likely.

Agreed that they would operate best if angled, the question was what angle?
27 January 2026 at 14:48 #834533
Charles Lamont
Participant
@charleslamont71117
The tilt angle of a cross tube will not do much for thermosyphon circulation initially, but once ebullition takes place in the tube, the tilt will give the steam bubbles a definite direction of flow. A large tilt would make it more complicated to arrange and fit the tubes.

I think Galloway tubes are tapered and are placed vertically in a horizontal flue, so probably not the right nomenclature in a vertical boiler.
27 January 2026 at 14:54 #834541
duncan webster 1
Participant
@duncanwebster1
Details of full size Sentinel boiler here Sentinel

Trying to get 2 sets atv90 degrees without them colliding would makd my head hurt
28 January 2026 at 12:01 #834671
Howard Lewis
Participant
@howardlewis46836
The Sentinel boiler was very efficient. If you can replicate that in miniature, you should have a good steam raising facility (within the limitations of its physical size)

Howard
28 January 2026 at 16:11 #834690
bernard towers
Participant
@bernardtowers37738
Just looked at Duncan’s link and methinks that would be an interesting challenge.
28 January 2026 at 16:20 #834695
JasonB
Moderator
@jasonb
Haining’s sentinel boiler has the same sort of arrangement but rather than the tubes being 3 wide he just has the one going round to make up the square.

Harris also shows cross tubes at a slight angle on one of his vertical boilers.
29 January 2026 at 10:32 #834779
Colin Teasdale
Participant
@colinteasdale
So to summarize:

What I referred to are properly called cross-tubes, not Galloway Tubes, which are a different beast entirely;

Installing cross-tubes at a slight upwards angle is ‘a good thing’, but probably won’t have a massive effect;

”a slight upwards angle” remains undefined!
29 January 2026 at 10:52 #834784
JasonB
Moderator
@jasonb
Haining mentions 2.5deg on one version of his Caradoc boiler, his Merryweather has them at just over 5deg and Harris ones look to be at about 5degrees.
29 January 2026 at 13:45 #834810
Colin Teasdale
Participant
@colinteasdale
Thanks for that, Jason.
29 January 2026 at 18:19 #834854
John Purdy
Participant
@johnpurdy78347
The angle of the cross tubes in Tubal Cain’s small vertical boiler isn’t stated specifically but appear to be inclined at about 5 degrees. He specifies the position in the drawing of the inner firebox. I have built this boiler and it steams very well.

John
29 January 2026 at 19:59 #834869
Bazyle
Participant
@bazyle
I think Galloway tubes (not cross tubes) should be angled slightly downwards so that an air bubble cannot form which would cause a hot spot before the flow got going.
29 January 2026 at 22:02 #834887
Colin Teasdale
Participant
@colinteasdale
As I now understand it, a true Galloway tube is itself tapered. Perhaps that would get round the air bubble issue.
29 January 2026 at 22:08 #834889
Nigel Graham 2
Participant
@nigelgraham2
Tapered possibly, diverging upwards, but more significantly they are vertical or nearly so, crossing the horizontal flue(s) in a Cornish or Lancashire boiler. Air or steam locks could not form in them.
29 January 2026 at 23:07 #834895
duncan webster 1
Participant
@duncanwebster1
According to the interweb, Galloway tubes are tapered to make them easier to fit
29 January 2026 at 23:33 #834897
John Purdy
Participant
@johnpurdy78347
Here’s how K. N. Harris describes “Galloway” tubes in his book “Model Boilers and Boilermaking”.

John
30 January 2026 at 06:52 #834901
JasonB
Moderator
@jasonb
Vertical or near vertical as per Galloways advert
30 January 2026 at 10:08 #834924
Bazyle
Participant
@bazyle
Ok I’m thinking of something different. What’s the name for the double concentric tube, the outer one closed at the end so the water goes along the outside of the inner tube getting heated then back down the inner tube. They project into the firebox like an inside out hedgehog.
30 January 2026 at 11:13 #834938
duncan webster 1
Participant
@duncanwebster1
Field tube
30 January 2026 at 11:42 #834946
Nigel Graham 2
Participant
@nigelgraham2
I love the spiny simile!

I suppose the Lancashire and the Scotch marine boilers, with their two or three furnaces and the rest of the complexity, might be an interesting model-engineering challenge, but perhaps better gas or paraffin-vapour fired.
6 February 2026 at 00:19 #836397
matthewwatts
Participant
@matthewwatts
Good morning.

I to am interested in building a small boiler.

I like the look of the Tubal Cain one above, although I would prefer coal fired just for the fun factor. The gas firing would certainly be quicker, cleaner and easier for running my small Stuart engines.

Could someone please explain the necessity of the stays in the fire box area. The Boiler shell itself is obviously strong enough as there are no stays above the fire box. The central flue would seem to act as a stay to the top of the boiler.

Therefore it would seem they are there to support the fire box itself. I would have thought (possibly/probably wrongly) that the tapered cylindrical / cone shape of the firebox would be strong enough and self supporting without the stays. Would the cross tubes act as internal stays even though they are at an angle?

Thanks for any help and explanation, Matthew
6 February 2026 at 01:21 #836406
John Purdy
Participant
@johnpurdy78347
Matthew

Tubal Cain in his write up in ME states at the beginning that he doesn’t think that the stays are required. The reason he put them in when he made it was that the thickness of the the material he used for the inner firebox was 30% thinner than the 18 SWG specified in the drawing.

When I made mine, back in the early ’80s, I used 16 SWG (because I had it) and didn’t put the stays in and it survived the 90 PSI initial test, no problem. I have never steamed mine above about 40 PSI as 10 PSI is more that enough to run the ST #10 at a faster than scale speed, even then the stop valve is just cracked open. It also runs my ST #9 quite happily.

Tubal Cain’s build article in ME ran from 18 Feb.’77 to 1 Apr ’77, he also did a 5″ coal fired one starting in 18 Aug ’78 running to 6 Oct ’78

John
6 February 2026 at 08:54 #836438
matthewwatts
Participant
@matthewwatts
Hi John.

Thankyou for reply. That makes perfect sense.

Ill look into Tubal Cain’s designs and search for back issues of ME.

When I run the Stuarts I’ve bought I have the regulator set lower that I can read on my gungy gauge. Certainly under 10 PSI.

I have just started building my own Stuarts, A 10v and H

Thanks again, Matthew
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