Best boiler size for small static engines?

What would be the best (or minimum) boiler size for a small static steam engine? For example a Stuart S50 and a Twin Oscillator.

I want to build my own boiler, and it appears that the common copper tube sizes are 90mm, 67mm and 54mm. What length boiler for these diameter tubes?

What difference does it make between a vertical and a horizontal boiler?

Thanks
Rod

The old Stuart 500 boiler was what they suggested as a minimum for teh S50 and that was a 64mm dia x 203mm horizontal. To give a bit more scope teh 501 would be a better bet at 73mm dia x 203mm long,

You maight also want to look at something along the lines of the GLR vertical boiler which can be had in several kit forms

I also meant to say that those sizes of copper you list are large size plumbing ones, you should be looking at one of teh ME suppliers that has a good range of tubes in various wall thicknesses, someone like Macc Models will have the right stuff and sell in short lengths

Here's a photo of a vintage boiler, it is 12" tall, probably a Stuart Turner design, the engine is an early(1930ish) ST 10V.    Ian S C

Edited By Ian S C on 01/06/2016 10:45:53

To the beginner, 203mm x 73 dia. appears to be huge in relation to the size of the engine(s). Is there a good reason for such a large boiler? Am I right in presuming that a boiler of this size really needs to be run on gas?

I do want to build my own boiler rather than buy one ready made. Looking at the Macc Models web pages, the alternatives for boiler tube appear to be:

16 gauge x 3" dia
18 gauge x 3" dia
16 gauge x 2-1/2" dia

Is there an advantage in buying one of these over the others?

Thanks
Rod

The "Standard" boiler kit from GLR is basically just a collection of materials and plans/manual for you to do all the work of making the actual boiler.

Size can depend on a number of things - steam usage, the bigger the capacity and speed of an engine the more steam it will consume. - Display or working, if just running the engine it won't use as much steam as if it were working powering something - Water Feed, some boilers that don't have provision for water feed will just run until empty (or preferably run out of fuel) so a larger boiler gives a longer run - Ease of use, a larger boiler can be easier to fire and get a consistant boiling rate.

Gas is probably the most practical, spirit or fuel tablets OK for small boilers, coal and charcoal a bit more fiddly but more like the real thing.

Once you have decided on a size the thickness of tube wall, endplates etc is usually governed by the pressure you intend to run the boiler at.

J

Try searching the ME mag index for 'test boiler'. There have been a couple of designs around 4 or 5 in and I think the plans were in the old MAP plans range. Probably 4 in for gas and 5 in for coal.

A horizontal can easily be fired with your propane burner you used to build it.

The boiler in my photo is coal fired, although in the bottom right of the photo you can see the wood box. I think the bits of wood about 10 mm square X 50 mm long would be OK for starting, maybe soaked in kero/paraffin. The above boiler is not in condition to steam, but it is on display in my mates museum about 100 meters down the street. Ian S C

One of the things people forget about is the steam space in a boiler. Typically the boiler will be 3/4 full of water and the remaining space is for the steam. If you take a 3-inch diameter tube it has a cross sectional area of 7-square inches. So a boiler 12-inches long has a total volume of 85-cubic inches. When 3/4 full of water the steam volume is only about 21-cubic inches, which isn't a lot if you are drawing off a lot of steam.

However, for a small engine running with no load the steam consumption will be low. If you load up the engine to maximum you can expect the steam consumption to increase considerably, perhaps as much as twenty times, hence you need a larger reserve of steam space to cater for this. You will also need far more heat output from the " furnace" to keep the steam generation up to the required volume being drawn off if the pressure is not to fall.

I don't envisage loading the engine. Perhaps posted replies assume that I do, because everyone is talking about large boilers.

I want to make a boiler that will run happily at low pressure to turn over the engines slowly and with no load., so that the motion of the engine can be actually observed rather than being a blurr. Furthermore, I don't really want a boiler that will dwarf the engine beside it.

So again... what is the *minimum* size boiler that would run an S50 or a V Twin Oscillator?

Thanks

Rod

You could probably get away with something about the size of a Mamod so 1.5" dia and 4" long for short runs. Have a look back through Brian John's posts about his littel boilers for an oscillator and small piston valve engine wit spirit burners

Ah! Thank you!

Save you searching, this is one thread

Hi

If you are interested there is a book available from Tee Publishing **LINK** it feature boiler designs for 3.5" x 6", 4" x 7" & 4.25" x 8" Vertical Boilers and 3" x 6.5", 2.125" x 6" Horizontal Boilers

There are also designs on HMEM in the download section by SandyC who I believe made boilers for a living. 3" vertical page 1 here **LINK** there is also a horizontal design. You will have to look through the whole download area because the pages are scattered about.

regards

Steve

Thanks Steve. I have just ordered the book.

Rod

I made the vertical boiler in Tubal Cain's simple model steam engines, part 2, but added an inch or two to the height.

Produces enough steam to run small engines. Looks very like Ians.

Neil

I remember holding a blow lamp under my brothers Mamod. Made enough steam to run my Stuart beam but did not do much for his paintwork

Rod

The attached photo shows the boiler I use to steam my Stuart 10V. It was described by Tubal Cain in the Feb '77 issue of ME. It's a 3" dia. water tube boiler (see attached plan). At 10 psi the stop valve is barely open to steam the 10V at a reasonable speed ( opened up the engine races way too fast). In the introduction to the article he states that this boiler should produce 8500 cu. in' /hr of steam at 60 psi, (enough for an engine of 5/8 to 3/4" bore) and 2-3 times that amount at 10 psi.

John Purdy

Hello John, I came across this post whilst researching the Stuart S50 engine in regards to steam usage and boiler size. I tried to open the boiler jpg and the plan of the boiler ,but i think its been deleted .

any chance you could copy them over to me please.

\

Best regards Mick

Mick

The pictures also seem to have gone missing from my album. I've put them back, but here they are.

John