What size boiler is recomended for a S50 steam engine?

[HenryBanjo]

what size boiler should I make for a Stuart S50 steam engine? I want to make a coal-fired, vertical firetube, steel boiler. the engines I want to run with it are a Stuart S50 and/or elmers#33. I believe that the S50 is that larger engine (S50 is 5/8 bore, #33 is a 1/2 bore)

 

[HenryBanjo]

just to clarify when I say Stuart S50 and/or Elmers #33 I mean only one at a time.

 

[Steamchick]

Hi Henry:
I spotted an earlier post asking a similar question - hope you understood my message?
Simply, I would not suggest a steel boiler.
I suggest you re-consider using something like: A piece of 3 in diameter copper tube, 6 in long - From a scrapyard possibly? - with some 1/8in thick ends will silver solder into the simplest tank for boiling water.... but it will need bushes adding for gauges, etc. and some stays through the length, so you can run it over 10psi. (Sensibly). You can probably get away with 2 1/2" OD or maybe even 2in OD copper pipe if that is all you can find?
The size of boiler to simply run these small engines (without driving dynamos, boat, etc.) can be very small, and therefore unsuitable for coal firing, in my opinion. But not impossible.
I would make an horizontal boiler for a very simple boiler like this, as then a gas burner beneath has a lot of surface to heat, so can generate adequate steam for those model engines..
I have a horizontal boiler, 3 in diameter, 6in long, and although it was set for 45psi max, I only ever ran it up to 20psi, and that was for an engine twice as big as yours for displacement. Usually I only used 5 ~10psi. when the engine was warm and unloaded. But 10~15psi if running a 1in bore x 1 in stroke engine to power a bicycle dynamo - Needed more speed and torque. It is much better than a 3in diameter 5 in long vertical boiler with central flue tube that can only take a burner of half the size of the horizontal boiler. I also have a Cornish boiler, that can only take a smaller burner, due to combustion in the fire-tube, but is in a boat. The 3 in dia x 5 in long boiler dominates the boat! It fills 3/4 of the interior, but the boat is quite slow because of the small burner. A slightly smaller boiler (2 1/2in dia) and bigger burner (blowlamp nozzle in a bigger tube) would be better = more power and speed...
IF you make a steel boiler, then (I guess?) it should have at least 1/8 of thickness for "corrosion allowance" - as well as 1/8 thickness for pressure and factor of safety. Similarly ends of 1/4in thick... for the same reasons... and - assuming you are a certified welder and know about types and preparation for welding - proper preparation and welded joints. I think it would be "overkill" to design a steel boiler to suit NZ regulations at that small size? - if they apply for such a small boiler?
If it is a vertical boiler, what do you want in terms of flue tubes for the coal smoke? - Will it be a forced fire from the exhaust steam from the engine? How do you plan to fit flue tubes? - you say "fire"-tubes, but that term usually refers to a large tube containing the fire, as in a marine or Cornish boiler, or exposed tubes in the firebox, or the inner tube that forms the firebox? Which do you mean?
Maybe you have something in mind so I can be clearer/more specific in my advice? Perhaps you can post a sketch or picture of an existing style of boiler?
Thanks,
K2

 

[steamedlou]

what size boiler should I make for a Stuart S50 steam engine? I want to make a coal-fired, vertical firetube, steel boiler. the engines I want to run with it are a Stuart S50 and/or elmers#33. I believe that the S50 is that larger engine (S50 is 5/8 bore, #33 is a 1/2 bore)

Hi Henry
An S50 needs very little steam. That was my first engine. I went very rudimentary for a boiler. I took a 2" sch 40 pipe nipple and two screwed ductile iron pipe caps. Good for hundreds of psi and the iron caps can be drilled and tapped. Put this in a piece of 4" steel tubing for a case and drilled holes in a 1/2" copper tube to burn propane.

 

[Steamchick]

Hi Harry, I am currently repairing my Dad's silver soldered copper boiler (30years of use!), that he had for his 1in bore x 1~2 in stroke engines that normally ran at about 5~10psi. The safety was set for 45psi, so it had been hydraulically tested at 90 psi - or a bit over, which had blown the ends as they were too thin for this pressure. So rather than de-rate the boiler to about 12psi... I have added stays to strengthen it for 30 psi - as that's what the calculations said.
So I have photos - mid-repairs, etc. - but can give you some idea of a simple boiler. It sits in a casing with burner beneath, and flue gases pass through the flue tubes then up a chimney. There is a single warming tube to dry the steam - not really enough for a superheater... - in the firebox.
Hope this shows what can be done simply in copper?
To help keep costs to a minimum he even used a tin can for the water butt for the feed water hand-pump. Still good after 30+ years!
The one thing that gave him problems in the early years: the chimney was smaller. Only half the cross-sectional area of the flue tubes - and was restricting every burner he tried to use. When he doubled the cross-sectional area of the chimney to be the same as the flue tubes, the burners all worked to max power. = More than enough steam for his engines, which are bigger than yours.
For heating for silver soldering (I have remade almost all the joints now) - I use 2 gasoline blowlamps. Much better than the same power butane portable torches.
Picture shown.
These cost about £10~15 on 3&ay... but need to be repaired before use. (New seals and a good clean!).
See last picture. - I use a firebrick hearth.
K2




Hope this helps you?
K2

 

[Maxjon]

What pressure of steam would an S50 run to its capacity? 25psi?

 

[Steamchick]

Stuart are a bit reticent in this matter, as their sales pages mis-out the Max working Steam pressure for their engines. - With relates to bearing sizes, etc. and wear and tear! But their Boilers are rated for NWP of 60psi (horizontal boiler) or 45psi (vertical boiler) so I should never exceed that for their engines, as listed with appropriate boilers. see: https://www.stuartmodels.com/products/boilers-pumps/
- and click on information buttons.
It really depends on what you expect to drive from the engine, - I Assume not a boat as the S50 is a "mill" engine for winding ropes on pulleys to the many floors in a mill, to drive spinning machines, weaving looms, etc, or as a winding engine in Coal mines, etc. - or a belt-drive to any other device you fancy!
BUT, guessing you, like me and many others, will simply run the engine as a demo of "heat into rotational mechanical power", then 25psi Max should be OK for the boiler. Running the engine in isolation (free-running only) it will probably run around 2~5psi to run really slowly, and just not stalling. - but that is pressure at the engine, so a 10psi to 25psi pressure in the boiler, controlled by a needle valve to get the running speed you want, is reasonable.
25psi at 1500rpm (That is really fast for an engine like this!) would consume water and steam to need about 180square inches of heating surface of boiler. A vertical 3 inch boiler with flue tubes, superheater, etc. is likely to manage this, but as small as a simple horizontal closed boiler (no flues) about 2in diameter x 5in long may do the job of idling the engine with no load attached.
You could do worse than but a cheap second-hand Mamod model or similar, and try that boiler (10psi limited) to see if that suits what you want to do?
My "Go to" boiler is a 3 inch diameter horizontal with flue tubes rated for 30psi, with about 70sq.in of heating surface, but only run it at ~10~15psi for running many small engines. - typically 1 in bore and stroke. Yours needs only half that steam at 5/8" bore. I also have a 3 in diameter x 5 in tall vertical boiler with centre flue, and superheater, with about 20sq.in of heating surface, that just manages the same freewheeling of engines, except the horizontal has space for double the size of ceramic burner and can power larger models easily.
Are you going to make or buy a boiler?
K2

 

[Maxjon]

Stuart are a bit reticent in this matter, as their sales pages mis-out the Max working Steam pressure for their engines. - With relates to bearing sizes, etc. and wear and tear! But their Boilers are rated for NWP of 60psi (horizontal boiler) or 45psi (vertical boiler) so I should never exceed that for their engines, as listed with appropriate boilers. see: https://www.stuartmodels.com/products/boilers-pumps/
- and click on information buttons.
It really depends on what you expect to drive from the engine, - I Assume not a boat as the S50 is a "mill" engine for winding ropes on pulleys to the many floors in a mill, to drive spinning machines, weaving looms, etc, or as a winding engine in Coal mines, etc. - or a belt-drive to any other device you fancy!
BUT, guessing you, like me and many others, will simply run the engine as a demo of "heat into rotational mechanical power", then 25psi Max should be OK for the boiler. Running the engine in isolation (free-running only) it will probably run around 2~5psi to run really slowly, and just not stalling. - but that is pressure at the engine, so a 10psi to 25psi pressure in the boiler, controlled by a needle valve to get the running speed you want, is reasonable.
25psi at 1500rpm (That is really fast for an engine like this!) would consume water and steam to need about 180square inches of heating surface of boiler. A vertical 3 inch boiler with flue tubes, superheater, etc. is likely to manage this, but as small as a simple horizontal closed boiler (no flues) about 2in diameter x 5in long may do the job of idling the engine with no load attached.
You could do worse than but a cheap second-hand Mamod model or similar, and try that boiler (10psi limited) to see if that suits what you want to do?
My "Go to" boiler is a 3 inch diameter horizontal with flue tubes rated for 30psi, with about 70sq.in of heating surface, but only run it at ~10~15psi for running many small engines. - typically 1 in bore and stroke. Yours needs only half that steam at 5/8" bore. I also have a 3 in diameter x 5 in tall vertical boiler with centre flue, and superheater, with about 20sq.in of heating surface, that just manages the same freewheeling of engines, except the horizontal has space for double the size of ceramic burner and can power larger models easily.
Are you going to make or buy a boiler?
K2

I'm not 100% sure if I'm going make, of buy a boiler. A cheap Wilesco or Mamod may be worth a try...We do have some Australian made ones here, see link...25 psi and bigger. I will most likely be simply free wheeling the engine for fun. I'm still waiting on the casting set from Stuart.

Stuart are a bit reticent in this matter, as their sales pages mis-out the Max working Steam pressure for their engines. - With relates to bearing sizes, etc. and wear and tear! But their Boilers are rated for NWP of 60psi (horizontal boiler) or 45psi (vertical boiler) so I should never exceed that for their engines, as listed with appropriate boilers. see: https://www.stuartmodels.com/products/boilers-pumps/
- and click on information buttons.
It really depends on what you expect to drive from the engine, - I Assume not a boat as the S50 is a "mill" engine for winding ropes on pulleys to the many floors in a mill, to drive spinning machines, weaving looms, etc, or as a winding engine in Coal mines, etc. - or a belt-drive to any other device you fancy!
BUT, guessing you, like me and many others, will simply run the engine as a demo of "heat into rotational mechanical power", then 25psi Max should be OK for the boiler. Running the engine in isolation (free-running only) it will probably run around 2~5psi to run really slowly, and just not stalling. - but that is pressure at the engine, so a 10psi to 25psi pressure in the boiler, controlled by a needle valve to get the running speed you want, is reasonable.
25psi at 1500rpm (That is really fast for an engine like this!) would consume water and steam to need about 180square inches of heating surface of boiler. A vertical 3 inch boiler with flue tubes, superheater, etc. is likely to manage this, but as small as a simple horizontal closed boiler (no flues) about 2in diameter x 5in long may do the job of idling the engine with no load attached.
You could do worse than but a cheap second-hand Mamod model or similar, and try that boiler (10psi limited) to see if that suits what you want to do?
My "Go to" boiler is a 3 inch diameter horizontal with flue tubes rated for 30psi, with about 70sq.in of heating surface, but only run it at ~10~15psi for running many small engines. - typically 1 in bore and stroke. Yours needs only half that steam at 5/8" bore. I also have a 3 in diameter x 5 in tall vertical boiler with centre flue, and superheater, with about 20sq.in of heating surface, that just manages the same freewheeling of engines, except the horizontal has space for double the size of ceramic burner and can power larger models easily.
Are you going to make or buy a boiler?
K2

I'm not 100% sure if I'm going to build or buy a boiler yet. I'm still waiting on the casting kit from Stuart. We have MSM boilers here in Australia...see link.....https://miniaturesteammodels.com/products/master

 

[Steamchick]

Maxjon,
I reckon that should suit you fine.
Also a larger sized Mamod-style should do the job.
A Stuart twin (Sun engine - twin single acting, about a similar displacement/steam demand to yours?) that was a bit tight on initial assembly, took about 25psi to get going, but soon freed-up, now runs as low as single-figure psi, but 10psi is nice and smooth for idling demonstrating.
Looking forward to seeing your engine build thread first though.

K2

 

[Maxjon]

Maxjon,
I reckon that should suit you fine.
Also a larger sized Mamod-style should do the job.
A Stuart twin (Sun engine - twin single acting, about a similar displacement/steam demand to yours?) that was a bit tight on initial assembly, took about 25psi to get going, but soon freed-up, now runs as low as single-figure psi, but 10psi is nice and smooth for idling demonstrating.
Looking forward to seeing your engine build thread first though.

K2

The casting kit is due to arrive on the 16th August...I'm in Europe all of September, so may not get a start on it till October, but I'm looking forward to it!

 

[Steamchick]

Just managed to buy a Mamod boiler (incomplete) for under £20. Just needs a safety valve - and test - as it looks complete with sight glass. A larger boiler from a traction engine I think, complete with factory fixed brackets for the engine and crankshaft. Not sure what I shall do with the brackets, but may simply remove them and make a simple full length firebox tin housing for a ceramic burner and chimney stack..., add superheater tube and valves and away we go!
I guess I'll have to post a thread when I get to do this project... as it may offer a simple solution for others to get a steam boiler for small bench models?
K2

 

[Steamchick]

A bit of progress: This may indicate how "easy~" it is to make some bits and the boiler starts to look like something. And a data sheet on the model the boiler has come from...
Next is a fire-box: I'll dismantle some tin cans for the metal - super cheap re-cycling!
The expensive parts are the pressure gauge (typically£30!!), Boiler (second hand for £20), You can buy a standard safety valve for £13... (I made one - to be tested!) and standard nuts and olives for the pipework!
Other bought parts are:
Stainless steel balls for valves, Stainless springs for valves, brass bar stock , fibre washers, lead solder (tin-free for higher temperature), etc.
Then I'll need to make a water pump, burner (probably a ceramic gas design), etc. and a board to mount the whole lot with an engine. - And a dynamo to be driven, so it does some work, and a lamp-post with light... - So I'll have to buy a gas tank or use small canisters... money, money, money. Then it won't be worth even the sum of all the material costs!
But lots of fun!
K2

 

[Maxjon]

I'm really keen on a coal fired boiler for my S50......However a lot seem to be gas burner type...Any coal fired suggestions???

 

[Jasonb]

For practical coal firing you really want to start looking at a 5-6" diameter multitube boiler, if it is your first boiler and venture into silver soldering then stick with something simpler to start with. Trying to get the dr\aft and keep a smaller boiler going can be a pain that is why gas or liquid fuel is more common as the boilers get smaller.

Typical 6" vertical pictured. note the firebox is surrounded by water which makes use of the radiant heat from the coal not just what goes up the flue tubes.

 

[Steamchick]

Some drawings attached.
This will produce far more steam than you need, but similar boilers at 3 in diameter wil suit you. However, your ngine needs so little steam compared to that available from coal fired boilers, the boiler will be 10 times bigger than you need, and hard to manage as there won't be enough exhaust steam to keep the fire going.
Which is why people use gas for little model engines. - And coal for 5 in gauge locos on a railway hauling people.
K2

 

[Maxjon]

Some drawings attached.
This will produce far more steam than you need, but similar boilers at 3 in diameter wil suit you. However, your ngine needs so little steam compared to that available from coal fired boilers, the boiler will be 10 times bigger than you need, and hard to manage as there won't be enough exhaust steam to keep the fire going.
Which is why people use gas for little model engines. - And coal for 5 in gauge locos on a railway hauling people.
K2

Is there such a thing as a 3 inch coal fired boiler? I think the 6 inch would be better. I hate the smell of gas, much rather the smell of a solid fuel, like coal.
But I have to finish the engine first. Its a Steam engine, not a compressed air, or gas fired engine haha! Thanks for the drawings guys!

 

[Jasonb]

As I said trying to get such a small coal fire to burn will be very hard, getting sufficient heat out of it even harder might have better luck with small pieces of charcoal soaked in Kerro

Poke a few hols in that can you are holding and see if you can get coal to burn in it, if it does then think about a small coal fired boiler.

 

[Maxjon]

As I said trying to get such a small coal fire to burn will be very hard, getting sufficient heat out of it even harder might have better luck with small pieces of charcoal soaked in Kerro

Poke a few hols in that can you are holding and see if you can get coal to burn in it, if it does then think about a small coal fired boiler.

Yes 6 inch would minimum size coal fired then....The Castle V6 is a work of art!

 

[Maxjon]

Some drawings attached.
This will produce far more steam than you need, but similar boilers at 3 in diameter wil suit you. However, your ngine needs so little steam compared to that available from coal fired boilers, the boiler will be 10 times bigger than you need, and hard to manage as there won't be enough exhaust steam to keep the fire going.
Which is why people use gas for little model engines. - And coal for 5 in gauge locos on a railway hauling people.
K2

Might be worth investigating a cheap 20psi Wilesco, and putting a firebox underneath, as opposed to the firelighter tray they come with....food for thought....I simply like the solid fuel idea....

 

[Maxjon]

Might be worth investigating a cheap 20psi Wilesco, and putting a firebox underneath, as opposed to the firelighter tray they come with....food for thought....I simply like the solid fuel idea....