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