Help: Looking for a Boiler for this 3 cylinder steam engine

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fizzy

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Have a look at the 5" diameter horizontal boiler made by Pendle steam boilers. This would be the size you will require to run your 3 cylinder engine.
 

Steamchick

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Or buy a cheap compressed-air in-line tool lubricator to keep the engines lubricated... I bought 2 for £5.. but the end connectors cost me a bit more. The compressor can be relatively tiny to run most models. - I use an ex-refrigerator compressor (It was scrap, and not inside the fridge when I found it, 40 years ago!). It runs all my singles 1" bore x 1" stroke, when they are run-in, as I only let them idle slowly anyway. The only problem running compressed air is the mains cable or air-line trailing through the lake behind the boat.... (Ha! Ha! - That is why you need a boiler!).
You'll need to do some real sums to determine the size of boiler needed... Even so, add 50% to the burner and boiler.... then size the boat to carry all the weight!
I bought a 48" hull and made a launch.... (Model of a Naval Picket boat) which was supposed to take 15lbs max load. The weight of Stuart SUN engine (Cast iron, 3/4" Bore and stroke SA> twin), + Boiler + fuel/tank, radio controls and batteries came to over 18lbs. ... but instead of sinking, it sat a bit low in the water. - Especially at the stern where the engine was located. The boiler could just about make the boat crawl along at "scale" speeds, but as it was meant to be a fast launch it simply didn't look fast... I changed to a smaller (Alloy STAR: 1/2" bore and stroke SA twin) engine - so the lower (volume) steam demand allowed a slightly increased steam pressure, and improvement in performance (less losses) with the same burner, and the boat had a sensible trim by losing nearly 3 lbs of dead-weight. A good change. The engine has something like 1/3 the displacement, and runs with the gearing in my drive to the prop. shaft reversed, to allow it to run about twice as fast as the SUN engine. - Hence 2/3rds the steam demand by volume, so increased from ~10 to a couple of psi more, and revs increased. The limiting factor is the gas supply and burner size. A gas can "warmer" using the condensate from the exhaust condenser helps against gas pressure drop.
What pressure do you think you need/want? You'll really need to calculate the engine speed - and compare with the thrust needed from the prop at the suitable prop speed. and then add to the displacement as a steam demand, you need to determine what power the prop needs at the speed decided upon. I used some info about props, speeds, and "recommended electric motors" to get the power needed versus thrust... but used the prop "recommended" for the hull. That gave me some clue as to how much power I needed to input to the prop shaft, then tried to estimate how much power from steam I would need... (at 10% efficiency!) so ended up with a 2.2kW burner, that runs at less due to the gas chilling... and loss of pressure. My boiler may be over designed, it's just that the burner can't stuff any more heat into it than it does... but the fellow modellers think my boats look more realistic with the gas exhaust wafting out of the funnel, and the speed being more "scale" than "Whizz".
Do tell us of your hull, boat plans, etc. so we can help with more detailed advice?
Cheers!
K2
 

Steamchick

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For other readers... Please ignore comments re: oiling, as the engine model selected has a biult-in oiler.
Richard V. The supplied oiler is designed for steam (displacement type, relies on condensed steam - as water - displacing the oil from the container to be heated, vapourised and carried through the engine where it condenses and lubricates, before being ejected in the exhaust steam.). If running on compressed air, invert the whole oiler. - This means the oil is draining towards the supply pipe, and as capilliary action draws a little oil out, it becomes replaced by air (helped by pulsations in the supply line) - which then pulses and pumps more oil out. Works well on my bench models, so should work if you run the engine on air for bench testing, etc. (in the bath - with an air-line?).
K2
 

Steamchick

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The engine spec...
Material: Copper
.Model: LS3-13S
.Size: base 48mm wide, 111mm long, 95mm high + 6mm thick sleepers
.Cylinder diameter: 14.0mm
.Stroke: 12.0mm
.Spindle diameter: 5.0mm
.Spindle center ground height: 17.0mm
.Operating pressure: 0.05Mpa-0.8mpa
.Recommended air pressure: 0.2Mpa-0.6mpa
.Inlet interface thread: M6-0.5 1/4-40
.Product Dimensions: 11.1 x 4.8 x 10.1cm
.Product Weight: 930g
.Package Dimensions: 21 x 16 x 16cm
.Package Weight: 1200g

But this does not state "max. speed" - I guess should be kept below 1000rpm because of the valve gear? I guess the prop will be only ~1 1/2" diameter...?? so ~1000rpm should be a max. workable design speed? Maybe you should ask the engine makers what they suggest for max speed?
As silver-soldered copper boilers are limited to 100psi (ASME Regulations, (Law in USA and many similar regulated countries), the steam demand for this engine at 100psi is something like 676 cu.in steam per minute: @ 100psi = 2.84 cu.in (~47cc, 47gm.) - or 0.104lbs. of water to be heated boiled and heated to 100psi per min.
I.E. 0.104 x 60 x 1243 BTU/Hr is required in "Heat" to supply the engine (max.) = 7730BTU/Hr = 2.3kW.
Assuming the boiler to be 60% efficient, you need a 3.8~4kW gas burner.... so the gas canister will need some heat to avoid the pressure drop from vapourising the gas (Waste heat from exhaust steam?). I should design for a 5kW gas burner as the superheater will also need some heat. (Necessary to avoid too much inefficiency from "wet" steam that must be pumped through the engine!).
The boiler will need (typically) just a tad more than 1/2lb of coal per hour if coal fired.... but "very small stokers" are hard to find, which is why we mostly use gas burners! So look at a gas burner catalogue to see what burner is needed for 5kW - to give you some idea...? e.g. the Sievert 25mm cyclone burner, or 28mm standard burner will do. with propane...
1632824391676.png

The boiler should have at least 110 sq. in of heating surface, to be able to transfer the heat from the burnt gas into the water in the boiler. For the simplest Cornish Marine boiler, with JUST a fire-tube, the tube will need to be 2" diameter x 9" long, or thereabouts. So a more complex boiler will be more compact?

Hope these ideas give you some clues. But please do some calculations yourself and let us know so we can give more direst advice?
Cheers,
K2
 
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The engine spec...
Material: Copper
.Model: LS3-13S
.Size: base 48mm wide, 111mm long, 95mm high + 6mm thick sleepers
.Cylinder diameter: 14.0mm
.Stroke: 12.0mm
.Spindle diameter: 5.0mm
.Spindle center ground height: 17.0mm
.Operating pressure: 0.05Mpa-0.8mpa
.Recommended air pressure: 0.2Mpa-0.6mpa
.Inlet interface thread: M6-0.5 1/4-40
.Product Dimensions: 11.1 x 4.8 x 10.1cm
.Product Weight: 930g
.Package Dimensions: 21 x 16 x 16cm
.Package Weight: 1200g

But this does not state "max. speed" - I guess should be kept below 1000rpm because of the valve gear? I guess the prop will be only ~1 1/2" diameter...?? so ~1000rpm should be a max. workable design speed? Maybe you should ask the engine makers what they suggest for max speed?
As silver-soldered copper boilers are limited to 100psi (ASME Regulations, (Law in USA and many similar regulated countries), the steam demand for this engine at 100psi is something like 676 cu.in steam per minute: @ 100psi = 2.84 cu.in (~47cc, 47gm.) - or 0.104lbs. of water to be heated boiled and heated to 100psi per min.
I.E. 0.104 x 60 x 1243 BTU/Hr is required in "Heat" to supply the engine (max.) = 7730BTU/Hr = 2.3kW.
Assuming the boiler to be 60% efficient, you need a 3.8~4kW gas burner.... so the gas canister will need some heat to avoid the pressure drop from vapourising the gas (Waste heat from exhaust steam?). I should design for a 5kW gas burner as the superheater will also need some heat. (Necessary to avoid too much inefficiency from "wet" steam that must be pumped through the engine!).
The boiler will need (typically) just a tad more than 1/2lb of coal per hour if coal fired.... but "very small stokers" are hard to find, which is why we mostly use gas burners! So look at a gas burner catalogue to see what burner is needed for 5kW - to give you some idea...? e.g. the Sievert 25mm cyclone burner, or 28mm standard burner will do. with propane...
View attachment 129452
The boiler should have at least 110 sq. in of heating surface, to be able to transfer the heat from the burnt gas into the water in the boiler. For the simplest Cornish Marine boiler, with JUST a fire-tube, the tube will need to be 2" diameter x 9" long, or thereabouts. So a more complex boiler will be more compact?

Hope these ideas give you some clues. But please do some calculations yourself and let us know so we can give more direst advice?
Cheers,
K2
ok. thanks. that's helpful
 

Steamchick

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Hi Richard,
If you are making a boiler, and this would be your first, then you really want to make a simple design, like a fire-tube - with return tubes to make it more compact than the 2 in diameter x 9" long fire tube that I explained above. A 1 1/4in ~1 3/4in. diameter fire tube with 8 or more return flues of 1/4" ID will do the job at around 5" long x 5" diameter (4 in long x 7 in diameter may be a better configuration for your boat? - What can your hull take? - Dimensions and weight?). This is the sort of thing Pendle and others will do, as the increased complexity is minimal, yet makes a much more compact boiler.
However, if you have a close partner who makes boilers, the most compact design would be a Yarrow boiler. Providing you have constant water feed from the engine, the water-tube boilers are the fastest steamers - short of flash boilers.
Let me know more numbers if you want a design to suit your boat and engine, as I can do this for you. But if buying a "ready-made " boiler from a model shop, you'll be best advised to seek their opinion. Generally they are honest, as modelling is their passion. (or so I have found). I.E. They won't "oversell" bigger than you need.
My advice is more suited to "home build for a specific application".
Cheers!
K2
 

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