It will work without superheaters but nothing like as well.

Living in Jersey where post and packing is extra expensive might well change the answer!  As does Garry’s comment that the engine will only be run in his workshop.  Unless there’s a track in Jersey the engine will have to be moved to the mainland!

There’s no advantage in superheat unless the engine is expected to do work.  Saturated steam will look, smell, and spin the wheels on a rolling road or short garden track just as well.   The engine won’t burn fuel as efficiently, accelerate, or pull a heavy load as well, but if that doesn’t matter, don’t superheat.

What I’ve read about superheated models in old magazines suggests they often fail to deliver much, or any, benefit.   Reason, I think, is fairly obvious.  In a small model the surface area of the superheater’s pipework is large compared with the volume of heat contained inside.  Therefore heat leaks rapidly, and the temperature drops!  Even inside the boiler the temperature is well below superheat, so it cools superheated steam.  Assuming the steam inside is still superheated,  the pipes have to get from the smoke-box to the valves and from there into the cylinders.  None of it is well-insulated and performance will be good only if convincingly hot superheated steam fills the cylinder.

At 150psi, saturated steam will be at 185°C, and red-heat in the firebox, say 600°C.   So 415° of superheat in the firebox isn’t difficult.  The question though, is how much of that sugar, if any, reaches the piston!   Much less value in steam that’s merely dry, or a bit less wet than normal.  In a small engine, I fear superheated steam is likely to re-saturate before it can do any useful work.  Anyone measured the temperature inside a model’s cylinder?  How hot is it?

Based on the ratio between surface area and volume of small pipes, my gut predicts most model scale superheaters aren’t ‘worth the candle’.  Guts being highly unreliable though, anyone able to prove me wrong?   Good start would be to measure two identical engine with a dynamometer over many comparative runs; engines identical that is apart from one having a superheater.

The history of superheat in full-size locomotives is interesting.   The scientists identified the advantages of superheat about 40 years before practical men could make it work.   A major problem was that wet steam is usefully self-lubricating and not hot enough to damage animal based lubricants.  Superheated steam is dry and hot enough to destroy natural lubricants, or at least all the affordable ones!  Result, a number of Victorian experimental engines that outperformed saturated steam locos until their pistons, cylinders and valves wore out after an hour or two…

Superheated locos had to wait until the Chemists developed cheap heat resistant lubricants, after which the mechanical part was a doddle.

Dave

With the trouble SOD has been having I would have thought that he would havd known that guts are very unreliable.

Bill Hall showed conclusively that superheaters work in model locos, but radiant ones for preference. The heat lost from the outside of a short pipe is small compared with the energy flow through if, so the temperature doesn’t drop much. Superheat doesn’t make a lot of difference to pulling power all else being equal, but it reduces condensation on the cylinder walls, so you need to boil less water,  meaning less coal burn. Or conversely for a given amount of coal burn you get a lot more useful steam. Bill Hall did a series of tests reported in SMEE journal which proved this beyond doubt. Not sure whether it ever got published in ME.

Re SpeedyBuilder’s concern for different expansion rates…

There are no joints where that could give trouble.

If the headers are of the same material as the superheater elements (copper or stainless-steel) the only joints with a different metal are those between the headers and the regulator outlet, and the pipe(s) to the valve-chests.

Those are by unions or flanges with studs, and judging by the number of superheated miniature locomotives in service are evidently able to cope with the extremely tiny difference in dimensional change with temperature.

Some miniature locomotives have steel boilers with copper tubes, a combination one might expect to be prone to differential expansion problems, but it seems to work.

Sometimes I feel we get too concerned with theory ! The issue of expansion in this context is of no consequence if only because the superheater is only constrained at one end. Whether of copper or stainless will make no difference.

That copper and steel are mated together in both model and full size would seem to prove that there is little to worry about .

As to there being no track available, I was given some 1″ box scrap about 150′, This was turned into a 50′ length of 5″ gauge track in my garden. Where there’s a will there’s a way. Good luck. Noel