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I have a question for you experts... my locomotive (#21) puts a lot of wet steam out the stack which ultimately ends up all over the tops of the tender tanks, etc.  Once I paint her a satin black, this may not be so easy to clean off.  Because she's a cab forward, the throttle and lubricator are in the cab and right above the cylinders, so the steam line from the lubricator drops straight down through the floor and the normal Accucraft setup of running it down the flue wasn't practical.

I'm now wondering if eliminating this line (what we usually call a "superheater") is in part responsible for wetter steam, and whether or not I shouldn't figure out a way to add it back in.  I was brainstorming with Chris Scott last night, and we thought about running the steam line through the flue and back under the lagging next to the boiler to the cylinders.  We also thought about reversing that and running the line under the lagging to the smokebox and back to the cylinders through the flue.

So my questions are...

a) would adding this steam drying line in actuality substantially reduce the wet water/oil drops on the tender and elsewhere?  In other words, is it worth doing?

b) if it's worth doing, should I go through the flue and back under the lagging, or under the lagging and back through the flue?
 

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Dwight,
I have two engines--an Accucraft 3-cylinder Shay without a superheater, and a Roundhouse 2-6-2 with a superheater running thru the flue. Even after clearing out the startup condensation, the Shay continues to spit quite a bit; it is visible on the engine and the first car following. The 2-6-2 shows much less of this on cold startup and very little after a run. I attribute the difference to the superheater in the 2-6-2. On our little boilers with minimal efficiency, a superheater appears to be worthwhile.

Larry
 

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Dwight

If the purpose of the superheating in your case is strictly to eliminate the messy stuff from the stack, are there not other alternatives? But if the purpose is to improve boiler efficiency, then I suspect superheating has its place. If you decide to add superheating, are there some simple tests you can do to document before/after boiler efficiency for the rest of us?

Regards ... Doug
 

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I'd consider reversing the run of the superheater if you install it.  Go under the boiler clading first and then thru the flue. This way the stream will be heated JUST prior to entering the cylinders. Maybe even going thru the lubricator after the superheating! This is a non-expert opinion and for a truly expert opinion call Click and Clack the Tappet Brothers.
 

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I don't se why the superheater can't go both ways inside the flue?? And just before entering the cylinders, branch off to the lubricator., wich is the setup in both my Maerklin / Regner and my one Aster loco. Someone here in the forum, earlier described superheaters as actually acting as "steam dryers" ;-) In any case, I would expect improvement. Two straight stainless steel tubes & a U-turn fitting in the far end, shoudn't really be too much work, or?
 

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Dwight,
I agree with Pauli. That's what I would do too. Recently there was a series of articles in "Model Engineer" about superheating. The conclusion was that superheating in our small boilers does not effect thermal efficiency that much, but helps to avoid condensation. About 80C (175F) temperature increase is all you need.
Regards
 

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I have a good friend who owns a 1.5" large scale Gene Allen mogul and it ALWAYS spews some spray and oil droplets out the stack when we first open the throttle at start-up. One thing we've found to stop this, is to open the cylinder cocks and run a few feet. Do you have mechanical or automatic cyl. cocks on the engine?
 

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Dwight, if you do run a line next to the burner be sure and use the correct steam oil that wont coke up in the pipe.  The Houston gang has found that the new formulated Roundhouse oil works great through superheater pipes. :)
 

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Discussion Starter · #9 ·
Thanks for all the comments guys. It seems it might be worth trying. :) If I do this, I'll introduce the oil after the superheater just before the cylinders.

Doug - there are other ways to reduce the spitting upon startup, but right now she has terrific stack talk, and I don't want to do anything like crimping the top of the line, etc. that may change that. I'm also not sure that even if I did that, it would have any affect on splatter on the tender, which happens during the run and not during startup. I think it has more to do with steam saturation and water content.

Gary - there are no cylinder cocks, and again, those would address startup issues anyway, even if I had them. :)

Pauli and Henner - I'd thought about running it both ways inside the flue as you suggest. Bending such a tight loop in the S tubing could be a problem. Pauli, you suggest a U-turn fitting. Can you elaborate?
 

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Dwight,
Martin Evans in his book "Manual of Model Steam Locomotive Construction" recommends a wedge shaped return fitting between the 2 tubes. I can send you a scan of the page or you can swing by my place during one of our workshops.
Regards
 

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I have a book someplace that describes how to make the return bend in superheater tubes. Of course this is for full sized practice so  they are working with at least 1/2 inch or larger pipes... I shudder to think of trying it with 1/8 inch copper tubing.  Just too weak to do what they suggest.

As I remember the instructions (can't find the book right now... just looked through about 30 books!):

Make a cut half way through a pipe, about 5 diameters from one end. Then slit the pipe from there to the end and flatten the quarter sections like the legs of a boiler firebox wrapper.  Do the same to a second pipe and lay the pipes next to each other so these "legs" overlap slightly.  Then you FORGE the overlapping parts together (i.e.: weld them to each other by beating them with a hammer) and fill the gaps at the cross cut with weldment.  Then you chuck the pipes together in a lathe (spining them on the axis of the point where they touch each other along the length)  and force the open end over until it seals.  (This requires one heck of a beefy lathe!)

Note this did not involve using a "solder" to join the pieces, but rather forged the separate pieces into a single piece of metal. This also makes the end much thicker than the wall of the tube itself.  This was useful in a coal burner to provide extra material against the wear of abrasive cinders blowing over the end of the tubes.  Often they would also add a second piece of metal as a shield over the end of the return bend that was easily renewable so they returnbend would last longer.

Another method was to use a double cap that the pipes are threaded into.  This piece is deep enough for a cross hole between two threaded holes.  The pipes are then threaded into the holes.  Again, no solder allowed, not even as caulking.

The superheater tubes are subjected to temperatures that are enough to melt the parent metal of the tubes if the heat is not carried away by the passing of steam!  In the first superheaters installed in 1:1 locos the throttle was ahead of the superheater... the superheater was just a retrofit installaton between the steam dome throttle in the boiler and the valves over the cylinders.  Newer types moved the throttle to the smokebox (so calld "Front End Throttle") so the steam from the boiler was always in the super heaters which at least kept them "wet" to extract heat from the tubes.

In our miniature boilers, the superheater tube is often AFTER the throttle and thus the tube is not protected by steam in the line when the throttle is closed.  This didn't use to be a problem as the superheater tube was usually in the bottom of the flue UNDER the poker type burner.  Then people started to turn the poker over to get the flame out  the bottom so more heat was against the bottom of the flue where there is less chance of it being without water next to it on the other side in a "low water" situation (a common occurance on small locos without a sightglass).  Unfortunately that puts the flame on the superheater tube!  Moving the superheater to the top of the flue now gets it out of the flame but...  "heat rises" and the tube is still in higher heat than used to be the case when it was in the bottom and the poker burner was upright.

This excess heat is probably not a problem as long as butane is the fuel and the throttle is not shut off for long periods of time... my assumption is that means like 20 or 30 minutes... which is probably longer than the standard amount of fuel can deliver... unless the fuel system has been modified to use propane or a much larger tank was installed.

Another thing that the "superheater in the flame" exacerbates is the caking of the steam oil so a better type of oil is needed, too.

It is all these considerations that people may not take into account when they claim no problems with some aspect of their engine.

I think the IDEAL is to have the throttle and oiler AFTER the superheater and the superheater not directly in the flame and only use butane and only a small quantity tank and a good high temperature steam oil.

But the worst situation is probably the easiest to accomplish given the supplied material in the usual commercial loco.  It is easiest to insert a superheater between the throttle/oiler and the cylinders than to re-plumb EVERYTHING to get it "right".

But compromises have to be made sometimes with the physical layout... so... If you have the worst of the possible configurations... throttle and oiler between the boiler and the superheater and the superheater is in the flame... then you have to mitigate the problems by using a better steam oil, butane for fuel, don't let it sit with the throttle shut off for too long and keep the runs short.
 

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Dwight, et al:

I think some photos are in store here to show exactly what henner and charles are talking about.  It's commonly known as the return flue superheater. 

Justin Koch's home built one using a steam return block:


Berkshire(the pipe on the left, exiting the boiler):

Lastly, please do not attempt to make any of these tubes out of copper!  You will end up with a very cool looking pile of copper dust turned tye-dye colors.  There was a mistake at the factory on the first batch of accucraft GS-4's (Meths Fired) that resulted in the return flue superheaters looking like this:

This was remedied with stainless steel tubing, which if heated to a cherry red, can be bent around a former by hand, giving you perfect no-kink curves.  You could also buy a squeezable tubing bender (like a mini-brake line bender). 

Here's the replacement superheater:
 

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On my Roundhouse Lady Anne, the steam line runs from the throttle to the lubricator and through the burner mounting bracket to the cylinders through the length of the central flue.  I guess you could call this a superheater of sorts.  The loco splashes and splatters a bit on starting; but, it's reasonably tidy.

Llyn
 

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The easy way would be :installing a condenser somewhere unobstructive to catch all the muck!!!

Manfred Diel
 

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Dwight,

The latest GR has a review by Mark of the Waterlines 0-4-0 in 7/8ths, and he comments positively on the valve at the smokebox that directs the exhaust down onto the track at start-up, redirecting it up the stack afterwards (when you move the handle, of course.)

More or less a replacement for cylinder drain cocks. Seems like a worthwhile idea - I've run my C-16 with a 180 degree pipe stuck in the stack from cold in order to direct the crud to the trackside.
 

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Manfred, Pete,
drying the steam also improves slow speed operation (less condensation). I know, Dwight loves to run his NPC #21 at scale speed. So he kills two birds with one stone using a steam dryer/superheater.
Regards
 
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