To superheat or not to superheat, that is the question?

OK - nearly time to design and build the 71/4 invicta boiler. Dia. 6", effective length 19", tube arrangement depends on answers herein. Boiler in steel with copper tubes. If i build it with no superheater it will be a doddle, steam straight out the top of the dome as in the original, if I follow the 31/2 inch type plan it will be far more difficult, so is a super heater worth the hassle?

definatel;y superheat, friend of mine added effective superheat to his loco and massively reduced his water consumption at a given load, hence could pull a lot more for same water consumption. Water is free, but you have to turnit into steam!

I don't think it's worth all the trouble making a super heater on models. I won't go into

the deatails here,but use a bit of maths here, focussing on the steam passing throuh the

superheater.When starting off a wonderful mouthfull of superheated steam enters

the steam chests, but the velocity and volume of steam after speeding up a little entering

the cylinders now falls far short of being"superheated" for the exposed area of the super

heater is way insufficient to make any sicnificant difference when operating a model.

If superheaters were fitted as in full size jobs, well then i can live with that, but as i mentioned

earlier a little maths epplied here will scare many builders off. My engines (5" & 7 1/4" runs

as good as any without super heaters, 20 pounds of coal on a steam day?? once a month

so what it's my hobby and pleasure superheaters will not change any of that or the evergreen

argument.

Greetings Mike

Mike, have you done comparative testing, with and without super heating, I'm not much into steam, but interested. I would have thought myself that super heating would at least dry the steam some what. Ian S C

Hi Ian

Yes we have done some comparison on two identical engines (Hybrids based on "Simplex"

in 7/14 in) One boiler was not equipped with super heater tubes only 25 flue tubes and

the other with 8 flues less but with 4 superheaters. I must say that the day when it was

steamed up i was worried sick, but i was surprised beyond expectation at the performance.

When both egines were eventually on the track no performance difference could be noticed

and even the late Basil Palmer made an appreciating comment. I,m not shooting superheaters

down but i'm not convinced that they are worth the trouble making them. However my

unsuperheated boiler is now removed for coverting to oil or gas burning to eliminate

the abrasive action on the flues due to the poor quality coal we are using here in RSA

and i,m thinking of turning one or maybe two flue tubes into small suberheaters to try

and improve the performance of the injectors and if that works? well that's as far i will

go on superheaters.

Regards all

Mike M

Thanks chaps...no superheater and a doddle of a boiler - remember, it has an external regulater so no fiddly bits!!

Superheaters - it's an eternal discussion.

1) full-sized USA geared locomotives are not superheated. (one or two exceptions, but that's maybe 0.1% of the total)

2) anyone good with maths and who has written, seems to think they are a waste of time;

3) local sweet pea owner had superheaters fail, put a straight pipe in, no difference to performance noted;

4) my 2-8-2 3-1/2" gauge - previous owner removed superheaters;

5) Tich locomotive - superheater flue blocked since day 1, so no superheat. Pulls 2 on a levellish track no problem, tons of steam and pump ram is too large. I'd rather have the flue space back, so if I do another Tich, no LBSC superheater!

One of our club members is adamant that superheaters make all the difference when running, but I think that's mainly lack of a true comparison like Mike M did above.

I don't think they are worth the hassle; *maybe* we have less efficiency and more water usage, but who cares??

I think Mike M's comments above need to be published in Model Engineer!

Another JohnS.

i would never build a loco without superheaters. the research of the late Jim Crebbin, LBSC, and Jim Ewins amongst others, plus recent research carried out by a friend, and my own empirical observations and study of IMLEC leave me in no doubt as to the advantages of superheated steam in miniature.

i think one can argue that it rather depends on what use will be made of the loco, and what size it is. a loco built just for fun with no real intention of serious passenger hauling, and where the driver isnt too bothered by the increased water and coal consumption, and doesnt 'notch up' the valvegear can do without superheaters. however if you want an efficient loco and have a good valve gear capable of being 'notched' up and driven properly, then superheaters are a must in my book.

yes, they are a pain to make and fit, but no more so than most other bits on a loco. yes, they will need replacing at some stage which can also be a pain. but if you want a well behaved loco that is a pleasure to drive then i think they are very worthwhile.

i wont go into the science too much, but with effecient superheaters the fluidity of the steam is much improved as is its ability not to condense in the cylinders, both of which are very important if you want to use expansive working. this requires a good valvegear and good valvegear setting, and an ability to drive the loco properly.

i wouldnt fit coaxial superheaters, prefering the 2 element type with return bend. they must be properly proportioned to the superheater flue and steam circuit and capable of being easily cleaned.

any way, that's my 'tupenny worth!

cheers,

julian

Thank you Mike, and Julian, Thats what I expected. Get a room full of engineers, and you get a room full of ideas, all different, most correct, Its probably like "which car is best" or which lathe should I buy. I imagine the for ordenary use a non super heated engine would have no disadvantages, where as if you are trying to get the utmost efficiency, super heat, properly designed would be the way to go. Ian S C

Like Julian, I wouldn't build a loco without superheaters for exactly the reasons that he gives. For similar reasons of efficiency and pleasure of running a well designed loco I wouldn't build a valve gear without thoroughly checking the design first and improving it if necessary. If I am going to spend a lot of time building a loco I want it to perform the best that it can. Just a personal thing I suppose.

I regularly drive my brother's unsuperheated loco (have done today) and it's a very sedate engine to drive. It's performance is steady but nothing special. You also get a continual shower as the exhaust is very wet. On cold days you can't see a damn thing in front of you for all the steam from the chimney!

To go one further on superheaters - I think the only ones really worth fitting are the radiant type that extend over the fire and do give a useful increase in steam temperature, whereas the normal LBSC type that end at the firebox really only dry the steam a bit.

Doug Hewson did some tests on his Y4 when the original superheaters burnt out. He tried various types and the radiant type easily outperformed the LBSC type, cutting water and coal consumption by half. He did try the coaxial type as well but found them to be pretty useless.

I think superheat is probably more important for small locos with limited boiler capacity and small fireboxes. The last thing you want to be doing with such a boiler is continually pumping water into it and feeding coal into the firebox.

John

Thanks all

I quite agree with Mike superheaters at this scale are a waste of time.

Mark P.

Forget all the theorizing, have any of the people who contributed to this thread actually driven an unsuperheated model steam loco? At all times of the year?

I can't believe anyone would actually choose to drive around in their own mobile fog bank, getting showered with oily water as the lubrication is washed off their cylinders.

Even in winter my 3 1/2"Q1 which has 2 full radiant return bend superheaters produces very little visible exhaust, and it is definitely possible to feel the superheater 'turbo' effect when the engine is working hard. On the other hand driving the club's unsuperheated 'Maid of Kent' in damp weather is a pain, but it's too much hassle to convert it.

The only real drawback is keeping the superheater flue clean as it's hard to get a brush in there, making and fitting them during construction is not difficult. They have to be stainless, copper eventually disintegrates at the firebox end.

Nick

And of course my forum pic shows plenty of steam from the exhaust!

A sure sign that boiler pressure was well down,

Or posed for effect!

A short, interesting and very technical article coming up in ME 4466 on this very subject

Diane