To superheat or not to superheat. That is the question...

[darrene]

The time has come to get a boiler on the 3.5" Hall.

I have done some research but given a total lack of experience and equipment, producing something both boiler shaped and capable of passing the current codes might be a bit of an ask.

I'm happy to be contradicted but perhaps it may be worth putting the cost of the materials and equipment towards a commercial offering instead.

Chatting with a friend of mine who runs several different sized locos including a Hall in fact, he suggested the option of not going with the six pair of superheater tubes in the LBSC design.

His argument is that it adds time, cost and effort for negligable benefit at this scale. His Hall does not use them and he opted instead for common sized tubes across the boiler.

I plan to ask the boiler maker  too but could I ask what your thoughts would be on the matter? It's probably the right point to make the decision and I'd be keen to get an idea of experienced consensus. I'll be occasionally steaming in the garden, so I suppose I wouldn't be running enough to notice economy anyway, but...

Thanks

Darren

[RGR 60130]

I'm inclined to turn your friend's argument around and say for negligible time and cost you get a better boiler. If cost is a big issue you could perhaps use fewer, bigger superheater elements. Having put lots of heat energy into raising the temperature of the water, a lot of which you won't get back, it makes sense to put a bit more heat energy in, happy in the knowledge that you can get all that useful energy back. Even if you only achieve a dryness fraction of, say, 0.7 rather than superheated steam it is all useful energy. I can guarantee some won't agree, but such is life.

Reg

[darrene]

Thanks Reg. Yes, the cost is comparatively negligible. Am I correct in thinking that with stainless superheaters, the potential for failure also becomes negligible?

Seems more like a case of why wouldn't you really..

[RGR 60130]

A set of stainless superheater elements should prove reliable if correctly made. Steam Technology who do the TIG welded boilers also make superheaters. It might be worth asking them for a quote for boiler and superheaters as a package. The last time I checked their lead time was one of the shortest among the professional boiler makers.

Reg

[coniston]

I would stick with the boiler as designed for super heaters, you don't actually have to fit them but at least the option is there. If not fitting the super heaters then it is usual to fit a twisted strip of copper into the flues to promote better heat transfer and provide a restriction so as to even out the gas flow through all the tubes.

My Super Simplex doesn't have super heaters and it is very noticeable by the amount of water used and the very wet steam exiting the chimney, although it does still steam very well, probably as well as a super heated one.

Stainless radiant super heaters that protrude above the fire should last a good time as Reg says. Not having super heaters does also free up space in the smokebox making pipework access a lot easier especially on a 3 1/2" loco.

Chris

[cplmickey]

The 3 1/2 inch Hall was the first boiler I made. Bearing in mind I'm an electrical engineer and almost totally self-taught when it comes to model engineering. The hardest part for me was making the formers as I'm no woodworker either but it's one of those jobs that's easy enough with a bit of patience. Ian

[darrene]

Cheers Ian. That's inspiring to hear.

Did you manage it on your first attempt? Most impressive if so!

I have wondered how much of a challenge it would be to try and make myself. I'd be starting from zero in terms of equipment, materials and experience, so there's a fair bit of outlay with no guarantee of success.

With that said, approached carefully and methodically there's really no reason I shouldn't manage it I suppose, and it would be an incredibly useful skill to have.

Without wishing to downplay the unquestionable amount of skill required to make a good boiler, I imagine good preparation, attention to detail and learning to control the heating of parts successfully is half of the battle!

I have a copy of Alec Farmers boiler making book for some bedtime reading in any case

[dhamblin]

Following on from Chris' point about partially filling the large flue tubes if superheaters are not fitted - a good example is the full size GNR 'Atlantic' No. 251. A recent piece in Steam Railway magazine noted it was a poor performer (steaming rate) when used for railtours in the 1950s due to the lack of superheaters in the large flue tubes, caused by the backdating of the loco to original condition (less superheaters) but keeping the newer boiler.

Regards,

Dan

[cplmickey]

Apr 24, 2021 19:40:53 GMT darrene said:

Cheers Ian. That's inspiring to hear.

Did you manage it on your first attempt? Most impressive if so!

Darren, I won't pretend it's the prettiest boiler I've ever made but it passes the tests and fits in the frames so I'm happy with that. I tend to be a lttle pedantic so spend a lot of time getting things just right before soldering them together. It's a case of not rushing and also working out how to clamp things and hold things that are going to be red hot. If I made another I wouldn't fit girder stays but the boiler inspector is happy so for now that's what I've got. Ian

[ejparrott]

I would not build a boiler without a superheater. It has been proven that significant gains are made by installing proper super-heaters. Much actual scientific research has been done on the subject, and not by Farcebook armchair hearsay experts.

[Jock McFarlane]

May 3, 2021 17:51:38 GMT ejparrott said:

I would not build a boiler without a superheater. It has been proven that significant gains are made by installing proper super-heaters. Much actual scientific research has been done on the subject, and not by Farcebook armchair hearsay experts.

I think you must be thinking fullsize here when you say it is proven and there is no argument that superheating saves coal and water. 

I wonder if anyone has actually run tests in 5" or 7&1/4"  comparing a superheated boiler with a saturated one. You would have to be really keen to go to all the trouble of running a proper test. A proper test would not involve simply removing the superheater tubes and comparing results but using a boiler built as saturated. I cannot imagine anyone would go to all that trouble and, in any event, it is much more fun to speculate.

JM

[jo479]

I have several engines, some are superheated some are saturated, unless you want to enter IMLEC you wouldn't notice much difference between them, except the saturated steam boilers use more water and a bit more coal.

[ejparrott]

May 3, 2021 19:30:02 GMT Jock McFarlane said:

May 3, 2021 17:51:38 GMT ejparrott said:

I would not build a boiler without a superheater. It has been proven that significant gains are made by installing proper super-heaters. Much actual scientific research has been done on the subject, and not by Farcebook armchair hearsay experts.

I think you must be thinking fullsize here when you say it is proven and there is no argument that superheating saves coal and water. 

I wonder if anyone has actually run tests in 5" or 7&1/4"  comparing a superheated boiler with a saturated one. You would have to be really keen to go to all the trouble of running a proper test. A proper test would not involve simply removing the superheater tubes and comparing results but using a boiler built as saturated. I cannot imagine anyone would go to all that trouble and, in any event, it is much more fun to speculate.

JM

Yes, it has been done, exactly as I said. Jim Ewins conducted extensive studies into it with his 5" loco, an LNER tank from memory.

[John Baguley]

I'm with Ed on this one. I wouldn't design or build a boiler without superheaters because I'm happy that it does make quite a difference, if only in the better performance that they give. However, there are superheaters and superheaters. I reckon that the coaxial type are neither use nor ornament and the normal LBSC type that only extend the length of the flues are only really steam dryers and give little in the way of actual superheat (but probably do help). In my mind, the only sort really worth fitting are the full length radiant type superheaters that extend to the back of the firebox and can give another 100°C or more to the steam temperature.

OK, unless you want to win IMLEC and are happy with a very wet exhaust that gives you a shower whenever you run then superheaters may not be worth the trouble. But if you want an economical to run loco with snappy performance then I consider superheaters (radiant type) to be essential. I'm sure that some locos that are normally hard to keep in steam would benefit from the addition of radiant superheaters if only to reduce the amount of steam needing to be supplied by the boiler. I'm sure that my Helen Long would struggle to keep up boiler pressure without the radiant superheaters to help.

Although perhaps not a true comparison between a boiler designed as saturated and one designed with superheaters, Doug Hewson did some comparisons on one of his Y4 locos when the original superheaters burnt out. He ran it for a while with no superheaters at all and noted the water and coal used over a given period. He then fitted coaxial type superheaters and found that they did nothing at all to reduce coal or water consumption. Finally, he fitted a new set of radiant superheaters and the difference was very noticeable. He wrote this up in Model Engineer at some point.

John

[pault]

May 4, 2021 18:25:22 GMT ejparrott said:

May 3, 2021 19:30:02 GMT Jock McFarlane said:

I think you must be thinking fullsize here when you say it is proven and there is no argument that superheating saves coal and water. 

I wonder if anyone has actually run tests in 5" or 7&1/4"  comparing a superheated boiler with a saturated one. You would have to be really keen to go to all the trouble of running a proper test. A proper test would not involve simply removing the superheater tubes and comparing results but using a boiler built as saturated. I cannot imagine anyone would go to all that trouble and, in any event, it is much more fun to speculate.

JM

Yes, it has been done, exactly as I said. Jim Ewins conducted extensive studies into it with his 5" loco, an LNER tank from memory.

There have been a number of people who have looked at this subject Jim, if I remember rightly Prof Hall was another. Personally I would always advocate radiant superheaters. Have a look at modeleng.proboards.com/thread/7812/7-1-4-dyno-car

[ejparrott]

Oh yes, fully radiant. My club and my own Romulus (Romulii?) have two elements which extend all the way to the door plate. My Manning Wardle is somewhat larger and has 4 elements which also go all the way to the door plate. The improvement in the behaviour of both engines with all the work I've done recently is considerable. I also upped the boiler pressure from 80 to 100 on mine, 90 to 100 on the clubs. Water consumption on both is hugely reduced from what it used to be, of great importance when your track is a mile long

[darrene]

So my take-away from this thread is given the boiler flues are being made to accomodate a superheater, now could be the time to look at a stainless radial type, extending the LBSC design lengths to the back of the firebox.

I will certainly do some more research into the whole field.

Out of curiosity, is there anyone here with the stainless fabrication skill and superheater knowledge, who might be prepared to take a commission to build one for me when the time comes?

[oldnorton]

May 4, 2021 18:51:36 GMT John Baguley said:

He then fitted coaxial type superheaters and found that they did nothing at all to reduce coal or water consumption. Finally, he fitted a new set of radiant superheaters and the difference was very noticeable. 

Totally agree with you on what has been found out and reported by others regarding the need for radiant superheaters.

Now, if the coaxials were stainless and extended over the fire, then you have a big surface to absorb radiant heat perhaps?

Norm

[ejparrott]

May 5, 2021 9:12:16 GMT darrene said:

So my take-away from this thread is given the boiler flues are being made to accomodate a superheater, now could be the time to look at a stainless radial type, extending the LBSC design lengths to the back of the firebox.

I will certainly do some more research into the whole field.

Out of curiosity, is there anyone here with the stainless fabrication skill and superheater knowledge, who might be prepared to take a commission to build one for me when the time comes?

The boiler makers Steam Technology have made me three sets now. In each case I've machined the parts and they've fabricated everything for me to my drawing. They post on Facebook semi-regurarly the ones they build for normal builds

[darrene]

Thanks Mr P