Boilers

[steamboatmodel]

Hi PDs,
This is a question for all but mostly Sandy, does any one have any experience in building Yarrow style Boiler, or Scott Marine types :?:
Regards,
Gerald

[derekwarner_decoy]

Hi PD's - Gerald, I am sure that our "ASTEEMED"  :nah resident steam technical officer will respond, but I think both the Yarrow & Scotch versions of boilers are beyond the design calculations of model steam

The former relies on a multi drum closed loop of water+heat=steam>work>condensing=water, then repeat the process

I think the latter relies on really, really HOT steam to do the work

The Stuart Turner range have a 'FLASH' steam driven high speed piston engine & PJ posted a question on FLASH steam a few weeks ago

So possibly 'Scotch, Yarrow & flash' are all interelated - thank goodness my ACS boiler is rated to 45 PSI only

In reflection, I think Tony with his 1/10 scale crew to shovel coal into boiler is the best bet - being NO gas needed     - Derek

[sandy_ACS]

Hi PDs,
This is a question for all but mostly Sandy, does any one have any experience in building Yarrow style Boiler, or Scott Marine types :?:
Regards,
Gerald

       :news

Hi PD's....Gerald....the answer here is yes, I have made both types in the past, however, I feel that a true Yarrow type is a lot more tricky to get right, due to the very high number of water tubes involved.
I have a design for a SCOTT water tube boiler, based on an original design by K.N.Harris, ACSHBHR-S of which I have now made 3 to special order, with a possible 4th on the cards from a very good customer in NZ, and is quite capable of keeping a 1" bore and stroke twin steam engine happy.

This type of boiler is an excellent compromise of all the issues between steam generation capability and complexity of structure and is an excellent boiler for model steamboat use. It has the advantage of high conversion rate (steam produced for heated surface area) and is a far easier boiler to build than the Yarrow.
It also has an advantage in that it does not require such a tall funnel as does the Yarrow and is more compact in it's main casing.

I believe our Derek    :respect2 was referring to a SCOTCH marine boiler, which is a return flue type, much used by commercial shipping, as was the Yarrow, however, he is excused this mistake since the SCOTT is not so very well known and it is an understandable error....NO PROBLEM DEREK...I also made the same mistake before I had seen the SCOTT design.  

I attach a GA drawing of the SCOTT water tube boiler for the benefit of all.

 :ohno  :sob  :hmmm

The down sides of this type of boiler are (a) the need to provide a constant water feed (the main barrel is relatively small, and the steaming rate very high) so a water pump is a must, and (b) of course the cost of such beasts. A boiler of this type will unfortunately set you back around £550.00 + shipping costs.
 :sob  :hmmm  

Best regards.

Sandy

[derekwarner_decoy]

Goodness PD’s – if this isn’t taking coal to Newcastle! – now we have a Scott talking about a Scott boiler – however saying this I think I had beta stick to boiling the billly with eucalyptus twigs instead of commenting on issues obviously beyond my mental comprehension – sorry - Derek
 
 
 
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[sandy_ACS]

Goodness PD’s – if this isn’t taking coal to Newcastle! – now we have a Scott talking about a Scott boiler – however saying this I think I had beta stick to boiling the billly with eucalyptus twigs instead of commenting on issues obviously beyond my mental comprehension – sorry - Derek

     :respect2

Hi PD's....Derek, you have absolutely nothing to apologies for my friend, and I will add, for the record, that your understanding of steam related topics is, generally, very high.

The Scott water tube boiler, so named after it's original designer 'Mr David Scott' is one of the more obscure, and as such, less well known types.
It was developed in the early 1900's, as a high rate steam producer, long before the coming of Flash steam.
I only came across the design concept about 10 or 11 years ago, whilst looking up something else. Subsequently I came across the design for a version of this type, in a book by K.N.Harris and decided to build one just to see how good it was, and it turned out to be much better than I expected, albeit, this original was fired with a blowtorch type burner.
Horrid, noisy thing.    :nose
I was so impressed with it, especially with the much easier construction, when compared to the Yarrow boiler, with it's 3 drums and large array of water tubes, that I refined some of the features, to include a ceramic burner and to improve the build, and this is the design I attached in my last post, and is now my ACSHBHR-S horizontal boiler, high rate special. Only built to special order and although the drawing states 90 psi max working pressure, which is high enough for most model ship use, this can be extended up to 150 psi without design change.

From a model steamboat point of view, the Scott type has a distinct advantage over the Yarrow, in that the overall height and width of the main casing are much reduced, thus lowering the C of G and requiring less beam width, and is an easy boiler to get into service whilst in a model...one things for certain...It is very easy to light the burner...  :music     ....
as it has a row of air inlet holes along the bottom of each side of the main casing, through which you can insert the fuse..... :? Er...match.

The Yarrow type, in a similar scale, is both a good bit taller, and with a very tall funnel, and also broader, with obvious implications on C of G etc, and usually needs the assistance of a blower (forced draught up the funnel) to draw the fire/combustion gasses whilst raising steam.

From a steam raising viewpoint, I must admit that the Yarrow (in larger sizes) probably has the edge on steam production rate (providing sufficient water tubes are employed, typically 30 or 40 are employed), however, in the smaller scale of boilers we employ in our model ships this becomes a problem, as the water tubes must be above a minimum 3/16" ID to work efficiently, any smaller and the bore is to small for efficient water circulation, due to surface friction, turbulation etc (unfortunately, you cannot scale physics, nature, or their laws), and tubes of this size spaced very close together are not an easy issue from a build point of view.
To overcome this issue, in the smaller scale versions of the Yarrow, it is usual to use fewer, but larger bore, water tubes, and thus the efficiency factor, and steaming rate is reduced.

At our scale there is little to choose between the two and the Scott is certainly the easier (relatively) to build.

One very big advantage, of both these boiler types, is the ease with which a true superheater and even a feed water heater, may be included, due to the large space available within the outer casing.

As a comparison, Derek and PD's, the Scott boiler design as posted, will generate at least 4 - 5 times as much steam output, in the same time frame,  than will the horizontal version of your PS DECOY boiler, and it is only a little larger overall. It does, of course, use just a TAD more gas in doing so....but hey!...   :wink:

Hope this sheds a little more light on this type of boiler.

Finally, Derek and PD's, there are a whole host of boiler types out there, some of which are not a lot of use to us in model ships, and a lot which are, or can be used for such, however, there are probably a whole host of others that even I, as a boiler/steam engine maker, have not yet come across, so you never know what is to come.

Perhaps my profession has provided me with a lot more exposure, and hence knowledge in steam related matters, than some other fellow modellers, but certainly not all by a very long chalk, as there are a good number of extremely knowledgable guys out there, and I certainly do not know all the answers and probably never will. The field is just to vast for anyone to know all of it.
Anyone who thinks/say's they do is either a fool or very delusioned.

What I do know will, with great pleasure, be freely passed on to anyone who asks.

               :wink:  :wink:

Keep happy

regards all.

Sandy

[steamboatmodel]

Hi PDs,
I have uploaded some shots of the Boiler from my Steam Launch (Sorry its not a Paddler, that one is still in the planing stage), It is my owen design a cross between a Yarrow and a Scott. It has been hydrostatically pressure tested to 90psig and runs at 25psig. I am still trying to get the burner to operate to my satisfaction, but that will be another subject. My question particulary to Sandy is I was told at the Hobby Show by someone who said that they were a Engineer that I should have the two drums on the bottom connected together. But I have never seen this done on a full size Yarrow and have never seen a working model of an Yarrow. What is your opinion?
Regards,
Gerald

[sandy_ACS]

Hi PDs,
I have uploaded some shots of the Boiler from my Steam Launch (Sorry its not a Paddler, that one is still in the planing stage), It is my owen design a cross between a Yarrow and a Scott. It has been hydrostatically pressure tested to 90psig and runs at 25psig. I am still trying to get the burner to operate to my satisfaction, but that will be another subject. My question particulary to Sandy is I was told at the Hobby Show by someone who said that they were a Engineer that I should have the two drums on the bottom connected together. But I have never seen this done on a full size Yarrow and have never seen a working model of an Yarrow. What is your opinion?
Regards,
Gerald

     :bow

Well done Gerald...it is not many modellers who would consider building their own boiler, let alone take on one of the more complex designs...and from the pictures you posted, your has the makings of a very good unit......however, I think you will need to make a few adjustments.

What follows, Gerald, is based purely on my obsevations of your pictures, and in no way is meant as a derogatory statement...rather, I hope you take my comments in the spirit in which they are meant...namely...to assist your path to getting the most from the unit.
I am not in the business of making derogatory comments, other than in fun....that said...YOUR BOILER IS RUBBISH..    :music  :nose .
  ...just kidding.

Seriously though, Gerald, from the pictures you posted a couple of things immediately came to mind, both of which have to do with thermal circulation.
1/    Water circulation.
2/    Combustion gas circulation.

Taking water circulation first..since this is the more obvious...and I believe it was this that your engineer chappie had cottoned on to when he suggested connecting the lower headers together.
If you take a look at the Yarrow diagram (attached) you will see the water circulation path indicated, as are the combustion gass flow paths.

I think the main area for alteration is the water tubes....you do not have enough of them, and those you do have are all (a)in the same place, with respect to the main barrel and (b) I suspect are all the same distance within the main barrel.
You thus have no way of getting a proper thermal circulation going.

Returning to the Yarrow, you will see that the water is rising in the inner sets of tubes (nearest the burner, hence hottest) and the replacement (cooler water) is passing down the outer sets.

On your boiler this second return path is missing, hence your circulation will be very erratic and unpredictable.

Without going into thermal dynamics to deeply, lets just state...materials of different density (hot and cold water) cannot occupy the same space at the same time....(chaos theory might find a way, but the best they have come up with so far is the WARP DRIVE...where matter and anti- matter try to occupy the same space, but only succede in destroying each other), hence your heated water cannot be replaced by cooler water in the same tube.

2/ Combustion gas circulation.....again I refer you to the Yarrow diagram, where you can see that the banks of tubes lie at an angle to the heat source...this permits the hot gasses to pass between the tubes, thus heating more of the exposed surfaces, giving much higher thermal transfer of the heat to the water.
On your boiler, the tubes are vertical and so very little of them is exposed to the direct heat, and since this heat rises straight up, until it meets the bottom of the main barrel, where it will be deflected to the side, the thermal transfer is severely reduced.

Another related issue here, is the fact that both of your sets of tubes are reasonably close together, in effect enclosing the available heat within a small space, which will generate a fair amount of turbulance, especially when you add in the effects of reflected heat (being reflected off of the inner, exposed, sides of the vertical water tubes).

  :hmmm      

Ok.. what can be done....

What follows may sound a bit drastic...but with care...can be achieved.

One thing is for sure... the engineer chappie's idea of connecting the water headers together, albeit in the right direction, will not overcome the thermal circulation problems.

1st.... I suggest that you bend the lower water headers outwards, to increase the spacing, and to get the existing tubes at an angle to the heat source, I am assuming these tubes are made of copper, so this should be reasonable do-able.
2.  Add a second row of water tubes, outside the existing ones, and staggered, as shown in the Yarrow cross section A-A. these should connect to the main barrel about 1/2" - 3/4" above the junction level of the existing tubes.

These two modifications will overcome the water circulation problems completely, and will vastly improve the combustion gas flow, and hence the thermal transfer of energy to the water, and may help with your, as yet undisclosed burner issues.(although I have my suspisions).
The steaming rate will be much higher and the fuel consumption, per unit of steam, will be lower.
I appreciate that this may require you to make a new (or modify the existing one) outer casing, but I think the work you have done so far deserves the extra effort, in order to get the best from it.

 :news          

Ok Gerald, and PD's...enough of the technical BULL***T,.

Hope this helps.

Best Regards.

Sandy.

[Eddy Matthews]

Sandy, reading your reply certainly shows just how technical a steam engine and it's related components really are!

I watched a documentary on steam engines the other day, and one of the things that was mentioned was that the Waverleys engines were about 35% efficient - I found that amazing considering that most "so called" modern internal combustion engines are less than 20% efficient!

Since steam engines have been used very little in the last 50 years (if we exclude steam turbines) it makes me wonder just how efficient they could have become with another 50 years of development - The mind boggles!

Another question that sprang to mind - If the Waverleys engines are 35% efficient, and they can now use fuel oil or gas (rather than bulky coal) to fire them, why don't large ships use them? Surely they could save a fortune in fuel costs compared to diesel engines?

[steamboatmodel]

Thanks for the suggestions Sandy, I think I follow it (I can't get my computer to download the pdf's rightnow) When I built the boiler I included five tubes which cross over the flame space (they are visible in some of the end views), plus the boiler was sized originally to fit in the casing of the Wilesco D48 Boiler shell. The narrowness of this constraint is part of the problems with the burner I think. I will try to incorporate the mods you suggest.
Regards,
Gerald

[derekwarner_decoy]

Hi PD's - when I look at various WEB pages on model boilers/fittings/engines I see red painted/black painted & unpainted  unions & elbows [the body of the fittings painted, the fitting nuts are usually left unpainted], however is there a protocol in the model world for colour coding :idea: [red for live steam, black for exhaust steam  :?:  :?: - Derek

[Khephre]

Fercripesake, Sandy! I'm glad you're on our side.... you and yr non-derogatory remarks! I laughed and laughed until I had to go and change my trousers!

Another fascinating post - just goes to show how much there is to learn about steam, and how much knowledge we've lost in the last 50 years.

[sandy_ACS]

Fercripesake, Sandy! I'm glad you're on our side.... you and yr non-derogatory remarks! I laughed and laughed until I had to go and change my trousers!

Another fascinating post - just goes to show how much there is to learn about stea :nose m, and how much knowledge we've lost in the last 50 years.

     :music  :music

Who?...Me?...Derogatory?.....Nah!!....                  :music  :music

I just tell it as I see it Tony,...far be it for me to critisize anothers very fine efforts...but I will offer advice, when asked, as to possible ways to improve things.

BTW...now you know why I allways wear Brown Corduroy Trousers....it saves rushing to change them...      :nose

Yes, it can appear a very complex subject...and it most certainly is...and yes, we have lost a lot of knowledge, and Knowledgable people over the past 50 years....this is why I enjoy, in my own modest way, passing on some of my own hard learned knowledge to others.

Keep smiling.

Best regards

Sandy.

[BC Electric]

Sandy, being new to the forum and what not, been reading lots of posts about of course live steam and boilers. I have printed in front of me the PDF file of your Scott Water Tube Boiler. Very nice and the photos of it you posted are even nicer. My question is mayby a matter of Canadian English terms being different than yours. You state all joints are "Silver Soldered" ! I have a boiler somewhat similar to yours,,lets call it the "this is the material I have so this is what I made type" but all joints on it have been "Silver Brazed".  Is this what you use on the boiler is just silver solder and I over did it with the silver brazing?

Have a great day
Jim
Abbotsford, BC

[sandy_ACS]

   

Hi Pd's......No I'm not going to post the next part of the saga...so you can all go back to sleep :nah    

Jim (BC Electric)

First off, welcome to the forum, I am sure you will enjoy, and hopefully join in,  the fun and games and the friendly banter that goes on.

Good for you, having a go at a boiler, and just so you know...silver soldering and silver brazing are one and the same...as you say, just different english.
Thanks for the comments on the Scott boiler, much appreciated.

The one shown in the photos has a slightly modified layout to the one you have on PDF, however, this is only with regard to the main steam dome, safety valve and pressure gauge locations, the rest is pretty much the same. The changes were made to suit my customers requirements and don't have any effect on the design as a whole.

I hope this clarifies things for you.    

How about some pictures of your one?. :twisted:  :twisted:  :wink:  :?:  :?:

More soon PD's.


Regards to all.

Sandy.

[BC Electric]

Sandy, so you know, here in the new world,,,,silver solder, and silver braze are two very different things. silver braze is in the 1200 degree range depending on the rod you use, and most times is done with standard torch set up. Silver solder is mostly done with just a propane hand torch or one gas using mapp in the 800 degree or less range.

More important, do you make these boilers as a busness, mighty fine looking I must say.

Jim
New World
Canada

PS. The long wait after you posted is not that I am slow, just we have a few hundred new students at work now,,all asking where to go,,hmmm and I can't really tell them,,where to go.