Author Topic: 3 inch boiler build  (Read 24772 times)

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #225 on: December 29, 2018, 06:50:35 PM »
I prefer the French alcool a bruler myself. Doesn't make your tongue go purple like meths does.

 :wine1:

Offline Gas_mantle

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Re: 3 inch boiler build
« Reply #226 on: December 29, 2018, 06:53:02 PM »
Sorry to hear it isnt going to plan Gary  :disappointed:

I think you did a fine job of building it so even if coal firing isn't an option it's still a project to be proud of.

It's similar in construction to my 3" boiler and I have pretty much the same problems that your are experiencing, having said that though you have put considerable effort into building it so I'd be inclined to try again after a few more improvements.

Firstly I think an electric blower will be an improvement on your hand fan and although you are reluctant to try I really think it is worth considering.

Looking at your fire box photo (2nd image in post 210), it looks to me that the fire hole opening/door is too low and too big - my guess it the airflow being drawn in is passing infront of and above the coal. Can you fit a tight band around the bottom of the opening and make a closer fitting door so that air is drawn though the grate?

I'd possibly look at making a temporary firebox of a smaller diameter and one where the coal is closer to the fire tubes. It seems to me to be expecting a lot for all that air passing through a large diameter firebox to then funnel into a 1" diameter chimney. My guess is the airspeed up the chimney will need to be fast and consistent in order to have any appreciable draught through the large diameter fire grate.
« Last Edit: December 29, 2018, 07:13:47 PM by Gas_mantle »

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #227 on: December 29, 2018, 11:23:53 PM »
Thanks for this Peter.

Everything you say here makes sense. I have been a bit dogmatic in not being drawn (no pun intended) to electric blowers, but having tried everything else I could think of and failed, it would be sensible for me to review my position!

I take your various points about the firebox design. This may point to a complete rebuild of the firebox, because - as it happens - this evening I have roughed out a housing for the Trangia meths burner, for which I 'borrowed' parts of the firebox. The meths setup is looking good, and I'm inclined to pursue it now because I feel I'm due a bit of progress. This would leave me with two options for solid fuel: (a) to make a new firebox for this boiler along the lines you suggest, so it can run on either fuel by swapping the firebox and the meths burner, or (b) to just keep this boiler for meths, and build or buy a bigger one with more tubes for coal at some point in the future.

At this point I'm more inclined to the latter...

Offline AOG

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Re: 3 inch boiler build
« Reply #228 on: December 30, 2018, 12:34:33 AM »
How long was the extender on you chimney? I recall reading that as a rule of thumb for good natural draft, the area of your chimney should be 4-5 times the total area of your fire tubes otherwise your not getting enough delta P for it to be effective.

Tony

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #229 on: December 30, 2018, 12:40:05 AM »
Hi Tony -

In reply # 219 MJM suggests a 2 metre length of pipe. I happened to have a piece about that length lying around. It made a good sliding fit inside the chimney so I just used it as is. Smoke came out of the top pretty quickly but I didn't see any significant change in the fire.

Due to my firebox design, I think. Time to re-evaluate...

gary

Offline Gas_mantle

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Re: 3 inch boiler build
« Reply #230 on: December 30, 2018, 12:48:29 AM »
Gary, I can see the sense in increasing the chimney height but if you you do it by sliding a tube into the chimney you are further constricting the airflow.

I'd be inclined to further experiment with the firebox and blower arrangement unless you can lengthen the chimney without reducing its cross section area.

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #231 on: December 30, 2018, 12:53:39 AM »
No problem with alcohol to fire an open fire or a plain pot boiler from underside, I agree, but with an internally fired boiler a vacuum fan in the chimney is mandatory to start steaming !
I also have a lot of excitement when models start to breath...

I did a brief test on 'alcool a bruler' this evening in a Trangia burner mounted on a small column inside a fairly open, airy housing. When I sat a sheet of brass on top of the housing, just as an experiment, the flames died down due to lack of air and no updraught. When I took the brass off and sat the boiler on the housing, the flames rose and gathered into a neat and hot cone pointing up the firetubes. This is looking good...

I'm going to go with this for a while now and try to get it ready for actual use so I can start looking at building my first engine. Details and pictures in due course.

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #232 on: December 30, 2018, 12:58:41 AM »
Gary, I can see the sense in increasing the chimney height but if you you do it by sliding a tube into the chimney you are further constricting the airflow.

I'd be inclined to further experiment with the firebox and blower arrangement unless you can lengthen the chimney without reducing its cross section area.

Fair point, Peter. Thinking about it, I'm guessing that's what MJM actually meant.

Will keep all of this in mind for when I come back to solid fuel (maybe with a bigger boiler), but I have done a lot of inconclusive experimenting and now feel it's Decision Time, hence going with meths as the next step.

Probably...

Offline MJM460

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Re: 3 inch boiler build
« Reply #233 on: December 30, 2018, 09:06:38 AM »
Hi Gary,

I have not disappeared, but with 10 hours time zone difference and holiday schedule (or lack of it) here, the conversation has certainly progressed since yesterday.

I think others are on the right track suggesting that the extended chimney should be larger diameter, rather than smaller than the boiler stack.  I was also thinking of perhaps a turned wooden or cork plug to get a reasonable seal.  Any cold air which enters at the connection will tend to destroy the draft, and that is about the lowest pressure area, so it is important to avoid unnecessary leakage.

I also like Peter’s comments about the fire.  If you think about it, if you want to extinguish a camp fire, or the fire in an open fireplace before you go to bed, it helps to spread out the coals. The larger area means the coals lose more heat, and soon are losing more than they produce, so the fire goes out.   On the other hand to encourage a reluctant fire, the newspaper over the fireplace opening trick, or blowing into the base of the fire encourages the air at higher velocity into the kindling, instead of bypassing it, and carefully stoking extra wood so the heat is held in (but allows air flow) means it loses less heat than it produces, so it all gets hotter and soon starts. 

I am sure there is quite an art to coal firing, though I will leave it to those who have had more practice to comment.  But certainly spreading the fire over too large a grate, along with restricted flow through the gas tubes, almost certainly contributes to your difficulties.  The trangia burner, by confining the fuel and combustion to the intended location around the lip ensures the burner operates well, even out in the open.  I am glad it appears to be working well for you.

I am not suggesting a boiler rebuild, though experimenting with a smaller firebox and grate may produce results.  And keep experimenting with all those means of assisting the draft.  Remember that an induced draft fan has to take the heat of the flue gas so no plastics!  A forced draft requires sealing the fire box well and introducing the air under the grate.  You don’t want heated air to escape below the boiler, and you want it all to participate in combustion.  Some locomotive operators talk about secondary air, above the grate.  Industrial gas burners also have both primary and secondary air supply and controls.  This all has to be carefully controlled to complete the combustion, but not cool the gas too much, and not destroy the draft - more variables to get to understand.  It all makes interpreting the results difficult, but that is why it is such a fascinating challenge.

There certainly has been a wealth of learning in all you have done so far.  You and all the rest of us will know so much more about what to look for in the next design you build.  I am sure there will be another.  But after you build your engine.  And first, get this one going for steam for your engine.

MJM460


The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #234 on: December 30, 2018, 12:41:07 PM »
Hi again MJM -

Yes, these global conversations develop their own rhythms over time...

Thanks for this great post - you have a great deal of knowledge and you communicate it clearly. Much appreciated.

All of the points you have made make perfect sense, and will be invaluable when I come back to solid fuel in due course. Regarding the extension tube, you were very clear about the need to seal it and so on. It was really an impulse on my part to grab the 2 metre length of copper pipe that I happened to have lying around and use it in the provisional way I did. I should have been clearer about that really. Again, I will certainly keep it in mind as an option for the future (but properly set up!).

Part of me remains reluctant to get involved with 'artificial' means of inducing a draft, such as a blower - which is one of reasons I like meths as a fuel. The idea of just letting it gently do its own thing without needing much attention feels nice and organic to me. That's where I'm heading now. It also has its own kind of beauty. And it reminds me of the Mamods of my childhood...

However, the idea of using coal remains a Holy Grail to me at this point, and I do expect to return to it in the future. Whether I do so with this boiler or save it for a bigger one remains to be seen, but I would like a bigger boiler at some point so it may make more sense to look to that for coal firing.

Yes, this thread has certainly been (and no doubt will continue to be) an education to me! So much knowledge and experience shared by you guys... If it has proven useful to others too, then even better.

I will take another look at what you have been doing in your own threads later - not only to return the courtesy but also because I like your approach and aesthetic. However, I'm going out to the shop now to grab an hour on developing the housing for the Trangia before I go to pick up my daughter...

Cheers   :ThumbsUp:

gary


Offline MJM460

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Re: 3 inch boiler build
« Reply #235 on: December 31, 2018, 06:55:14 AM »
Hi Gary, thank you for the nice compliment, it always gives a lift to the soul to find that my contribution is appreciated.  The things that were the bread and butter of my career are proving most useful to understanding so much of our hobby.  After all, it is the same laws of physics.  So it is a pleasure to share, a small contribution in return for all the stuff about engines and machining which I am learning from others.  In machining, I really am a beginner, but I do also have a very good instructor who shows me more of the “how” whenever we get together.

I expected you to try what ever pipe you had to hand, (though not plastic) and there is learning whether it works or not.  A lot quicker than trying to calculate the answer.  I would expect a larger diameter might be more helpful, but again, difficult to predict by theory how much better.  With only a small pipe to hand, I also would have tried it.  The same volume of gas through a smaller diameter requires more velocity.  The friction losses tend to be proportional to velocity squared, so increase quickly with a smaller diameter chimney.  Likewise with a larger diameter, they rapidly reduce, leaving the draft to draw the air through the firebed and flue tubes with minimal extra friction to overcome.

All my reading on model locomotives suggests that some form of draft assistance is normally required.  Many of industrial furnaces have had induced draft or forced draft fans in addition to a tall stack.  I agree with your preference for natural means, so probably exhaust steam when the engine is running, but how to get enough steam to start?  Perhaps a small auxiliary boiler, meths fired, like one of your Mamod boilers.  This would not be far from full scale practice.  Ocean going ships often have somewhere on board a small generator driven by an engine that can be hand cranked to start, to generate enough power to get the main equipment started in case some fault trips everything.  It was called a “Black Start Generator”.  At sea in the dark, the engineer needs some way to get started without outside assistance once the problem has been fixed.  Some land based remote mining or oil facilities have something similar, though there are more options for land based plants. 

By the way, you can see the similarity to the little Mamod boiler in my first boiler, in fact, it’s first firing actually used the Mamod burner.

But with the long term plan in mind, what ever gets you started provides information on how much draft you need, and even whether draft alone is sufficient to achieve the performance you require.  You can always replace your initial attempt when you know you have the right problem.

I hope the Trangia adaptation works well, looking forward to the continuing story.

MJM460
The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #236 on: December 31, 2018, 01:33:56 PM »
Hi MJM460 -

Using a small boiler to drive a steam blower is an excellent idea! The fact that the other day the boiler was going like a demon on wood for a little while when the steam blower was active suggests that with some additional draughting on startup the system might be viable. And making a small meths-fired pot boiler would be easy enough and a nice project in its own right.

I'm going to go ahead and get the housing for the Trangia made, as I'm pretty sure that I know where I'm going with that and feel it's time (hopefully!) for a success. But after that... well, I was looking at some lovely bits of pipe of various kinds that I liberated from a skip outside our local water provider's works and one of them would be ideal to make a smaller, neater and simpler firebox, as suggested by Peter and yourself... so I might still yet give it a go   :)  Also, fitting a door to the previous firebox was going to be tricky, whereas with the idea I have in mind it would be relatively easy. I have been kindly offered a loan of a fan blower so I may accept that to see if the new system works, and if it does I'll seriously consider your starter boiler idea.

But I'm getting ahead of myself here! I'm in the midst of doing the meths burner so I'll stick with that for now. Some photos later...

Happy New Year to you, Peter and everyone else on this great forum.

 :cheers:

gary

Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #237 on: January 01, 2019, 01:06:39 AM »
Currently working on the housing for the Trangia meths burner.

I cut the flared end off a ductile cast iron water pipe and faced the cut end:



Twenty minutes with an angle grinder and five million years with a file...



...plus spotting through the holes in the end cap from the old solid fuel firebox using my new transfer punches, and drilling and tapping resulted in this:



Beginning machining a slab of brass for the base (and showing off my Christmas present):



And that's it until tomorrow.

Not too bad a day's work I reckon.

Offline Zephyrin

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Re: 3 inch boiler build
« Reply #238 on: January 01, 2019, 09:31:03 AM »
 steam raising fans are commercially available and pretty expensive, but most of us can do it for nothing, just need a look at the junk box in the home workshop...
As soon as the alcohol burner is enclosed, it requires a draught to burn consistently.
A butane burner is far simpler to use as regard to draught.

http://argyleloco.com.au/product/draft-fan-2/
http://trains.de.jardin.free.fr/minidampf/brazil_uk/steaming.html




Offline gary.a.ayres

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Re: 3 inch boiler build
« Reply #239 on: January 01, 2019, 12:51:04 PM »
Thanks Zephyrin. Nice picture and cool little loco  :-)

The alcohol burner housing I'm building is fairly wide open, with a fair bit of room round the burner for air to circulate. On testing a mockup of it the Trangia burned fine with the boiler in situ. I think it will be ok, but I'll see how it goes. If it does struggle, there's plenty of room on the housing for me to drill some big holes.   :)