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Amber

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Discussion starter · #1 ·
I've been doing a fair amount of research on what type of vertical boiler that I'd like to build. There are a lot of different configurations for vertical boilers! There are monotube boilers, multi flue tube boilers, water tube boilers of various kinds, dry firebox boilers, wet firebox boilers....lots of choices!
I have a bit of analysis paralysis right now.
I'm leaning toward the wet firebox design because it's more efficient for solid fuel burning, and multiple firetube flues. I want a fairly deep firebox for burning solid fuel, but I also want to be able to install a gas burner if the solid fuel doesn't work out so well. I'm looking at a couple of prototype designs for what they called a submerged flue boiler. In that design, there's an extension of the boiler water jacket that goes higher than the top of the flue plate, and that's where the steam is collected from. Under normal use, the water level is kept above the top of the flue sheet. It's probably not necessary in a copper boiler where corrosion of the top of the flue tubes is not a problem, but it is an interesting design.
I am also thinking of putting 1 large flue tube in the middle of the boiler, surrounded by smaller flue tubes, that way I could run a "superheater" tube down the big flue and back up. I just have to figure out how to make the superheater tube. I'm guessing that I would need to silver braze a U fitting onto 2 tubes for that, I doubt that the copper tubing can be bent to a tight enough U shape to fit down the flue tube.
I have a 4 inch copper pipe for the boiler shell and a 3 inch pipe for the firebox, and for the upper steam area if I do a submerged flue boiler. I just need to figure out how deep to make the firebox as compared to the length of the flue area. I have about 13 inches total to work with so I was thinking about 4 inches for the firebox and about 8 inches for the flue tube area, give or take a bit . I have to make the flue sheets, which means I have to split a piece of pipe for the material to use, or I have to find sheet copper of sufficient thickness to work with. I also need to get various supplies for the boiler such as rivets and fittings.
At least I have an idea of where to start now.
 
#2 ·
Amber,
for my A-Climax build
http://forums.mylargescale.com/18-live-steam/26243-skew-bevel-gears-ride-climax-build.html
I also need a vertical boiler about 6" diameter and 10 1/2" tall, similar to yours. I also want to switch between coal and gas. So far I have seen many different vertical boiler designs, all of them steaming pretty well. It seems that this type of boiler ls not very design sensitive. However you should be careful using different flue sizes. The cross section should be closely matched ("normal" tubes and larger tubes with superheater elements inserted), as the resistance of tubes changes with the power of 4(!) with the diameter. So an unobstructed tube with twice the diameter of a normal flue will have 16 times more gas flowing through.
I have also seen varying tube diameters, down to 1/4" ID, which seem to work fine. I will probably go with 3/8" or 1/2" ID.
I am not even sure if a wet firebox is necessary, as the wall thickness of our little boilers is comparatively large, which means heat conduction between the (dry) firebox and the water is pretty good.
I will discuss my design with an experienced large scale live steamer. You can follow up on the results in the thread mentioned above.
You also asked about T-boilers. Bill Allen will describe one in his thread about the Byers locomotive:
http://forums.mylargescale.com/18-live-steam/41921-john-f-byers-build-log.html
Regards
 
#4 ·
I think Bill built a T boiler for the "Hot Rod Ruby" thread.

I'm interested in seeing updates, build experience, tools used, your design and build process. I'm in the planning stage of a boiler for my Roundhouse steamer.

Matthew
 
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Discussion starter · #5 ·
I figured that I would go with either 3/8ths or 1/2 inch flue tubes for the vertical boiler. I haven't found any hard copper tubing smaller than 1/2 inch locally, but 3/8ths soft copper tubing is easy to get.
I've found a fair amount of discussion about the wet firebox vs the dry firebox in the various things I've read lately on vertical boilers. What I got out of it was that a wet firebox is not necessary to have a decent steaming capability in a vertical boiler that's gas or alcohol fired, but it does add some efficiency to a boiler that burns solid fuel. With a boiler that is as small as a 4 inch vertical boiler with a 3 inch firebox, I'm not sure how good of an idea it is to burn solid fuel, I'm guessing it will have to be stoked fairly often, which means following it around to keep up with it's fuel needs. I'm guessing a solid fueled steamer needs fuel more often than water.
I'm sure the whole fueling issue is easier if you're riding the engine, but those are bigger than what I want to tackle.

Torby, I think you would need at least 2 vertical boilers for an articulated engine, but it would be an interesting looking beast... :)
 
#6 ·
I've seen the return bends on the superheater loops done two ways. One way is bend the copper tubes to about 45 degrees, cut thru the bend parallel to the tube and silver solder them together. It makes an arrow point that fits nicely in the flue. Another method is drill two holes, side-by-side in a small chunk of bronze. Drill an angled hole to connect. Silver solder the copper tubes in the block. Whittle off the excess material.

Check figure 3-8 on page 39 of Harris' book. Modify that into a superheater, would be an option.
 
#7 · (Edited)
Amber said:
..... wet firebox is not necessary to have a decent steaming capability in a vertical boiler that's gas or alcohol fired, but it does add some efficiency to a boiler that burns solid fuel. .....
Click to expand...
I disagree with that. Vertical boilers have a very rapid flow of gas thru the flues. In fact the flow is too fast for efficiency. To prevent that, vertical boilers should have a turbulator in the chimney. A turbulator is a length of sheet metal strip twisted into a candy cane spiral and inserted into the chimney. The slower flow keeps the fuel's energy in the firebox longer. And since most of the steam in a boiler is produced from the firebox, you want to fuel burning in there longer. Slower flow caused by the turbulator also helps ensure all the fuel is combusted.

The turbulator is determined by trial and error. Too much and it chokes the fire. Too little burns more fuel.

Dryside fireboxes radiant a lot of energy out the side unless they are heavily insulated.

Go with the wetside IMHO.
 
#8 ·
Bob,
first my apologies for not having mentioned your Nina T-boiler, especially as I have one right under my nose, built by Ron.
Recently I have seen a coal fired vertical boiler with a dry firebox which worked surprisingly well. Due to the wall thickness (about 1/8") heat transfer between the firebox and the upper part of the boiler is pretty good. Remember how difficult it is to maintain some temperature difference while silver soldering. With a full sized boiler this would not work, as the ratio between wall thickness/heat transfer would leave the dry walls overheated.
Regards
 
#10 ·
Hi Henner. How's everything?

Turbulators work very well. Especially on gas fired boilers where there is built in draft from the velocity of the fuel gas.

Dryside firebox boiler work, there are plenty of them around. It's only a few more steps to do a vertical right, the way the real ones are.
 
Discussion starter · #11 ·
I seem to have a bit of a problem with building the wetside firebox. The piece of 3 inch pipe seems a bit thin to me, compared to the other pieces that I have. The 4 inch copper pipe is plenty thick enough, it's slightly over .100 thick. The 3 inch piece on the other hand is around .045 thick, as best I can measure it with the caliper. The 2 inch pipe that I have is around .059 thick. I have about 4 feet of the 2 inch pipe, I was going to use that to make the flue sheets with. If I split it lengthwise, I can get a sheet about 6-1/2" wide, perhaps a bit more, depending on the saw kerf. That's plenty wide enough for the material for the flue sheets including the flange.
Anyway, with the 3 inch diameter piece of pipe being .045 thick, I'm not sure if it is thick enough to handle 100 PSI in the boiler. I could be wrong about that, but I'm not sure.
The difference between the .045 wall thickness of the 3 inch pipe and the .059 thickness of the 2 inch pipe is pretty obvious when you compare them side by side. I guess I'll have to go back and read the materials chapter of the E book again to see what I can find out.
The other thing I'm wondering about is if using solid fuel in a small boiler is more trouble than it's worth. I have to wonder how often I'm going to have to put fuel in it to keep up the steam pressure. You might have to tweak the gas valve when you're running it on butane or propane, but probably not as often as you might have to shovel in wood or coal.
I know that you have to keep up with the water level, but I'm guessing that's not as often as putting solid fuel in the firebox. If this was a ride on, or ride in engine, that would be different, you'd be with the engine constantly to keep up with it.
 
#12 ·
Amber, you should look online and obtain a copy of the Australian Model Boiler code document that is available...plus reference your K.N. Harris book and others I've heard you mention. There is an accepted standard for thickness of copper for the various parts of a model boiler...you should abide the recommendations, even if we don't have regulatory demands here in the USA....those of us building boilers for our own use still build to the safe and accepted standards...not good enough to "guess" at the best thickness to use.
 
#14 ·
The Australian Model Boiler Society Code (AMBSC) is in 3 parts. Part 1 is steel boilers, part 2 is (larger) copper boilers and part 3 is miniature (hobby) copper boilers. Part 3 is limited to boilers 77mm (3") diameter or less at 75 PSI or less. The AMBSC details construction materials, minimum thicknesses, construction methods, etc. It covers several types of boilers as well.

I don't have the part 2 for larger copper, so that's out of my league. So is steel.

AMBSC, part 3 is a great source. It's worth getting a copy. I don't think it's an online download anymore, you have to order a paper copy from them.

When it comes to safety, boilers require testing. It's generally accepted practice to test new boiler weldments to twice operating pressure. After all the plumbing and fittings go on they require annual testing to 1.5 operating pressure.
 
#15 ·
Thanks for that reminder Bob...I had forgotten they changed to a purchase only model for the miniature boiler code....certainly worth obtaining for anybody considering manufacturing a live steam boiler. Here's a link to the index page for the part 3 document...looks like a link at the bottom for ordering a hard copy:
http://www.aals.asn.au/AMBSC/AMBSC_Code3.htm
 
Discussion starter · #16 ·
Well, from the calculations in the Harris book, it looks like I'll have to use copper that's at least .062 thickness for a 4 inch boiler at 90 PSI, and that' has an 8 times pressure safety factor built in. So I'll need basically 1/8th inch thick copper for the firebox on the vertical boiler. The 2 inch copper pipe that I have is about that thick, within a couple thousandths, so that will work, except that I would have to fabricate a firebox with it. I think that might be more of a pain than I want to do.
 
#17 ·
Amber, if I'm not mistaken the Harris book has a very nice vertical boiler for solid fuel already worked out....let me check when I get home tonight and I'll be back in touch...As I recall it was a wet firebox boiler with multiple smaller flues in about the size you are discussing...all the thicknesses, dimensions and details are worked out...

Maybe you could provide some guidance...what are your priorities...use the materials you have on hand or make a boiler to a certain size even if it means purchase of new materials...if you could help us with key priorities it would be easier to provide assistance. I know copper is expensive so using what you have is of key interest, please give us a laundry list of what you have on hand and available...diameter, thickness, and how much...from there we can make suggestions.

Much is possible with what one has on hand....
 
#18 ·
Amber:
I checked my K.N. Harris book....two vertical boilers laid out there in detail. Design #5 is a plain multitubular (Dry firebox for alcohol or gas burner), and design #9 which is multitubular coal fired design. Follow the dimensions approximately of either and you'll be certain to have a good firing boiler.

Two comments:
1) Design #5 would be MUCH easier to build.
2) Note both designs use many firetubes of smaller dimension (1/4" and 5/16").
This provides maximum heat exchange surface...to be recommended.

I would think your 4" diameter copper piece would be a good starting point...
 
Discussion starter · #19 ·
I think I might have to go with the dry firebox design, simply based on the materials on hand. The 4 inch tube is well over the necessary thickness necessary, and I can use the 2 inch tube for material to make the flue sheets as it's thick enough to use.
I'm going to have to make a former to use to make the flange on the flue sheets, that should be interesting.
 
#20 ·
What are you planning to run with the boiler? Reason I ask is 90 PSI is reasonably high. My 7.5" gauge 3 cylinder Shay, geared 2:1, propane fired, with a rather smallish boiler, can haul 10 adults at 70-80 PSI. If yours is for stationary or light service, 30-40 PSI is probably enough.
 
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