3” boiler project.

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ajoeiam

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Hi Doug,
snip
Personally, I avoid the complexity of the firebox of locomotive-style boilers. I don't need to do all that work for stationary boilers.
But a very efficient/powerful "stationary or marine" boilers is the 3 tube with multi-water-tube Yarrow type of boiler. I have a book with about 50 designs in it... the best I have read - by K.N. Harris. But there is another highly recommended that I have not bought yet... by Alex Wise.
Worth getting one or both to help you make the decision,
Regards,
K2
Hmmmmmm - - - - think I have an electronic copy of the Harris - - - but what is the one my Wise called - - please?
 

DJoksch

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I initially calculated the thicknesses from my reading and was concerned since this was my first boiler. I am fortunate finding this group as this the first to actually respond with technical comments. Í have much more information for the next build this Summer. I try to include an artistic balance so I can keep my projects in my home office after completion. The horizontal project will be 3” X 6” using another cutting from the material I used in this project for the shell. Thanks for the reading suggestions.
 

Steamchick

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Or this?
But they all seem to be out-of-stock?

Download it here?


K2
 

Steamchick

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Hi Doug. As the copper sheet is thin (more than 3/16" is starting to get thick) I suggest you keep it for the "internal pressure" components only. You can get much more heat from an external burner than in a flue tube burner, as you would need for a marine boiler. So the trick is a large radiant shining onto the underside of the boiler, and some water-tubes, then the flue gases pass through the boiler flue tubes once or twice. The boiler with flue tubes is within your experience. The external water tubes beneath the boiler shell can be fitted into bronze bushes in the underside of the shell, all silver soldered together.
I'll see if I can find a design and post it?
Regards, K2
 

ajoeiam

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Or this?
But they all seem to be out-of-stock?

Download it here?


K2
Thanks
 

Steamchick

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Hi Doug,
I have been working to improve my understanding and calculations relating to the strength of boilers.
There seems to be a big gap in the papers I have researched that no-one has checked things like flue tubes in compression, yet the way they are situated in boilers means they must be calculated as a significant part of the boiler. (e.g. a compressive collapse of a tube would be likely to be catastrophic, as the end silver soldering would be expected to fail and the boiler eject its contents very rapidly!).
I have de-rated the "Permissible compressive stress" - following the ASME rules, plus converting the "ASME Permissible tensile stress" to "Permissible compressive stress" by the factor of:
Comp. stress = 45 (MPa) = 0.214
UTS at room temp. 210 (MPa)

So Here's my calculations on your flue tubes:
At 70psig:
σc = [(14.7 x 0.252 – 84.7 x 0.282) / (0.282 - 0.252 )] - [ 0.252 x 0.282 x (84.7 – 14.7) / { 0.252 ( 0.282 - 0.252 )}] :

σc = [(14.7 x 0.0625 – 84.7 x 0.0784) / (0.0159)] - [ 0.0625 x 0.0784 x (84.7 – 14.7) / { 0.0625 ( 0.0159)}] :

σc = [(0.9188 – 6.640) / (0.0159)] - [ 0.0625 x 0.0784 x (70) / { 0.0009937)}] :

σc = [(– 5.72) / (0.0159)] - [ 0.343 / 0.0009937] :

σc = [-360] - [ 345.2] = -705.2 psi:
This is less than the 767psi limit for copper at the temperature for NWP = 70psig.
I.E. The flue tubes are acceptable for NWP = 70psig.
This supercedes my post of #82, so if you need the correct calcs, please do not use post #82.

I understand you have rated your boiler at 50psig NWP., so it is OK.
Regards,
K2
 

DJoksch

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I updated my folder. Thanks! This has been a learning experience. I am sketching out a horizontal boiler around a remaining 12” length of the same material used as the shell for this project, but have not done the calculations yet. I’m deciding on either a fire tube or a Yarrow type. The revised tube calculation will help. Once I decide on the structure, I will post the design and the calculations. A 3-drum Yarrow design has some interesting issues at a small scale as well as how to pipe the water return to the lower drums. Need to study a bit more while I finish the layout board for the current boiler.
 

DJoksch

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I actually finished the layout board. Model clay bricks were intended to provide insulation between the burner and the base board. After running a while at a full 50psi, I could touch the boiler and base board without burning my fingers. I just reworked a rather problematic PM #3 from E-Bay and it now seems pretty happy to run. A double gauge regulator nicely controls the propane pressure. I‘m going to make a proper coupler to connect different engines and devices.
 

Steamchick

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Hi Doug.
Good to see you running with the boiler. I am glad you have some satisfactory insulation, as it is a fundamental part of the Engineering, and was first applied by Newcomen, when he made his first major improvement to his atmospheric steam engine to improve efficiency.
His original engine filled the cylinder with steam, heating all the metal on the way, then he sprayed water into the cylinder to create the vacuum that permitted the atmosphere to do the work of lifting water from the mines. In his major improvement he then lagged the cylinder when he added a separate condenser, that created the vacuum, and was connected by a valve to the working cylinder. So lagging the cylinder was a very early introduction to the system engineering. Boilers became lagged soon after, as did interconnecting pipework. All long before Trevethick and his use of high pressure steam.
I realise that you are using a temporary steam connection, in the plastic hose from boiler to engine.
Please will you consider a safer connection by using a lagged metal steam pipe, or at least an hydraulic hose certified for the temperature and pressure of your boiler, that can carry the steam safely. NOT PLASTIC!
I cannot repeat enough that STEAM IS A DANGEROUS MEDIUM.
The plastic pipe will soon stretch, weaken and fail, as it cannot take the temperature and pressure for very long. When it bursts, you will have a flapping hose waving steam directly from the boiler, as it rapidly loses all the steam. This steam will have an invisible part before the visible condensate plume, which will be the equivalent of a flame and can cause severe scalding if/when it hits flesh. And I don't want to hear your screams....
Any incidental damage to the boiler while rapidly depressurising won't be your biggest problem, as the boiler is probably strong enough to withstand the rapid stress changes.
I know someone who has permanent scars from scalding. Not nice. Hospital, 3 months off work.... skin grafts, the lot! Your boiler has the stored energy to do that...
Sorry to "preach" about safety, but you MUST work safely, and demonstrate Safe Working Practice on anything you publish on a public domain, such as your videos on this site. Innocent people copy what we show and advise, and I don't want anyone getting hurt. Equally, I would hope that anyone who spots my errors would tell me immediately, so I can correct them.
I use regular copper tubing, even as small as 1/8" bore, that is cheap enough from brake tube suppliers, caravan gas fittings suppliers, etc. And I use proprietary 1/8" BSP fittings, or larger, depending on the tube, (or modern metric equivalents). Lagging is simple cotton string wound around the pipework, then painted with white household emulsion, that gives a good representative finish to the model pipework and reduces the condensate in the wet steam.
Incidentally, you can see the condensate in the tubing, which should be avoided as much as possible. This is "wasted heat". Also there is a lot of further condensation produced inside the cylinder as the steam expands. All the condensate has to be purged at each stroke, but a build-up inside the cylinder is not only wasteful, especially when it sucks-in a blob of water from the condensate in the feed-pipe, but can cause an hydraulic lock, which stops the engine dead in a single stroke. This can cause damage such as buckling of rods or hammering of bearing bronzes, as the energy in the flywheel has to be instantly lost somewhere as with a hammer hitting metal on an anvil!
You may have felt some hydraulic locking when applying the steam initially, when you should apply it with just a cracked valve, and turn the engine by hand until it has warmed through on both strokes. You can damage an engine by whacking the steam valve wide open onto a cold engine. I saw it on a TV programme once, where the con-rod was bent by the operator doing just that! (A highly qualified mechanical engineering graduate without "steam" training!). The engineer couldn't figure what stopped the engine -dead. But it was water from condensed steam.... that drained away when the engine stopped. - Probably only filling the last tenth of the stroke, after the exhaust valve cut-off...
Hope that helps?
K2
 

DJoksch

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I was wondering if someone was going to comment on the fish tank hose. I will install an insulated hard line to the base with a solid mount to avoid any stress on the boiler Itself. I’m deciding on a means of connection. A flange mounted to the boiler base would be simple enough with the same off the engine displacement lubricator. I also found some neat little 1/8” quick connectors. The problem is finding flexible high pressure hose that will handle the heat. It would be nice to be able to simply plug in the device. Also need to see if the quick connector can handle the heat.
 

Steamchick

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As I said, I use proprietary BSP pipe connectors, as they have been proven for security, reliability and serviceability, and I have half a dozen boilers and a dozen or so engines. It makes it easy to swap anything if they all have the same type of connector. I find buying common parts isn't too expensive, and make a lot of non-standard stuff. I also use these connectors as gas connections - as those MUST be leak free. (Safety - not artistic interpretation - is my top priority for gas and steam fittings - but I do meet "rivet counters" who say it isn't a "true replica model" when I use them. But how many engines really are "true replicas"? - Buried in a boat it is hardly ever seen, and on static models people see the engine and boiler, not the details of pipe connectors.).
.
I'm sure you can find your local national standard fittings.
K2
 

Steamchick

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Doug, if you must have a flexible hose for steam, there are hydraulic hoses that can take the temperature and pressure (but NOT Brake hoses!) - but expensive and special!
Try this search?
High Pressure Steam Hose Boilers Steam Pipe
Or this:
The hose is silicon, for the temperature, with steel braid to take the pressure. Need proper connectors. Probably looks really huge next to the model?
But fixed copper tube with BSP gas or hydraulic fittings are simply the best in my opinion. And lag with string and white paint to look "real" (and reduce heat losses!).
K2
 
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