Improving the performance of simple boilers.

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Tony Bird

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Hi,

I have been trying to complete some unfinished models with some success having finished two copies of an Bowman Eagle steam launches I am now working on completing a model of a Bowman Swallow steam launch. I have already made one Swallow a year or so ago, the incomplete model is quite well on needing the boiler soldered together and a little work on the engine.



For some reason probably because I had the metal I stated making two boilers for the Swallow. the boiler is made from some thin copper sheet reclaimed from on old hot water cylinder.

Photograph of one boiler before being soldered.



As there are two boilers I thought I would see how much difference it would make to their steam raising performance by fitting hedgehog pins to one of them.

A simple pot boiler fitted with hedgehog pins used in a small locomotive which is fired using Sterno.



It is quite difficult to solder pins in a thin boiler shell without them moving. They can have a shoulder turned on them which works OK but thin copper wire doesn't like turning. Threading the pins works well but is quite time consuming. So I came up with the following I don't think it can be an original idea but I haven't seen it done.

'U' shaped hedgehog pins which hold themselves in place very well.



The result looks like this.



Both boilers nearly finished.



One of the boilers being tested.



It will be interesting to see how different the two boilers perform.

Other successful ways I have tried of improving the performance of simple boilers all of which work well.





I will post the results of the test after they have been done.

Regards Tony.
 
Hi,

Today I did not a very accurate assessment of the steam production of the two boilers.

First a tray for the Sterno was folded up.




The tray in use.



The test system. Both boilers were filled to about half their capacity with 60 ml of cold water. The boilers were fitted with a pressure gauge that had a valve below it that was open until steam came out when it was closed and the time between lighting the Sterno and the pressure gauge reaching 20 psi was measured. The boiler with the pins took 3 minutes and 30 seconds the boiler without the pins was 20 to 30 seconds slower. Between tests the tray was filled with Sterno. The tests were carried out twice with about the same results. It will be interesting to see the difference when the boat is on the water.

Test approaching 20 psi.



Swallow as it looked at end of play today. The engine needs a couple of hours work after which the model can be checked out in a test tank.




Regards Tony.
 
Looking forward to the final test. Great looking boat
 
Tony, what is the small pipe that exits from the bottom of the boiler? If it is for steam does it reach up on the inside to a higher point?
DW
 
Tony,
If you had used tubes instead of solid 'U' pieces, you would have found the boiler much faster at steaming.
Hedgehog pins don't work very well as the burner is heating the bottom of the boiler anyway. If they were tubes, the water in the tubes would heat up much faster than when in the boiler itself. The water moves through the tubes by convection, so pulling cold water down into them as the hot water moved out. Much the same as old style non pumped radiators on cars worked.
Instead of pins going through your flue, tubes would have been much better, and is how modern day boilers are made.

John
 
Hi David,

Tony, what is the small pipe that exits from the bottom of the boiler? If it is for steam does it reach up on the inside to a higher point?

Yes if you look at the second part built boiler photograph (third photograph from the top) you can see the steam pipe where it goes up into the dome. The Swallow is a copy of a commercial toy made by Bowman in the 1930's. A lot of toys then didn't have regulator valves; their engines running straight from the boiler.

Hi John,

If you had used tubes instead of solid 'U' pieces, you would have found the boiler much faster at steaming.
Hedgehog pins don't work very well as the burner is heating the bottom of the boiler anyway. If they were tubes, the water in the tubes would heat up much faster than when in the boiler itself. The water moves through the tubes by convection, so pulling cold water down into them as the hot water moved out. Much the same as old style non pumped radiators on cars worked.
Instead of pins going through your flue, tubes would have been much better, and is how modern day boilers are made.


The boiler is quite small 4.5" (117mm) long and 1.5" (38mm) in diameter and is fitted in a hull 19.5"( 500mm) long and 3.5" (90mm) wide so the boiler cannot have a high C of G. I think that fitting long larger diameter water tubes under the boiler which is the usual practice isn't very practical in this case. I am not sure that using 2 mm OD tubes instead of pins would be much better, their holes would be very small and soon fill with boiler debris. Also bending the tubes so tightly could be a problem. If my sums are correct the 16 'U' shaped pins used increase the boilers heating surface by more than 10% and as they project into the boiler as well they also increase the heat transfer area.


Regards Tony.
 
Tony, I have made small boilers like yours and by using 1/16" or even 1/32" bore tubes steaming times can be greatly reduced.
I was involved in the 'ministeam' sailing project in the UK many years ago, designing a tiny V-twin self starting engine with throttle control and boilers to fit into hulls a lot smaller than yours. If I remember rightly, around 20" long.
We got around 2 mins steam up times with 15 minutes radio controlled sailing. Shame I didn't keep any photo details of the twenty or so steam plants that I made, it would have been most helpful to yourself.
But I do still have a bit of info left in my one remaining brain cell that you can tap into anytime.

John
 
This is a very interesting and informative thread, for such a cute launch in the end. Bravo Tony.
For me the weakest point in a steam plan is not the boiler, which, as far data on the evaporative capacity are given, compare rather well with a full sized boiler. A miniature boiler can be an efficient boiler too, and this is not the case for a small engine, where the reduction in size is disastrous for the yield.
 
Hi,

Yesterday the engine of the Swallow was finished and tested on air. Today the Swallow had its first steam and water test. I am quite pleased with the results the weather wasn't ideal being damp overcast and a bit windy for an out door test, the temperature was 5C which at least showed the steam well! The boiler was filled with 80 ml of water and the fuel tray filled with Sterno. After lighting up it took nearly 4 minutes to make enough steam to power the engine which ran for a further 19 minutes before the Sterno burnt out, there was about 20 ml of water left in the boiler. The 'Test' tank is the waterproof storage box for a Bowman Eagle that I made some time ago. Any storage box I make for model boats is waterproof which allows the model to be tested in the minimum amount of water. I think this Swallow will turn out to be quite fast but as it has an open deck and a low free board it will have to be a very calm day before she takes to the pond.

Photographs.

Not really relevant to this thread, the jig used to mark out the steam ports.



Again not really relevant the flywheel was balance, which I find makes small engines smoother running.



Running on air.




First run on steam.



First time on the water.




Empty tray.



Last job the water level plug to replace the screw used on the test.



A pair of Swallows.



Video I hope! I'm never quite sure with Photobucket these days.

<embed width="600" height="361" type="application/x-shockwave-flash" allowFullscreen="true" allowNetworking="all" wmode="transparent" src="http://static.photobucket.com/player.swf" flashvars="file=http%3A%2F%2Fvid895.photobucket.com%2Falbums%2Fac154%2Fgaynorandtony%2FVideos%2FMVI_1631_zps1n5o8o1h.mp4&title=">

Regards Tony.
 
Hi Gedeon,

For me the weakest point in a steam plan is not the boiler, which, as far data on the evaporative capacity are given, compare rather well with a full sized boiler. A miniature boiler can be an efficient boiler too, and this is not the case for a small engine, where the reduction in size is disastrous for the yield.

I agree boiler rarely give any problems especially if they are gas fired, meths burners sometimes can be a bit iffy though.

Regards Tony.
 
The video worked for me, but in general photobucket videos are a little bit finnicky compared to youtube vids for me.

Nice little boat, I'd like to see a video of it out on a pond when you get a chance.
 
Tony that second video works great! I too would love to see it on the pond. Cool little boat. Thanks for sharing.
dw
 
Tony, how do you decide how much material to remove from the flywheel to achieve balance?

John
 
Hi,

It is unlikely that the Swallow will take to the water in the near future however while at the Abbey Pumping Station in Leicester a few weeks ago I took a short video of Swallows bigger brother an Eagle going through its paces. It was very cold and windy and neither of the boats performed as well as they usually do.

I hope these videos work!





Obviously the water was too cold as well!



Regards Tony.

Hi John,

Tony, how do you decide how much material to remove from the flywheel to achieve balance?


I just balance on knife edges I use aluminium pistons so I don't make any allowance for them. Usually a small flywheel with its crank pin and a hole drilled for the securing screw is a long way out of balance. The three of the holes shown in the photograph nearly go through the flywheel. Hope this helps?

Regards Tony.
 
Thanks Tony, a simple answer as usual. This is what makes your advice so valuable.

John
 
Yes, I agree, always the simplest way to resolve points in these theads...
According to the usual formula the counterweight equal the weight of the rotating parts (crankpin & conrod big end part) plus half of the weight of alternating ones (piston, gudgeon pin & small end of the conrod). not easy to estimate weight on such tiny conrod! But reducing vibrations is certainly beneficial to the motion of these little launchs.
 
Hi Gedeon,

For me the weakest point in a steam plan is not the boiler, which, as far data on the evaporative capacity are given, compare rather well with a full sized boiler. A miniature boiler can be an efficient boiler too, and this is not the case for a small engine, where the reduction in size is disastrous for the yield.

I agree boiler rarely give any problems especially if they are gas fired, meths burners sometimes can be a bit iffy though.

Regards Tony.

Hi Tony,

Had to gas fired to run Tubal Cain's Oscillating Engines . Somehow meth took long time to fire up steam. Solid fuel did better but sooty.When to gas fired and got very good steam output. My wife thinks I gone nuts spending hours run these mini engines.
 

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