Author Topic: Wood cladding of boilers.  (Read 1481 times)

Offline Gas_mantle

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Re: Wood cladding of boilers.
« Reply #15 on: March 30, 2017, 04:13:32 PM »
Thanks MJM

I've now got the wood strips so intend to have a go at doing the cladding over the weekend.

At the moment I have a 450g gas cartridge attached and it hasn't yet run out so it's difficult at the moment to assess how much fuel I burn. I do have a hand feed pump so running out of water isn't an issue and I'd rather have a tank that will hold enough for a reasonable run time without needing a refill. The reason I asked is the purpose built tanks seemed small to me and I kind of jumped to the conclusion I'd need a large one even on a 3" boiler with the burner I have.

I did time it earlier today to see how fast it boils in it's present unlagged state and it takes 2.5mins to lift the gauge off 0psi, 4.5 mins to 30psi and 6.5 mins to 60psi. I've never done this before so no idea how that compares to other boilers but I thought that seemed fairly quick although it does only hold about 0.45 ltr

I'm just curious to see how much difference the lagging will make :-)

Thanks
Peter

Offline Gas_mantle

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Re: Wood cladding of boilers.
« Reply #16 on: March 31, 2017, 07:41:20 PM »
Thanks to those who offered advice, I've managed to lag the boiler sooner than expected so I took a before and after photo. It's not perfect by any means but I'm reasonably happy with how it turned out.





As for the performance, it reaches 30 psi in about the same time but achieves 60psi in about 5 mins 45 sec compared to 6 mins 30sec  unlagged - admittedly it was a crude test but the boil time does appear to have reduced.

The main improvement I can see is it can now maintain 60psi whilst powering a Stuart 10h at high rpm, previously it could only maintain about 30psi.

Just need to clad the top cap now - I hadn't intended doing that but it doesn't look right without  :)



Offline MJM460

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Re: Wood cladding of boilers.
« Reply #17 on: April 01, 2017, 03:57:51 AM »
Hi Gas Mantle,

That is a beautiful little boiler and your cladding looks excellent.  Doing the top cap as well will not improve the performance any but will reduce the chance of burnt fingers due to the accidental touch, so well worth while.

I understand your feeling that it is hard to tell on the face of it how much it has helped, however consider this.

Hard to do much with the heat up time apart from repeating the experiment a few times to see if it is consistent, or at least so you can take an average.  This is because you are heating up the copper shell, fire box metal and even the timber cladding, hard to quantify without a lot of measurements.

But at 30 psi the water boils at 133 deg C (271 F) while at 60 psi it boils at 152 deg C (305 F).  If the ambient temperature was at 20 deg C (68 F), the heat loss would be about 20% more at the higher temperature without your cladding.  With your cladding you have maintained pressure despite 20% more heat loss, a significant improvement.  This is based on the temperature difference assuming a constant heat transfer coefficient.  However convection loss would be more vigorous with the higher temperature difference so the actual saving would be higher.  Steady temperature means the shell etc is no longer relevant.

I am assuming you throttled the steam at the boiler outlet when running at the higher pressure, otherwise the engine would be running a lot faster, or driving a bigger load to keep the revs about the same.  Running throttled means that the energy consumption of the engine is only just slightly higher at the higher pressure, due to slightly lower efficiency, but you have maintained this despite the higher boiler temperature which translates into being able to drive a higher load or run longer from the same amount of fuel.

If you put a second layer of planks, you might get a further say 15% reduction in heat loss, getting to be a serious improvement.

An excellent job and an excellent result.

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

Offline 10KPete

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Re: Wood cladding of boilers.
« Reply #18 on: April 01, 2017, 04:22:49 AM »
That's a really nice boiler! Good and clean...

A vertical boiler is one of the things on my list to do soon. I have the materials and just need to finish up some shop "chores" to make space...  I really like the fire door!

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!

Offline Nick_G

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Re: Wood cladding of boilers.
« Reply #19 on: April 01, 2017, 09:06:03 AM »
.
That's a really good result.  :ThumbsUp:

Nick

Offline ImIndoors

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Re: Wood cladding of boilers.
« Reply #20 on: April 01, 2017, 11:04:16 AM »
An excellent looking result and an apparent improvement in performance also. Well done.
Jim
The person who never made a mistake never made anything.

Offline Gas_mantle

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Re: Wood cladding of boilers.
« Reply #21 on: April 01, 2017, 12:04:33 PM »
Thanks guys, I bought it on ebay so don't know anything much about it. It seems to be a home made job but appears to be strongly constructed and well soldered - with 9 fire tubes and a 2" burner it boils fast :-)

I have tried it running on coal and it will power the Stuart 10h but takes a lot of effort getting the fire to draw in a small model. Realistically with coal it's a struggle to get up to even 15 - 20psi although I'd like to give it another try now it's been lagged.

I had considered drilling the back of the top cap and soldering a bushing allowing me to route exhaust steam up the stack, I hoped a bit of added draught up the stack may help it to run on coal more effectively -  but the very least should make it more attractive to see in action :-)

Pete - what sort of boiler are you planning on making ?  I've been thinking of making a very simple one - I've never made one before but thought if I keep it simple I might be able to make something that would power small engines

« Last Edit: April 01, 2017, 09:24:37 PM by Gas_mantle »

Offline Ian S C

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Re: Wood cladding of boilers.
« Reply #22 on: April 01, 2017, 12:34:13 PM »
Another thing to do, if you have a small set of digital scales, before use weigh the gas can, after a given time, reweigh the can to give the amount of gas used, by this you can work out how much gas required to boil, or per hour, or per boiler fill.
Ian S C

Offline paul gough

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Re: Wood cladding of boilers.
« Reply #23 on: April 12, 2017, 09:25:02 AM »
Peter I'm a bit behind and may be too late to assist with the current boiler but something to keep in mind perhaps for a future small boiler or smaller cylinder lagging is the ceramic sheeting as used on gauge one loco boilers. It is 1mm thick, though I believe there are other thicknesses, and is pretty firm, no need for supportive packing under the timber strips. Many owners of gauge 1 Aster Lions/Thunderbolts replace the brass sheet cladding with timber strips over the ceramic sheet. There are people who claim insulation is superfluous and rely on an air gap, and yes still air is a good insulator, but whether you have a sufficient gap and still air would only stand up under close scrutiny and experimentation. My view is that insulation is valuable, we modellers have ratios with very small volumes to large surface areas in boilers, piping, cylinders etc. and anything that helps hold in the heat is worth that little extra trouble in my view. Regards Paul Gough.

Offline Gas_mantle

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Re: Wood cladding of boilers.
« Reply #24 on: April 12, 2017, 11:32:50 AM »
Hi Paul

I have now fitted lagging and cladding but thanks for your comments.

I ended up going for a 1mm thick material (I have no idea what it is but it's sold by the hobby dealers as proper boiler lagging) - I'm convinced it does make a difference to the performance and probably fuel efficiency as well, so I'd certainly do the same to any future projects.

What I want to do is to make a small boiler of my own but keep things very simple and this boiler has proved useful in knowing what to expect from small ones.

I'd really like to have a go at making something like the GLR or PMR kit boilers but at the moment that is beyond my skill until I've had a chance to make a simple one of my own first.

Peter.