Author Topic: COLUMBINE'S BOILER  (Read 45327 times)

Offline Robert Hornby

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COLUMBINE'S BOILER
« on: February 06, 2014, 05:49:55 AM »
A start has been made on Columbine’s boiler. The materials arrived this morning so like Sheldon’s ‘the Flash’ I was in the workshop doing stuff.
Truing up the  tube ends of the tubes was first although the 4” main tube had to be supported in the lathe steady with the sliding bars removed as it only just fitted with a bit of duct tape to provide some protection (although the surface will not be seen eventually).
Drilling the fire tube was straight forward and after cutting the 6 cross tubes it is ready for silver soldering, which will be tomorrow as it is almost happy hour down under.

I have been doing some minor searching for what I thought was going to be a problem in sourcing the ceramic tile for the burner assembly. A visit to the local gas thingies supply shop to ask a REALLY long shot question of where can I find/buy a tile. On explaining my need for one he disappeared around the back of the shop and said, ”Is this what you are after?” and in his hand was the very/almost exactly the thing. On asking the price he said “Free to you son, good to see boilers being made again, call again soon” and I certainly will. The tile will require some shaping to fit but I am over the moon with the find. it is a second hand tile but is in excellent condition. :cartwheel:

Robert
Age and treachery will always overcome youth and skill

Offline Nicolas

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Re: COLUMBINE'S BOILER
« Reply #1 on: February 06, 2014, 06:29:22 AM »
Great start, it is looking very good so far :ThumbsUp:

Looking forward to the next update :)

Nicolas

Offline Ramon Wilson

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Re: COLUMBINE'S BOILER
« Reply #2 on: February 06, 2014, 10:16:28 AM »
Looking good Robert  :ThumbsUp:-
I'm not far behind you - just off to pick up some tube for the uptake and taking the parts for the initial inspection. Nice find on the ceramic - 20 quid over here ::)

Regards - Ramon
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Online steamer

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Re: COLUMBINE'S BOILER
« Reply #3 on: February 06, 2014, 10:25:05 AM »
That does appear to be a nice boiler design Robert.   I am sure it will steam well!    Great when the person behind the counter likes what your doing!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline b.lindsey

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Re: COLUMBINE'S BOILER
« Reply #4 on: February 06, 2014, 11:29:04 AM »
I am liking this already Robert and will definitely be following your progress!!

Bill

Offline SandCam

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Re: COLUMBINE'S BOILER
« Reply #5 on: February 06, 2014, 01:56:18 PM »
Hi Robert,

Good to see that you have made a start on the boiler, however, I have a few questions/concerns before you go too far. :thinking:

I presume that you received the drawings I sent you and that you have scaled them up to suit 'Columbine'.

Have you done the stress calculations for the new sizes?

What is the OD and thickness of the new centre flue?

What working pressure are you planning on using?

It is not clear from the drawings you have posted, but what is the distance between the top of the ceramic in the burner and the bottom plate of the boiler?... it looks a little too small on screen... you should be aiming for a minimum of 5/8" (16mm) for a 4" boiler.

From the work already done, which looks to be of a high standard, I can only see one thing which I would suggest you address... the cross tubes appear to be horizontal across the flue... they should be at an angle, otherwise you can get steam/air bubbles trapped in the tubes which will prevent correct water flow, and can cause overheating of the tube/s. :'( :help:

I would also suggest that you put a shallow countersink on the outside of the cross tube holes to accommodate a fillet of silver solder and encourage proper penetration.

You show a water inlet bush in the top side of the barrel, I am assuming this is for a pumped water makeup supply... this would be better lower down on the barrel, otherwise the cold makeup water will be injected directly into the steam space... causing it to lose pressure far quicker than if the water were introduced at the bottom.

Again, just looking at the posted drawings, the 2 gas deflectors (you show them as flame deflectors) should be much further apart... especially the one on the jet tube side... their purpose is to cause the gas/air mix, entering from the jet tube, to split and fill the whole of the space beneath the ceramic... if this one is too far from the jet tube it will not perform this function correctly... leading to uneven burning... I would suggest a gap of no more than 5/16" (8mm) between the inner end of the jet tube and the outer surface of the deflector stud, It should also be tall enough to be above the inside top edge of the jet tube or the gas mix will just pass over it... the other deflector is less critical, however, I would fit it on the same PCD as the initial one.

On your posted drawings, you don't show any supplementary air holes in the firebox sides, at burner level, but perhaps you have left them out for clarity... you will certainly need these though.

How are you planning on mounting the boiler and burner?

The ceramic plaque you have acquired looks to be just perfect for the job, so well done on finding that. :ThumbsUp:

Ok then, my apologies if the above appears to be a little negative... far from it... I am just trying to help you end up with a successfull working boiler without having to resort to any tricky remedial work. ;D

My very best regards.

Sandy. :cheers:



Offline Robert Hornby

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Re: COLUMBINE'S BOILER
« Reply #6 on: February 08, 2014, 03:14:19 AM »
Sandy,
Firstly, I apologise profusely that I did not attribute the design of my intended boiler to your good self before going off half cocked with words and pretty pictures.
So thank you very much Sandy for posting your designs for our benefit. I do very much appreciate your comments and take them on board as I am sure they will minimise many issues along the way for me.
I tend to subscribe to the theory that if it looks OK then it probably is OK, this has got me into trouble in the past but more often than not does seems to work for me.
So to your comments on my progress so far.
No, I have not done any stress calc’s as I don’t know how to do them. However in my defence I have/will increase the main boiler wall from 1.6mm to 2.0mm, this is the thickness of my Drag Saw Boiler built to Ernie Winters design for a working pressure of 100 psi boiler.
The centre flue is 38mm dia. x 1.6mm wall, again the same thickness as the Ernie Winter design.
Boiler pressure anticipated:-
Based on the 10 psi at the boiler required for my drag saw working cutting wood and with the boiler feed pump working (bearing in mind mechanical losses in the drive train and cross head for the saw) ( it will cut with as low as 7 psi.) My new engine runs on no load at 5 psi air pressure. I am thinking in the order of 30 to 40 psi at the boiler to drive my launch at around 2 or 3 knots. I have no calc’s to back up this assessment, just a gut feeling, and I well know designing boilers on gut feelings is not considered acceptable by boiler certifiers. I did pressure test the draw saw boiler at 100 psi for 4 hours with no leaks in very hot water (about 90C if memory serves me well) and will test the new on at 100 psi also. I would be forever grateful if the calc’s could be done by your self or the formula to work it out. I did ‘Google’ this but got stuck with the ‘allowable stress in tension’ and the constant figure.
The location of the ceramic tile to the bottom plate was only drawn indicative at this stage. Thank you for the suggested 16mm gap, I will adhere to this.
With regard to the cross tubes I did take note of the angle and at first wondered why, my conclusion was that the angle would help water flow due to the thermal properties of heated fluids raising. As the boiler in the hull will be mounted at around 3 degrees from vertical (as is the prototype) and that the boat itself is hardly a stable platform there shouldn’t be too many restrictions to water movement through the tubes. I take your point regarding the air bubbles and in hind sight would have made them angled anyway as it would be no harder to do them that way.
I am going to chamfer the holes to provide more solder penetration, just haven’t done it yet.
Again the water inlet port is shown not in its true position and it will be lower down at around the lower water level position. I will take more care in my drawings and not just “stick things anywhere” until I work them out properly, especially if I post them on the forum (I had a similar issue with the engine crankshaft drawing – will I never learn?)
Thank you very much on the gas deflectors locations I will position them as suggested, and the air holes in the firebox sides.
Your drawing calls for a No. 8 gas jet. When I tried to purchase one, the gas shop man had no idea of the actual size and after consulting some chart he had deduced it would have a 5mm hole!!!!!! More like a hose than a jet I am thinking. This is obviously not correct and after some research I seem to come up with a hole size of 0.25mm for a No. 8 jet. Is this correct? And should that still be OK for my larger boiler?
I am not quite sure about your question of the mounting of the boiler and burner. Your drawing show quite clearly the burner mounting and I will follow this design.
Sandy, please do not feel as if you are being negative to my project I truly welcome all your comments and suggestions. At the end of the day I want a model I can be proud of, and all the help I can receive in obtaining that objective is most welcome.

So once again thank you Sandy.

Robert
Age and treachery will always overcome youth and skill

fcheslop

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Re: COLUMBINE'S BOILER
« Reply #7 on: February 08, 2014, 07:28:58 AM »
T=2T x D
         2t
T= Thickness of shell in inches
P= Working pressure
D= Internal dia of shell in inches
t= Max safe stress of boiler shell material in LB per sq inch
For copper using a safety factor of eight
t=3,125 lb per sq inch
Have a look for the book Model Boilers & Boiler making by K N Harris well for the few quid it costs although he does not show the formulae for tubes under compression .
cheers



Offline SandCam

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Re: COLUMBINE'S BOILER
« Reply #8 on: February 08, 2014, 03:30:15 PM »
 :hammerbash:
Almost Frazer!!! but not quite!!! :LittleDevil:... just teasing ;D

Quote
Posted by: fcheslop
« on: Today at 07:28:58
T=2T x D
         2t


For tubes subjected to INTERNAL pressure: - thickness T = P x D / 2t

And for maximum safe working pressure P = 2T x t / D

Your formula Element descriptions are correct though. :ThumbsUp:

For tubes subject to EXTERNAL pressure this is a whole different ball game.

Most importantly... the safe stress figure for copper under EXTERNAL (crush) pressure is just a little less than 1/3rd of its INTERNAL (tension) stress value.
It is therefore necessary to adjust (REDUCE) the INTERNAL stress figure by a factor of 3.5.

This gives a revised figure for S of 3125 / 3.5 = 892.85psi

The formulae for EXTERNAL pressure are: -

For thickness = T= (PD / (2S + P)) + 0.005D

For Pressure = P = S[(2T - 0.01D) / (D - (T - 0.005D))]

Where T = Tube thickness.
          P = Pressure in psi.
          D = OUTSIDE diameter.
          S = Safe working stress (892.85psi)

Ok thats got that cleared up I hope.

Robert,

I posted some figures on your other thread but I will repeat them here to save switching back and forth: -

Your original 4" x 1.6mm thick shell would be safe up to 100psi. working pressure.
Your 4" x 2mm thick shell will be safe up to 128psi. working pressure.

Your 38mm OD x 1.6mm thick centre flue will be safe up to 72.736psi. working pressure.

Since you are planning on 30 - 40psi then you will have no issues with tube strength.

I can provide the specific calculations if you need them. (PM if required)

Hydraulic test should be 2 x working pressure and using water at nominal room temperature (62deg F)... there is no need to use HOT water.

For steam testing the boiler should be fired at MAX burner rate and the safety valve MUST lift at the working pressure... once the safety has lifted the pressure should not be permitted to rise above working pressure + 10% with the burner at MAX... if it does rise more than this you will need to change the safety valve to one having a higher throughput (discharge rate)... or use a burner with a lower maximum output.


The cross tubes being horizontal should not be much of an issue for marine use, as you say, the boat will not be horizontal for much of the sailing period.
It is more of an issue with fixed (land based) installations.

Gas Jets.

Quote
When I tried to purchase one, the gas shop man had no idea of the actual size and after consulting some chart he had deduced it would have a 5mm hole!!!!!!
:ROFL: :lolb: :ShakeHead:

I guess he don't know much about MODEL boilers and burners. :slap:

A number 8 jet is, as you say, 0.25mm jet hole size.
A number 12 jet is 0.3mm jet hole size.

For a 4" boiler you will need to increase the OD of your burner to about 3 1/2" but keep the other dimensions the same.
For 30- 40psi I would start off using a number 8 jet and see how it behaves... if you have difficulty keeping pressure with the engine running then you may be better off using a number 12.

Ok on the mounting arrangements... I was not sure what you had in mind from your posted drawings, since they did not show these features.

I look forward to seeing your build.

Best regards.

Sandy. :cheers:



« Last Edit: February 08, 2014, 03:53:07 PM by SandCam »

fcheslop

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Re: COLUMBINE'S BOILER
« Reply #9 on: February 08, 2014, 06:05:24 PM »
oops sorry
Early in the morning for me

Offline Bearcar1

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Re: COLUMBINE'S BOILER
« Reply #10 on: February 08, 2014, 06:11:39 PM »
I am enjoying all of your pics and descriptions Robert,,, :ThumbsUp:  and SandyC IS the BEST when it comes to pressure vessels that we use…. A WELL DONE to him as well…. :praise2:


BC1
Jim

Offline Robert Hornby

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Re: COLUMBINE'S BOILER
« Reply #11 on: February 10, 2014, 05:51:42 AM »
Thank you gentlemen for all the good info on the boiler spec’s and calc’s.

As I don’t have Oxy Acetylene any more and must rely on lesser kit i.e. PLG and MAP I thought it wise to minimise heat loss, so I cobbleled together a hearth, not sure how effective it will be but has to be better than non at all.

The PLG burner will only apply general heat and the MAP to bring each joint to full temp.

So if tomorrow is a bit cooler I shall “Just Do It”


The hearth.

Robert
Age and treachery will always overcome youth and skill

Online steamer

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Re: COLUMBINE'S BOILER
« Reply #12 on: February 10, 2014, 02:44:17 PM »
I think you'll need a bigger torch. ........
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Doc

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Re: COLUMBINE'S BOILER
« Reply #13 on: February 10, 2014, 03:45:06 PM »
I think once you get things warmed up it should work.
Looks good!

Offline Ramon Wilson

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Re: COLUMBINE'S BOILER
« Reply #14 on: February 10, 2014, 05:38:39 PM »
Looks like you are a 'few bricks' ahead of me Robert  :D

I have my flue and tubes ready to go too but the weather here is so wet and miserable it will be a day or three before I can do like wise I fear.

I think Dave may have a point about the heat - I'd be inclined to get the airspace around a lot smaller - if the heat isn't there it does tend to get a bit sticky  :(

Good luck with it  :ThumbsUp:

Regards - Ramon
 
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