# Type L copper tube for pot boiler ?



## jmp (Oct 4, 2008)

I was thinking about a meths fired pot boiler for a loco project and was curious about the suitability of type L copper tube. It's heavy walled stuff at appx .07" . The tube is a liitle over 2.6" od so plenty of heating surface. Is it too thick for proper heat transfer? 

Thanks,

Mike


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## Jack - Freshwater Models (Feb 17, 2008)

Mike, 

The type L will work but might take a lot of fuel to get to temperature but will then hold the heat for a while. 

There are a few considerations in designing a boiler which one should ponder before designing one and building it. It would be wise to look into boiler design and determine design parameters based on your locos requrements. 

Up to 2" diameter running at 60psi .032" thick might be a good thickness. McMaster Carr sells copper tubing of various sizes and thicknesses. 

What loco do you want to build? 

Jack


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## xo18thfa (Jan 2, 2008)

Posted By jmp on 13 Feb 2010 07:09 AM 

I was thinking about a meths fired pot boiler for a loco project and was curious about the suitability of type L copper tube. It's heavy walled stuff at appx .07" . The tube is a liitle over 2.6" od so plenty of heating surface. Is it too thick for proper heat transfer? 

Thanks,

Mike

On the "plus" side, the heavier copper will add some useful weight on the drivers. Adding some "porcupines" to a ot barrel will ad some more heating surface too.

Was looking at another website and a guy built this little pot boiler oscillator. It is rather innovative.










Would like to see your project idea.

Bob


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## jmp (Oct 4, 2008)

No design decided on yet other than it will be a simple indutrial type along the lines of the pic that Bob posted. Simpler in construction though. It's going to be a project for my two young sons. Been reading up on pots but 18 gauge is the thickest I've seen mentioned. Guess we'll give what we have a try and see what happens maybe add quills just in case. A mechanical contractor customer gave me a bunch of type L drops up to 4" dia so I'm hoping to get some use from them. If we actually finish it I'll post pics 

Mike


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## Jack - Freshwater Models (Feb 17, 2008)

Another possibility to get steam up faster is to have some water tubes on the bottom of the boiler similar to a "Smithies" boiler. It also helps water circulation in the boiler. K&S offers some 5/32 copper tubing that would work. 

Building locos is fun and IF your sons are truly interested they will certainly learn something. It might be fun to help them both build identical locos! 

Jack


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## Steve Shyvers (Jan 2, 2008)

K&S 5/32 copper tubing might be too delicate to use for external water tubes even though the wall thickness of 0.014" is strong enough for 30 psig or so when used for a round section of 5/32" diameter. The potential problems are the difficulty to bend such thin wall tubing around a tight radius and the overall durability of the soft thin copper. Solid quills will probably provide almost an equivalent heating advantage, and be a heck of a lot easier to fabricate and to fit. 

I made a steamline from K&S 5/32 copper tubing recently because I wanted the relatively larger ID for steam flow and the small OD for appearance. I planned from the start to lag the steamline with cotton string and Elmer's glue, so I wasn't too worried about the tubing's strength. Before I lagged the steamline I decided to give it a good inspection using an eye loupe, since the steamline had been a real challenge to bend to the configuration I needed. Right where I'd had to work the hardest to form the steamline I found a small crease in the tubing wall and a divot, that could have actually been a pinhole. Hard to tell for sure. If I'd gone ahead and lagged the steamline either defect could have become a steam leak and then been a real headache to repair. I wound up wrapping the area on the steamline with fine copper wire and then flooding the wrap with silver (hard) solder to reinforce it. 

Steve


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## Jack - Freshwater Models (Feb 17, 2008)

Small thin wall copper tubing can be tricky to bend but it is doable if you are careful. The bend can't be too sharp. 

There are two approaches. In either case you need to anneal the tubing with a torch first. Annealing is very important since the K&S tubing is work hardened. Annealing can be done periodically while bending to keep the copper soft. 

One approach is to bend in a metal form turned from round stock. The form is just a turned groove in a bit of round stock. This supports the sides of the bend. One advantage to using a form is that one can bend a little and then anneal and then bend some more. 

Another method is to use teflon rod inside of the tube. The teflon rod helps keep the tube from collapsing. Once the tube is bent to shape you can pull the teflon rod out of the tube. 

I do agree with you that quills do increase heating area but I don't think they would produce the same advantage as a circulating tubes. I have always been amazed at how much steam a Smithies boiler can produce. 

IMHO a boiler for this type of loco doesn't need to have quills or circulating tubes IF the shell is reasonable thickness and the steam line is run through the flame. Saturated steam make for a nice plume of exhaust! I am currently working on an 0-6-0t that I hope to use a pot boiler for. 

Jack


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## Dan Rowe (Mar 8, 2009)

Jack, 
There is at least one more method of bending thin wall tubing. That is to wrap it with wire. I have a small set of comercial wire benders but any wire will work. I had never heard of using teflon rod and that method requires the correct diameter of rod to be on hand. A similar method is to use a low temperature melting metal to fill the tube then melt out the metal. This metal can be found at machinist supply stores and it is sometimes called foundry metal as it is also used for short run molds. 

Dan


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## Jack - Freshwater Models (Feb 17, 2008)

Dan, 

Yes, there are lots of ways to skin a cat! 

My personal preference is using a form as it is quick and cheap. I've tried the wire method and had varying results. The low melt metal ( AKA Wood's metal or Cerro Bend) works well but are a bit limited in the sharpness of the bend and is a bit tricky. One shop I worked at made surgical instruments and involved a lot of thin walled SS tube bending. We used teflon mostly and it worked fairly reliablly. The tubing was used to house fiber optics and we were trying to maintain shape/size. 

Jack


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## xo18thfa (Jan 2, 2008)

Posted By Jack - Freshwater Models on 14 Feb 2010 10:37 AM 
Another possibility to get steam up faster is to have some water tubes on the bottom of the boiler similar to a "Smithies" boiler. It also helps water circulation in the boiler. K&S offers some 5/32 copper tubing that would work. 

Building locos is fun and IF your sons are truly interested they will certainly learn something. It might be fun to help them both build identical locos! 

Jack 
Water tubes would really enhance the steam production and are not much more work to put in.

As they say: "Go big, or go home."


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## jmp (Oct 4, 2008)

I didn't consider water tubes but you all have given food for thought. Definitely less labor intensive than drilling a million tiny holes for quills. I had an Aster Mogul with a smithies and it steamed well for me and it's hard to imagine a less complex boiler. If I go water tube then I'll turn some simple bending forms . 
Probably only build one loco at first in case it's a flop . Plus I'm trying to finish up a loco that I've been plodding away on for some time. 
Thanks again for the input!

Mike

p.s. every serious boiler maker should have one of these  http://www.youtube.com/watch?v=8F7pV2sz6vQ


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## Brooks (Jan 2, 2008)

This gentleman claims porcupine quills work better than water tubes (he calls them circulation pipes): 
http://home.iae.nl/users/summer/16mmngm/Articles_htms/porky.htm


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## Jack - Freshwater Models (Feb 17, 2008)

Brooks, 

Circulation and heating surface area are key to producing steam. Porky quills only address heating surface area. Water tubes as in a smithies boiler address both area and circulation. 

Jack


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