# Boiler Theory



## Artie (Dec 30, 2009)

Im on my knees begging for help.......... ;D

Im in the process of thinking about my boiler. My build will use the boiler to mount the engine pairing and therefore has to be (at least mocked up) in place to mount the cylinders and slide carriage pretty soon.

Ive read lots about miniature boilers but must admit to becoming a little confused with the info flow Ive tried to inhale. So... a couple of questions for the boiler-aholics on here...

My boiler is 120mm (approx 5 and 3/4") high and 250mm (approx 9 and 3/4") long. Ive read that it is advisable to move to welded steel at around this size.

No problem, but is there a specific type of tubing recommended?

Im guessing that heavy wall truck exhaust tubing is not advisable? (Too heavy a wall and getting it to temp would take ages considering steel wont absorb heat as readily as brass or copper and these have a defined 'seam')

I am concerned about the inherent dangers of working with and around live steam and I feel I understand the needs of the safety valve but I want redundancy in this area (2 valves, a secondary valve set slightly higher then the primary valve and each capable of venting faster than steam is generated. This unit is intended for a radio controlled paddle wheeler and may well be a distance away should anything go wrong).

Is there a precedent here?

Is there anything I should know? (I have NO experience in this area and am feeling my way forward very slowly, reading is no substitute for experience, hence my questions).

I hope to be working at around 40 to 50 PSI (the engine will dictate this obviously) and will hydraulically test to 100 before commisioning the unit.

Have I missed anything here?

Thanks in advance.

Artie

Just added a PS. Its propane fired with a throttlable flame control and self igniter using little camping disposable propane bottles (recycling a camping cooker... ;D)


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## PTsideshow (Dec 30, 2009)

The groups in OZ have a very good and complete miniature boiler code about building that is followed around the world. MY link to the site no longer works maybe one of the members from OZ can give you the correct info.
Also it isn't a good idea to used, seamed tubing. As most of the truck exhaust tubing is endless welded mandrel bent tubing. Don't know what it is down your way.

Somebody was building a welded boiler meaning the ends and flue tubes were welded together not necessarily the shell. Most I have seen are pipe seamless.
 ;D


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## GWRdriver (Dec 30, 2009)

Artie  said:
			
		

> My boiler is 120mm high and 250mm long. Ive read that it is advisable to move to welded steel at around this size.


Artie,
Not necessarily, and from what little I know so far I think copper will make more sense for you, but a lot will depend upon the skills, materials, and resources you have available. We need to know more about the boiler, such as the orientation. Is the diameter 120mm the dimesnion? If so I assume it will be a horizontal flue marine boiler.





> is there a specific type of tubing recommended?


The choice for model boilers is always seamless hard drawn tube, whether steel or copper. Some off-sized boilers must be rolled to size from sheet and will have a welded or silver soldered seam, and there are prescribed ways of doing that, but whenever possible most people stick to the nearest available seamless tube.





> Im guessing that heavy wall truck exhaust tubing is not advisable? (Too heavy a wall . . .


Well a heavy wall (within reason) is GOOD for a steel boiler, in order to provide a corrrosion allowance, but my guess is exhaust tube is a welded (seamed) low grade steel and your guess that it isn't advisable for boilers is correct. Brass should not be used anywhere in the boiler.





> Is there a precedent here?


There's lots of precedent, depending upon the technical resources you use, and for your part of the world the Australian Code (AMBSC) makes sense.


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## Artie (Dec 30, 2009)

Thanks Harry and Glen.

Im in the process of chasing a copy of the Aus boiler codes and sent an email to the suggested address a little while ago but as yet havent received a reply. The website only lists the books contents and contains no technical info. This needs to be paid for (no problem) and I guess I will just have to wait.

Im not sure which post I read the recommendation to move to steel at around 6" dia, but I 'think' it was on HMEM. I cant be too sure now as I have read so much about this of late from so many sources. 

Horizontal flue marine boiler it is.

I guess I really need to know with the seamless tube is... how thick a wall do I need? Ive read suggestions that in copper 1.6mm (approx 1/8") is the minimum, but nothing on steel.

Keep it coming guys, all offerings gratefully catalogued...

Artie


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## GWRdriver (Dec 30, 2009)

Artie  said:
			
		

> Im not sure which post I read the recommendation to move to steel at around 6" dia, but I 'think' it was on HMEM.


It may very well have been me, I've commented on that question a couple of times recently. In any case what I would have said is this, generally speaking the decision point for copper vs. steel is about 6" in diameter. At 6" diam and below the thickness of steel (including a sufficient corrosion allowance) can force critical spaces, such as the water legs and the grate area, to be smaller than they need to be to perform well. That typically isn't a problem with copper and below 6" diam the cost of copper is merely painful, rather than pure torture. Above 6" diam the effects of the steel corrosion allowance are less problematic, and at the same time the cost of copper becomes considerably more, so for some people steel begins to be a better choice. Overriding all this are your individual skills and resources. For instance, some of us are good silver-solderers but lousy welders, or vice versa. Some of us might have a brother-in-law who is a good welder and has access to certifiable steel. Individual resources almost always play a part in the decision.


> .. how thick a wall do I need? Ive read suggestions that in copper 1.6mm (approx 1/8") is the minimum, but nothing on steel.


For steel certainly not less than 1/4" and that's cutting it close IMHO. Copper is a bit different in that the minimum shell thickness depends only on the diameter and working pressure, which aslo introduces temperature into the equation, and the strength of copper is temperature-dependant. There are formulas to determine what that thickness should be but generally by the time you get to 6" diameter a 1/8" wall is typical. It's possible that the shell of a 5" boiler with a design WP of 50psi could be as little as 2.5mm but that's an educated guess on my part and the shell data thickness should be run through the formula. When I fudge, of find myself between two standard sizes, I always fudge thicker or heavier.

I don't know how complex your boiler will be, although you won't have water legs to worry about, but you could make it a composite boiler, ie, a steel shell and heads with copper flues. This is a common combination in larger scale model locomotives in the USA and works just fine. The only ongoing disagreement is whether 'tis better to silver-solder the flues in, or roll (swage) them in, but I can say that for practical reasons rolling seems to be preferred.

The formulas I refer to for copper are found in books by K. N. Harris and Martin Evans, both long-time contributors to Model Engineer magazine. No doubt the AMBSC will have tables or formulas to develop the same information in generally the same way.


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## Artie (Dec 30, 2009)

Thanks Harry, that all makes sense.

My welding and silver brazing skills are competant so either medium is ok from that respect. I think I glean from your posts that you would go with copper and thanks to your insights, I feel that is probably the direction I will go (unless someone comes up with a compelling reason not to.... :-\).

I think one of my concerns was in using the propane burner. Yes it is throttlable, but I was concerned with the hard solder at the end caps and this intensity of flame (much higher than a spirit burner). I think Im being overly cautious (yep thats me..) as with water in the boiler the joint should never get near melting point of the solder. I think a guard near the ends of the boiler to stop the flame encroaching upon the joint may make me feel better.

I decided upon the propane burner as this is a large model and the engines are comparitively large as well (20mm bore x 40MM stroke x 2) and I wanted this to be able to create the necessary steam with a margin. Is my thinking flawed in some way in your opinion? (anyones opinion... this is an area in which I am totally out of my depth... and I dont like it..... )

6mm (1/4") is an awfully thick wall for a boiler. I understand its to help counter corrosion (im thinking internally plus the effects of the burner?). I think it would take a month of Sundays to heat. But when it did it would stay hot for another month of Sundays.

In my previous post I stated that 1.6mm was 1/8", that should be 1/16" as 1/8" is 3mm (approx), sorry if I confused... (I do it to myself, why not you lot?).

Leaarning heap so far, thanks all.

Artie


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## GWRdriver (Dec 30, 2009)

Artie,
I'm not trying to stear you in one direction or another although the majority of my individual experience is with copper boilers.


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## shred (Dec 30, 2009)

Fire-tube? Water tube? Pot boiler?

All of those decisions are going to affect the design. 
Lots of small-scale live steamers run butane burners on silver-soldered copper boilers.


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## hammers-n-nails (Dec 30, 2009)

in the book steam Boilers: their thoery and design by Harry de Berkeley Parsons  http://books.google.com/books?id=DO...steam+boiler#v=onepage&q=steam boiler&f=false page 155 the formula that is given for burst strength of a seamless tube is- pressurexdiameter=2xthickness of wall x tensil strength af material. boiler plate here in the states is a516 dont know if its the same there or what the seamless tube equivalant is, interesting fact: they also use this steel for armor plate because it streches more than normal before the bullet breaks through. anyway a factor of safty that was reccomended to me was 6-10. as for sweging the tubes, if thats what you choose to do, a roller can be made fairly easily for copper, i think there pretty expensive to buy. thats all i have, get ahold of me if you need anything else i can try to help, im not an expert but ill sure try.


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## steamer (Dec 31, 2009)

Sandy may pipe up here as he was the Chair of the Au model boiler code panel. What I have read of it, its well thought out and specific...check it out when you can.

Dave


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## ianjkirby (Jan 2, 2010)

Hi Artie,
 With all due respect to Dave and Sandy, its me who used to be Chairman of AMBSC, and I can offer the following advice.
 There is no hard changeover size between steel and copper, but at around 6-8" one needs to consider both materials before making a choice. Certainly for a 6" marine type boiler I would recommend copper if you can get it, and 2.5-3.0mm would be fine.
 My strongest suggestion concerns how you intend to use the boiler. If you wish to use it near any 'public' persons (in Australia, this means anyone other than yourself, including family members!), you should consider insurance cover. The best way, in my opinion, is to join a club, and as you are at Griffith, the nearest is probably at Wagga, or maybe Jerilderie. There you will be able to discuss your project with a club boiler inspector, and get a certificate for your boiler when it is satisfactorily finished, and your club membership will provide a degree of insurance cover for operating near the public. As several have suggested already, a copy of an AMBSC code, steel or copper, is also good advice. You can get them here http://www.ameng.com.au/ame_retail_dvds_boiler_codes_and_miscellaneous.htm.
Regards, Ian Kirby.
Wollongong NSW


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## Artie (Jan 2, 2010)

Sorry to be so slow getting back to this, tis the season.....

Harry, have no fear, my choice of material will be mine alone but I do thank you for your input.

Ian, great to hear from you and thanks for the link. 3mm wall thickness 120mm tubing if I can source it is the direction I would like to go, but, I will wait until I receive my copy of the Copper Boiler codes and (taking your advice) talk to the nearest club I can find.

In the interim I will construct a mock up boiler so I can mount the engine components and get this thing started.

My thanks all who have input into this discussion.

Artie


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## bob ward (Jan 2, 2010)

Artie  said:
			
		

> 6mm (1/4") is an awfully thick wall for a boiler. I understand its to help counter corrosion (im thinking internally plus the effects of the burner?). I think it would take a month of Sundays to heat. But when it did it would stay hot for another month of Sundays.



Artie I have a copy of the AMBSC steel boiler code, part 2, issue 4, 1995. The minimum thickness for steel is 6mm.

Without wanting to derail Artie's thread, there seems to be an anomaly between the skills certification required for steel and copper boilers. 

Welding on a steel boiler in accordance with AMBSC must be carried out by someone certified to AS 1796 or by a person working under the direct supervision of someone so qualified.

As I understand it, anyone can silver solder a copper boiler together. Have I got that right, any comments?


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## ianjkirby (Jan 3, 2010)

Hi Bob,
 I'll try to keep this is short as I can.
 Yes, you have correctly interpreted the requirements regarding the joining of these materials under AMBSC regulations.
 Copper boilers are easily soldered (provided certain simple preparations are done), and the results are easily inspected by amateur club boiler inspectors. One only has to see that penetration has occurred, and you can be very confident that the joint is full-strength, and will not fail.
 Steel is a different case. There are welders, and there are welders. Proper penetration is less obvious, and amateur club boiler inspectors are, in the main, not qualified to inspect electric arc welding. The requirement to have the welding done by a professional welder in a commercial shop has three distinct advantages; (a) the shop guarantees the outcome, and that it complies with current regulations; (b) the shop's product liability insurance helps to "spread the risk" for insurance purposes, and (c), the club boiler inspector is not putting his neck on the line in an area in which he has little skill.
 As I have stated many times in the past on several forums, AMBSC codes only apply in Australia and NZ. Elsewhere, use them as a guide by all means, but it is up to the individual to ensure that their boilers comply with their local pressure vessel requirements.
Regards, Ian.
ex-AMBSC Chairman.


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## steamer (Jan 3, 2010)

My apologies Ian,

My intent was to, for the sake of safety, have Artie speak to a knowledgeable member of the board of AMBSC. It was Clearly my gaff to put forth the incorrect name.  Please accept my apologies Ian. I meant no slight. I believe the other name has an affiliation with the UK society, not the Australian. Again, my confusion.

Artie, my apologies for the digression, please continue.....

Sincerely,

Dave


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## ianjkirby (Jan 3, 2010)

Hi Dave,
 Please don't feel the need to apologise for such a trivial mistake. I am not the slightest bit offended. I only pointed it out so that it would not be perpetuated!  
Regards, Ian.


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## steamer (Jan 3, 2010)

Ian,

Your a Gentlemen....Thankyou!   Artie...where ever we left off..

Dave


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## Artie (Jan 3, 2010)

Gentlemen, thank you all. No digression has occurred. The information that has come from the discussion is EXACTLY that which I (and Im certain, others as well) required...guidance in an area I had no knowledge of.

Thanks

Artie


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## steamer (Jan 3, 2010)

Artie  said:
			
		

> Gentlemen, thank you all. No digression has occurred. The information that has come from the discussion is EXACTLY that which I (and Im certain, others as well) required...guidance in an area I had no knowledge of.
> 
> Thanks
> 
> Artie




Ahhh another Gentlemen, this is why I love this Forum!

Dave


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## Artie (Jan 5, 2010)

I have yet to recieve the boiler codes.........

BUT I was talking to a mate who manages an engineering shop about the pro's and con's of steel vs copper. He asked about what the steel had to be and then asked what size did I have in mind.

He walked away and came back with this 'offcut'. Its 5" OD X 4 7/16" ID (been bored and honed for an hydraulic ram housing) and 9 1/2" long . Converting that to 'my' language, (I wanted 120 OD with at least a 6mm wall thickness and 250mm long) this is 127mm OD, 7mm wall thickness and 240mm long. So its 7mm wider and 10mm shorter than I wanted but is 1mm thicker in wall thickness. So its all good. 

This is hydraulic tubing (seamless) with a 2600PSI working rating. Best part, it was donated! Next best part, he has a welder with pressure vessel certification who will weld the ends in for me.

I havent yet decided to go with steel but this is certainly pushing me that way... ;D Still I will wait until the codes arrive and then make up my mind...


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## tel (Jan 5, 2010)

That bit of stuff will be no good Artie - best send it on up to me, to remove the temptation.


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## Artie (Jan 5, 2010)

tel  said:
			
		

> That bit of stuff will be no good Artie - best send it on up to me, to remove the temptation.



Tel, pm me your address..Illsend...something along... ;D


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## GWRdriver (Jan 5, 2010)

Artie,
If I was in your place I would consider the decision made.
Harry


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## Artie (Feb 13, 2010)

Hi again Harry, well for a while the decision _*was*_ made.... and then I received my copies of the boiler codes, both copper and steel. Extremely well written documents and very helpful in determining my direction. The requirements for this sized boiler are *ONEROUS*, if I wish to comply with club regulations and as such are able to enjoy insurance cover. I do wish to comply and I do wish to enjoy the insurance cover.

It became very clear quite quickly that I was aiming for something way out of my league. Let me explain, one of the members of the miniature steam association kindly offered to open his workshop doors and show me why this was so.

So I drove 3 hours (each way) to meet Ross and see his absolutely gorgeous, dismantled steam loco. No he didnt dismantle it for me it was due for a boiler inspection, but he did wait til I arrived before reassembling it.

Basically he explained that the boiler I was contemplating was not much smaller than his, which operated 2 50mm (2 inch) bore engines and could tow 16 people with a weight of over 2 tonnes with the carriages included. We discussed the lack of torque required by a (relatively light and small at 7 foot) paddle steamer which has 'slip' when it drives in water and his situation which is mechanically linked to the track with high friction.

It boils down to me not needing the boiler size I thought I did. As such I could drop down into the sub-miniature boiler codes (which Ross was able to supply me as he sells them for his club). Ross's engines where 50mm bore mine are 25mm bore,this makes sense to me.

The requirments for the sub-miniature category is much less stringent and as long as I comply with the following I can be clased as sub miniature. Less than 75 psi working pressure, less than 75mm boiler diameter and 1 litre or less in boiler capacity.

The usual requirements exist for copper tube design etc, but it is a much simpler set up than is required for the larger boiler. Tel, still want that piece of steel tubing?? I no longer need it!

The boiler size mandated is cosmetically too small for the boat so I am building a dummy, more scale looking boiler which is simply a cover for the real thing and a mount for the cylinders/engines. This will allow me to build the boiler as 'spartan' in appearance as it needs to be to simply operate.

A good result, I simply need to source a 220mm length of 75mm dia seamless 1.6mm wall thickness copper tubing. Any Aussies have any ideas on this one? I havent gotten that far yet, Ive just got back from the choo choo ogle (and it was an ogle...wow it was gorgeous!)

Also someone mentioned that you cannot use brass in any capacity in a boiler. This isnt true but when used it must be noted by the boiler inspector on the boiler compliance certificate.

Compliance and certification is still required, that side is no different, but building the boiler itself is much more realistic and therefore less problematic. Incidentally, the boiler is a horizontal fire tube marine style unit if anyone is interested.

In an effort to gain efficiencey from the smaller diameter boiler I may route the firetube through the boiler more than once. This may require a trial build to see. Not sure on this bit yet.

I also walked away from Ross's workshop with a new found respect for model loco engineers! On two fronts... the technical engineeing was of a high order. Simply marvellous. Also on account of the financial investment these guys have in their loco's. In excess of $30,000 aussie bucks isnt unheard of. Smaller 2nd hand machines go for around the $18,000 mark (dependant upon condition and size etc). That alone blew me away.

My thanks to those who contributed to my journey of discovery, to Ross in Echuca (thanks again mate) and to the guys who have drafted up the extremely comprehensive and well written miniature boiler codes.

It all means that I have had a blast, an education and have settled on a safe, sensible, useable result.


 th_wav th_wav th_wav th_wav th_wav 

*discussion*


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## GWRdriver (Feb 13, 2010)

I love happy endings . . . except . . this may be more of a happy beginning.


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## AlanHaisley (Feb 13, 2010)

Ian,
As I looked at this site:



			
				ianjkirby  said:
			
		

> You can get them here http://www.ameng.com.au/ame_retail_dvds_boiler_codes_and_miscellaneous.htm.
> Regards, Ian Kirby.
> Wollongong NSW



I realized that I had no idea what the difference between a "miniature boiler" and a "sub-miniature boiler" were. Could you provide information on the difference?

Alan


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## Artie (Feb 14, 2010)

Hi Alan, miniature boilers are 76mm or larger, have a capacity larger than 1 litre and the operating pressure is up to the designer (within reason).

Subminiature is obviously smaller than these figures (75mm or less, 1 litre or less and max of 75psi pressure.). 

The standard miniature copper and steel codes recognise that these engines and boilers will have people in close proximity. Such as a driver and passengers, and therefore these people need to be protected from ANY eventuality.

The subminiatures will have trouble or in most cases simply wont be able to carry the load and therefore will not have such close proximity..or will be marine use..... as in my case.... and then even further from people.

If anyone has any questions I am happy to refer to the codes for an answer. I wont list any portion of the codes online however, this is copyright area and I wouldnt anyway. If you need them, do as I have and buy them.

Cheers


Artie


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## tel (Feb 14, 2010)

> . Tel, still want that piece of steel tubing?? I no longer need it!



If it's up for grabs I do!



> A good result, I simply need to source a 220mm length of 75mm dia seamless 1.6mm wall thickness copper tubing. Any Aussies have any ideas on this one?



Let me have a hunt through my stash - I _might_ be able to help


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## Artie (Feb 14, 2010)

Its yours mate, for what I paid for it.... oh, wait...... it was free..... ;D 

Done bloke, just gotta organise a way of getting it to you. I'm down the South Coast in a few weeks, might go home via Sydney then Bathurst.

Incidentally, I used your recipe for casting cores again tonight. Do yours come out very dark in colour? Or am I using too much molasses.......


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## tel (Feb 14, 2010)

They come out fairly dark, yes, even with the 'yellow brickies' that I use


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## bob ward (Feb 15, 2010)

Artie  said:
			
		

> A good result, I simply need to source a 220mm length of 75mm dia seamless 1.6mm wall thickness copper tubing. Any Aussies have any ideas on this one?



Crane are one of the major copper pipe suppliers in Oz. Their website will show you what is available and the standards it is made to. http://www.cranecopper.com.au/sizes/

When you know what spec you need, the best people to approach will be commercial refrigeration companies, commercial air conditioning contractors and larger plumbers. I imagine that what you seek should be negotiable for a six pack.


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## tel (Feb 16, 2010)

Well, the stash isn't as well stocked as it was in days of yore, however I did come up with two bits - either would potentially make a good boat boiler.





T'were me, the bigger piece would be good for a horizontal, the smaller a vertical in, say, an open launch.


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## Artie (Feb 16, 2010)

Thanks Tel, unfortunately Im limited to a firm max of 75mm od. Im sure you can find a use for these yourself. I have a mate who is chasing up a commercial refrigeration installer who he reckons has what I need (75mm od x 1.6mm or thicker x 247mm). The 247mm length gives me the 1 litre capacity maximum I can use.

Mate, how do you want to take possession of the steel tube? I was hoping to detour through your area next month but it seems I will be short of time. I do the south coast run every month as I have an office in Batemans Bay. If you arent in a hurry I have to pick up a bag of bentonite at some point.
Artie


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## Artie (Feb 16, 2010)

And thanks Bob, as in the prev. post im investigating the refrigeration tube situation as we speak. Good info and I like your valuation of the tubing, if only the world moved on Carlton United Brewerys' back...... 

Incidentally I was able to lengthen the tubing a little by calculating the volume on the cylinder using the ID, previously I had calculated it on the OD. Every little bit helps. 

Artie


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## tel (Feb 16, 2010)

There's no rush at all mate, it will be oiled and added to the stash, tho' I do have a project in mind for it a little further along.

Must chase up the bentonite as well - Victoria never did get back to me.


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