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pockets
01-20-2006, 01:01 PM
What are the Brits talking about when they refer to a thermic siphon, in a boiler? What is it and why do I need one?

Because, in the context of the article I was reading, it is connected to the firebox I assume (and we all know where that word gets you) that it's purpose is to improve circulation in the water legs....

Best regards,
Greg B.

GWRdriver
01-20-2006, 01:56 PM
Pockets,
Yes, you've just about got it. It's basically a tube (usually a series of tubes) which connect some upper level of the water space (usually near the crown sheet) with a lower level of the water space, typically the water legs, with the purpose being to promote circulation by water temperature differential.

I promote the use of "cross-tubes", a form of thermic siphon, in the small scale, typically single-flue copper boilers I build because they are easy to install and substantially improve circulation, heat absorption, and steaming. Cross-tubes are installed in the largish single flue, not in the firebox, to scavenge heat from the exiting flue gas and to create vigorous water circulation, which they do. I once sectioned and steamed a small boiler to see if cross-tubes did indeed actually create circulation and boy did they! But if not carefully installed both cross-tubes and siphons can be a souce of leaks which are in most cases unrepairable.

You rarely see thermic siphons of the firebox variety in US models because they add difficulty to the building process and for their trouble aren't thought to add that much advantage in steaming capacity and also represent a potential source of leaks or failure if not well made and carefully installed. They are much more common in British boiler designs but still not all that often used.

I'm a proponent of thermic siphons IF they can be added to a boiler without compromising the strength of the design and IF they are stoutly made so as not to create a potential weak link which will otherwise last the life of the boiler. On way I would achieve this in a copper boiler, failing a piece of very heavy-walled copper tube I would make any siphon located in a firebox of bronze bar drilled through. In this application a piece of standard copper tube would have a shorter life than a flue because a thermic siphon lives in a much more hostile environment. Suitable material for steel siphons shouldn't be as much of a problem as copper because heavy walled small diameter steel tube is readily available.


[This message has been edited by GWRdriver (edited 01-20-2006).]

pockets
01-20-2006, 04:01 PM
GWRdriver,
This really interrests me. If you remember, from previous posts, my boiler is rather large and will be constructed of steel, but cursed with pretty thin water legs at the sides of the firebox. This may be a solution to what I envision as almost stagnant water.

Thanks
Greg B.

fred v
01-20-2006, 04:15 PM
somewhere i saw a pic. where the guy screwed fittings into the crown and rear flue sheet and ran copper tube. i think it was a Briggs boiler. that seemed to be an easy way to do it in a steel boiler.
fred v


<font face="Verdana, Arial" size="2">Originally posted by pockets:
GWRdriver,
This really interrests me. If you remember, from previous posts, my boiler is rather large and will be constructed of steel, but cursed with pretty thin water legs at the sides of the firebox. This may be a solution to what I envision as almost stagnant water.

Thanks
Greg B.</font>

GWRdriver
01-20-2006, 06:20 PM
I suppose you could do that, something using breakable (as in make-or-break) connections and make the siphon tubes "elements" which could be replaced when necessary. The problem would be (or one problem anyway) that all this would be inside the firebox.

willy
01-20-2006, 09:13 PM
Seems to me IF you are trying to use screw in fittings to increase the percolation, you would need to limit yourself to a (cough, cough sorry andy) propane fired boiler where the fire would be less likely of melting the fittings.

Willy

Bill Shields
01-23-2006, 11:39 AM
Willy:

I guess you have never seen a Boy Scout boil water in a paper cup that is sitting in an open fire?

Irrespective of that, I really don't like the idea of any type of screw fitting inside the firebox of any type of boiler.

Heck, if that were the case, we could put our firetubes in the rear sheet with swagelok fittings so that they would be easy to remove.... http://bbs.livesteam.net//biggrin.gif

[This message has been edited by Bill Shields (edited 01-23-2006).]

andypullen
01-24-2006, 05:13 PM
Hi Greg,

Be sure you put some kind of washout plug on the outside of your firebox so you can clean and inspect the inside of your siphons. A threaded bushing with a straight thread and a copper washer will make things easy to access.

Full sized locomotives had washout plugs opposite all the siphons to make them easier to keep clean. I've repaired dozens of plugs. They had square threads and annealed copper rings to seal in the bushing.

From all I've heard and read about LSB4000; that stuff ought to help you keep things open.

Good luck....

Andy Pullen

andypullen
01-24-2006, 05:14 PM
<font face="Verdana, Arial" size="2">Originally posted by willy:
Seems to me IF you are trying to use screw in fittings to increase the percolation, you would need to limit yourself to a (cough, cough sorry andy) propane fired boiler where the fire would be less likely of melting the fittings.

Willy</font>

GRIN!

Andy

pockets
01-24-2006, 05:26 PM
I'm getting confused. Some do. Some don't and some might, if you ask them nice. Sounds like my highschool prom!

What is the criteria for determining if a siphon is needed?

Regards,
Greg B.

Bill Shields
01-24-2006, 06:27 PM
Greg:

Q? What makes you think that you need a siphon anyway?

A siphon would be the LAST thing that I would put in a boiler...given all the potential problems.

I have never had or seen a model bolier that needed one.

If I need more steam, I just turn up the propane a bit, adjust the nozzle, cutoff or use 'lighter' water that will boil easier, as opposed to 'heavy' water that is used for other purposes.

But then, all of the above is just one man's humble opinion....

[This message has been edited by Bill Shields (edited 01-24-2006).]

GWRdriver
01-24-2006, 06:41 PM
Greg,
It's an optional enhancement, and like Bill I've never seen one in a large scale boiler in the US, for the reasons I mentioned above. They will improve water circulation and steam generation, BUT they add work (and cost) and the potential for leaks and burnouts and most people feel that when well-designed and properly fired most model boilers will perform just as well without them and the improvement is not worth the time and effort to add them.

The small scale work I mentioned really doesn't apply to most conventional large scale designs.

willy
01-24-2006, 07:47 PM
A good way to realize if you need them is, if, when firing the locomotive, you cant create enough steam to keep going on the track.

How ever. If you are lifting your safeties and have to leave the fire door open a crack. You have plenty of heating surface already and do not need the headaches.

Willy

GWRdriver
01-24-2006, 08:21 PM
There's a dozen things which will cause a boiler not to steam up to capacity, . . . fuel type & grade, grate area, draft, grate to heated area ratio, flue length to diameter ratio, front end design, meaning the relationship of grate to cylinder to stack diameter and exhaust, AND poor or inexperienced engineers. Any of these can keep a boiler from steaming up to capacity. Lack of siphons is so far down the list of possible causes it's not worth mentioning.

pockets
01-24-2006, 11:08 PM
Thank you, gentlemen.

Bill,I don't think I need them. I was trying to find out what they are and if they would enhance this boiler. Propane isn't an option for me. 'smurf has addicted me to coal.

GWRdriver, the effort of installation isn't an issue and based on the overall cost of this puppy, I don't think that the price of a valid improvement would be, either. I am, however, probably going to fall well within the catagory of poor/inexperienced engineer. At least for a while...

willy,I'm still in the pencil and eraser phase of this project. Most of this gang has been in on it from near the begining. It will be some time before I know how this thing is going to steam. It should be obvious that I have a lot to learn.

Andy, as usual, sound advise. My intent is to have the customary two blowdowns occupying the space above two corners of the mud ring and two washouts occupying the other two corners.

To all of you, my heartfelt thanks,
Greg B.

willy
01-25-2006, 04:15 AM
Instead of percolators? Why not ribs? If you ever look at a oil furnace they have little nubs of iron that protrude into the firebox to increase the efficiency. If you used ribs it may enhance the structural support?

Go ahead Harry, I would love to hear your thoughts on my hair brained curriosity.

Willy (loco is still on time, now 8 hours from delivery).

andypullen
01-25-2006, 11:04 AM
Hi Greg,

Thanks.

My take on siphons in model work is: Don't do it. The maintenance headaches more than defeat the efficiency gained. Cinder erosion will occur and you'll get a leak. Believe me about cinder erosion. I worked on full sized steam for a time and whenever we went into a smokebox to do any maintenance; you could see where the cinders had eaten away the metal. (Sure Mr. Propane, propane doesn't do this) Oil burners used sand to clean the flues. Just as abrasive. Plus the fact that the insides of the tubes need to kept clean of scale. Not an easy task in a 1/4" pipe inside a firebox.

I'll dig up the article I have on proportioning smokebox parts and send it down to you. There is more to it than just being a smokechamber.

Andy

GWRdriver
01-25-2006, 11:46 AM
Willy,
Actually it's a good idea, or a better one than siphons . . . an all-quills and baffles boiler is called a "porcupine" boiler.