My definition of arch tubes, is that they go from the flue sheet or throat sheet to the back head. Circulators go from the side sheets to the crown sheet. That is just my own visualization of how they work. Maybe the 1385 won't have a brick arch. I wonder if the surviving Challengers still have their circulators after being converted to oil like the 4014 does. Sorry to go off topic.

I believe, subject to correction, that N&W called this style lateral arch tubes.

Guys, "arch tubes" are simply members that provide a water-cooled support to the brick arch structure, made in the form of tubes for strength with minimum weight and maximum pressure resistance, and 'cooled' with the boiler water.

The 'older' form is longitudinal, as noted, usually passing from the backhead inner sheet to the throat sheet, as noted. These were *supposed* to provide augmented circulation due to the exposed surface, but (as noted) they could change the rest of the circulation in the firebox legs and convection section for the worse. They also constitute black, naked, relatively cold pipe right in the evolving gas plume going around the arch, after the manner of syphons, making a nifty quench of luminosity.

Lateral tubes go from side to side as noted, with the arch sections made to fit. This leaves most of the firebox geometry open to 'other' forms of circulator, if desired, and provides somewhat better geometric support for the arch brick.

It's a fairly obvious step to take lateral arch tubes and 'convert' them into security circulators by providing a central vertical branch, with or without flow shaping in the tube at the T-junctions. This is a bit like a Cunningham in reverse, taking water from the points forward in the legs and preferentially circulating it to the forward section of the crown, at the expense of some tubing 'late' in the gas plume. It can also provide a little extra stiffness to the arch tubes themselves, which may or may not be of benefit to the welds where the tubes join the inside firebox sheet. It might be interesting to see whether directed flow from Cunningham nozzles into each arch tube could produce better steam generation or less stress.

It appears the designers of this new boiler took a simpler approach, rather than introduce the stresses at a welded T connection to an upward leg, they just used pairs; one goes down and left, the next goes down and right.

It's interesting that there are overfire air inlets (jets to be added?) just below the level of the arch tubes. I wonder if the original boilers were rebuilt with this arrangement, or if it was a new design for this build.

From one of their 2006 posts, it doesn't appear that 1385 ever got the improvements.

And with no circulators or flues in the bottom of the barrel, I'm not at all surprised they had problems with cold spots.

"That's enough tubes, Bob. I'm tired of drilling. Let the stay guys finish it out...."

The old boiler did have the over fire air inlets along with the jets. It did not have any muffling device around the nozzle. In the side view of the firebox, the air inlet tubes can be seen in a plane parallel to the ground. It also had the longitudinal arch tubes. In the photo of the interior of the firebox, the sheet that the tubes were welded to had been removed during the initial tear down.

Ed

I must beg to differ. Gary Bensman flanged the backhead, throatsheet and rear tubesheet and firedoor sheet as noted here: https://www.midcontinent.org/bending-steel/ ...mld

Only things that don't have flanges/knuckles on the new boiler are the fire door and the front flue sheet from what I saw.

On a different boiler repair we had problems when the guy fitted the rear tube sheet he cut the flanged area of the new tube sheet to fit the firebox. Putting the welded seam into the knuckle or too close to the knuckle. Seems to be a differing opinion on that being a good practice. Being that many repairs or cracks seem to form on or near the knuckle it would seem to me that the seam or weld should be further back from the knuckle? But I have seen instances where the radius is very sharp on firebox knuckles on inside sheets? This being on railroad repairs not current day fab work. Not a boiler guru by any stretch but thought the radius of the knuckle was important feature. Am I off base with my thoughts? Appreciate the feedback in advance. I like to know this stuff. What boiler makers can get away with on stationary boilers v/s locomotive boilers I think may be where some of the difference of opinions come from? But I really don't know. For once I feel this to be an informative thread rather than berating someone elses work.

I offer this picture from AK RR #557 as example to my question of the welded seam being further back from radius.

http://www.557.alaskarails.org/restore/ ... isplay.jpg
Regards, John.

TrainDetainer,
A good discussion of the old design longitudinal arch tubes, 1385 old boiler defects and tube bundle placement can be found in the first few pages of this thread:
viewtopic.php?f=1&t=37766&hilit=1385+arch
So far as we can tell the old boys didn't simply quit installing tubes because they were tired but it seemed they had good reason.
mld

Is there a rendering of the 'new' circulator layout in the SolidWorks model that shows the construction of the actual arch, or that depicts the expected combustion-plume flow in the rebuilt firebox?

I note that Matt in the old thread discussed the possibility of addressing the 'belly' problems by replacing some of the 'removed' tubes even though they open under the arch and would therefore 'spoil' some of the extemded plume generation around the arch. I presume this was carefully investigated, including the fine points of 'tuning' the Master Mechanic front end baffle and lip to optimize the rebuilt flow, and that the current construction represents a consensus that this was either unnecessary or involved too much work for the benefit. If so, are any steps being taken either to improve circulation or otherwise address the issue?

For those who are unable to tell the difference, my 'quote' was a joke. Do you really think I (or most anyone else at this point) have any knowledge whatsoever of an idle conversation between boilermakers at the end of a workday probably 70 or 80 years ago? Or that said professional boilermakers would arbitrarily quit or alter a job like that? Please.

But thanks for the link. I will read as soon as I'm able. I hope to get some idea from it about the reasoning for the odd tube arrangement at least.

Without being able to see your face or hear your inflection it is quite impossible. That's the greatest difficulty of communicating via keyboard. You immediately took my comment as some sort of insult and not playing along with the joke. Again, you could not see my face or hear my voice. Before this derailment becomes fatal, please allow us to move on. To borrow a phrase from the esteemed Mr. Rowland, "Hope springs eternal". mld

No derailment at all. I was just having the full crew synchronize their watches before there was a head-on. :-) It was a rather tone-dependent statement, apologies.

Reading the linked thread. I see the CNW employee comments about plugged flues and can't help but see design problems combined with narrow thinking at CNW engineering office. Seems like a lower arch curve (larger radius, and not lowered arch tubes) and better front end design would have cured their ills rather than removing tubes and making cold spots. Koopmans/Austin/Janssen discussion is interesting - I follow Koopmans as the most well-rounded theorist from that conversation, and have to say I'm a bit concerned (but not surprised) by the comments of some others there, but I don't know who's a RRer and who's a fan. The new 1385 boiler looks like it addresses most of the concerns, although I'm a little up-in-the-air on the high longitudinal angle of the arch and the placement of the combustion air inlets. Does this design closely follow the CNW fix or is it a variation by the MCM committee? Probably fine for the normal use it will get. And what kind of front end does 1385 have (or getting)? Adjustable? Damper?