Big Boy firebox question

I beleive those are "thermic siphons." The lower "crossbar" parts of those structures are well below the water level of the boiler--doesn't matter how far into the firebox they protrude, the water in them won't turn to steam, since it's under pressure.

Locomotive boilers have a constant circulation going on, with "cooler" water injected towards the front sinking, being heated, and rising. The T structures you saw help that current.

They also supported the arch brick. Look up some photos of the firebox interiors of UP 4000 or 3900 class locomotives, and you will see how those circulator/arch tubes support the arch bricks. Pretty much all big, modern coal burning steam locomotives have an arch in the firebox. 

They work on the principle that hot water becomes less dense and rises to the top of the boiler. Thats the "thermic syphon" technology. Nothing new, the original model T Fords used this principle to cool the engine. The Model T had no water pump.

 

 Cold water is heavier than hot water, so in a locomotive boiler, the heating of the water in the syphon or circulator tubes causes the heated water to rise towards the crown sheet, and as it rises, it draws the cooler water into the syphon. It does aid in the efficiency of the boiler.

Actually, I think what you are describing as the 'T' shaped tubes are called 'circulators'.  The thermic syphons that DigDug mentions are what is in the 1225 and 765, among other engines.  From the side, they look like tornados that widen up as they go up to the crown sheet.

 

There are a few different styles of this theory, depending on where they are attached to the firebox.  You also have arch tubes, that I believe run from the throat sheet up to the crown sheet or back head of the firebox.  The 611 has tubes that run across the firebox (side to side) and then go up to the crown.  A look at the jacketing on the firebox shows a series of small doors that slope down as they go to the front of the firebox.....they cover the washout plugs. 

 

All of these circulator/syphon/arch tube designs were used to do that same basic thing.....take advantage of the natural circulating off the water in the boiler to increase heat transfer and evaporation, as Dig mentioned.

 

I do have a raging head cold so some of my descriptions may be a little off.

I can strongly recommend the book, "The Steam Locomotive in America" by Alfred W Bruce, for anything you need to know about steam locos.  Available used for a reasonable price.  Included on page 150 are drawings of both syphons and circulators.

 

ChipR

Speaking of the 611, go straight to the 7:31 & 7:43 mark and you can see the tubes.....

 

Perfect, thanks for pointing that out Chris!  Great way to show them.

thanks all

 

i found it impossible to skip any of that video.  

Young Mr. Nasaracer there knows quite a bit about the J.

He used to run it.

uh, 'run' is a stong word.

Those lateral tubes in the 611 are properly called "Circulators" and are not "Thermic Siphons" as found in the 765. The principle of operation is the same (cooler water in the bottom which fountains out the top as steam) as they are two different tools for the same job.

 

So...nasaracer32, if you didn't "run" her, what did you do? I got a chance to ride the 611 cab twice. Once was when I was shooting cab scenes for my "Queen of the Fleet" Hopewell video with Frank Collins running, and another time I was just along for the ride with Bob Saxtan running. I recall it rode very nicely. I never had a chance to run or fire her, however.

Thanks for the info, Rich.  Like you said, there were different setups that were all aimed at doing the same thing.

 

I was very fortunate to be around the engine the last year and a half or so that the program was running.  I met those guys while volunteering on the 4501 in Bristol on a weekend that both engines were in town.  In fact, on my 21st birthday weekend, I was in Asheville for a trip up and down Saluda instead of a bar getting hammered.  I still say I had more fun too!!  I had to chance to fire just a couple of times and usually made pile in the middle of the grates, but never did anything in the right hand seat except run the water.  Fortunately, I was able to learn a lot from Bob, Jack, Steve, John B. and others and to this day can still call them good friends.  Given what happened at the end of '94, I was very lucky.

 

Seems my signature didn't carry over with the new web layout....

 

Will Sadler

www.nhvry.org

 

Wow...you were very fortunate indeed Will. 

My 1952 copy of Bruce's excellent book has the drawings on page 150 as well.

Inside Bigboy 4005 Firebox at the Forney Museum of transportation Denver CO

Nice shot.

that's the shot i was looking at that started this whole thread  

Yeah those are circulator's.

Nice shot of the Circulators. Relatively "cool" water comes in at the sides, is rapidly heated in the heart of the fire and fountains out the top as steam.