# Why are some boilers tapered and others straight?



## Jerry McColgan (Feb 8, 2008)

I am sure there is a very simple answer to this but I have never seen it.

Every picture I have seen of boiler tubes has them going through the boiler and coming out in the same pattern (same dispersal). 

Is the tapering of the boiler on some locomotives (I've noticed particularly the 4-4-0's and Pacifics) somehow related to their being Passenger locomotives? The Freight locos like the Moguls and Mikados seem to mostly have straight boilers as do (I think) most Northerns.

Is it more room for steam expansion or what? 
Apparently various NYC lines used a lot of 4-4-0's for freight because their line was so flat but I have not noticed any non-tapered boilers on any 4-4-0's.


Thanks,

Jerry


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## Spule 4 (Jan 2, 2008)

Different circulation and firebox designs. Weight savings in those cases too.


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## DKRickman (Mar 25, 2008)

A straight boiler is stronger and easier to fabricate. 

A tapered boiler gives more steam and water space over the firebox, where you want it. It also helps keep the weight over the drivers, which was desirable with a 4-4-0 (which had too much weight on the front truck, and not enough for traction). 

I have seen some studies which suggest that the majority of steam generation in a boiler happens around the firebox. As such, it is helpful to have as much space around the firebox as possible. Enlarging the firebox end of the boiler also helps when the engine is on a grade, because it increases the water volume around the firebox and thus decreases the chance of uncovering the crown sheet. 

Finally, as boilers became larger (and thus domes became smaller to fit withing the loading gauge) the wagon top boiler and its later variants (notable the USRA style boiler) had the advantage of giving a natural collection point for the steam.


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## DKRickman (Mar 25, 2008)

Posted By Jerry McColgan on 31 May 2010 09:17 AM 
Is the tapering of the boiler on some locomotives (I've noticed particularly the 4-4-0's and Pacifics) somehow related to their being Passenger locomotives? The Freight locos like the Moguls and Mikados seem to mostly have straight boilers as do (I think) most Northerns.

I meant to address this in my earlier post, but forgot. Sorry.

A lot of early freight engines had the same wagon top boiler design as passenger engines, although sometimes the waist was longer to accommodate a longer engine. Later freight engines frequently used a tapered boiler of some sort as well. Look at the USRA designs, which shared common boilers among different designs, both freight and passenger. The reason that some freight engines look like they had straight boilers (some did, but rarely) is that the boilers almost completely filled the loading gauge, laving little room for taper, domes, or anything else. There was little if any difference between freight and passenger boilers, except that some high speed passenger engines needed larger fireboxes in order to keep up a head of steam at speed (think of the PRR and C&O engines with 6 wheel trailing trucks to support massive fireboxes)


Also, remember that Northers were originally heavy passenger engines, not freight. They were an enlargement of Hudsons, which were themselves Pacifics with larger fireboxes.


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## Jerry McColgan (Feb 8, 2008)

Hi Kenneth,

I appreciate your detailed explanation.

Your quote: 

"Never attribute to malice that which is adequately explained by stupidity."

is very perceptive regarding the Internet.

Jerry


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## Charles (Jan 2, 2008)

Jerry
Reference: PRR D16sb for non-wagon top boiler on a 4-4-0 


BTW- Northern locomotives were not necessarily designed for the sole purpose of passenger services (e.g. GS4- General Service)


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## Scottychaos (Jan 2, 2008)

Posted By Jerry McColgan on 31 May 2010 09:17 AM 


Apparently various NYC lines used a lot of 4-4-0's for freight because their line was so flat but I have not noticed any non-tapered boilers on any 4-4-0's.


Thanks,

Jerry 




The most famous NYC 4-4-0! 




While the vast majority of the more "modern" wheel arrangements (from the 20th Century) have straight boilers:
2-8-0 (yes, I know I listed 2-8-0 twice, that was intentional! ;)
2-8-2
4-6-4
4-8-4
etc..



Scot


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## Scottychaos (Jan 2, 2008)

Posted By Charles on 01 Jun 2010 10:28 AM 

Jerry
Reference: PRR D16sb for non-wagon top boiler on a 4-4-0 


BTW- Northern locomotives were not necessarily designed for the sole purpose of passenger services (e.g. GS4- General Service)








While its true the first 4-8-4 northerns were probably designed as passenger locomotives (as Ken said, basically enlarged hudsons)
Only a smaller percentage of Northerns, overall, ended up being "passenger only" locos..
some were designated as "dual service"..
but the majority of the 4-8-4 class ended up being built as modern Freight locomotives..Freight only.

I havent seen any data that offers an actual breakdown..but based on some North East roads (LV, DL&W, Reading) its probably about 25% passenger service to 75% freight service.
(with some notable exceptions..such as the NYC 4-8-4 Niagaras..among the most modern steam locomotives ever built..which were primarily passenger locos)

Scot


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## Dwight Ennis (Jan 2, 2008)

On the Southern Pacific, the Northerns were "GS" class locomotives - GS = General Service. 

Jerry - there's a lot of good info on locomotive design and its history in Fletch's first Mogul MasterClass. He talks about how larger firebox sizes and placement led to new boiler designs.


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## Charles (Jan 2, 2008)

"While its true the first 4-8-4 northerns were probably designed as passenger locomotives (as Ken said, basically enlarged hudsons)" The design of any locomotive was more specific to the needs of the RR company than a generalization. Some like the NYC and N&W had specific purposes in mind: passenger service. Others such as the Reading T1 freight therefore Northerns cannot be denoted as a passenger engine. In fact, the design of a Northern, other than going from the wheel classification of 4-6-4 to 4-8-4 probably did not share much in common as to developmental design: they did not stretch a Hudson into a Northern nor just add a driver. Finally, indicating that a Northern was basically an enlarged Hudson is no more correct that saying that they were enlarged Mountains (GN and N & W) prior developed locomotive power.


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## Jerry McColgan (Feb 8, 2008)

Posted By Dwight Ennis on 01 Jun 2010 11:08 AM 
On the Southern Pacific, the Northerns were "GS" class locomotives - GS = General Service. 

Jerry - there's a lot of good info on locomotive design and its history in Fletch's first Mogul MasterClass. He talks about how larger firebox sizes and placement led to new boiler designs. 

Hi Dwight,

Do you have a link to Fletch's article?

Regarding the 4-4-0's I was wrong. The book I have been reading "New York Central's Early Power 1831 - 1916" has a lot of photos of 4-4-0's with straight boilers.

Its my kind of book - lots of pictures. 

Unfortunately while it has a lot of information a lot of it amounts to "Look at the ****""" and I have no idea what it is that I am supposed to be looking for. Its a great book I just wish I had more interest in the NYC.

Jerry


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## Scottychaos (Jan 2, 2008)

Posted By Charles on 01 Jun 2010 12:05 PM 


"Finally, indicating that a Northern was basically an enlarged Hudson is no more correct that saying that they were enlarged Mountains (GN and N & W) prior developed locomotive power.




I disagree..I think it is accurate to say the Northern is "an enlarged Hudson"..
at least in its initial planning stages..
The early Northerns had much in common with the Hudson..simply "adding a set of drivers" to the design of the Hudson give you the Northern..

the Northern Pacific Railroad..who developed the 4-8-4 (and gave it the name "Northern") did in fact design the 4-8-4 to be a passenger locomotive:
http://www.steamlocomotive.com/northern/np.shtml

Not all locomotive evolution is clear-cut, there are a lot of branches on the family tree..
but I believe its fairly reasonable to say that passenger locomotives in particular have a fairly clear progression:

Start with the classic 4-4-0.

The 4-4-0 was enlarged in two ways..adding another set of drivers created the 4-6-0 ten wheeler..common in passenger service.

Needing a wider firebox for more power, they moved the firebox back so it was behind the drivers, rather than between the drivers, requiring a trailing truck, the result is the 4-4-2 Atlantic.

Enarging the Atlantic still further, by adding a new set of drivers, creates the 4-6-2 Pacific.

A larger firebox on the Pacific, making a more powerful locomotive, now requires a 4-wheel truck to support the firebox..the result is the 4-6-4 Hudson.

Enlarging the Hudson, making it still larger and more powerful by adding another set of drivers, gives us the 4-8-4 Northern passenger locomotive..basically the top of the food chain.

to me, the progression is clear! 

sure, there is more to it than that..lots of other technology was also evolving along with wheel arrangements..
and individual railroads did a ton of custom building back in the day..fine-tuning things for their own needs..
(its not well known, but there were a fair amount of 4-6-2 Pacific freight locomotives!)

So IMO its quite reasonable to say the 4-8-4 was initially "an enlarged Hudson"..

Scot


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## Charles (Jan 2, 2008)

Scot
As to engineering goes one would have to add the 4-8-2 to that progression prior to the 4-8-4. 


Given the numerous RR companies without Hudson locomotives that had Mountains such as SP, GN, N& W, UP etc most importantly the one from which the "Northern" was truly denoted: Northern Pacific did not have a Hudson in their progression of locomotives but did have other x-8-x locos


Of the 21 RR companies with Hudsons 17 when on to order Northerns of which only 4 of those 17 did not have Mountains in their inventories. Based on that I would conclude your support for the logic of progression indicates the Northern was an enlarged Mountain locomotive. 




"The early Northerns had much in common with the Hudson..simply "adding a set of drivers" to the design of the Hudson give you the Northern." If this was true then very few would been able to develop the 4-8-4 wheel based without a "Hudson" I would say that the Northern development had much more to do with all the prior x-8-x. Again, the N &W probably made the jump from the Mountain as did many others if that was a factors given their needs and experience with locomotive power on hand. More companies had 4-8-2 locos thus much more influence given the very close running setup (only have to add a truck set not have to account for all the impact of an additional driver: weight, rods, frame, steam requirement, impact on railroad such as PRR did with the N&W J class experiment) .

As to being a passenger locomotive by definition (along with the developmental line) that would be more attune to the needs and purpose of each railroad (again Reading T1 was freight) thus I do not believe it to be denoted in the history books as "passenger locomotive." Both.....The 4-8-4 was the ultimate wheel configuation for the modern passenger and fast freight steam locomotive. 

Anyways...all hypothetical until someone read:

Data from tables in 1930 Locomotive Cyclopedia. See also (see Locobase 232). See also Robert A LeMassena, "The USRA HEAVY 4-8-2 and its Illustrious Ascendants", Railway & Locomotive Historical Society Newsletter (Vol 23, #2 - Spring 2003). 

Boiler had feedwater heater. Only 15 "Heavy" mountains entered service under the USRA aegis. Baldwin built two engines for the C&O, Alco-Brooks supplied three more to the C&O as well as 10 more to the N&W. LeMassena argues, however, that this particular design influenced not only 4-8-2 designs, but also encouraged the development of the larger 4-8-4. 

and this article:
http://www.trains.com/ctr/default.aspx?c=a&id=120
Had Northern Pacific used better quality coal, these engines would likely have been 4-8-2s.


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## Jerry McColgan (Feb 8, 2008)

Posted By Charles on 01 Jun 2010 01:43 PM 
Given the numerous RR companies without Hudson locomotives 







That is one thing that surprises me. Very few railroads owned Hudsons and I love Hudsons. They just have that balanced look - like the Northern. Of course if any manufacturer dared to make a plastic 1:29 Hudson a lot of folks would scream it was not prototypical - but I would buy it anyway. I LOVE Bubba's USAT Hudson and I run it every time he lets me (which fortunately for me has been a lot). I just cannot part with the money for one only to run it 6+ feet above the ground on my layout. I would swap my LGB WP&Y Mike for a LGB Hudson (same condition) in a heartbeat. I would really like to have a UP Hudson and or Northern (#844?) because I have more UP 1:29 rolling stock than other railroads.

I am far less concerned with prototypical accuracy as the fact that with my O Gauge, Hudsons have always been far better at backing trains into sidings and not derailing with that two axle trailing truck. Even the LGB Mikado does not back into sidings well. I suspect that if anyone ever comes out with G Gauge plastic Hudsons and Northerns they would both be great runners and great at handling reverse moves into sidings.

Jerry


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## Charles (Jan 2, 2008)

Jerry
Good and bad news...

Bad- UP did not have Hudson

Good- You could easily convert an Aristocraft Mike into a Northern. 

Finally, to keep on topic both Hudson and Northern have straight boilers.


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## Jerry McColgan (Feb 8, 2008)

Posted By Charles on 01 Jun 2010 04:21 PM 
Jerry
Good and bad news...

Bad- UP did not have Hudson

Good- You could easily convert an Aristocraft Mike into a Northern. 

Finally, to keep on topic both Hudson and Northern have straight boilers. 



I knew that about UP (I looked it up long ago) but if I had an unmarked one...

I bought a MTH NYC Hudson with the intention of eventually changing it to UP. It shares the MTH UP coaches with the Challenger. I run the Hudson indoors and the Challenger outside (at least that was the plan). I don't care for the MTH Northerns.

Until the economy and the US dollar tanked, Lewis had been talking about coming out with a Northern. I wonder if anyone converted a LGB Mike to a Northern? I have a couple of spare LGB Mike drive units but neither the talent nor the skill to build anything with them.

Perhaps someday...

I personally like the look of straight boilers better on large locos.

Jerry


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## xo18thfa (Jan 2, 2008)

I read somewhere, don't remember now, but the smokebox in front has a lot to do with the efficiency of the boiler. The blower and exhaust blast going up the smoke stack creates a little vacuum in the smokebox that pulls the fires thru the boiler. Consequently a smaller volume smokebox works better. Larger volume fireboxes are better becuase most of the steam production comes from the firebox. Tapering the boiler gives the best of both. 

Don't know if it's true, but it makes a good rumor.


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## Chucks_Trains (Jan 2, 2008)

Stretching a Hudson didn't make a 4-8-2 Mokawk..it couldn't because the first J1a Hudson #5200 wasn't made until 1927. The first Mohawk L2a #2700 was built in 1925.

Hudson models J1 & J2 all had straight boilers but starting in 1935 the NYC placed an order for 50 Super Hudsons model J3A right in the middle of the great depression. The J3a's had a tapered boiler and I've never read as to why but I believe that it's because only the J3a's had a combustion chamber ahead of the firebox but before the rear flue sheet. The more heat gained by allowing the gases to burn more completely more than compenstated for the loss of flue length or that's how it was with the Hudsons. If the NYC did anything right it was finding ways to gain more power (horsepower at speed) from an existing locomotive than about any other road. 

Jerry, Did you know that the Milwaukee Road placed an order with Alco for the Hudson type before the NYC did?? The only reason the NYC got them first is because the Milw. had problems raising the $$$.


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## Dwight Ennis (Jan 2, 2008)

Do you have a link to Fletch's article?The MasterClasses are under *Features* in the top menu bar. Part 1 of the first Mogul MasterClass starts *here*. Each section is pretty much divided into two parts - *Background* and *Construction*. The info I referred to can be found in the *Background* sections throughout the MasterClass.


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## Scottychaos (Jan 2, 2008)

Posted By Chucks_Trains on 01 Jun 2010 09:20 PM 
Stretching a Hudson didn't make a 4-8-2 Mokawk..it couldn't because the first J1a Hudson #5200 wasn't made until 1927. The first Mohawk L2a #2700 was built in 1925.






No one said that! 
we were talking about "stretching a Hudson" to make a 4-8-4 Northern..

Scot


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## Jerry McColgan (Feb 8, 2008)

Posted By Dwight Ennis on 01 Jun 2010 09:34 PM 
Do you have a link to Fletch's article?The MasterClasses are under *Features* in the top menu bar. Part 1 of the first Mogul MasterClass starts *here*. Each section is pretty much divided into two parts - *Background* and *Construction*. The info I referred to can be found in the *Background* sections throughout the MasterClass. 

Thanks Dwight,

Jerry


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## Jerry McColgan (Feb 8, 2008)

Posted By Chucks_Trains on 01 Jun 2010 09:20 PM 
Stretching a Hudson didn't make a 4-8-2 Mokawk..it couldn't because the first J1a Hudson #5200 wasn't made until 1927. The first Mohawk L2a #2700 was built in 1925.

Hudson models J1 & J2 all had straight boilers but starting in 1935 the NYC placed an order for 50 Super Hudsons model J3A right in the middle of the great depression. The J3a's had a tapered boiler and I've never read as to why but I believe that it's because only the J3a's had a combustion chamber ahead of the firebox but before the rear flue sheet. The more heat gained by allowing the gases to burn more completely more than compenstated for the loss of flue length or that's how it was with the Hudsons. If the NYC did anything right it was finding ways to gain more power (horsepower at speed) from an existing locomotive than about any other road. 

Jerry, Did you know that the Milwaukee Road placed an order with Alco for the Hudson type before the NYC did?? The only reason the NYC got them first is because the Milw. had problems raising the $$$. 


Hi Chuck,

No I was not aware of that. Unfortunately I don't model either the Milwaukee Road or the NYC but if someone made a Hudson I suspect the MR would be colorfully painted and hard to convert to UP.

Since you mentioned the flues, this brings up another question (for anyone). As I understand it, steam was recirculated through the boiler to raise its temperature but - where are (or were) the flues in this loco?












Jerry


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## Scottychaos (Jan 2, 2008)

Jerry, 
Are you interested in modeling The Frisco? 
they ran down in your area I believe.. 
they had some Hudsons: 

http://www.yesteryeardepot.com/FL1060.JPG 

http://www.yesteryeardepot.com/FL1062.JPG 

http://thelibrary.springfield.missouri.org/lochist/frisco/friscoline/images/photos/p01349.jpg 

http://thelibrary.springfield.missouri.org/lochist/frisco/friscoline/images/photos/p01348.jpg 

I would like to someday model a DL&W Hudson..fairly obscure as Hudsons go: 

http://www.rr-fallenflags.org/el/loco/dlw-s1151bgd.jpg 

Scot


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## Totalwrecker (Feb 26, 2009)

Jerry, 
Regaring the pic; The flues are behing what you see. The front of the boiler blew off revealing the superheater tubes (they captured heat from the exhaust and steam in the smokebox). Behind them are the flues. Superheaters heated the water prior to injecting into the boiler so the boiier worked more effeciently. 

John


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## Dwight Ennis (Jan 2, 2008)

Superheaters heated the water prior to injecting into the boiler so the boiler worked more efficiently. You are referring to feedwater heaters, which heated water prior to boiler injection. Superheaters raised the temperature of the steam prior to being fed to the cylinders, drying it and raising its available energy = more work from the same steam.


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## Jerry McColgan (Feb 8, 2008)

Posted By Totalwrecker on 02 Jun 2010 09:00 AM 
Jerry, 
Regaring the pic; The flues are behing what you see. The front of the boiler blew off revealing the superheater tubes (they captured heat from the exhaust and steam in the smokebox). Behind them are the flues. Superheaters heated the water prior to injecting into the boiler so the boiier worked more effeciently. 

John 
Hi John,

That was the only photo in the book of that loco but it just seemed that there was hardly any room for flues behind the tubes.

Since I posted the photo I found that there was a newer SP4402 that was a SD-9 and the original 4402 was a GS1 4-8-4.

This photo seems to explain a lot. I guess the darker smokebox was long enough for the superheater tubes. After looking at the air tank I changed my mind. The smoke box does not appear to be long enough for the superheater tubes.











Thanks,

Jerry


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## SteveC (Jan 2, 2008)

Posted By Totalwrecker on 02 Jun 2010 09:00 AM 
{snip...}[/i] Superheaters heated the water prior to injecting into the boiler so the boiier worked more effeciently. {snip...}[/i] John

I don't think that is quite correct regarding "Superhearters."
"In steam locomotive use, by far the most common form of superheater is the fire-tube type. This takes the saturated steam supplied in the dry pipe into a superheater header mounted against the tube sheet in the smokebox. The steam is then passed through a number of superheater elements—long pipes which are placed inside special, widened fire tubes, called flues. Hot combustion gases from the locomotive's fire pass through these flues just like they do the firetubes, and as well as heating the water they also heat the steam inside the superheater elements they flow over. The superheater element doubles back on itself so that the heated steam can return; most do this twice at the fire end and once at the smokebox end, so that the steam travels a distance of four times the header's length while being heated. The superheated steam, at the end of its journey through the elements, passes into a separate compartment of the superheater header and then to the cylinders as normal." 
For further information on locomotive superheaters click here[/b].


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## Jerry McColgan (Feb 8, 2008)

Posted By Scottychaos on 02 Jun 2010 08:52 AM 
Jerry, 
Are you interested in modeling The Frisco? 
they ran down in your area I believe.. 
they had some Hudsons: 

Scot 





Hi Scot,

Just when I thought I had Arkansas mainline railroads figured out I bought the book "Railroad Stations and Trains through Arkansas and the Southwest" only to find that not only MoPac and the Cotton Belt but also the Frisco and Rock Island and even KCS had a lot of track in Arkansas.

I can't model all of them and fortunately a lot of locos and rolling stock is not made in large scale. I will probably stick with MoPac because it ran nearby with huge shops in North Little Rock and the Cotton Belt which had a huge operation in Pine Bluff.

Since I have no personal or family history with any railroads I am more or less free to pick and choose according to what is on sale and that I like. UP has 844 and 3985 and Cotton Belt has 819 and the caboose is MoPac. That helps me to limit the number of railroads I try to model.

Regards,

Jerry


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## Jerry McColgan (Feb 8, 2008)

Posted By SteveC on 02 Jun 2010 10:33 AM "In steam locomotive use, by far the most common form of superheater is the fire-tube type. This takes the saturated steam supplied in the dry pipe into a superheater header mounted against the tube sheet in the smokebox. The steam is then passed through a number of superheater elements—long pipes which are placed inside special, widened fire tubes, called flues. Hot combustion gases from the locomotive's fire pass through these flues just like they do the firetubes, and as well as heating the water they also heat the steam inside the superheater elements they flow over. The superheater element doubles back on itself so that the heated steam can return; most do this twice at the fire end and once at the smokebox end, so that the steam travels a distance of four times the header's length while being heated. The superheated steam, at the end of its journey through the elements, passes into a separate compartment of the superheater header and then to the cylinders as normal." 

As I read the above it suggests that each of the superheater tubes was in a flue. Something had to be supporting those long superheater tubes.

That seems to put us back to square one (my original question). Where are the flues? Did they all fly off?

I would think that in a boiler explosion the pressure would be on the outer skin of the boiler and the boiler apparently blew off. Why would each and every flue have blown off (forward) as well and if it did where is the back plate (or whatever it is called) that held the back end of the flues?

I don't understand what I am looking at in reference to what was there before the explosion. Just when I think I am starting to understand something, a picture or something else comes up and makes me wonder how much I do or do not know.

Jerry


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## Jerry McColgan (Feb 8, 2008)

The (air?) tanks seem to show that the superheater tubes extended well toward the cab end of the boiler.

Jerry


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## SteveC (Jan 2, 2008)

Posted By Totalwrecker on 02 Jun 2010 09:00 AM 
{snip...}[/i] Superheaters heated the water prior to injecting into the boiler so the boiier worked more effeciently. {snip...}[/i] John

What you are describing sounds more like the system used to preheat the boiler feed water. For one design of a system to do this click here[/b].


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## SteveC (Jan 2, 2008)

Jerry

In looking at the above photograph what I believe you're looking at is the rear of the smoke box. The reason that I believe this is true is because of the number boards that you can see on the upper part on the left and right.

The device that all the tubes are connected to in the background if I'm not mistaken is the superheater manifold, which would be located just forward of the smokebox flue sheet which is missing. The 'U' shaped tubes that you see are the superheater tubes that were inside the flue/fire tubes. There's no way of knowing from the photograph if when the boiler exploded the smoke box was blown forward, or the boile backward, or if the picture was taken after the destroyed boiler had been removed from the wreckage.


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## SteveC (Jan 2, 2008)

Here's a link to a book in Google Books, the link will open to a listing of pages concerning 'Superheating' start by clicking the Page 459 link, it provides a pretty complete explanation of the how, why, & what-for's of superheating. There's also a section on feedwater heating also. Just use the 'Search this book' field located on the left just below the 'About this book' link use the search value of feed water heater and click the 'Go' button.

The Locomotive Up To Date (c 1921)[/b]


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## Jerry McColgan (Feb 8, 2008)

Hi Steve,

You are right about looking toward the front of the loco. I expanded the original and it is pretty obvious abut the number boards. I tried uploading the full size but it is 22 meg and for some reason it just Will not upload.

Since it looks like the smoke-box is still attached to the frame it makes one wonder what happened to the cab etc.

That must have been one heck of an explosion.

Jerry


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## Dwight Ennis (Jan 2, 2008)

Posted By Dwight Ennis on 02 Jun 2010 10:30 AM 
Superheaters heated the water prior to injecting into the boiler so the boiler worked more efficiently. You are referring to feedwater heaters, which heated water prior to boiler injection. Superheaters raised the temperature of the steam prior to being fed to the cylinders, drying it and raising its available energy = more work from the same steam. 

You guys sure are using a lot of words to say what I already said in two sentences.


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## SteveC (Jan 2, 2008)

Posted By Jerry McColgan on 02 Jun 2010 11:00 AM 
The (air?) tanks seem to show that the superheater tubes extended well toward the cab end of the boiler.

Jerry
Again I'm not certain but the tanks that you mention as "air?" I believe are in fact part of the boiler feedwater heater system.


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## Semper Vaporo (Jan 2, 2008)

The superheater tubes could extend to within inches of the firebox. 

The photo shown in this thread is taken from about where the tender deck would be,facing toward the front of the engine. The rear truck wheels and outside frame of the rear truck can be partialy seen at the bottom of the photo. The rear drivers are clearly seen just above that. The cab, boiler barrel, rear tube sheet, flue (both small and superheater sized) and the front tube sheet are no longer in the area. The boiler may have ruptured at the front and the boiler parts all exited toward the rear, removing the cab and crew in the process.


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## Semper Vaporo (Jan 2, 2008)

The air tanks on the sides (one slightly forward of the other) are part (compressed air storage) of the air-brake system.


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## SteveC (Jan 2, 2008)

Yep, C.T. you're most likely correct.

No. 4402 was a SP GS1 (Golden State/General Service) one of 14 Northern's built for SP by Baldwin and delivered in October 1930, the following is a picture of No. 4401. The thing that I find amazing is supposedly there were no fatalities nor injuries when the boiler exploded, as stated here[/b]


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## Totalwrecker (Feb 26, 2009)

Some mornings..... I should finish my coffee before showing off my ignorance.... 

Thanks guys. 

John


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## SteveC (Jan 2, 2008)

Well John, the one thing you can count on is you won't be by yourself, the only thing that I think I've figured out is there's a whole bunch that I don't know.


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## Jerry McColgan (Feb 8, 2008)

Hi C.T.,

Thanks for filling in the blanks.

I was reading the book "Train Wrecks" and that photo was for me the most interesting because it seemed so illogical. I guess when boilers exploded one never knew what was going to go where.

It is also possible, as suggested, that the railroad may have already started disassembling the loco. Even the smokestack is gone.

Jerry


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## Semper Vaporo (Jan 2, 2008)

I can't seem to find the photos now, but the ones that really bother me are the ones where the superheater tubes are sticking out the FRONT of the smokebox, apparently having been shoved out of the flues by being folded backwards and then straightening out again. I just can't get my mind around how that could happen, but the photos sure make it look like it did.

I have seen drawings of the distances that some boilers have been tossed in an explosion and it is amazing. Sometimes there is evidence that it bounced once or twice OVER obstructions; Train cars, highway bridges, utility wires etc.


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## Jerry McColgan (Feb 8, 2008)

Posted By Semper Vaporo on 03 Jun 2010 10:51 AM 
I can't seem to find the photos now, but the ones that really bother me are the ones where the superheater tubes are sticking out the FRONT of the smokebox


Perhaps this is what you were looking for:


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## Semper Vaporo (Jan 2, 2008)

Posted By Jerry McColgan on 03 Jun 2010 02:37 PM 
Posted By Semper Vaporo on 03 Jun 2010 10:51 AM 
I can't seem to find the photos now, but the ones that really bother me are the ones where the superheater tubes are sticking out the FRONT of the smokebox


Perhaps this is what you were looking for:












Yeah, that sort of thing. Like it had an upset stomach! "Bleah, don't feed me that kind of coal again!"

I suppose what happened is that the superheater tubes broke off of the header in the smoke box and got blown only part way out, not that what is sticking out is from the firebox end and they are still connected to the header. Still I have seen other very similar photos where I think I can see the return bends sticking out it front.

Plumber's nightmare!


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## Jerry McColgan (Feb 8, 2008)

It could be said that the loco coughed its guts out.

I've had days I felt like that.

As much as I love steam locos I have to admit the thought of being scalded alive in a boiler explosion might have kept me awake at night if I ran one for a living. I have read stories of engineers telling the fireman to keep the water level low to get maximum performance out of the loco.


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## Dwight Ennis (Jan 2, 2008)

Posted By Jerry McColgan on 03 Jun 2010 02:37 PM 

Perhaps this is what you were looking for: 








The *sandbox* shot off? Looks to me like the stack is missing and the sand dome is still there.


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## Jerry McColgan (Feb 8, 2008)

One advantage of having the original rather than a 640 x 480 image is this:










Something was there. Now whether it was a sand dome or something else, I have no idea.


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## Scottychaos (Jan 2, 2008)

based on the location, right above the cylinders, it would have to be the stack.. 

Scot


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## Spule 4 (Jan 2, 2008)

Posted By Jerry McColgan on 03 Jun 2010 02:37 PM 
Posted By Semper Vaporo on 03 Jun 2010 10:51 AM 
I can't seem to find the photos now, but the ones that really bother me are the ones where the superheater tubes are sticking out the FRONT of the smokebox


Perhaps this is what you were looking for:









Wow, bad case of boiler worms.......


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## DKRickman (Mar 25, 2008)

Posted By Jerry McColgan on 02 Jun 2010 11:00 AM 
The (air?) tanks seem to show that the superheater tubes extended well toward the cab end of the boiler.

Jerry
Many superheater tubes extended all the way into the firebox, in order to get the direct heat from the fire. It all depended on how much superheat was called for in the design, etc.


Posted By Jerry McColgan on 02 Jun 2010 10:55 AM 

As I read the above it suggests that each of the superheater tubes was in a flue. Something had to be supporting those long superheater tubes.

That seems to put us back to square one (my original question). Where are the flues? Did they all fly off?

I would think that in a boiler explosion the pressure would be on the outer skin of the boiler and the boiler apparently blew off. Why would each and every flue have blown off (forward) as well and if it did where is the back plate (or whatever it is called) that held the back end of the flues?

I don't understand what I am looking at in reference to what was there before the explosion. Just when I think I am starting to understand something, a picture or something else comes up and makes me wonder how much I do or do not know.

Jerry

The flues were an integral part of the boiler. They were attacked to, and worked as longitudinal stays for, the front tube sheet and the front of the firebox. When the boiler "exploded" it usually ruptured somewhere (frequently the crown sheet) and was propelled away from the rest of the locomotive by the thrust from the escaping steam. The smokebox was not an integral part of the boiler, though it was of course attached to it. The rapidly departing boiler tore the connection between the two, leaving the smokebox in place. The superheater tubes were supported (but not attached) inside the flues, so that the hot gasses could pass over them and heat the steam beyond the boiling point, as mentioned previously. When the boiler took off, it left the superheater tubes hanging by their only attachment points - the header inside the smokebox.

Posted By Scottychaos on 01 Jun 2010 10:48 AM 
While the vast majority of the more "modern" wheel arrangements (from the 20th Century) have straight boilers:
2-8-0 (yes, I know I listed 2-8-0 twice, that was intentional! 
2-8-2
4-6-4
4-8-4
etc..


Scot

I have to take a little issue with this. Most modern locomotives had ALMOST straight boilers, but few were truly straight tubes. The vast majority had a slight taper (roughly 10" over the length of the boiler, at most) back to the course ahead of the firebox, and a tapered section (sometimes just sloping along the top, but not the sides) over the firebox. They look more or less straight, because they're so large that the taper is mild compared to older boilers, but they were tapered all the same.

Just ask the nitpickers who complain about a brass PFM Southern Ps-4, because the boiler is just right at the smokebox end, but a couple scale inches off at the firebox end.


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## jgallaway81 (Jan 5, 2009)

The "classic" boiler explosion was in fact a rupture of the firebox crown sheet.... either through defect in the metal or more likely because the water dropped below the top of the sheet.

Even when boiling, the water is MUCH cooler than the fire, and therefore cools the metal. As soon as the water drops below the top of the firebox, teh steel is exposed to the superhot fire in the firebox, which is hot enough to, if not actually melt steel, than at the very least, weaken the steel. The crown sheet would then loosen around the staybolts and the steam pressure in the boiler would be sufficient to cause teh sheet to rupture inward toward the fire. The catch here is that under pressure, water boils at higher and higher temperatures. (http://www.personal.utulsa.edu/~kenneth-weston/appB.pdf -> At 270.6 psi, water boils at 406 degrees F). So, if your boiler is operating at 270psi, the water is sitting at ~405-406 degrees. Now, when the crown sheet fails, the pressure drops to atmospheric pressure close to instantly. This causes the remaining water to flash-boil into steam. Several books say that it is theorized that at this instant the boiler pressure can easily exceed 10,000psi. This steam then escapes through the ruptured sheet, acting like the thrust of a rocket engine, propelling the firebox end of the boiler upward. Because of the fact that a boiler is only anchored to the frame through the smokebox to the saddle, this force causes the boiler to be propelled up and forward of the engine, leaving a vacant spot from the smokebox to the tender... including the crew.









The picture showing the superheaters coming out the back of the smokebox shows this clearly. The superheaters just sit in the larger tubes in teh boiler, and so when the crownsheet ruptured, they just slid out as the boiler barrel was propelled up and away from the locomotive frame.


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