Why two "exhaust stacks" for some steam generators?

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Why two "exhaust stacks" for some steam generators?
Posted by 7j43k on Thursday, October 12, 2017 6:05 PM

It seems like the roofs of most steam generator equipped F units have two vents, or whatever.  Clearly, one is the exhaust for the "fire".  But I wonder what the other is. I had been assuming it was an air intake.  But someone pointed out that the whole carbody was pretty open, so there was no need to bring in outside air from the roof. In addition, GN apparently did some of their own steam generator installations, and those have only the single exhaust.

So, I'm asking if anyone knows what's with the "extra" exhaust.  Or intake.  Or whatever.

 

Ed

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Posted by Firelock76 on Thursday, October 12, 2017 7:16 PM

Just guessing, but it could be a vent for the steam generator's safety valve.

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Posted by SD70M-2Dude on Thursday, October 12, 2017 10:31 PM

GMD1 roadswitcher with steam generator in the short hood:

http://www.railpictures.ca/?attachment_id=17034

One stack and the little hatch is right at eye level for someone exiting the cab.  Maybe it is an air intake, I'm not very familiar with diesel locomotive steam generators.

Greetings from Alberta

-an Articulate Malcontent

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Posted by Miningman on Thursday, October 12, 2017 10:58 PM

....and a "buried" hint for the Classic Quiz!

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Posted by SD70M-2Dude on Thursday, October 12, 2017 11:27 PM

Guess again, the passenger GMD1s were all B-B, only the freight ones were A1A-A1A.  Also they were not exclusive to one railroad, Northern Alberta had a few too. 

Back on topic, the Vapor-Clarkson diagrams near the bottom of this page seem to indicate a blower with an air intake at about the same height as the hatch seen on the GMD1's short hood:

http://rollymartincountry.blogspot.ca/2017/02/1967-confederation-train-documents-and.html

Greetings from Alberta

-an Articulate Malcontent

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Posted by blue streak 1 on Saturday, October 14, 2017 8:53 PM

Fooled me twice shame on me.  Thought your title meant electric generators on a steam loco ?

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Posted by 7j43k on Sunday, October 22, 2017 2:05 PM

I am not turning up anybody who "officially" knows, both here and elsewhere.

Photos and drawings of Vapor-Clarkson generators show an exhaust vent and an intake vent for a forced draft for the fire.  If this was typical, then there were two stacks/pipes/whatever.

It appears that, typically, both the exhaust and the air inlet were piped up through the roof (hatch).  But GN, typically, did not pipe the air inlet that way.  It appears that they used a free air inlet inside the locomotive.

Why either choice was made is still a mystery.  I don't see the gain in sucking air from outside, at the roof--only thing that comes to mind would be fan noise.  And I do see downsides.

Anyway, thanks for commenting,

 

Ed

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Posted by Overmod on Sunday, October 22, 2017 2:44 PM

I am coming into this late.  Are we talking about the equipment on an F-unit roof that would be represented in a model by this?

If so: the rectangular part is the stack, and the two-piece round part is the air intake.  While the 'round thing' may look like the vent for a home gas furnace or water heater, the Vapor-Clarkson combustion always involves a considerable forced draft when running and I expect a domed sheet-metal 'exhaust' would lose its paint (or worse!) in fairly short order...

Some locomotives that were 'winterized' drew the combustion air from inside the carbody, the principal drawback being the required airflow to the generator would upset other air circulation in the unit's carbody (of course these were long before the 'pressurized-engine-room' days).  It has been a long time since I saw a Vapor-Clarkson installed in something like this, but if I recall correctly there were provisions in the fairly detailed operating placards against flashbacks when starting the unit 'flooded' with oil.  This would be no fun, even with wire flame arrestors, inside an F-unit engine room...

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Posted by 7j43k on Sunday, October 22, 2017 3:08 PM

We-re talking F unit steam generators.

The lower two pieces in the above photo look like what I think is the air intake.  Which could explain why it has a top cover.

The upper doesn't look like any steam generator exhausts (on F units) that I'm familiar with.  All the ones I know of are round:

 

 

In the model photo above, the "arrow" points to the exhaust, below that is the intake.  I believe.

The GN style is also round, but shaped differently.  And there is usually no roof inlet.

 

Ed

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Posted by Overmod on Sunday, October 22, 2017 3:43 PM

The ones I'm familiar with are round where they go through the roof as well; most of the pictures I recall seeing of generators running in service have what appear to be 'cylindrical' exhaust when you see the exhaust lifting.  (Remember that these are once-through monotubes and do not require 'pops' the way most locomotives do, so those white plumes you see in some photos are likely combustion-exhaust water, not steam that would have to be vented outside.  There was at one time a small relief jet into the stack that was intended to help stop short cycling, but I believe it was gone by 1948) 

Note that in your picture the 'stack' should be through-drilled: it is a hole with a pipe through it, although I do not remember what arrangements are made to 'catch' environmental water going down it before it ponds in the OK-4625 or whatever exhaust plenum.

I don't have time to find a detail shot from 'above' of the stack on a GG1, but it should be very similar; it never occurred to me to check whether the boiler combustion air came from outside or inside!

Can anyone with a link to an online copy or scan of Vapor Heating Corporation manual 1-208 and/or 2-203 please post it here?  I suspect this will help determine what is intended to do what.

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Posted by ATLANTIC CENTRAL on Sunday, October 22, 2017 4:26 PM

7j43k

It seems like the roofs of most steam generator equipped F units have two vents, or whatever.  Clearly, one is the exhaust for the "fire".  But I wonder what the other is. I had been assuming it was an air intake.  But someone pointed out that the whole carbody was pretty open, so there was no need to bring in outside air from the roof. In addition, GN apparently did some of their own steam generator installations, and those have only the single exhaust.

So, I'm asking if anyone knows what's with the "extra" exhaust.  Or intake.  Or whatever.

 

Ed

 

I have a pdf of an EMD operators manual for an E8. It has diagrams identifying all the external fittings.

It clearly labels the rear most dome on the steam generator roof panel as the "boiler air intake" and the other as the "boiler stack".

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, October 22, 2017 8:15 PM

Some more info, generally from memory......

A fair number of roads bought F3's with steam generators, only a few bought F7's with steam generators.

ATSF bought ABBA sets, steam generators in the B units, extra water in that space in the A units.

Steam generators came in a number of sizes, from at least two different suppliers, so exact position of vents/intakes could vary.

Burlington E units had two smaller steam generators, giving them two intakes and two exhaust vents on the roof. I don't know if any other E's were built this way.

IIRC, GN and NP had F unit sets with various set ups, some A units with, some without like the ATSF. The NP also had two FP7's.

The introduction of the FP7 corrected the water storage problem of steam equiped/dynamic brake equiped F series A units, a fair number of steam equiped F7B units were built to run in sets with the FP7's.

Taking the combustion air from inside the car body would likely present a number of problems, dispite the open nature of an F or E unit.

External air would have a more consistant temperature, and be cooler and dense, beter for combustion.

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, October 22, 2017 8:37 PM

Overmod

.......

Note that in your picture the 'stack' should be through-drilled: it is a hole with a pipe through it, although I do not remember what arrangements are made to 'catch' environmental water going down it before it ponds in the OK-4625 or whatever exhaust plenum.

I don't have time to find a detail shot from 'above' of the stack on a GG1, but it should be very similar; it never occurred to me to check whether the boiler combustion air came from outside or inside!

.......

On an HO model, like the one pictured, drillng that hole thru would be impractical on several levels. It would simply expose the gear box and wiring to some limited view, and the hole would likely collect dust with time.

Sheldon

    

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Posted by Overmod on Sunday, October 22, 2017 9:15 PM

ATLANTIC CENTRAL
On an HO model, like the one pictured, drillng that hole thru would be impractical on several levels. It would simply expose the gear box and wiring to some limited view, and the hole would likely collect dust with time.

But it would have the advantage of looking prototypical; that shell with the simplistic molded surround doesn't.  (Of course you don't leave the hole open, you put a section of appropriate thin-wall tubing in its center and weather it to resemble the exhaust duct... with the inside lower part blackened and closed shy of fouling any of the mechanism.)

This is one of those things like drilling out the mouths of horn bells that gives relatively high return for the effort if you care about close-up appearance.  (Yes, I know, this is more appropriate for the MR forum, but the general idea can be discussed here...)

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Posted by ATLANTIC CENTRAL on Sunday, October 22, 2017 9:31 PM

Overmod

 

 

 
ATLANTIC CENTRAL
On an HO model, like the one pictured, drillng that hole thru would be impractical on several levels. It would simply expose the gear box and wiring to some limited view, and the hole would likely collect dust with time.

 

But it would have the advantage of looking prototypical; that shell with the simplistic molded surround doesn't.  (Of course you don't leave the hole open, you put a section of appropriate thin-wall tubing in its center and weather it to resemble the exhaust duct... with the inside lower part blackened and closed shy of fouling any of the mechanism.)

This is one of those things like drilling out the mouths of horn bells that gives relatively high return for the effort if you care about close-up appearance.  (Yes, I know, this is more appropriate for the MR forum, but the general idea can be discussed here...)

 

All true, but many of today's models actually don't have the room inside for that. Even Athearn's long time ago tooled F unit has a big cast metal weight you would hit within 1/4". Weights, speakers, gear towers, wiring are carefully designed to take advantage of every cubic mm inside the shell.

But a little flat black paint in the hole, and some "exhaust" weathering does look pretty good for all but the closest examination. 

Sheldon

    

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