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Old 19th September 2007, 18:48   #1
krokodil
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Default Mallet

Last week I visited the Baltimore RR Museum. There is one wonderful Mallet engine with these interesting devices. Does anybody know what are they for?
They are on the sides of the firebox.




Thank you!
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Old 29th September 2007, 21:01   #2
Ga_GardenGranny
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Default Re: Mallet

No, but a photo of the entire engine certainly would have been nice.
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Old 3rd October 2007, 10:05   #3
krokodil
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Default Re: Mallet

If this helps!



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Old 3rd October 2007, 12:47   #4
Howqua
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Default Re: Mallet

Have some wheels !!
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Old 15th October 2007, 20:06   #5
RailRon
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Default Re: Mallet

Those 'interesting devices' are so called overfire-jets. They deliver additional air above the flames in the firebox. The oxygen in this air helped to burn coal soot and thus reduced the black smoke of these engines.
(Other loco manufacturers strived for the same effect by adding simple holes on the side of the fireboxes. You can see them e.g. on the firebox sides of some of the UP Big Boys and Challengers.)

To my knowledge the Chesapeake & Ohio 2-6-6-2 engines were almost the only locos with this type of jets. They were quite effective engines, second only to the still mightier Alleghenies (2-6-6-6) of the C&O. Sometimes they were nicknamed 'Baby Alleghenies' - quite a Baby!

Hope this helps!

Ron

PS: By the way - it's a shame how these mighty engines are deteriorated!
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Old 16th October 2007, 00:48   #6
Howqua
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Default Re: Mallet

Quote:
Originally Posted by RailRon View Post
PS: By the way - it's a shame how these mighty engines are deteriorated!
Not enough of us care about our history these days if at any time in history.
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Old 21st October 2007, 09:34   #7
krokodil
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Default Re: Mallet

Quote:
Originally Posted by RailRon View Post
Those 'interesting devices' are so called overfire-jets. They deliver additional air above the flames in the firebox. The oxygen in this air helped to burn coal soot and thus reduced the black smoke of these engines.
(Other loco manufacturers strived for the same effect by adding simple holes on the side of the fireboxes. You can see them e.g. on the firebox sides of some of the UP Big Boys and Challengers.)

To my knowledge the Chesapeake & Ohio 2-6-6-2 engines were almost the only locos with this type of jets. They were quite effective engines, second only to the still mightier Alleghenies (2-6-6-6) of the C&O. Sometimes they were nicknamed 'Baby Alleghenies' - quite a Baby!

Hope this helps!

Ron

PS: By the way - it's a shame how these mighty engines are deteriorated!
Hi RailRon


thank you very much for the explanation.

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Old 20th November 2007, 11:41   #8
krokodil
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Default Re: Mallet

Quote:
Originally Posted by RailRon View Post
Those 'interesting devices' are so called overfire-jets. They deliver additional air above the flames in the firebox. The oxygen in this air helped to burn coal soot and thus reduced the black smoke of these engines.
(Other loco manufacturers strived for the same effect by adding simple holes on the side of the fireboxes. You can see them e.g. on the firebox sides of some of the UP Big Boys and Challengers.)

To my knowledge the Chesapeake & Ohio 2-6-6-2 engines were almost the only locos with this type of jets. They were quite effective engines, second only to the still mightier Alleghenies (2-6-6-6) of the C&O. Sometimes they were nicknamed 'Baby Alleghenies' - quite a Baby!

Hope this helps!

Ron

PS: By the way - it's a shame how these mighty engines are deteriorated!

Hi Ron

I have got a different answer direct from Museum in Baltimore. What do you think about this?




I have an answer to the question you posed about our #1309
engine. Those are pressure release valves for a secondary pressure
release system. It is a back-up or safety feature in the event of
excessive pressure or malfunction in the primary system.



Thank you for your reply.
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Old 21st November 2007, 12:34   #9
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Default Re: Mallet

Hi Krokodil,

Sorry, I can't approve to the explanation of the museum. And I'll explain why:

They wrote: Those are pressure release valves for a secondary pressure
release system. It is a back-up or safety feature in the event of
excessive pressure or malfunction in the primary system


I never heard or read anything about a 'secondary pressure release system' on steam locomotives. (This also holds true for European engines. ) There is only ONE SYSTEM - and these are the safety valves to blow off excessive steam pressure.
According to the A.A.R. standards (AAR = Association of American Railroads) every engine has to be equipped with AT LEAST TWO or MAXIMUM THREE safety valves, set at (#1) normal top boiler pressure, (#2) to b.p. + 2 pounds in excess, and eventually (#3) b.p. + 5 pounds in excess of the first valve. And: Safety valves have to be located at the HIGHEST POINT of the boiler.

This makes perfectly sense, because you have to blow off excessive STEAM! Now when you look at those devices on the C&O engine: They are mounted BELOW the water surface in the boiler (which MUST be always higher than the crownsheet/top of the firebox). So if they came into action they would blow out boiling water (imagine standing beside the engine in this moment! ), and worse, this would lower the water level in the boiler, the crownsheet would be uncovered - an then... BOOOM! Boiler explosion!
IMHO now this really would be a very strange safety device...

I have to admit that I didn't find an exact description or technical details of those overfire jets. As I told before, many other engines had 'simple holes'. They were called 'combustion tubes' and conducted air from the outside through the lateral walls of the firebox into its interior.
Looking at your pic I believe that there are thin (steam?) tubes leading to those cylinders. (This is also the case on the Cal-Scale brass detailing parts. They offer also a set of 16 overfire jets!) Now if the lines really are steam pipes, I figure that those overfire jets worked somehow like a water jet pump. Probably they could be activated by the fireman when there was too much soot in the smoke of the engine. This way the stack exhaust became cleaner - not bad when running through densely populated areas. And perhaps the vertical cylinders are also acting as sound mufflers.

As I said, I am not 100% (only 95% ) sure, that mine is the right explanation - in any case, to me it seems much more logical than the museum-proposed 'underwater secondary safety system'.

Ron
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Old 21st November 2007, 22:33   #10
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Talking Re: Mallet

Hi Ron

thank you for the explanation, of course I know that on that position you cannot have standard safety valves
(in best case you can lead the steam somewhere from the top of the boiler to those devices - with thin pipes. Those devices are just mounted on the outer side of the firebox to distribute the steam from the this pipes and reduce the usual noise of the overpressure valves - this is just an idea perhaps an explanation for the B&O Museum ).

I agree with your explanation, there is also a link

http://deepblue.lib.umich.edu/bitstr...6.0001.001.txt

describing the over fire jets, unfortunatelly there are no pictures at all.
From your explanation and from the text I think you are 100& right.

Thank you
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