Steam propelled from the stack.

The stack is the combination exit point for both the spent exhaust steam from the cylinders and the hot gasses (and sometimes cinders) from the firebox.

Rusty

Rusty,

Thanks, that makes sense.

Do you (or anyone else - Rich?) know whether different steam locomotives have different steam/gases piping arrangements to the stack? The reason I ask is that I looked at more videos, and the 765's steam exhaust appears to be more forceful or go higher than other locomotives.

Thanks for your reply!

Alex

The Steam is expelled from the cylinders through the blast nozzle into the smoke box. The steam delivers it's last expansion at this point as it goes up the petticoat pipe and out the stack. This last expansion produces a very large amount of draft which aids the combustion in the fire box and sucks the exhaust gasses through the flues.  When a locomotive is really working hard the fire will literally be jumping up off the grates. It is quite a sight to see.

Ron

The force of the exhaust from a steam locomotive stack is directly related to how far the throttle is open. In many of the scenes in that video, we are either executing a photo run or accelerating from a stop after a photo run. In both cases the throttle is open pretty far.

The steam which goes out the stack is the steam exhausted from the cylinders after it has done its work. As you can plainly see, there is still a tremendous amount of energy in that steam, which is why steam locomotives were so inefficient. At best, a steam loco might achieve 12-15% efficiency.

The steam is exhausted from the cylinders through the exhaust nozzle. That nozzle is directly below and perfectly aligned with the stack. The 765's exhaust nozzle is 8.5" in diameter. The steam exhausts into the Pettycoat Pipe, which is like a huge upside-down funnel hung on the bottom of the stack. The Pettycoat Pipe channels the flow of steam from the nozzle to the stack in a nice, cylindrical column of gas. It is the movement of this steam that pulls a draft on the fire, pulling air through the fire and the flues.

When the Exhaust Nozzle, Pettycoat Pipe and stack are in perfect alignment, the engine will blow smoke rings out the stack. Do a YouTube search for 765 in Rock Island at last years Trainfest and you'll see LOTS of smoke rings...like in this video...

http://www.youtube.com/watch?v=aIylymnfYQ0

There is some excellent footage of the 765 back in 86' accelerating from a stop in St. Albans,Wv...don't know who was at the throttle that day but after getting everything moving he went after it in a big way and there was some spectacular sounds coming out of that stack.....to me it was one of the most aggressive accelerations I have heard and it had to be ear pounding in person.  She lost her footing for a moment but then he went right back after it again...The footage is in a Greg Scholl video called Nickel Plate 765 Autumn Spectacular...pretty good footage in there.   

I'll take the bow.

You'll like this one, too. This is getting away from Charleston, WV after a station stop. By the time Larry Randolph finishes blowing the whistle, I had her on the roof. She had 32 cars behind her on this trip!

And here's a video that will illustrate how the stack action follows the throttle. In this video, the 765 is the lead engine in a doubleheader with PM Berkshire #1225. The 765 is doing most of the work. In the first runby, you can clearly see the exhaust from the 765's stack is going much higher in the air than the exhaust from the 1225.

We are making WAY too much smoke in the 765 in order to please the photographers. You have no idea how much I dislike photo charters. 

All of which will be in relation to the amount of cut-off being used at the time.

Are you firing with reduced excess air that allows you to do this? Thanks

Bob Di Stefano

No, just too much coal.

Right. Increasing the fuel to air ratio by increasing the coal loading would be the equivalent of reducing the excess air. Thanks

Bob Di Stefano

Rich, and everyone else -

Thank you so much for all the explanations; this is a most welcome learning experience for me.

And the videos are great!

Alex