Steam & Excursion > Steam Engine Exhaust

After thinking about the beauty of steam engines for many years and, at the same time, never completely understanding how they functioned, I have decided to admit my ignorance and start asking some dumb questions. So, here goes my first one;
Why do some engines have a very sharp exhaust 'bark' while others have a more soft, or mushy sounding exhaust?
Ron W

chichi41 Wrote:
-------------------------------------------------------
> After thinking about the beauty of steam engines
> for many years and, at the same time, never
> completely understanding how they functioned, I
> have decided to admit my ignorance and start
> asking some dumb questions. So, here goes my first
> one;
> Why do some engines have a very sharp exhaust
> 'bark' while others have a more soft, or mushy
> sounding exhaust?
> Ron W


When a locomotive is run with the valve motion in full stroke, this means the valve remains open admitting steam to the piston almost the full stroke of the piston. This will cause the exhaust to have a sharp crack 'bark' because of the volume of steam being exhausted. As the percentage of valve motion is decreased 'hooked up' the valve will close and stop admitting steam before the full stroke of the piston. This will cause the exhaust to sound softer or mushy because there is less volume of steam being exhausted.
It is a common practice to hook up, decreases back pressure, less steam and full consumption. Makes the engine run more efficiently. 'Back pressure is the pressure against which the piston acts during its return exhaust stroke'. The more steam admitted to the power stroke the more dead steam that is exhausted, causing a higher back pressure.
There are many other factors involved but this is the basic reason for the difference in locomotive barks.

28hogger Wrote:
-------------------------------------------------------
> chichi41 Wrote:
> --------------------------------------------------
> -----
> > After thinking about the beauty of steam
> engines
> > for many years and, at the same time, never
> > completely understanding how they functioned, I
> > have decided to admit my ignorance and start
> > asking some dumb questions. So, here goes my
> first
> > one;
> > Why do some engines have a very sharp exhaust
> > 'bark' while others have a more soft, or mushy
> > sounding exhaust?
> > Ron W
>
>
> When a locomotive is run with the valve motion in
> full stroke, this means the valve remains open
> admitting steam to the piston almost the full
> stroke of the piston. This will cause the exhaust
> to have a sharp crack 'bark' because of the volume
> of steam being exhausted. As the percentage of
> valve motion is decreased 'hooked up' the valve
> will close and stop admitting steam before the
> full stroke of the piston. This will cause the
> exhaust to sound softer or mushy because there is
> less volume of steam being exhausted.
> It is a common practice to hook up, decreases back
> pressure, less steam and full consumption. Makes
> the engine run more efficiently. 'Back pressure is
> the pressure against which the piston acts during
> its return exhaust stroke'. The more steam
> admitted to the power stroke the more dead steam
> that is exhausted, causing a higher back
> pressure.
> There are many other factors involved but this is
> the basic reason for the difference in locomotive
> barks.


Above I meant fuel consumption

Whether a steam locomotive's exhaust is sharp or mushy has nothing to do with where the cutoff is set. It has everything to do with the condition of the valve gear, the exhaust ports, the valve pistons and the valve rings.

If the valve rings and seats are worn, the exhaust port will be uncovered (opened) in a somewhat ragged manner, yielding a mushy, dull exhaust sound. On the other hand, if the rings are sharp and clean, seal properly on the cylinder wall and the valve ports are cleanly machined and perfectly aligned, you get a sharp "shotgun" exhaust.

The valve gear plays a role as well. If the valve gear is worn, there will be "slop" in the movement of the valves themselves. That slop changes the valve timing slightly, and the gear does not move the valve in a precise manner. This also yields a sloppy-sounding exhaust.

Rich_Melvin Wrote:
-------------------------------------------------------
> Whether a steam locomotive's exhaust is sharp or
> mushy has nothing to do with where the cutoff is
> set. It has everything to do with the condition of
> the valve gear, the exhaust ports, the valve
> pistons and the valve rings.
>
> If the valve rings and seats are worn, the exhaust
> port will be uncovered (opened) in a somewhat
> ragged manner, yielding a mushy, dull exhaust
> sound. On the other hand, if the rings are sharp
> and clean, seal properly on the cylinder wall and
> the valve ports are cleanly machined and perfectly
> aligned, you get a sharp "shotgun" exhaust.
>
> The valve gear plays a role as well. If the valve
> gear is worn, there will be "slop" in the movement
> of the valves themselves. That slop changes the
> valve timing slightly, and the gear does not move
> the valve in a precise manner. This also yields a
> sloppy-sounding exhaust.


As I stated in my thread there are many other factors involved. All of what you have stated is very true, and maybe I didn't understand the question BUT adjusting the cutoff definitely changes the sound of the exhaust. I've had a few 24's running these things.

In addition to all the above, the size of the exhaust nozzel also has an effect. Take the same boiler pressure, same size cylinder for example on 2 4-8-4 engines with one expected to run 70 to 100 mph and the nozzel will be slightly larger than one expected to run 40-60 .MPH The smaller nozzel will develop more draft than the larger one at the same speed of 40-60 and the "bark" will be louder and sharper.

Frisco was known for their sharp exhaust and Frisco engineers used to say Missouri Pacific steam engines always sounded like they were working water. Had an old retired MP engineman tell me he liked 1522s exhaust and said their engines always sounded like they were working water. Cracked my fireman and me up!

Rich_Melvin Wrote:
-------------------------------------------------------
> Whether a steam locomotive's exhaust is sharp or
> mushy has nothing to do with where the cutoff is
> set. It has everything to do with the condition of
> the valve gear, the exhaust ports, the valve
> pistons and the valve rings.
>
> If the valve rings and seats are worn, the exhaust
> port will be uncovered (opened) in a somewhat
> ragged manner, yielding a mushy, dull exhaust
> sound. On the other hand, if the rings are sharp
> and clean, seal properly on the cylinder wall and
> the valve ports are cleanly machined and perfectly
> aligned, you get a sharp "shotgun" exhaust.
> The valve gear plays a role as well. If the valve
> gear is worn, there will be "slop" in the movement
> of the valves themselves. That slop changes the
> valve timing slightly, and the gear does not move
> the valve in a precise manner. This also yields a
> sloppy-sounding exhaust.


Rich -

The 765 was barking beautifully running westbound through a 10 mph slow order on the NS at Lafayette Junction, IN on its way to STL last September. Thanks again to the 765 crew for a great show in 2012. Looking forward to 2013.

John Troxler

765 did sound great here in St. Louis. I stood in the doorway of the crew car and listened to her and the Wabash whistle (sounded like 1522s whistle on steroids from higher BP). Very melancholy ride.

It's all of the above plus the hogger factor. Some hoggers love to hear that stack talk and others not so much!! For me ...the louder the better as that's her " talking to ya!!".

Hooked up at 80 per its just one continuos roar, but sweet non the less.

IMHO-Ross Rowland

Yes I know, we got a taste of that when you sat down on the 1522 up in Wisconsin.

And I'll never forget the speed and sound that the 765 made when it left Attica, Indiana headed west. There's no way Rich was the engineer. <G>

Thanks Frisco 1522, I still remember that trip in 1987(?)fondly, as it was the first exposure to mainline steam for my young girlfriend Mandy and she came away duly impressed.

As I recall she ( the engine) was a good runner and did a great job with that long train especially on the one meaningful grade we had while I was running.

Sweet!

Ross Rowland

Remembering the PRR K-4's leaving my home town of Rahway, NJ. bound for the NY&LB. Some really barked leaving town.
Ed K. cp Laurel Run

---

co614 Wrote:
-------------------------------------------------------
> Thanks Frisco 1522, I still remember that trip in
> 1987(?)fondly, as it was the first exposure to
> mainline steam for my young girlfriend Mandy and
> she came away duly impressed.
>
> As I recall she ( the engine) was a good runner
> and did a great job with that long train
> especially on the one meaningful grade we had
> while I was running.
>
> Sweet!
>
> Ross Rowland


I'll bet she was impressed. Especially as fast as you were going on that last southbound trip. I commented to Dwight Johnson, the ONLY Wisconsin Central Officer around that Sunday, that your excessive speed was potentially dangerous. Dwight had you removed from the cab at a water/service stop.

The biggest difference in the sharpness of steam locomotive exhaust is weather the locomotive is superheated or not. Non-superheated (soaks) locomotive have a softer bark while a superheated locomotive has a crisper snap to the exhaust.

Lurch

Hot Water I think you've confused me with someone else. IIRC I ran exactly the slot I was supposed to and had a pilot engineer right behind me the whole way dictating my speeds at all times. I do remember being quite impressed with her performance on the one hill of any consequence we encountered, despite her small size.

All in all a very pleasant trip.

Good memories both on and off the train!!

Ross Rowland

I guess the SLSTA folks got their asses chewed out mistakenly for running so fast the crossing gates were still coming down when we went over them? Must have been a different trip I guess.

Must be, 1522, must be.


Ross Rowland

A DVD or any other kind of recording is not going to tell you very much,
let alone teach you anything. It will not record all of the sound,nor
will it record the many nuances that affect it, such as temperature,
boiler pressure, the surrounding terrain (hills, trees, buildings, etc.),
all of which have affect on the sound as much or more than throttle and
reverse gear position, trailing load, and many other things.

Furthermore, no 2 locomotives, even of the same class, will perform or
sound exactly the same even under the same conditions.

Then there is the matter of who is on the seatbox and his methods.
That will also vary wildly.