We all know the sound, CHUFF CHUFF, CHUF,CHUFF, of a steam locomotive. It is one of the best sounds, In my opinion, that man has ever created.
But something that I never have understood is what exactly is happaning when you hear that chuffing sound? I know it’s something to do with airflow, but I don’t know much else…
What is happaning during those shuffing sounds?
-Justin
The cylinders exhaust through the blast pipe to aid the draft. Since the exhaust isn’t continuous, the chuffing sound is the result. Compound locomotives will also have a different sound than simple locomotives.
The steam engine works by using steam that is created in a confined space (the boiler) and letting that steam into a cylinder that has a piston in it that can move due to the pressure of the steam. That moving piston is connected to the main rod to turn the wheels 1/2 turn.
When the piston has reached the end of its travel, there is still pressure in the steam and in order for the piston to return to the other end (and the wheel to continue to rotate) the pressure of that steam must be released.
The steam that is released is put to one more use after most of the pressure has been used in the cylinder to move the piston. That steam passes though some pipes to the bottom of the smoke box directly below the chimney. There a pipe, appropriately known as the “Blast Pipe” aims the steam directly up the chimney. The moving steam in the chimney creates a draft of air going up the chimney.
The air that is moved up the chimney has to come from somewhere and that is through the flue tubes in the boiler. That air has to come from someplace and that is from the firebox at the other end of the boiler. And of course, that air has to come from somplace and that is from the openings in the grate on bottom of the firebox where the fuel is being burned. The fresh air being drawn in that way helps the fire burn hotter which creates more steam to be used to make the pistons move and thus move the locomotive.
Anyway, it is that sudden release of steam up the chimney that makes the chuffing sound. On the most common configuration of a locomotive there are FOUR chuffs per revolution of the wheels. There are two pistons, one on each side of the locomotive, and each piston is alternately pushed to one end by steam and when the piston reverses direction and pushed from the other end by steam, the steam is released, creating a chuff. You hear a chuff from the front end of one cylinder, then a chuff from the fron
Actually, when running compound, a Mallet sounds like a standard 2-cylinder simple loco - only louder.
What sounds different is a locomotive with two separate single-expansion engines (including Mallets in start-up all-simple mode.) The exhaust is not a simple uniform succesion of chuffs. Rather it’s two sets, drifting in and out of synchronization but more often out than in. Then, too, locomotives with two sets of machinery could have one slip while the other gripped…
Three cylinder locos were different in that there were six chuffs per driver revolution rather than four.
Chuck
Chuck
I got to witness the N&W Y6’s in action in 1956 and when running in the compound mode and they were hushed compared to when they were in simple mode. We were amazed at the quiet sound of the Y6b class compared to the A class, which were really loud. The recording available in the coal fields for the Y6a class were in simple mode when they were working slowly if that was your reference. The reason that the compound mode is hushed compared to the simple mode is the large cylinders are using exhausted steam from the smaller rear cylinders and the total presure in the larger compound cylinders is reduced to a lower level. That is the reason the front compound cylinders are larger to have the same amount of force with less PSI.
In simple mode, those Y6’s were very loud because the full steam presure was coming out of those 39" size compound cylinders.
CZ
Question: Am I to understand the Mallet’s such as the Y6’s with the two different size cylinders…are capable of running in “compound mode”, and also run in “simple mode”…?
And what is the difference between the Y6a and b class…?
If both “modes” are available in the Y6’s…how is the different size pistons dealt with when running in “simple mode”…? Does that cause slipping problems…?
If it is possible to run both or at least one of the above class engines in both “modes”, that would seem to be an advantage for starting power, and then switch to compound mode for running…and perhaps use less steam…
Any comments on this…?
The N&W perfected the Compound locomotive and made many changes over the first version that was designed by the USRA. The Y6a and Y6B had a valve or control that the engineer could start a train in Simple mode for extra tractive effort. The N&W designed this control valve which was not used on any other compound locomotive that I am aware of. The Y6a and Y6b had a traffic effort listing of 152,206 in simple and 126,838 in compound. Traffic effort was always calculated on steam presure along with piston force and in the case of the larger 39" cylinders with the boiler presure, the traffic effort was much greater. You also have to realize that on poor or wet rail, this extra force might not be so useful at times. I know the engineers tended to use them in simple mode for switching out coal at mines since the engine would respond better than waiting for the steam to exit the high presure cylinders and start towards the low presure cylinder for extra force. With the locomotive in simple mode, you got response when the thottle was yanked. And you are correct about switching to compound for normal running and saving steam for a coal savings also.
I would have to make a guess about running in simple at higher speeds, but this would probably had caused a lot of rail pounding since the large cylinders would be exerting way too much force and would overcome the normal counter balancing. These engines were designed to run in compound once the train was underway on the road.
I know the Y6b had the SA feedwater system and the Y6a had some other type, but most of the rest of the details were common to the Y6a. Both were equal in the traffic effort tables and both were very capable locomotives. The one at St. Louis museum is a Y6a if I remember correctly.
CZ
…Thankyou { CZ}, for that interesting, and comprehensive answer…What you say of the designs and operating sure makes sense to me.
Interesting Data.
…Oh what history…! Never heard anyone comment of such an engine before. Wonder if “Google can produce a photo”…?
Image of CP two-cylinder Compound locomotive. The large low-pressure cylinder is obvious on the locomotive’s left side. http://members.shaw.ca/cprsteam/m2.htm Here is a Tandem Compound locomotive with BOTH high and low pressure cylinders on the same piston rods on each side. http://www.flickr.com/photos/imlsdcc/5020620389/sizes/o/in/photostream/ Thank You.
A couple of comments on what I’ve read about mallets: To start, you almost had to be in simple mode since only one engine would be working. The low pressure cylinders ran off the exhaust from the high pressure engine, so if you were just starting, there was nothing to feed the low pressure engine in compound mode.
In simple mode, the steam being fed to the low pressure cylinders was run through a pressure-reducing valve or regulator first. If you ran full pressure to the those big cylinders, they would exert much more force than the high pressure cylinders so that you would not get much effort from the smaller cylinders before the big ones would slip.
Thanks for sharing the two links, Kootenay Central. I had never have seen anything(maybe never noticed anything) quite like these two classes of Locomotives.
http://members.shaw.ca/cprsteam/m2.htm
FTL: “…the Richmond or cross-compound system, was particularly adaptable to freight locomotives such as No. 778. In the Richmond system, the high-pressure cylinder was placed on the right-hand side of the locomotive, with the low-pressure cylinder in corresponding place on the opposite side. The illustration above shows this arrangement clearly, the much larger low-pressure cylinder, with an inside diameter of 35", appearing prominently in the foreground. The diameter of the high-pressure cylinder was only 22"; both, of course, had the same stroke: 26"….”
http://www.flickr.com/photos/imlsdcc/5020620389/sizes/z/in/photostream/
This flickr photo is fasinating, I’ve never seen a cylinder set up like this one on this; A TANDEM Compound configuration on this CPR Locomotive.
…And again, {Paul}, that certainly makes sense. I wonder if it was possible to switch back to “compound” then…after the load was under way in moving. On the other hand…doesn’t seem that would have been any help in “power”…Just economy, so to speak.
Now, I’m starting to wonder where the advantage might have been to have available the two different modes of control…It almost sounds to me the only advantage to reverting back to compound…would be the less use of steam / fuel…water…
Understand powering the large cylinders at start up, and doing so thru some kind of steam supply orfice…so I really don’t see any “power” advantage to this compound / simple control…
Makes one think though…
Read the following and learn something:
…That’s a lot of homework…But we’ll get to it and work on it. Thanks.
Quentin,
My understanding is that the Y-6b’s were always in compound - i.e. the exhaust from the high pressure cylinders went to the low pressure cylinders. To get extra tractive effort, some high pressure steam was admitted to the piping between the high pressure and low pressure cylinders to increase the pressure being admitted to the low pressure cylinders which then increased he tractive effort.
."
http://www.flickr.com/photos/imlsdcc/5020620389/sizes/z/in/photostream/
This flickr photo is fasinating, I’ve never seen a cylinder set up like this one on this; A TANDEM Compound configuration on this CPR Locomotive.
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Thank You for activating the links! There were changes to the system a while back. I tried several hints from the Forums to get the links to work from this end, but, to no avail. ONLY the 778 is a CPR locomotive. The Tandem Compound is another road’s. I understand Santa Fe had Tandem Compounds. I do not have a CP steam roster here, but, I understand that many of their Compounds, regardless of ‘System’ of Compounding were later superheated and rebuilt to straight simple locomotives, several lasting until the Diesels came. Others were never rebuilt and went directly to scrap, the last operating as a Compound c. 1928. The Depression eliminated many old locomotives no longer required. Thank You.
No, the Y6b was just like all of the others. They could be simpled if the need arised.
If you have read the information in the link I provided above, you will see that the reducing valve was originally located in the high pressure cylinder saddle. This caused some maintainence problems in that the valve needed to be kept well oiled for proper operation.
In the early 1950’s, the N&W developed the external reducing / booster valve (seen as a round cylinder above the right side high pressure cylinder) to help solve the maintainence problems. This brought the reducing valve to a more accessible location and added the benifit of the ability, while working in compound, to add a small amount of superheated steam to the reciever going to the low pressure cylinders. While this added a small amount of steam pressure the bigger difference in power was gained from the amount of heat this added to the exhaust steam from the high pressure cylinders.
It was found that the extra power caused the front engine to slip, so lead was poured into the front frame to gain the weight needed to stem the slipping.
If the train could not be started or was about to stall while moving in “Compound”, then the engineer could “Simple” the engine. Simple operation could be used up to around 10mph. Working in compound the “booster” valve could be opened for more power up to around 15mph.
The external reducing valve worked well and all of the Y5, Y6 Y6a & Y
…Thanks fellows. Seems I opened up a subject that requires quite a bit of studying, and understanding just what the capability of these brutes were.
I never realized they could be fed steam in two different ways before these conversations.
Can’t right now, but we’ll study what is here to see, and I’m sure we’ll understand a bit better what really was possible with these engines.