Chuffing?

[Paul Milenkovic]

tomikawaTT

At some relatively low speed, the high pressure cylinder exhaust would be diverted to the receiver, and thence to the low pressure cylinders, by the intercepting valve.  This happened automatically.  (The major difference between the Y6b and earlier Mallets was that the interceptor valve wouldn't go to compound mode until the locomotive reached 10MPH, and would revert to simple if the speed dropped below 10MPH.  Earlier Ys changed over at 4MPH.)

When I first heard the term "intercepting valve" regarding the changeover from simple to compound operation, I thought, well, there is this valve in the cab with a handle you turn to operate it.

In the context of Chapelon's work on the importance of non-restricting steam passages in both the admission and exhaust lines to the cylinders, it occured to me that maybe this intercepting valve is a substantial hunk of metal, perhaps operated with a steam power assist in the way of the power assist for the reversing link on a big locomotive.

Am I right, that the intercepting valve, which has to route and reroute substantial volumes of power producing steam, is of substantial size, and perhaps operated by a steam servo cylinder?  On an N&W Y-class, where is it -- is it buried in the smokebox or steam dome or between the front cylinders, or can you see it as this lump or wart on pictures or drawings of the locomotive?

Maybe off-topic, but on a Mallet or simple articulated, you can see the massive steam pipes connecting the front engine.  On a Beyer-Garratt, I can't see the steam pipes -- as with the intercepting valve on a Mallet, where are the steam pipes hidden?

[BigJim]

Paul,
If you read the explanation of the ALCO - Mellon document at the link I provided early in this discussion (here it is again and I highly recommend that  you take the time to read it: http://www.catskillarchive.com/rrextra/mallet.Html) , it is explained that the supply of live steam at a reduced presure to the low pressure cylinders and the subsequent changeover to high pressure cylinder exhaust steam, when starting, was automatic and was initiated by a differencial in pressure acting on the sliding intercepting valve.

The pictures show how the reducing and intercepting valve are housed deep in the high pressure cylinder saddle.

Also, a "starting" or "simpling" valve was located in the cab ( of all compound locomotives) for the engineer to use IF the need arised to help start the train or to keep the train moving if it was about to stall. This valve piped high pressure steam to one face of the intercepting valve in order to move it into "simple" position.

What the document doesn't tell you, because it hadn't been invented yet, is that when Mr. Pilcher of the N&W designed the "external reducing & booster valve, some of the chambers inside the high pressure cylinder saddle were removed and changed how things operated.

[Lehigh Valley 2089]

Everyone seems to have answered the basic question, but I will provide a guide as to how many you hear per revolution of the drivers.

Non articulated, 2 cylinder: 4 per

Compound Mallet, 4 cylinder: 4 per (uses steam 2 times, results in 4 per)

Non articulated, 3 cylinder: 6 per (extra cylinder adds 2 per)

Simple articulated, 4 cylinder: 8 per

Duplex drive, 4 cylinder: 8 per (steam used once in each cylinder)

Geared engines will have a much higher count than any listed here, because they have drive shafts and gears and not drive rods, so it takes many more revolutions to sustain a low speed, because the gears are much smaller than a standard drive wheel. Same with cog locomotives.

[Deggesty]

bubbajustin

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

In all responses to Justin's question, I do not recall seeing one thing mentioned--what causes the chuff? As the used steam reaches the atmosphere, it is still under compression, and expands suddenly, this, and the noise of the expansion is the chuff.

I am sure  most of us know this; even Justin may have been aware of  it, but for the benefit of any who may not have been aware, I have posted my response.