Chuff rate

Carter,

The 'chuff' happens as used steam is exhausted from the cylinder. Steam is admitted and exhausted on both the in and out part of the stroke(just from different sides of the piston). Also most engines have two sets of cylinders(the one on the other side of the engine) and they are 'quartered'(90 degrees out of sync). What this means is you get 4 'chuff's' for each rotation of the drivers. Run the engine real slow and time the 'chuff's - then adjust as needed. The DSD-B280LC is adjusted for the drivers on he 2-8-0(63" IIRC). The 4-8-2 has something like 72" drivers, IIRC.... The 'idle' sound is the air pumps - I would not try to adjust them.....

Jim Bernier

Carter Braxt> I just installed a Soundtraxx DSD-B280LC decoder into a Bachman Spectrum

A conventional two cylinder steam locomotive 'chuffs' FOUR times per driver revolution. Such a locomotive is a two cylinder double acting steam engine. Each cylinder/piston produces two power impulses per revolution, one 'pushing', one 'pulling' (that's what "double acting" means).

A three-cylinder loco would have SIX 'chuffs' per driver revolution, and so forth. A Shay (usually) has three cylinders AND is geared down, so it typically produces something like 15 'chuffs' per driver revolution.

Articulated and 'Duplex' locos have FOUR cylinders, in two non synchronized sets. Each set 'does it's own thing', making for a strange (eight 'chuffs' per driver revolution) exhaust that goes in and out of synch as one engine or the other slips or changes 'phase' with the other. Sometimes railroads specified one driver set to be an inch or so different in diameter than the other so as to FORCE a lack of synchronization (which could result in some odd out of balance motions hard on the loco or adversely affecting it's 'tracking' qualities)

An exception to the above were the "Mallets", which, though four cylinder articulateds, only had a single exhaust from the front engine (Four 'chuffs' per driver revolution). The rear (high pressure) engine exhaust INTO the front engine, and hence had NO external 'Chuff'.

Then there were the Triplexes .... and other odd balls.

I've yet to see/hear anyone get the 'chuff' rate correct on a Soundtrax unit without using the sound-cam option. It can be matched at some reasonable running speed, but the acceleration rates of the actual loco and the sound unit 'chuff' rate do not seem to matchable over a range of speeds. I've seen several knowledgeable DCC types attempt this by doing all sorts of things with the CV values, to little or no avail. I'm not saying a reasonable job can't be done, but I've not seen (or heard) it done.

Having seen a LOT of real steam locos, and having long been installing synchronized 'DC' sound units in my steamers, I've gotten used to how a loco SHOULD sound at various speeds. The (usually) NOT synchronized sound from most DCC sound units is REALLY annoying to me. Kind of like an off-key note would be to a musician.

The best non-synchro (?) sound I've heard is from the new Broadway USRA heavy Mikado. It is sufficiently good that I wonder if it IS synchronized? Broadway's website does not mention this (actually, it doesn't seem to mention the 2-8-2 at all?) If so, it's a BIG leap forward in DCC sound.

Broadway's website DOES say their non-synchro sound can be closely synchronized at LOWER speeds, but is purposely programmed to be too slow at higher speeds. THEY think this sounds better. I feel this is debatable, though it may be a quirk of how the sound unit functions or sounds at higher 'chuff' speeds.

Broadway's sound unit in the N&W 'A" and 'T-1' DOES attempt to represent the in and out of phase sounds of the simple articulated and duplex locos. It's not real convincing from my experience, or the sound recordings I've heard of the real locos. It's probably better than ignoring the effect, however.

I HAVE seen/heard user-installed synchronized (sound-cam) sound using Soundtrax decoders, and that's NICE! VERY nice!

Dan Mitchell ==========

Carter Braxt>

On of the things that bothers me about sound systems, other than I don't like them, is that on real steam, the beats are (usually) not even.

If you listen carefully, as a two cylinder engine accelerates, it will beat as follows.

CHUFF, chuff, chuff, chuff, CHUFF, chuff, chuff, chuff, CHUFF, chuff, chuff, chuff............

Sound systems don't do this.

-- Cheers Roger T.

Home of the Great Eastern Railway

I agree, the syncronized chuffing is the only way to go. Without the syncronization, you can have a loco sitting there chuffing along without movine or the other side of the coin, moving without ever making a sound but then again, when a loco is drifting, there is no sound from the exhaust. The Shay gives a whole bunch of chuffs and, at anything over a very slow speed of maybe 4 mph, the exhaust tends to blend together for both the reason that there are so many chuffs and that the exhaust pipe is so long that it acts more like a minimal muffler. I've done sound systems on a number of locos and have dealt with both the remote PFM style sound systems and local to the loco sound modules and none of them have been that great as the real sounds from a loco are quite varied from the starting long chuffs to the running choppy chuffs when the Johnson Bar is in the company notch to the absolute silence when the throttle is closed. Unsyncronized chuffs from a DCC system would just be a cartoon of reality and I'd rather not hear such nonsense. I'll also note that most sound systems that I've heard have been way too loud.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!

"T> On of the things that bothers me about sound systems, other than I don't "T> like them, is that on real steam, the beats are (usually) not even. "T> "T> If you listen carefully, as a two cylinder engine accelerates, it will beat "T> as follows. "T> "T> CHUFF, chuff, chuff, chuff, CHUFF, chuff, chuff, chuff, CHUFF, chuff, "T> chuff, chuff............

This might be due to variations in the actual distance between you (the listener) and the *four* different exhaust ports.

"T> "T> Sound systems don't do this. "T> "T> "T> -- "T> Cheers "T> Roger T. "T> "T> Home of the Great Eastern Railway "T>

"T> "T> "T> "T> "T>

\/ Robert Heller ||InterNet: snipped-for-privacy@cs.umass.edu

|| snipped-for-privacy@deepsoft.com /\FidoNet: 1:321/153

Real steam locos should not make such sounds either ... but, yes, they often do. Such a non symmetry denotes either some malfunction, or, more likely, a minor valve timing issue. Steam locos are meant to be 'square' (railroad shop term), meaning all beats SHOULD be equal, denoting proper valve timing. Perfection rarely happens, however.

And a minor discrepancy can result in a nice 'beat' to the exhaust, as you describe. The old" I think I can" ... etc. exhaust.

Dan Mitchell ==========

"Roger T." wrote:

Perhaps. But experience in the cab also shows that the fire and everything else rattles with the same syncopated rhythm..

CHUFF, chuff, chuff, chuff, CHUFF, chuff, chuff, chuff, CHUFF, chuff, chuff, chuff............

-- Cheers Roger T.

Home of the Great Eastern Railway

I don't agree. In my experience, the "chuff" sound originates at the stack. I can happily recall several Burlington trips behind 4960, 5632, etc. leaning out the baggage car door listening to the echo of the locomotive off the walls of the warehouses south of Chicago Union Station. The echo was louder than the direct sound path from the front of the loco to the side of the baggage car. I heard all four chuffs per revolution of the drivers about equally, which would not have been the case if the sound originated at the valve ports in the cylinder block on the two sides of the locomotive. The sound also distinctly changed as we passed under the many street overpasses, which would not be the case if the sound was originating low on the locomotive. I do agree there was an unevenness as one "chuff" always seemed louder than the other 3, and I concur with other posters that this is due to minor differences in the mechanical features of the exhaust steam paths. GQ

The "chuff" on the prototype begins at a variable point in the movement of the piston, adjusted by "cutoff". The beginning and end can be almost the moment when the piston begins to move (rod across the centre of the wheel) to almost half way through the movement where the rods are top or bottom. At slow speed and heavy load, the cutoff is adjusted for the longest power stroke and at moderate speed with a light load the cutoff is at maximum with the shortest power stroke.

A two cylinder locomotive has four beats per revolution.

That noise is the Westinghouse brake pump - it works on the prototype like that to counter any leaks in the brake pipes, of which there are many in a long train. So long as the pump can keep up with maintaining brake pipe pressure there is no problem.

One more sound would be the steam powered generator for the lights which maintains a constant hiss - generally turned off when the lights are extinguished.

Here's a reference on the basics of a steam engine FYI:

The exhaust ports all feed into the one blast pipe that exhaust up the same chimney. Even with double chimneys and multiple blast nozzle systems the chimneys are so close together that they are, in effect, one chimney.

Robert Heller wrote:

snip

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And the problem with Soundtraxx Steam sound units. They should have some way to sync with a wheel instead of trying to do it electronically. We spent an entire evening doing it by trial and error because every locomotive is going to be just a bit different.

This would be the air compressor or air pump sound. Try setting CV123 to zero.

For a good understanding of when the "chuff" occurs, run the simulation for your model's type of valve gear as found at Charlie Dockstader's super site:

"KTØT" wrote in news:nvENb.26350$ snipped-for-privacy@twister.rdc-kc.rr.com:

According the the MR Cyclopedia, vol. 1, the cylinders exhaust into a Venturi tube in the stack. That creates a suction that provides the draft needed for the firebox and boiler. That suction pulls air into the firebox to help combustion of the fuel and then pulls the hot gasses on through the boiler tubes and into the smokebox in front of the boiler. I suspect that some earlier engines did not have this arrange which may be one reason why they had such tall smokestacks. Look at some of the earliest engines, like the DeWitt Clinton, and you see a stack that is almost as tall as the engine is long. The tall stack was partially to provide a draft for the fire in the boiler and partially to try to carry sparks over the top of the train. (It didn't work so well at that, since many early RR passengers who rode on the car tops complained about sparks burning holes in their clothes. Look at illustrations of the earliest RR's in this country and you see seats on top of cars and the cars converted from Concord Coaches.)

: > Here's a reference on the basics of a steam engine FYI: : >

: According the the MR Cyclopedia, vol. 1, the cylinders exhaust : into a Venturi tube in the stack. That creates a suction that : provides the draft needed for the firebox and boiler. That : suction pulls air into the firebox to help combustion of the : fuel and then pulls the hot gasses on through the boiler tubes : and into the smokebox in front of the boiler. I suspect that : some earlier engines did not have this arrange which may be : one reason why they had such tall smokestacks. Look at some : of the earliest engines, like the DeWitt Clinton, and you see : a stack that is almost as tall as the engine is long. The : tall stack was partially to provide a draft for the fire in : the boiler and partially to try to carry sparks over the top : of the train. (It didn't work so well at that, since many : early RR passengers who rode on the car tops complained about : sparks burning holes in their clothes. Look at illustrations : of the earliest RR's in this country and you see seats on top : of cars and the cars converted from Concord Coaches.)

Thank you Woodard! Bob

"Woodard R. Springstube"

That's called the blast pipe. It's position in the smoke box and its diameter all have a strong bearing on how well a kettle does, or doesn't, steam.

-- Cheers Roger T.

Home of the Great Eastern Railway

Except that what you hear as "chuff" is the exhaust steam leaving the orifice(s) at the top of the blastpipe. The beats are an indication that the valves are not set absolutely square.

Yairs! It's amazing how critical a seemingly minor misalignment of the blastpipe and petticoat can be. Or carbonisation of the blastpipe orifices. Or simply not having the smokebox door shut TIGHT!

Very few people apart from engineman appreciate just how important the front end is to steam loco performance.

[ ...]

The idling chuff is the air pump. Air pumps had a governor, and did not run continuously. When air pressure dropped the pumps started and worked to get pressure back up, then slowed down as pressure neared the desired level, then stopped. So, you should turn it off after a while to make it sound right.

Another idling sound is the blower. That is a ring of pipe around the blast nozzle that directs a number of small steam jets up the stack to maintain the draft when the engine isn't moving. This would be a mild hiss when the engine is just sitting and the steam pressure is high enough. It would increase to a bit of a roar when the fireman needed to raise the steam pressure. You should hear some blower whenever and while the engine is stopped.