# Chuff rates for steam trains



## musicwerks (Jan 4, 2012)

Hi,

How is the chuff rates of steamers per wheel revolution ?

How about articulated 2-8-8-2?

Kiong


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## Big Ed (Jun 16, 2009)

musicwerks said:


> Hi,
> 
> How is the chuff rates of steamers per wheel revolution ?
> 
> ...


Do you mean for real locomotives?
Never heard this question before. 
Research time.


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## musicwerks (Jan 4, 2012)

Yes... Real locos 2-8-8-2...and hopefully can replicate on our models to the prototype


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## Big Ed (Jun 16, 2009)

I think it all depends on the locomotive.

I found this a copy and paste,

Normally, in a standard locomotive when starting under load from standing start, the engineer would observe his rearmost driving wheels and compare their movement to the movement of his locomotive over the ground. As locomotives grew larger, the engineer would listen to the rhythmic sound of the exhaust (the characteristic “chug-chug”) and compare the rhythm of this sound with the movement of his locomotive over the ground.
If, as he opened his engine’s throttle, the rate of increase of the “chug chug” sound was out of sync with the forward progress of his locomotive, he knew his wheels were slipping. A passenger locomotive with 72-inch-diameter (1,800 mm) drivers would travel twelve (12) feet or four (4) yards per “chug-chug”. It was therefore easy to correlate the rhythmic sound of the exhaust of a starting locomotive with the locomotive’s progress from a standing start. An engineer could thereby avoiding applying too much power to a starting locomotive (by opening the steam throttle valve too much, and too quickly) and causing the wheels to slip.


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## Big Ed (Jun 16, 2009)

That is for the PRR S-1

More added to the above.

The S1’s duplex engine design meant that two separate engines were concurrently and in sequence exhausting into the single smoke stack. This made it nearly impossible for a locomotive engineer to distinguish the behavior of an individual engine set, based upon the sound of its exhaust. Unless both sets of engines experienced wheel slip simultaneously, the sound of the normal set would mask the sound of the set that was slipping and over speeding. If the wheels began to slip he would have no knowledge of this fact until he had already damaged the tires of the duplex engine’s wheels; or he heard the crashing sounds of a duplex engine tearing itself apart, in over speed.
The S1 had a further handicap in the area of slippage. Unlike virtually all other steam locomotives that faced wheel slippage when starting, the S1 (because of the very light weight on the driving wheels) would experience engine wheel slip over the road at operating speed. The adhesion of the wheels to the rails was so light, that even minor variations in the roadbed would cause either the forward or rearward duplex engines to slip. This hazard more than any other doomed the operating life of this engine. The loss of adhesion at speed (30 – 50+ mph) always did serious mechanical damage to the engine, which lost adhesion, and to the locomotive as well.




So I guess it all depends on the locomotive and engineer.


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## gunrunnerjohn (Nov 10, 2010)

The chuff rate for most locomotives is four for a driver rev, one for each end of the piston travel on each side. An articulated would have eight chuffs, as they have two sets of pistons. There are exceptions to that rule, like the Climax I believe has 8 chuffs for a driver rev.


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## D1566 (Jun 8, 2012)

Not so common in the US but a three cylinder loco would have 6 beats, but 4 cylinder ones were generally back to 4, though the British Southern Railway 'Lord Nelson' Class 4 cylinder locos had 8 beats due to the way the cranks were orientated.


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## Big Ed (Jun 16, 2009)

I searched for chug rates, not chuff rates. 

I found this,

How many exhaust chuffs should your locomotive produce to be realistic? 

Locomotives produce 2 exhaust chuffs each time the cylinder moves forward and back. Most locomotives have 2 cylinders that produce 4 exhaust chuffs per 1 wheel revolution (wheel rotating 360 degrees). 

Some locomotives have 3 cylinders (such as shays and 3-cylinder rod engines) and thus produce 6 exhaust chuffs per full wheel revolution.

If you have Soundtraxx there is a way to adjust the rate.


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## Big Ed (Jun 16, 2009)

gunrunnerjohn said:


> The chuff rate for most locomotives is four for a driver rev, one for each end of the piston travel on each side. An articulated would have eight chuffs, as they have two sets of pistons. There are exceptions to that rule, like the Climax I believe has 8 chuffs for a driver rev.


Is that the same as I found?
Your just doubling the chuffs per side?


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## gunrunnerjohn (Nov 10, 2010)

That's the "generic" rule Ed, though I'm sure there are exceptions. Since each cylinder produces two chuffs for each complete cycle, just multiply the cylinder count by two.

The sound file for my cab forward with two sets of unsynchronized cylinders sounds pretty cool at low speeds, but once you get moving at a reasonable clip, it loses the definition of each chuff.


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## Big Ed (Jun 16, 2009)

gunrunnerjohn said:


> That's the "generic" rule Ed, though I'm sure there are exceptions. Since each cylinder produces two chuffs for each complete cycle, just multiply the cylinder count by two.
> 
> The sound file for my cab forward with two sets of unsynchronized cylinders sounds pretty cool at low speeds, but once you get moving at a reasonable clip, it loses the definition of each chuff.



OK, but when you multiply by 2 wouldn't the sounds of the multiplied cylinders be synchronized together with the chuff? 
Yours sounds good at low speed but loses the definition at high speeds, isn't that how a real one sounds once it really gets rolling?


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## gunrunnerjohn (Nov 10, 2010)

Yep, the real one sounds the same from what I understand, just describing what I hear.


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