Just reset one on my QSI locos to factory settings and notice how fast the chuff is by default. Then noticed the manual says 4 chuffs per revolution. I thought I had read 4 revolutions per chuff. The latter seems more accurate judging from what I have seen on the real local steam loco in town.
I will have to look really closely. In the meantime, which is it in your experience?
The typical 2 cylinder steam locomotive will have 4 exhaust "chuffs" per revolution of the drive wheels. You might have observed the local train coasting or braking, during which time no exhaust chuffs would be heard, but you might have heard the intermittent exhaust from the air compressors at that time - could appear under those circumstances to just give a chuff every few revolutions of the drivers. Hope that helps!
- James
there are generally 4 chuffs per revolution on a steam locomotive. This is because there are two cylinders on each side with two chuffs each.This is also why drivers need to be quartered. The first cylinder pushes forward (lets say for this example it is the right one) turning the wheel a quarter turn. the left cylinder will then be pushed forward turning the wheel another quarter. The right cylinder will now push back turning the wheel another quarter and finally the left will push back for the last quarter of a revolution. The cycle then repeats.
On articulated locomotives there could be as many as eight chuffs per revolution as there are two sets of drivers. This depends if the front set of drivers is in sync with the rear set of drivers.
The mechanical mechanism of a steam locomotive is quite impressive. Keeping all the parts so they are in the proper rotation is a feat in itself.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
Gerome Then noticed the manual says 4 chuffs per revolution. I thought I had read 4 revolutions per chuff. The latter seems more accurate judging from what I have seen on the real local steam loco in town.
To help you to visualize what is going on as a steam locomotive driver makes one full revolution with its axle, take a close look at the gif animation shown here-
http://home.roadrunner.com/~trumpetb/loco/
Pay particular attention to the valve in the upper cylinder, atop the larger flat piston, and note the apparent openings that it passes over to allow steam to either escape or to enter the cylinder, depending on the direction of travel of the piston. Now, if that sheds some light, remember that there is exactly the same thing happening on the other side of the frame of the steamer, but the crank pins are all set at 90 degrees from the position of those you can see in this gif. Depending on the railroad asking for the specs in their engines, they were 90 deg leading or 90 deg trailing those on the other side of the engine.
So, in one revolution of a driver on one side of the locomotive, the ones on the other side must also complete one full revolution since they travel precisely the same distance and both are fixed on the same axle...no independent spinning. If the valve timing on the visible side allows one admission of steam and one exhaust of spent steam up the blast pipes and up the stack, won't the valve on the other side do exactly the same thing, except retarded or advanced by a fraction of a second due to the 90 deg offset? Yes, you can see that it must. So, two exhausts plus another two from the other valve equals four exhausts, meaning four chuffing sounds from the steam blasting up out of the smokebox and stack.
Crandell
Thanks for the info.
It all makes sense.
Although less common here than in the U.K. I believe, some steam engines have a third cylinder located between the two normal cylinders, connected to a crank on the axle of one of the drivers. These engines would have six "chuffs" per revolution.
Note too what with a "true" Mallet with double-expansion (i.e. the steam is first used in the smaller rear cylinders, then exhausted to the larger front cylinders and re-used, and then exhausted out the stack) would only have four exhaust "chuffs" per revolution. On a "Simplex" or simplified articulated, where boiler steam is fed directly to all four cylinders, each pair of cylinders would generate four chuffs per revolution, so if the two sets of drivers were out of phase you could hear a double "chuff-chuff...chuff-chuff...chuff-chuff".
And just when you thought it was safe... some cound locos (so 4 chuffs per revolution) had a starting mode where high pressure steam was used in both sets of cylinders, so while starting out they could be out of sync with 8 chuffs but once the trainw a smoving they changed back to compound mode and the extra chuffs would go away.
I'm still waiting for an HO articulated with two motors and two sets of chuff sensors for the decoder so I COULD go in and out of sync. Most HO and smaller articulated drive the pair of engines like diesel locomotives, with a motor in the middle running out to gearboxes on each set of drivers. Impossible for this decign to ever go out of sync. With two independent drives (like the 2 motors Bowser PRR T1), you could easily have one motor slip while the other one does not. Add chuff cams to accurately synchronize the chuffs and you have everythign needed to have very realistic sound.
--Randy
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Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
The Soundtraxx Tsunami "Heavy" decoder, for one, has a CV setting (forget which without the manual handy) to allow the digitally induced chuffs to go in and out of synch.
Hi all,
I've a Roco UP Y3B with a QSI Rev chip that kicks up one heck of a racket if you twitch the knob a bit fast, the chuff rate gose out of sync, throws a wobbler and even sounds like one set going mad and the other coasting. I let one of our new juniors have a go (the lad's a bit heavy handed). He thought he was in real bother from the row it was making when I spun round at the bench, till the whole room crached up laughing.
That was awhile back, he turning into a resonable modeller, now he's listening.
Be in touch,
pick.
wjstix Although less common here than in the U.K. I believe, some steam engines have a third cylinder located between the two normal cylinders, connected to a crank on the axle of one of the drivers. These engines would have six "chuffs" per revolution. Note too what with a "true" Mallet with double-expansion (i.e. the steam is first used in the smaller rear cylinders, then exhausted to the larger front cylinders and re-used, and then exhausted out the stack) would only have four exhaust "chuffs" per revolution. On a "Simplex" or simplified articulated, where boiler steam is fed directly to all four cylinders, each pair of cylinders would generate four chuffs per revolution, so if the two sets of drivers were out of phase you could hear a double "chuff-chuff...chuff-chuff...chuff-chuff".
quite a few 3 cylinder loco's in the UK, and even some 4 cylinder loco's , the GWR 'KING' class for example.
The SP & UP used 3 cylinder Locos also. The 4-10-2 wheel arrangement was referred to as "Southern Pacific" class on the SP and "Overlands" on the UP. The SP had 49 of these and the UP had 10. The UP was not satisfied with the performance of the 4-10-2 and had ALCO create the 4-12-2, or "Union Pacific" type. The UP rostered 88 of these monsters. This obviously made for a very long wheel base. These Locos were designed for lifting heavy freights over Sherman Hill (what else?) and over the Wasatch. To hear one of these Locos was an interesting experience.
To carry this to its logical extreme, how about a triplex starting simple? Not four, not six, not eight but TWELVE well-syncopated, slow chuffs! Of course that only lasted for about three turns of the drivers. Unlike most N&W Ys, which ran simple to 4 MPH, the triplex changed over to compound as soon as there was pressure in the receivers. As far as matching the 10 MPH changeover of a Y6b, the triplexes had all they could do to reach that speed at all...
Chuck (Modeling Central Japan in September, 1964)