Designing for the "Big Chuff"
Designing for the "Big Chuff"
I've noticed that some locos have a very muted exhaust, and others have a very sharp, distinct exhaust sound. It's not directly related to the size of the loco, either. What design elements affect this? Is it valve design (lap, lead, clearance, etc.), boiler pressure, exhaust nozzle design, backpressure, superheat, or what?
Would be interested to know what your experience indicates.
TIA,
Dan
Would be interested to know what your experience indicates.
TIA,
Dan
Dan Watson
Chattanooga, TN
Chattanooga, TN
Contrary to everything posted and all fact that I have seen, a fellow live steamer put a piece of 3" exhaust pipe on his engine as a stack, it does not extend into the smoke box, it should not draft at all, but it does. The most amazing thing about it is the sound is incredible!!! It sounds like an engine 3-4 times it size. It is a 1 1/2" raritan, it's not a pretty engine but it pulls and sounds like a brute!! He does all kinds of crazy experiments with it just to see how it changes steaming and drawbar.
Scott
Scott
"Building a steam locomotive is just like eating an elephant, one bite at a time!!"
Quite by accident we found one of the secrets to the big chuff effect in a rebuild of a Little Engines 1 inch Pacific into a Northern.
The bigger boiler might of had some effect but the boiler pressure remained unchanged. We opened up all the supply lines from the dry pipe, throttle valve, branch pipes, all the way to the inlet to the slide valve steam chest castings. We also lapped the valves with diamond dust flat to a millionth of an inch and lapped the valve faces of the cylinder casting to remove any mill marks. If I remember correctly, all pipes were opened up to the next larger diameter to give more volumne and reduce restriction of steam flow.
It sounded good on air during the test in the garage but the first run at the track was incredible. This 1 inch locomotive sounded and acted like a 1.5 inch locomotive and everyone was asking what did you do? It was much more than we were expecting and was a hard lesson of what to do in the future.
I am currently rebuilding a 1.5 mikado with the same thoughts in mind and after removing about 360 degrees of 90 degree elbows and replacing them with larger diameter tubing and gentle bends, expect the almost same results. Should be interesting. This time I am going to insulate the branch pipes under the branch pipe casing to reduce any temperature loss to the steam outside the smoke box.
I may play with the blast nozzle orifice diameter but will wait for the plumbing rebuild to see what happens before making too many changes at once.
Superheating also gives a more audible exhaust sound and increased performance but that would require a boiler modification I am not planning on.
Robert
The bigger boiler might of had some effect but the boiler pressure remained unchanged. We opened up all the supply lines from the dry pipe, throttle valve, branch pipes, all the way to the inlet to the slide valve steam chest castings. We also lapped the valves with diamond dust flat to a millionth of an inch and lapped the valve faces of the cylinder casting to remove any mill marks. If I remember correctly, all pipes were opened up to the next larger diameter to give more volumne and reduce restriction of steam flow.
It sounded good on air during the test in the garage but the first run at the track was incredible. This 1 inch locomotive sounded and acted like a 1.5 inch locomotive and everyone was asking what did you do? It was much more than we were expecting and was a hard lesson of what to do in the future.
I am currently rebuilding a 1.5 mikado with the same thoughts in mind and after removing about 360 degrees of 90 degree elbows and replacing them with larger diameter tubing and gentle bends, expect the almost same results. Should be interesting. This time I am going to insulate the branch pipes under the branch pipe casing to reduce any temperature loss to the steam outside the smoke box.
I may play with the blast nozzle orifice diameter but will wait for the plumbing rebuild to see what happens before making too many changes at once.
Superheating also gives a more audible exhaust sound and increased performance but that would require a boiler modification I am not planning on.
Robert
Sounds exactly like unrestricting flow in an automobile, with modified exhaust and intake. Makes perfect sense I suppose.
I personally do not believe in creating exact mechanical scale models for the sake of hyper-accuracy if it will significantly degrade the performance of the engine. Overcoming the physics of scale should be a priority for an engine that will be run a lot and will be pulling trains.
--M
I personally do not believe in creating exact mechanical scale models for the sake of hyper-accuracy if it will significantly degrade the performance of the engine. Overcoming the physics of scale should be a priority for an engine that will be run a lot and will be pulling trains.
--M
I had a mogul that I foolishly sold. I had the smokebox apart one day. I took a piece of straight exhaust pipe and slid it up and down over the nozzle till the correct "chuff" was heard. Then yes it too would pull like a brute!
When I sold it, the fellow altered the smokebox, and now to this day it does not work like it did. Real simple to put it back, but, oh well. His loss.
Willy
When I sold it, the fellow altered the smokebox, and now to this day it does not work like it did. Real simple to put it back, but, oh well. His loss.
Willy
- makinsmoke
- Posts: 2262
- Joined: Thu Jul 10, 2003 12:56 pm
- Location: Texas Hill Country
the Big Chuff
Ah, So, a topic I have been interested in since firing my first.
Nelson's book describes machining the cylinder ports square for better performance and sound. When I look at Gene's drawings and castings it looks like the ports are designed to be elongated and round on the ends.
Of course what Nelson may have been referring to is the vertical faces of the ports.
Can anyone elicidate?
Also, Gene's castings are a little rough on the inside of the petticoat pipe and the stack. Would "porting and polishing" all of these surfaces inprove not only performance but sound?
Brian
Nelson's book describes machining the cylinder ports square for better performance and sound. When I look at Gene's drawings and castings it looks like the ports are designed to be elongated and round on the ends.
Of course what Nelson may have been referring to is the vertical faces of the ports.
Can anyone elicidate?
Also, Gene's castings are a little rough on the inside of the petticoat pipe and the stack. Would "porting and polishing" all of these surfaces inprove not only performance but sound?
Brian
i took the same approach building my Allen Chloe. i've built race engines in the past and opening everything up helps. i went to larger stack, steam pipes and exhaust pipes. the blast pipe has to be played with. i had a flared peticoat pipe at first but removed it and the boiler still steams great. the bark is noticeably louder than other Chloe's and will out run any of them.
fred v
fred v
My friend and I have RX-7 race cars. Mine is in "stock" with the original three catalyic converters, stock exhaust manifold but no muffler. His has headers, no cat, bigger pipes and a bigger carb. Mine does 8,000 RPM, his does 10,000 rpm.Fred_V wrote:i've built race engines in the past and opening everything up helps.
And, yes, his has a much better "bark" than mine.
Steve
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- Joined: Tue Mar 21, 2006 2:44 pm
- Location: East Hartford, CT
Re sound
It stands to reaso the beter you let them breath both on the supply and exit side and tune the stack is a lot like putting poorting and polishing a a combusion engine, and then adding a tuned exhaust header makes it even better.
The one thing I rember form the mussle care era of the 60's was a tunned header was about the only perforamce option that incresed both horse power and fuel ecomony!
But one design constraint most steam locomotives had was smoke stack height, had fit through tunnels and bridges. So as engines kept getting bigger and bigger, the stacks got shorter.
Rob
The one thing I rember form the mussle care era of the 60's was a tunned header was about the only perforamce option that incresed both horse power and fuel ecomony!
But one design constraint most steam locomotives had was smoke stack height, had fit through tunnels and bridges. So as engines kept getting bigger and bigger, the stacks got shorter.
Rob
There's an old book I read called "scientific design of intake and exhaust systems". The author showed that it wasn't just "bigger is better" but proper tuning.
He rigged up a rotary valve driven by the camshaft with one input and a whole bunch of outputs. These were each sent to a manometer, so he could measure backpressure at the manifold through an entire cycle of intake, compression, power and exhaust. The manometers acted as an oscilloscope. He could then tune the exhaust to reduce backpressure at the manifold just at the moment the exhuast valve was opening so that he could get maximum scavenging.
It was very creative and extremely interesting. I suspect that some pressure transducer and a laptop could do the same thing now. Maybe this could be of some use in "tuning" an exhaust on a steamer.
Steve
He rigged up a rotary valve driven by the camshaft with one input and a whole bunch of outputs. These were each sent to a manometer, so he could measure backpressure at the manifold through an entire cycle of intake, compression, power and exhaust. The manometers acted as an oscilloscope. He could then tune the exhaust to reduce backpressure at the manifold just at the moment the exhuast valve was opening so that he could get maximum scavenging.
It was very creative and extremely interesting. I suspect that some pressure transducer and a laptop could do the same thing now. Maybe this could be of some use in "tuning" an exhaust on a steamer.
Steve
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- Posts: 652
- Joined: Tue Oct 28, 2003 10:56 am
It is worth remembering that noise = energy.
A real hearty "chuff" might sound good, but is consuming energy that would be better spent in providing motion.
There has been a lot of work dont on exhausts, in full size and models, and the maximum efficiency is with a very soft exhaust.
Prof Jos Koopmans recently did many trials on assorted engines in various scales, and proved some interesting innovations that give more power, to the wkeels, that is, not to the could effects.
A brief synopsis written by Jos can be read at:
http://www.alanstepney.info/page14.html
If you want sound effects, a small box of electronics would provide all you want!
A real hearty "chuff" might sound good, but is consuming energy that would be better spent in providing motion.
There has been a lot of work dont on exhausts, in full size and models, and the maximum efficiency is with a very soft exhaust.
Prof Jos Koopmans recently did many trials on assorted engines in various scales, and proved some interesting innovations that give more power, to the wkeels, that is, not to the could effects.
A brief synopsis written by Jos can be read at:
http://www.alanstepney.info/page14.html
If you want sound effects, a small box of electronics would provide all you want!
http://www.alanstepney.info
Model Engineering, Steam and workshop pages.
Model Engineering, Steam and workshop pages.
- Dick_Morris
- Posts: 2845
- Joined: Sat Jan 04, 2003 2:09 pm
- Location: Anchorage, AK
Just a thought - I wonder if tuning the shape and size of the stack, pettycoat, exhaust nozzle, etc., could be done to give a more satisfying sound without affecting the efficiency. Musical instruments are designed to give a particular sound - some of the same principles should work with a locomotive.
My oil burning locomotive buzzes at some settings of the oil, atomizer, and blower. I've heard a friends 1/3 scale wood burning Case do the same. There is apparently some kind of resonance that sets in.
My oil burning locomotive buzzes at some settings of the oil, atomizer, and blower. I've heard a friends 1/3 scale wood burning Case do the same. There is apparently some kind of resonance that sets in.