upon growing up in the 1st generation diesel era, i was wondering about the physics behind the “chug” of a steam engine, what causes this, especially upon starting out. i am a dummy when it comes to steam. i always watch “Trains and Locomotives” on the RFD cable channel on Mon. eve at 5:00 PM CST. and 90% of the shows feature steam. also i was wondering why sometimes the stacks blow black smoke and then white smoke. just need some info from one the “old timers” of this era. thank you. regards, michael.
The short answer is that the typical two cylinder steam locomotive has four power strokes per revolution of the drive wheels, and the used steam is released from the cylinders and exhausted up the stack at the end of each power stroke resulting in a “chuff”. As far as the smoke, that depends on the type of fuel, skill of the fireman and operating conditions. Coal will typically give off black smoke when it is first shoveled on the fire. Once the volatile elements burn off, the stack will clear up. A skilled fireman will fire light and often to keep the smoke to a minimum. An oil burner will usually have at least a faint haze at the stack, although it can vary from clear to black. Even without smoke, the steam can condense into a white cloud, too. That is the short answer… the long answer can (and has) filled many books!
- James
To break your question into pieces:
“Chugs” - each one is the exhaust event from one end of one cylinder. For normal 2-cylinder locomotives, there are four for each turn of the drivers, 90 degrees apart. The few 3-cylinder locos had six exhausts per driver revolution. Simple articulateds and compound articulateds starting up have eight exhausts, usually but not always syncopated since the articulated’s two engines aren’t connected to each other mechanically. And then there is the Shay - three cylinders, plus reduction gears and small drivers, make a Shay running at ten MPH sound like a 2-cylinder rod engine running at 50…
Color of smoke at the stack - can vary from nothng, to a white cloud of condensing steam, to grey, to midnight black. The main thing at work is, the fuel-air mixture. The dark component of the smoke is unburned carbon, sometimes aided and abetted by impurities in the fuel. Coal may have un-burnable particulate matter. Oil has less, but it’s still present. A skilled fireman can keep the stack almost clear - steam or nothing, no black. A less-skilled person (or a careless one) will leave a grey, brown or black cloud behind. The absolutely blackest smoke, though, is generated deliberately. When an oil burner has built up some soot in the tubes and flues, the fireman will wait until the loco is working hard, open the fire door and hold a scoop of sand in the airstream. The sand scours the soot, generating a cloud that can send birds to roost. You don’t want to be anywhere nearby when this happens!
Chuck (Modeling Central Japan in September, 1964 - where steam locos burned poor quality coal)
The steam in the cylinders is under tremendous pressure, so when it’s allowed to escape it ‘whooshes’ out the cylinder and up the stack, causing a draft that pulls smoke from the firebox with it - and sucks air into the firebox, helping the fire.
Gidday, I am pleased that James and Chuck have answered your question succinctly, because I knew if I had to put it into words I’d have not only confused you but myself !!
Here are a couple of [8D] animations that might be of further help.
http://www.animatedengines.com/locomotive.html
http://home.roadrunner.com/~trumpetb/loco/
If you “google” "steam locomotive animation engines there are more.
Cheers, the Bear.
what about the sound that is made, the chuff?
when starting from a stop, i assume the steam pressure is high, that the valves open and close most slowly and therefore, the steam starts out escaping at a high pressure, presumably making the most noise, and it has a long time to completely escape. There may be a more noticable period of silence between chuffs.
but at normal operating speeds, i would think the pressure is lower, and the valves open and close faster, meaning that it starts escaping at a lower pressure, with less noise, has less time to escape and does not escape completely. therefore the noise of it escaping is cut off abruptly as the valve closes.
while maintaining speed up a hill, the period of the chuffs would be the same, but since the pressure is higher, the initial noise level would be higher
i’ve tried researching this on the web but didn’t find much. i’m sure the developers of the sound cards have given this a lot of thought, but aren’t willing to give away trade secrets.
greg
Well, if the steam didn’t escape completely, the engine would stop running as it would have steam on both sides of the cylinder pushing against each other.
A steam engine using steam pressure of say 290 psi (pounds per square inch) has a lot of pressure. I forget the exact number, but I think a square foot of water creates like 7000 sq.ft. of steam. The steam is going to exit incredibly quickly as soon as it gets an opening, plus of course there’s steam on the other side being introduced, pushing the piston and pushing the steam out.
That being said, how the engine is operated can affect the sound. An inexperienced engineer will get a “mushy” sound out of the engine, an experienced engineer will get sharper exhaust like a shotgun’s crack.
http://science.howstuffworks.com/transport/engines-equipment/steam1.htm
Sometimes they seem to bark.
Richard
A steam locomotive’s speed is controlled by the valve gear. As the valve slides back and forth, as the animation shows, it uncovers ports, one an inlet and the other an outlet. When first starting, the engineer sets the reverser lever fully forward, meaning the valve gear travels fully forward and backward in its stroke to the extent that it covers and uncovers those ports for longer durations. This process is called ‘cut-off’…as in, the valve cuts off the admission of steam into the cylinders as it reaches the end of its power admission stroke in its own cylinder atop the larger working cylinder.
When attempting to lift a heavy train, the fully forward reverser, which ensures full cut-off, forces the valve to admit high pressure steam into the cylinder for a longer portion of the working piston’s stroke backward/forward, thus imparting full steam force to the piston’s working surface. A careful operation of the throttle keeps the force of the steam overcoming the adhesion of the drivers on the slippery rails, so that even with full steam pressure and for the first 85% of the stroke (typically this is the maximum cut-off), the locomotive won’t spin and fail to lift the train.
The nifty part comes as the train gains momentum. The engineer should shorten the cut-off by pulling back on the Johnson Bar, the reverser, and letting less steam into the cylinders. This is a matter of both speed adjustment and economy. This is often termed ‘hooking up’. As a passenger train gets toward its top speed of 79 mph, per federal regulations, an efficient passenger locomotive, such as a Niagara or FEF, would have its admission cycle restricted to about 20% of the stroke. The idea is to let the gained momentum and the power inherent in the smaller portions of steam gaining admission to the cylinders do the work for the full length of the stroke of the working piston. It should now be obvious that the much smaller admission time, the greater worki
Methinks you meant cubic feet. It’s a volume thing.
That sharp cannon boom is a sign of:
- Locomotive operating at low cutoff - high exhaust steam pressure. This is usual when starting.
- Inefficient exhaust system design. In my experience, the loudest `crackers’ were the oldest, least developed teakettles, which had restricted blast pipes and high backpressure exhausts.
On the other hand, a `mushy’ exhaust indicates:
- Long cutoff, low exhaust pressure - which indicates skilled use of the reverse lever.
- A modern, low-backpressure exhaust - Giesl, Kylchap or similar, with carefully designed blastpipes that move lots of smoke with less steam, but don’t lift it very well. That’s why many more modern steam locos had elephant ears or other smoke-lifting arrangements.
That mushy exhaust actually indicates efficient operation.
Chuck (Modeling Central Japan in Septem
Hey Ratdogsoo, thanks for asking about that stuff. I’ve alwa7s wondered about the smoke color myself! Just never got around to asking about it.
Thanks to the rest of the group for the information.
thanks to all that replied! i now have an understanding of the many aspects of steam power, even down to an inexperienced fireman. very interesting. i just find it hard to believe steam power could produce so much “horsepower” and tractive effort. if anyone hasn’t watched “Trains and Locomotives” on RFD TV on Monday 5:00 CST, you are missing a treat. 90% steam programs, some diesel, some electric. thanks to all! i can sleep now. regards, michael.
Chuck hit the nail on the head with his explanation of exhaust sound. In later years, the desire to run trains at ever increasing speeds dictated the need to reduce cylinder backpressure in order to develope maxium horsepower at those higher track speeds. At the same time, maximum draft needed to be induced in order to produce the large quantity of steam needed to sustain those speeds. The modern front-end arrangements that Chuck mentioned were designed to meet those two conflicting requirements, and had the side effect of a quieter exhaust blast.
Although I can appreciate modern mainline steam, I prefer the older teakettles with a classically designed nozzle, petticoat pipe and stack just for the thunderous exhaust they have when working upgrade at a relatively sedate speed! I use those time-tested formulas on my 12" gauge steamers so they will have a healthy bark under load and pull a strong draft, too. No need for high speed efficiency on those little guys… :>)
- James
i’m sure someone can explain why steam is coming out of the bottom of the cyclinder. here’s a video of a union pacific engine.
and here’s a video of NYC engines where steam is coming out of the back of the tender around the 1 min mark.
greg
Greg.
On the bottom of the cylinders there are drains or drain cocks/ cylinder cocks. Controlled by the engineer. They allow condensed water to escape the cylinders to avoid a hydraulic lock. When the loco sits for any amount of time the steam will condense back into water in the cylinders and water does not compress. Either the loco will stall or severe damage will occur.
Tenders will have either steam heat pipes or even some had heated water from the locomotive circulate back into the tender to keep the water from freezing or ice chunks from forming. There was also a steam heat pipe for passenger car heaters. Feeding the boiler with hot water was better for keeping up steam when the demand required it. The NYC loco had a steam powered coal pusher that would push the coal forward.
Pete
Everyone has done well in giving answers on steam power peculiarities. The last bit about the engineer controlling the blow down of condensation is also great.
Now that you know how things sort of work. You must realize that 100% of the steam engines that you will probably observe operating today, especially in the station, yard or taking off or in photo runs, are operated for show! This is key. What you see may or may not represent the way a real hogger would handle his engine in the 1930’s. It was about eficiency, conserving fuel and water and getting the job done then.
Today it is a show, and sights and sounds are more important to paying customers than operating a railroad according to 1930’s revenue hauling protocol.
Lots of throaty blasts high into the air, black smoke and huge billowing clouds with lots of sustained hissing in start off and crawl with steam venting 20 feet on each side are the order of the day. The folks want a show and the fireman and the engineer at their controls are ordered to give it to them and that they do. A lot of blowdown action, wheel slip and filthy black smoke with choked off flu controls, once steam is up is prime show material. But back in the days of revenue steam it was improper operation or show boating and wasteful. A prime example of show is seen here 20 seconds into the clip as the mike crawls forward. No need to watch it all once the engine steams past.
http://www.youtube.com/watch?v=fwdyuotS2GI
Also a burnout of another narrow gauge mike to show just how fast you can get steam tonnage moving in a showboat move.
http://www.youtube.com/watch?v=rAQ-txvlpSQ
Likewise, some incredible genuine slip is seen here also a similar NG mike trying to back up a slight hill with a large passenger train resisting its efforts.&nb
To enlarge a little on the above, these were just a few of the things the Norfolk & Western did not want:
- Lifted safety valves (“Introduce cold water with the injector to reduce steam generation.”)
- Extended or excessive use of whistles.
- Excessive use of cylinder petcocks (“Three or four turns of the drivers should be sufficient to clear cylinders of condensation.”)
- Smoke (“Firemen should strive to keep a clear stack at all times.”)
- Insufficient cutoff (“Sharper than usual exhaust and faster than usual acceleration is wasteful of steam.”)
(The quotes were what I remember from a long-ago tour of the N&W shops,)
It has also been noted that Norfolk & Western publicity photos never, ever showed a smoking locomotive.
On the opposite side of the continent, in the Los Angeles basin, any display of smoke by a steam locomotive could be `rewarded’ with a citation if noticed by a city or county law officer.
Chuck (Modeling Central Japan in September, 1964)
A steam locomotive engineer had two controls over engine speed - the throttle and the cutoff. The cutoff, or valve timing, is part of the reverse control (generally poser assisted in more modern engines). A typical cutoff range might be from 85% to 15%. That is, the steam will be let in to the cylinder for 85% of the power stroke in a given direction, and the same on the piston return travel. When this happens, there is very high pressure as the valve opens for the exhaust, producing a barking sound. Once a train was in motion, the engineer could lower the cutoff. This gave the steam more time to expand, gaining efficiency, and produced a gentler exhaust noise - more a chuff than a bark. Climbing a grade could result in the need to raise the cutoff back and also produce the barking exhaust of a steam engine under load.
The cylinder exhausts came together in a blast tube inside the smokebox, some distance below the stack opening. The venturi effect provides the necessary draft for the fire. When the locomotive stops, there are no more exhaust pulses to supply the draft, and the fireman would have to activate the “blower”, a smaller jet pipe fed by the boiler.
The figure I heard for a ruptured crown sheet in a 250 psi boiler (with 384 degree water at that pressure) was 1600 to 1 - each cubic foot of water released to atmosphere would instantly become 600 cubic feet of steam with disastrous results for locomotive and crew.
Not to hijack this thread, but how I’m curious about RFD TV. Every so often someone mentions it in a post, but I can’t find hide nor hair of it on my cable system as an offering. Is it only available in certain areas, or only on satellite or ??
[:S]
The RFDTV website: www.rfdtv.com has a schedule tab to pull up the schedule and a box you can click on to request RFDTV from your cable or satellite provider. Trains and Locomotives is on Mondays and I Love Toy Trains is on Thursdays.