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#1
Old 06-15-2011, 01:13 PM
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Freight Train Questions

Driving up to Flagstaff this weekend we noticed several trains with maybe 80-100 cars double stacked with containers. Obviously the total weight of these trains is staggering.

Anyone know if there is an legal/upper limit of the number of cars one train can pull? How about an legal/upper limit on the weight than can be pulled. Lastly, any estimates of the amount of time or total distance it would take for one of these trains to roll to a stop from 20 MPH on a flat surface?
#2
Old 06-15-2011, 01:28 PM
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Quote:
Originally Posted by SanDiegoTim View Post
Driving up to Flagstaff this weekend we noticed several trains with maybe 80-100 cars double stacked with containers. Obviously the total weight of these trains is staggering.

Anyone know if there is an legal/upper limit of the number of cars one train can pull? How about an legal/upper limit on the weight than can be pulled. Lastly, any estimates of the amount of time or total distance it would take for one of these trains to roll to a stop from 20 MPH on a flat surface?
No legal limit of length that I know of (I understand Class I railroads have tested 2+ mile long freights), and the former physical limit of coupler strength (i.e. how many freight cars you can pull before the coupling between cars fails) can be gotten around by having distributed/remote power units - a fancy name for remote-controlled locomotives cut into the middle of the train, to ease the strain on the couplers.
As for weight limits, there are physical limits that track is rated for - most track can now handle 286,000 lbs cars, some track has been upgraded to handle 310Klbs frieght cars - the previous standard was 263Klbs. I know there have been 125ton freight cars (the load limit, not the weight of the car itself) for awhile now, not sure if 130tons or greater are out there in force.
And the braking distances are pretty darn long, IIRC assume a mile or more at moderate speeds.

BTW, Intermodal trains (those containers trains you saw) are not necessarily all that relatively heavy compared to unit trains of 110t coal or ore freight cars, so keep that in mind...

Last edited by SirRay; 06-15-2011 at 01:32 PM.
#3
Old 06-15-2011, 07:17 PM
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Quote:
Originally Posted by SirRay View Post
BTW, Intermodal trains (those containers trains you saw) are not necessarily all that relatively heavy compared to unit trains of 110t coal or ore freight cars, so keep that in mind...
Could have been a big shipment of pillows!
#4
Old 06-15-2011, 07:32 PM
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If there are legal restrictions on length are they justified by the physical limitations of the equipment or by how much time it would take to clear a crossing? The couplings may be able to tolerate a two mile train but I don't think your average commuter would.
#5
Old 06-15-2011, 11:47 PM
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Here's a picture of a 197-car train (2.5 miles long) that ran—apparently as a matter of course—through Illinois yesterday.
#6
Old 06-16-2011, 12:13 AM
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There used to be practical limits on the length of freight trains because of the amount of force exerted on the couplers. Just like the old high-school physics demonstration with the blocks hanging from strings, the couplers in the front of the train have to handle the entire weight of the train while accelerating. Distributed power, which is a relatively new technology, allows the addition of remote controlled locomotives in the middle or at the end of a train, which can allow much longer trains. Another limiting factor was the delayed and reduced braking effectiveness near the end of the train with conventional airbrakes, which has been addressed with electronic controlled airbrakes.

The limit has recently been 12,000 feet (about 2.3 miles or 3,658 meters) for trains with electronically-controlled brakes. I'm not sure if this limit is (or was) legally enshrined or just the position of the AAR. Some of the big rail roads have been running some experimental "monster trains", such as this 3 and a 1/2 mile long one, but I don't know if any are regularly running them yet or not.

Last edited by GreasyJack; 06-16-2011 at 12:13 AM.
#7
Old 06-16-2011, 12:17 AM
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Could have been a trainload of empty containers.
#8
Old 06-16-2011, 12:19 AM
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If you have to insert a locomotive in the middle of a 2 mile long train to distribute and power the load, why not just have two 1-mile trains?
#9
Old 06-16-2011, 12:34 AM
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Quote:
Originally Posted by Musicat View Post
If you have to insert a locomotive in the middle of a 2 mile long train to distribute and power the load, why not just have two 1-mile trains?
The additional locomotives are controlled remotely from the cab in front, so they don't require additional crew.

Also, from a logistical (traffic management) standpoint, a 2-mile long train is still just one train that needs to be scheduled and routed. Two 1-mile long trains would need to be scheduled and managed as 2 trains, with adequate distance between them so they don't run into each other.
#10
Old 06-16-2011, 12:37 AM
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Quote:
Originally Posted by Musicat View Post
If you have to insert a locomotive in the middle of a 2 mile long train to distribute and power the load, why not just have two 1-mile trains?
Also two trains take up two signal blocks, whereas one big train only uses one. A signal block is (to hugely simplify) the track between two signals which only one train is allowed to occupy at a time. It doesn't matter if it's a 2 mile long coal train or a small service vehicle. Obviously it becomes an issue if the trains are so long they're taking up multiple signal blocks, but otherwise a typical rail network will be able to handle a lot more cargo with fewer long trains than more short ones.
#11
Old 06-16-2011, 05:17 AM
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I think I read somewhere that some municipalities limit train lengths. Also I think there is some limit to the duration that a railroad can block a grade crossing.

This can become critical in some areas, usually smaller towns, where ambulance access to a hospital on one side of the tracks must be maintained.
#12
Old 06-16-2011, 05:47 AM
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If a super-long train is run with no additional crew, what happens if there is a problem (or suspected problem) with the train? It would take a crew member nearly two hours to walk to the back of the train and return to the front in order to inspect the train (plus time to actually deal with the problem).

Last edited by Alley Dweller; 06-16-2011 at 05:48 AM.
#13
Old 06-16-2011, 07:53 AM
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Quote:
Originally Posted by Alley Dweller View Post
If a super-long train is run with no additional crew, what happens if there is a problem (or suspected problem) with the train? It would take a crew member nearly two hours to walk to the back of the train and return to the front in order to inspect the train (plus time to actually deal with the problem).
I've been a conductor for a major US railroad for six years. That's how I got my screenname! I know the rail is steel, and has been for like 100 years, but it used to be iron.

Basically, the conductor will do anything he can to fix problems on the road. If we can't fix it, or set the problem car out, we just tell our dispatchers and they send help.

By federal law, a crew can only perform actual train service for 12 hours, after that we "outlaw". The only exception is in a case of a major emergency.

We let our dispatchers know when we have been on duty for 9 hours. At some point, the train will get re-crewed if we outlaw. Keep in mind, I'm simplfiying things somewhat.

Last edited by ironbender; 06-16-2011 at 07:56 AM.
#14
Old 06-16-2011, 10:01 AM
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Originally Posted by ClevelandProud View Post

Could have been a trainload of empty containers.
I guess you didn't look at the picture. It was a mixed manifest train. Discussions of it on an Illinois railfan listserv suggest that it wasn't that unusual, that trains over two miles long are now fairly common in the Midwest and Prairie Provinces.

As for checking a problem, I'm not sure why it would take someone walking four mph more than a half hour to walk to the back of a two-mile-long train. In practice, the conductor would usually just step down at a grade crossing or similar location, then have the engineer pull the train slowly forward until the suspected trouble spot was adjacent.
#15
Old 06-16-2011, 10:31 AM
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Quote:
Originally Posted by Musicat View Post
If you have to insert a locomotive in the middle of a 2 mile long train to distribute and power the load, why not just have two 1-mile trains?
One 2-mile train also disrupts less traffic at crossings. While it takes longer for the train to pass you will still have a fixed amount of time to wait before and after the train reaches the crossing. With 2 1-miles trains you have twice that.

(But people will complain either way).
#16
Old 06-16-2011, 11:41 AM
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Another limiting factor to overall train length is the length of sidings along the route....the "pullouts" where two trains can pass. Obviously a siding has to be long enough to accomodate an entire train*. I believe the standard length for passing sidings is generally about 8000 ft. or just over 1-1/2 miles although some railroads are now building 13,000 ft. sidings.

The total weight of a train is not much of a factor in determining length. The effect of weight on track, bridges etc. is determined by axle loadings....the amount of weight on each set of wheels. As long as each individual railcar is not loaded over capacity, the weight of the entire train is mostly irrelevent insofar as infrastructure is concerned

*There actually is a process known as a "saw-by" by which two over-length trains can pass on a short siding, but it is usually avoided as it is tedious & time-consuming involving a lot of backing & filling, uncoupling and re-coupling cars, etc.
#17
Old 06-16-2011, 12:03 PM
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Can one of you knowledgeable train guys (sexist assumption on my part) offer an estimate of how long it would take a mile-long train to roll to a stop on its own?
#18
Old 06-16-2011, 01:07 PM
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Quote:
Originally Posted by SanDiegoTim View Post
Can one of you knowledgeable train guys (sexist assumption on my part) offer an estimate of how long it would take a mile-long train to roll to a stop on its own?
Operation Lifesave more or less agrees with my post yesterday
Quote:
Trains cannot stop quickly:
Average freight train stopping distance:
55 mph = over 1 mile.
Eight-car passenger train stopping distance:
79 mph = over 1 mile.
Not too sure if mile+ long freight are normally travelling at 55mph on the main - may be more like 40mph except for intermodals or refrigerated product unit trains.
As for how long it would take without application of brake (coast to a stop) - I dunno, you'll need to test that yourself on the Trans Austrailan Railway
(Actually the FRA railroad testing facility at Pueblo probably has done 'coasting to a stop' tests, but with little track friction and good roller bearing on the axles it will be a long distance).

Last edited by SirRay; 06-16-2011 at 01:08 PM.
#19
Old 06-16-2011, 01:08 PM
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Quote:
Originally Posted by SanDiegoTim View Post
Can one of you knowledgeable train guys (sexist assumption on my part) offer an estimate of how long it would take a mile-long train to roll to a stop on its own?
Info from Operation Lifesaver:
Quote:
Trains cannot stop quickly:
Average freight train stopping distance:
55 mph = over 1 mile.
Eight-car passenger train stopping distance:
79 mph = over 1 mile.
Another very general rule of thumb I've heard is that a train takes its own length to stop. Neither rule is particularly dependable as there are so many variables. Speed, track condition, type of equipment, operator's course of action/reaction time, etc. Train brakes have a "full emergency stop" function....the equivalent of locking up the brakes on an automobile.... but as with autos, it is rarely used as it can have some very bad effects. On an automobile it can send the car into an uncontrolled skid, with a train an emergency application can result in derailment and/or damage to equipment and track. And it still doesn't stop right away.

Another thing to consider is that train brakes are controlled by a pressurized air line running the length of a train. It can take 15 seconds or more from the time the brakes are applied at the head end of a train until the pressure change is felt at the rear and all brakes begin to take hold. Electro-pneumatic braking is currently being experimented with and promises much faster application times, but it is likely to be many years before it can be applied to the tens of thousands of pieces of rail equipment out there.

ETA: drat you SirRay!!

Last edited by SeldomSeen; 06-16-2011 at 01:09 PM.
#20
Old 06-19-2011, 12:00 AM
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I was a conductor and yardmaster for Norfolk Southern. For my particular area we weren't allowed to build trains bigger than 150 cars but that was an unofficial rule.

There are areas where making them too long would block road crossing for too long.

As far as weight, we had a section in our rule books which dealt with grades over a particular area and how much horsepower you'd need to pull over that railroad. A rule of thumb as a yardmaster was to use a 1 to 1 ratio when making up a train. So 4000 tons would require One 4000 horsepower engine, 12000 tons 3 engines.

We operated over CSX railroad & I remember a 200 car train (one of theirs) broken into 4 separate sections...all knuckles breaking. That big of a train is going up and down hills at the same time, plus it was a mixed freight train which usually has full & empty cars scattered all over the train.
#21
Old 06-19-2011, 01:24 AM
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Originally Posted by GaryM View Post
Could have been a big shipment of pillows!
Or helium-filled zeppelins.
#22
Old 06-19-2011, 01:26 AM
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I don't believe there are any legal limitations to the length of a train. Union Pacific ran a 3 1/2 mile long train from Chicago to LA to see how it would work out.

Here is an article from the LA Times that puts it bluntly: "There are no state or federal limits on the length of trains or requirements to notify agencies about unusually long train configurations, officials said. Union Pacific said it did alert local federal regulators, who observed the train’s movement. "

Keep in mind that railroads are (generally speaking) privately owned and (generally speaking) do not run on publicly owned tracks.

http://latimesblogs.latimes.com/lano...-la-basin.html
#23
Old 06-19-2011, 06:05 AM
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Very interesting thread, always learn something new on this site.

Something that has been puzzling me and though it's a bit of a hijack as there are some railroad experts here perhaps I can post the question.

I may be a dumb question but with the weights of freight and length of trains involved how do they ever get the whole train moving?

The engines have steel wheels riding on steel rail, I don't know the number of driving wheels an engine may have but it can't be more than say 10, the actual wheel to rail contact can't be more than a few square inches.

How can this be enough grip area to get a two mile long train rolling?

What am I missing?
#24
Old 06-19-2011, 06:37 AM
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Sand, electric motors, and the weight of the engines.
#25
Old 06-19-2011, 07:05 AM
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Gotta love the SDMB. I was just at a railway museum and wondering what the tubes that come down in front of the drive wheels on many of the engines where for. I assumed it had to do with traction but but thought it was perhaps something related specifically to steam engines.

Turns out it is for delivery of the sand ironbender mentions. Love when my ignorance is fought.
#26
Old 06-19-2011, 12:03 PM
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Mauritania is supposed to have the world's longest and heaviest train. I don't know if it's a true claim but here is a link
#27
Old 06-19-2011, 12:04 PM
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Quote:
Originally Posted by Chickenwrangler View Post
with the weights of freight and length of trains involved how do they ever get the whole train moving?
Slack coupling makes the laws of inertia work for you rather than against you. The locomotive gets the first car moving and once it's underway a fraction of an inch, the coupler pulls taut and starts the second car moving, and so on down the line. Anytime you're next to a long freight train that's starting up you can hear, moving from front to back of the train, the sound of the couplers tightening. It will take a couple of seconds for a long train. This means that the very last car gets quite a jerk, going from a stop to 15 mph in an instant, and was one of the reasons cabooses were dangerous places to ride. Generally the conductor and brakeman would hear the couplers coming toward them and have time to brace for the wild start.

For this same reason, slack coupling is not used on passenger trains.
#28
Old 06-19-2011, 03:44 PM
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Originally Posted by Mr Downtown View Post
For this same reason, slack coupling is not used on passenger trains.
How is that avoided?
#29
Old 06-19-2011, 04:02 PM
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Passenger trains use close coupling, with no slack in the knuckle. For one thing, they have bellows fittings around the train doors, allowing passengers to walk from car to car. I'm not sure exactly what hardware is used on the couplers to ensure things are tight. Really modern trainsets, as used on high-speed trains in Europe and Asia, are articulated trainsets where a set of 9 or 10 cars are permanently joined together, with the trucks (sets of wheels) under the "coupling" rather than at both ends of the car. This reduces friction and gives a smoother ride. Lengthy high speed trains will have two trainsets coupled together. Each trainset has a "locomotive" at both ends, so passengers from the front trainset cannot reach the rear trainset while rolling.
#30
Old 06-19-2011, 06:40 PM
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Originally Posted by Markxxx View Post
Mauritania is supposed to have the world's longest and heaviest train. I don't know if it's a true claim but here is a link
Here's a coal train over 7km long. According to the description it has 8 engines and a special control system to keep them in sync, but only one driver.

You'd have to be a really big fan of trains to watch the whole video.
#31
Old 06-19-2011, 09:37 PM
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Originally Posted by ironbender View Post
Sand, electric motors, and the weight of the engines.
OK sand and weight of engines I can understand but what does the electric motor do? and what about the great age of steam before they had electric motors?

The slack couplings make sense. I remember as a kid hearing that clonking down the line of a freight train as it moved about, thought it was just loose couplings didn't realize it was part of the system.

#32
Old 06-19-2011, 09:50 PM
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Originally Posted by Chickenwrangler View Post
OK sand and weight of engines I can understand but what does the electric motor do? and what about the great age of steam before they had electric motors?

The slack couplings make sense. I remember as a kid hearing that clonking down the line of a freight train as it moved about, thought it was just loose couplings didn't realize it was part of the system.

Modern locomotives are diesel electric - the diesel engines turn generators to provide electricity for the electric motors which drive the wheels. One reason this is done is that an electric motor can provide full torque at low RPM, whereas an ICE is only effective over a narrow RPM range. Steam engines operate well at low RPM also.
#33
Old 06-19-2011, 09:52 PM
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Originally Posted by Chickenwrangler View Post
OK sand and weight of engines I can understand but what does the electric motor do? and what about the great age of steam before they had electric motors?
They had steam engines, coupled to the wheels.

In modern diesel-electrics, the diesel generates electricity from fuel (oil) and the electricity powers the driving wheels. I'm sure someone will tell us why, but I can think of at least one reason. Electric motors operate efficiently over a wide range of speeds, so don't require a transmission. Reciprocating, internal combustion engines run well only at a narrow range of speeds, and need a transmission to cover a wide, more practical range.
#34
Old 06-19-2011, 11:34 PM
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The transmission was particularly a problem in the 1930s as diesel-electrics were being developed. Small industrial locomotives sometimes do use transmissions and directly driven wheels, but a mechanical transmission for something with the power of a 3800-horsepower locomotive is just not practical. Switching equipment to control electric motors was already well-developed, though. A related problem is powering multiple sets of driving wheels.
#35
Old 06-20-2011, 12:24 PM
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Originally Posted by Musicat View Post
They had steam engines, coupled to the wheels.

In modern diesel-electrics, the diesel generates electricity from fuel (oil) and the electricity powers the driving wheels. I'm sure someone will tell us why, but I can think of at least one reason. Electric motors operate efficiently over a wide range of speeds, so don't require a transmission. Reciprocating, internal combustion engines run well only at a narrow range of speeds, and need a transmission to cover a wide, more practical range.
As to why, you are correct that an internal combustion or diesel engine develops torque as RPMs increase (to a point), thereby creating the need for a transmission. Electric motors develop torque instantly. Perhaps some more knowledgeable than I can tell me if or to what degree torque increases with RPM levels with an electric motor.

Anyone know what RPM ranges the diesel engines and electric motors in locomotives operate within?
#36
Old 06-20-2011, 01:53 PM
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How many engines?

Quote:
Originally Posted by SanDiegoTim View Post
Driving up to Flagstaff this weekend we noticed several trains with maybe 80-100 cars double stacked with containers. Obviously the total weight of these trains is staggering.

Anyone know if there is an legal/upper limit of the number of cars one train can pull? How about an legal/upper limit on the weight than can be pulled. Lastly, any estimates of the amount of time or total distance it would take for one of these trains to roll to a stop from 20 MPH on a flat surface?
They would need a heap of power.
#37
Old 06-20-2011, 03:23 PM
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Originally Posted by Chickenwrangler View Post
Very interesting thread, always learn something new on this site.

Something that has been puzzling me and though it's a bit of a hijack as there are some railroad experts here perhaps I can post the question.

I may be a dumb question but with the weights of freight and length of trains involved how do they ever get the whole train moving?

The engines have steel wheels riding on steel rail, I don't know the number of driving wheels an engine may have but it can't be more than say 10, the actual wheel to rail contact can't be more than a few square inches.

How can this be enough grip area to get a two mile long train rolling?

What am I missing?
I saw a show on tv that said steel wheels will start spinning on the rail once traction is broken. It went on to say that an advantage of the diesel generator/ electric motor is that traction and torque can be monitored electronically to provide maximum torque and can be instantly adjusted if the wheels start to spin. Don't know if it's true or not.

The show also mentioned that they carry sand in tanks and can blow it under the wheels for extra traction, as others here have stated.
#38
Old 06-22-2011, 06:32 AM
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Can I put out just one more question while we're all here?

The old steam engine always seemed to give their wheels a quick spin before starting to move, what was the reason for this? Laying sand to get grip before moving off perhaps?

Can't somehow think it was "laying down rubber" like a drag racer
#39
Old 06-22-2011, 10:16 AM
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Originally Posted by Chickenwrangler View Post
Can I put out just one more question while we're all here?

The old steam engine always seemed to give their wheels a quick spin before starting to move, what was the reason for this? Laying sand to get grip before moving off perhaps?

Can't somehow think it was "laying down rubber" like a drag racer
It look good in the movies. A good engineer would never spin his wheels, to expensive.
#40
Old 06-22-2011, 09:28 PM
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(Former steam locomotive engineer at your service)

Wheelslip on a steam locomotive is undesirable, mainly because you can generate enough heat via friction to actually throw off the driving wheels' tires. Yes, tires.

In looking at a driving wheel, you're actually looking at a couple of pieces. The hub (and spokes, if any) and the flanged outer ring (the tire.)

The pieces aren't joined by welds, bolts, screws, or anything else. They're sweated on. Large rings of fire heat the tires to expansion, and then they're placed over the hubs. As they cool, they contract until eventually they are tightly attached to the hub.

Spinning the wheel builds up heat, which expands the tire...and you can spin it right off.

As to why steam locomotives tended to spin the drivers, it really boils down to the guy on the throttle. Since it takes a lot more power to start the train than it does to keep it moving, you'll be opening the throttle quite a bit if starting a heavy train (moreso on an incline. Moreso if the slack is stretched.) The difference between "enough steam to get us moving" and "too much steam and spinning the wheels) is, really, a fraction of an inch of throttle travel. When they start to spin, lots of times the only way to stop them is to completely close the throttle and start again from scratch.

What's even crazier than that is to watch some videos of articulated steam locomotives, which have 2 sets of drivers (essentially, 2 engines) under one very long boiler. Union Pacific's "Big Boy" 4-8-8-4 or "Challenger" 4-6-6-4 locomotives are good examples. Lots of times, one set of wheels would spin while the others wouldn't. Looks mighty funny.
#41
Old 06-22-2011, 09:34 PM
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Originally Posted by SanDiegoTim View Post

Anyone know what RPM ranges the diesel engines and electric motors in locomotives operate within?
Can't speak for the motors, but in the midrange setting, the modern Amtrak P42 locomotive's diesel is running at 900 RPM.
#42
Old 06-23-2011, 04:54 AM
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Thank you all for your comments, most interesting thread.

:-)
#43
Old 06-23-2011, 09:54 AM
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Quote:
Originally Posted by Hbns View Post
Gotta love the SDMB. I was just at a railway museum and wondering what the tubes that come down in front of the drive wheels on many of the engines where for. I assumed it had to do with traction but but thought it was perhaps something related specifically to steam engines.

Turns out it is for delivery of the sand ironbender mentions. Love when my ignorance is fought.
On some trains the sand is delivered manually (see at 0:25).
#44
Old 06-23-2011, 09:59 AM
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Found a little clip of a tire being heated by a burning ring of fire:

http://youtube.com/watch?v=W5I8hZvM1CQ
#45
Old 06-23-2011, 10:25 AM
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Quote:
Originally Posted by BlakeTyner View Post
burning ring of fire
I see what you did there.
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