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Railway trains, and the things I didn't know.

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Railway trains, and the things I didn't know.

Old 24th Dec 2010, 20:13
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Railway trains, and the things I didn't know.

Last night, I found out how they stay on the rails. I had no idea how they tracked so nicely on the rails. Furthermore, I hadn't realized that the left and right wheels are (sometimes) coupled with an axle. Even given this, I'd assumed they didn't corner hard enough for it to matter. I was wrong about every aspect.

Further-furthermore, I'm still not sure how the power is applied to the driving wheels. When I was young, I assumed the visible rods were driving them, but later I realized they were (often) too skinny to carry that much power - especially since it's applied so near to the center of the wheel, so assumed they carried the information back to the valves for sequencing.

Can anyone elucidate?
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Old 24th Dec 2010, 20:21
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It simples...

The live rail is connected to de train wheels,
De train wheels is connected to de axels,
De axels is connected to de sequencing valves,
De sequencing valves is connected to de driving wheels,
De driving wheels make the wheels on de train go round and round, round and round.....
De wheels on de train go round and round all day long.....
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Old 24th Dec 2010, 20:28
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Third line, you sang an F# instead of G natural.
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Old 24th Dec 2010, 20:40
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Steam Engines

The power from the piston is carried to the driving wheel with the connecting rod. The rod that couples the wheels together, if more than 1 driving wheel, is called the coupling rod and spreads the power across multiple wheels to add adhesion and pulling power. The larger the wheel the faster the engine will go, but smaller wheels produce more power, so freight engines tend to have smaller wheels than passenger loco's.

The smaller rods, driven (normally) from the eccentric on the main driving wheel, control the entry and exit of steam from the cylinder (in which the piston runs).
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Old 24th Dec 2010, 20:41
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Old 24th Dec 2010, 21:14
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And the smaller rods are connected to...

…the reversing gear which besides changing the direction of motion is also adjusted by the driver in combination with the regulator (throttle) to maximise the efficiency of the engine, this being achieved by varying the travel of the valves relative to the position of the pistons.

Vaguely similar to the manual advance and retard control often found on the steering wheel of the more aged variety of motor vehicles as well as upon the handle bars of many a motor cycle.
Ah. I remember well the joy in one’s youth of having the right leg severely damaged by trying to start such a two wheeled contrivance omitting to make the necessary adjustments…


jg
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Old 24th Dec 2010, 21:38
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Interesting thread, just shows how much we take for granted on things we thought we already got a grasp on...............but now just thinking about it do the left side and right side pistons drive in sync or is that determined by available traction of each rail?
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Old 24th Dec 2010, 21:55
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Left and right side throws are disposed at 90 degrees from each other. Otherwise locomotive could stop on dead centre and never re-start.

After an excellent landing etc...
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Old 24th Dec 2010, 22:00
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Leaves snow or ice don't stop these buggas.
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Old 24th Dec 2010, 22:00
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No, it's fixed by the relationship between the bits driving the valve gear (return cranks if outside Walschaerts (or in only one case, outside Stephenson's), eccentrics for inside valve gear. Right hand always leads the left hand.

For even quite tight radii (eg 7 chains) the difference between the wheels isn't enough to really worry about, compared with flange wear pulling the loco into the curve. Which is why locos like the Great Marquess suffer a lot of wear running specials from Fort William to Mallaig. 7 chains was the tighest radius in the Feltham marshalling yards.
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Old 24th Dec 2010, 22:03
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Thanks for the reply Flash, It makes sense but what locks them at 90 deg.
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Old 24th Dec 2010, 22:12
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Cranks & Flanges

The driving wheels are mounted on the axles with 90 degrees difference between the opposite sides (called Quartering).

The locomotive (and rolling stock) wheels have a lip, called a flange, on the inner face of the wheel. However the tread of the wheel is tapered and the rails are set at a slight inward angle so that the wheel makes contact with the rail across its width. So when running on straight track the flanges are not in contact with the rails. On higher speed curves the line is raised on the outer edge (superelevation) to keep the flanges from making contact.
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Old 24th Dec 2010, 22:23
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Thanks Yak, I can follow that but I still don't see the mechanical seperation of the "Timing" to keep the drive wheels at 90 deg.
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Old 24th Dec 2010, 23:00
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Hey Guys! -- or maybe, these days, Gals! -- when is someone going to contribute an apercu on the Walschaert (NOTE: NOT Walschaerts, as often misstated) gear? Your locomotive locomotes by its agency ...... one of the prettiest pieces of engineering known to man. First Sea Lord? Anyone?

It would be impertinence for me to make the attempt, but we must have someone here who is up to it.
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Old 24th Dec 2010, 23:15
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More than you ever wanted to know about Walschaert's gear here
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Old 24th Dec 2010, 23:24
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JSP. The "timing" of the inlet of steam into each cylinder is controlled by its own set of valve gear, whether there are 2 or more cylinders (although some use linkage to drive cylinders between the frames - ie Gresleys conjugated drive). All the sets of valve gear are linked to the same reversing lever which sets the same "cut off" to all cylinders. The 90 degree offset is to ensure that there is always a cylinder with a setting that allows movement from stationary - it is possible to have the cylinder stopped where adding steam will not produce movement. (I hope I've explained that right)
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Old 25th Dec 2010, 04:51
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I just knew I'd get a wonderful response on this one.

The locomotive (and rolling stock) wheels have a lip, called a flange, on the inner face of the wheel. However the tread of the wheel is tapered and the rails are set at a slight inward angle so that the wheel makes contact with the rail across its width. So when running on straight track the flanges are not in contact with the rails. On higher speed curves the line is raised on the outer edge (superelevation) to keep the flanges from making contact.

Something I would never have guessed in a hundred years, but even in a thousand years I would never have guessed where my curiosity-piquing would have come from.

After being more than a little annoyed and disappointed with Richard Dawkins, I noticed an hours chat with another Richard, Feynman, in one o them little windows to the right. He talked of vibrating atoms, and elastic bands, then of the difficulty of explaining magnetism, and literally a dozen or more other interesting things, but he went on to talk about being a Freshman at MIT. It seems they were primed to be prepared for some searching questions.

The Tapering of the train wheel's surface must surely have been trial and error. No - even late - Victorian could have worked out the g-forces on the curve, or the precise ratio of circumference needed to cope with the n-chains of curve . . . could they? That is serious engineering.

The side-g, moves the train over so that the wheel surface angle makes the diameter correct for the circumference difference on the inner and outer wheels - am I getting that right?

Oooo...The Rivetess has suggested looking at the moon. One's brain has suddenly failed.

Last edited by Loose rivets; 25th Dec 2010 at 05:39.
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Old 25th Dec 2010, 04:59
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This is not true...but I thought it was funny when I first read it:

American railroad tracks are 56.5" wide (the "gauge") because the English built the first railroads in America and they used that width. Why did they use that width? Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gauge they used. Why did "they" use that gauge then? Because the people who built the tramways used the same jigs and tools that were used for building wagons which used that wheel spacing.

Why did wagons have that particular odd wheel spacing? Because older wagon ruts throughout England used that spacing, and if they changed it, wagon wheels would break by either falling into or being forced out of the old ruts, which were 56.5" wide.

The old ruts were that size because the roads were built by the Romans, who arrived in England in 54 BC and left about 400 AD. Their wagons, and their chariots before their wagons, used that spacing, and that spacing was used all over Europe and wherever Rome conquered, because their wagons used the identical wheel base everywhere. So the modern railroad track width derives from the Roman chariot.

Why was the Roman chariot track width 56.5"? Because that was the width of a chariot that would equal the width of two "standard" Roman horses. Thus, wagon and horses would fit through the same narrow street. Specifications and bureaucracies live forever!

Such curious dimensions continue today. A space shuttle sitting on its launch pad has two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs, made by Thiokol at their factory in Utah. The engineers who designed the SRBs might have preferred to make them a bit fatter, but the SRBs had to be shipped by train from the factory to the launch site. The railroad line from the factory had to run through a tunnel in the mountains. The SRBs had to fit through that tunnel. The tunnel is just wide enough to accomodate a railroad car, and the railroad track is about as wide as two horses' behinds, (and we now know why) so the booster rockets were made to fit.

The major design feature of what is arguably the world's most advanced transportation system was determined over two thousand years ago by the width of a horse's ass!
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Old 25th Dec 2010, 05:10
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(1)This is not true...;
(2) but I thought it was funny when I first read it:
Gordy:

(1) Where is it not true?; and
(2) What is the joke?

Asking out of interest.
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Old 25th Dec 2010, 05:20
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.. but I thought it was funny when I first read it!
"Funny!" Its friggin hilarious dude!

MC Gordy and btw, this is my final month with the service.

HM
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