Hump Yard Operation


ThirteenHorsehoes said:
Sorry to revive an old topic, but I'm a new forum member and currently working on a small hump yard.

My background includes physics...

more prototypical would be to use a pressure sensor placed under the track section at the top of the hill to weigh each car at the top to predict the speed at the bottom -- but there's more room for error there due to differences in the rolling friction of each car
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Physics, eh? That sounds like a repeat of Galileo's demonstration that heavy objects fall faster than light ones. Or am I remembering it right?

As always in these discussions, it's all about "retarders". Folks, why are retarders needed or used? To slow the cars down, you say. Then I'll ask why the cars were going so fast to begin with. And there never seems to be an answer to that.

Once I calculated how high a hump should be on a model railroad in order to get cars rolling at a scale speed. The result was so absurd that I ended up repeating the math three times. It's a good demonstration of how gravity and energy don't scale well.

I think any model hump yard that involves cars running much above scale speed has already failed. If I can't figure out a way to keep the speed realistic, I will never build one (and so far it hasn't happened).
 
The reason real railroads build hump yards is so they can switch thousands of cars per day. Does a model railroad really need to switch 100's of cars a session? When you combine all the problems with getting it to work, is it really even worth it? A well designed flat yard can handle a couple hundred cars a session.
 
Larry Keeler (Kansas City area) had an operating hump yard back in the 80's. He experimented with every combination of wheel sets and side frames to get consistant free-rolling characteristics that he demanded. He also wrote a computer program to completely run his layout, including the hump yard. I want to think that he used air to retard the cars, but I can't confirm it. The layout is long gone along with his CTC-80 systems.
 
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As someone stated back in the earlier activity of this thread, Ed Ravenscroft did start using an air retarder system on his hump yard back around 1960. It must have worked well, because he was still using it in 1972, when the then editor of MR, Linn Westcott, visited him for an interview. I remember the cover, as it was a picture taken overhead of the yard with a fish eye lens.

The basis for his system was a series of air jets, that were located on the hump track and at the start of each individual bowl track, IIRC. The yard was either curved or 'S' shaped.

Ed had to build a series of what I think he called air headers. These were made out of brass and could contain up to 12 separate air nozzles, again made from brass tubing, soldered at an angle, into holes drilled into a larger piece of tubing. There were different number of nozzles per header, depending on where it was located. These were mounted between the tracks, and blew up onto the car at a preset pressure set by a regulator, off of a shop air compressor. The controls consisted of simply of an on off valve, that the yard master would turn on or off for each individual car, as it rolled down the hump.

Ed was very innovative at the time, even selling pre-made headers and valves to anyone who wanted to use his system. Ed said the yard was his favorite place to operate on his entire layout. He even went as far as to modify horn hook couplers with uncoupler levers and better springing to make them ultra-reliable. Of course he settled on one brand of couplers, rail-lines, which were metal.
 
Cjcrescent said:
As someone stated back in the earlier activity of this thread, Ed Ravenscroft did start using an air retarder system on his hump yard back around 1960. It must have worked well, because he was still using it in 1972, when the then editor of MR, Linn Westcott, visited him for an interview. I remember the cover, as it was a picture taken overhead of the yard with a fish eye lens.

The basis for his system was a series of air jets, that were located on the hump track and at the start of each individual bowl track, IIRC. The yard was either curved or 'S' shaped.

Ed had to build a series of what I think he called air headers. These were made out of brass and could contain up to 12 separate air nozzles, again made from brass tubing, soldered at an angle, into holes drilled into a larger piece of tubing. There were different number of nozzles per header, depending on where it was located. These were mounted between the tracks, and blew up onto the car at a preset pressure set by a regulator, off of a shop air compressor. The controls consisted of simply of an on off valve, that the yard master would turn on or off for each individual car, as it rolled down the hump.

Ed was very innovative at the time, even selling pre-made headers and valves to anyone who wanted to use his system. Ed said the yard was his favorite place to operate on his entire layout. He even went as far as to modify horn hook couplers with uncoupler levers and better springing to make them ultra-reliable. Of course he settled on one brand of couplers, rail-lines, which were metal.
Click to expand...

Darn! Forgot about Ed's layout. It was in November 1961 MR.
 
John P said:
Physics, eh? That sounds like a repeat of Galileo's demonstration that heavy objects fall faster than light ones. Or am I remembering it right?

As always in these discussions, it's all about "retarders". Folks, why are retarders needed or used? To slow the cars down, you say. Then I'll ask why the cars were going so fast to begin with. And there never seems to be an answer to that.

Once I calculated how high a hump should be on a model railroad in order to get cars rolling at a scale speed. The result was so absurd that I ended up repeating the math three times. It's a good demonstration of how gravity and energy don't scale well.

I think any model hump yard that involves cars running much above scale speed has already failed. If I can't figure out a way to keep the speed realistic, I will never build one (and so far it hasn't happened).
Click to expand...

The reason for retarders is that not all cars will roll the same speed. The hill has to be steep enough to get the most difficult car rolling fast enough to reach the yard tracks. In doing so the easier rolling cars would be moving too fast and need to be slowed down. You can't adjust the grade of the hill.

I agree that they're going to move too quickly no matter what, but modeling a hump yard is an interesting idea, and I'd like to see someone build a highly reliable and functional one.
 
I've seen 2 HO scale operational hump yards, within the last few years, here in NJ. One is on the HO scale layout of the New York Society of Model Engineers, in Carlstadt, NJ. Their current layout was started about 1990 or so, as I recall. You can see some photos of the end opposite the hump, here: http://www.modelengineers.org/Pictures.htm. As I recall, it has about 4-6 tracks in its bowl, and is part of a larger yard. In the photos, shops are adjacent to the flat end of the bowl. On their previous layout, they also had a hump yard, with about 12 tracks. The last one had 'air retarders.' If the car was light weight, the car could be shot back up the hump. The current version seems to be refined some, with a smaller bowl. I'm not a member of the club, so can't provide any 'insider' info, besides what I've observed during open houses.

The other one I've seen is on the Pacifc Southern, in Rocky Hill, NJ. It dates back to the 70's or early, when the original owner built it. Don't know how it works besides, 'gravity.'

My recollection is that the Pacifc Southern hump is higher than the one at the NYSME. The NYSME I'd guess is about 4-5" at most, as a yard lead runs underneath it to a flat yard.

Observation leads me to believe that having properly weighted, free running cars, with a modest bowl (6-8 tracks at most) will improve operations.
 
This is a long running thread, and I stand by what I said on 12-25-2008.

But I'm at the club right now, and we have 60 years of Model Railroader. I looked through Ed Ravenscroft's 1961 article. It's fascinating stuff, and he did a lot of work. There actually was automation, including counting of cars and a timing system that only hit the cars with air if they were going too fast. No electronics except a photocell, and even that was optional--he started with a whisker operating a microswitch to detect cars.

Because it was Christmas Day when I posted in 2008, I finished with "Hump yard? Bah, humbug." Indeed.
 
Also because of different car weights. A loaded hopper would roll faster than an empty one, and a 60 foot box car would roll faster than a 50 footer.
 
Dave S said:
Wouldn't it also be because the first cars have further to travel along the siding than the last ones do?
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Yes I suppose you're right. But they typically have a locomotive on the opposite end of the yard that's constantly grooming the tracks - making sure all the cars are coupled and re-positioning them within their track.

I've been to the North Little Rock yard a few times to watch trains roll over the hump.

http://goo.gl/01onL

It's pretty cool to watch. Their yard has 64 ... SIXTY FOUR tracks. Each track only holds a couple dozen cars and trains leave with 80 to 100 cars on them. I assume the sorting includes what position within the departing train the cars need to be in and a departing train is actually multiple hump yard tracks. So as cars roll over the hump, even if they're destined for the same next yard, they're sorted by front / middle / end of the departing train. So in 64 tracks they're really only making 20 or so trains. This way they can keep the heavier cars at the front, lighter cars at the back, or have them presorted a little for the next yard so that they're less work to do there when building the next set of trains.

I can only imagine what it would cost to build something like the NLR hump yard in HO scale. Not even counting all the surrounding track, it's probably thousands of dollars in track alone. I estimate about 1500' of flex track and 128 custom turnouts. Shiza ... The real problem is, it would be more than 10' wide. Probably 12' or more, so you better get that track right or have a plan of how you're going to reach the middle with an over-head crane or something! :D
 
That is pretty massive. Guess that's what selective compression's for!

The inertia problem comes up in Armstrong's track planning book, in figuring out how to do a 'flying switch' (think that's what it's called?) where you dry to coast a car into a facing-point spur without a runaround. IIRC he suggested some kind of flywheel setup on an axle. It might be a little tough to hide the weight, but I suspect it might carry the car farther than just sticking weight inside. Maybe wrap a couple layers of thin solder around the axle, and give that a whack.

Technically, gravity accelerates all objects at the same rate. Discrepancies in car speed are probably due to friction... plastic wheels, tight bearings, crud on the treads, flange depth, electrical wipers, etc.
 
With a hump yard all the traffic goes one direction only. I don't know if real hump yards are sloped more than the hump area, but in a scale model I'd have it sloped quite significantly past the half way point of the yard tracks. That would help keep the cars rolling. The trick would be finding the right amount of slope that would roll the cars but not roll them so fast that they continue to accelerate.
 
the hard part is knowing what's the hard part

Thanks for all of the responses to date...great food for thought

while we don't put enough cars through to "need" a hump, our local yards (plural) have hump(s) (plural) so the kid has been asking for one on the layout -- hey, how hard could it be?.......(groan)

plus, it's still a faster way to sort than a lot of back and forth movements into and out of our flat yard -- BTW our flat yard, as you might have guessed, consists of 13 double ended tracks laid around a horseshoe curve -- to satisfy our superstitious customers

granted that on the layout we have much less space available for a hump, but then we don't need a cross under so it will be a small hump with 4-8 tracks in the bowl -- I've test rolled cars down different slopes -- we use all metal wheels -- so far, no cars failed to roll on 2%, will try less

on the how to make it all work issues....

I was thinking about some form of brush moved by a servo to apply friction -- so I thought the control system would be the main problem -- calculating how much friction is needed for each car

physics first -- it does seem that the weight of the car shouldn't matter for the speed at the bottom of the hump since "mass" appears in both the PE and KE equation it cancels out when the PE at the top of the hill becomes KE at the bottom of the hill -- in a frictionless world it should be the same for all cars

the main problem does seem to be that there will be different distances to roll on each bowl track while each car has roughly the same starting speed as it begins rolling down the bowl track (before being retarded)

that means different decelerations are needed for each car -- and by F=ma that means different friction forces for each car to cause the decelerations, which will also depend on the different mass of each car -- so it still seems to me that the cars need to be weighed at some point

the prototype makes one speed adjustment to slow cars down when they have less distance to roll, so once in the bowl track, a relatively constant amount of friction can (nearly) stop them in less distance (so they aren't going too fast when the reach stopped cars) -- they don't count on the rolling friction in the bowl varying for different cars (unless the wind becomes an issue)
 
ThirteenHorsehoes said:
Thanks for all of the responses to date...great food for thought

while we don't put enough cars through to "need" a hump, our local yards (plural) have hump(s) (plural) so the kid has been asking for one on the layout -- hey, how hard could it be?.......(groan)

plus, it's still a faster way to sort than a lot of back and forth movements into and out of our flat yard -- BTW our flat yard, as you might have guessed, consists of 13 double ended tracks laid around a horseshoe curve -- to satisfy our superstitious customers

granted that on the layout we have much less space available for a hump, but then we don't need a cross under so it will be a small hump with 4-8 tracks in the bowl -- I've test rolled cars down different slopes -- we use all metal wheels -- so far, no cars failed to roll on 2%, will try less

on the how to make it all work issues....

I was thinking about some form of brush moved by a servo to apply friction -- so I thought the control system would be the main problem -- calculating how much friction is needed for each car

physics first -- it does seem that the weight of the car shouldn't matter for the speed at the bottom of the hump since "mass" appears in both the PE and KE equation it cancels out when the PE at the top of the hill becomes KE at the bottom of the hill -- in a frictionless world it should be the same for all cars

the main problem does seem to be that there will be different distances to roll on each bowl track while each car has roughly the same starting speed as it begins rolling down the bowl track (before being retarded)

that means different decelerations are needed for each car -- and by F=ma that means different friction forces for each car to cause the decelerations, which will also depend on the different mass of each car -- so it still seems to me that the cars need to be weighed at some point

the prototype makes one speed adjustment to slow cars down when they have less distance to roll, so once in the bowl track, a relatively constant amount of friction can (nearly) stop them in less distance (so they aren't going too fast when the reach stopped cars) -- they don't count on the rolling friction in the bowl varying for different cars (unless the wind becomes an issue)
Click to expand...

I don't know what is standard for hump design but the North Little Rock yard is designed such that each car rolls through two retarders. One is before the first turnout (which happens to be a three-way), and then there is a second retarder on each of eight intermediate legs. I suppose that is multi-purposed. Main purpose is to more accurately tune the speed of cars as they come down the hill, and the second is so that they can do maintenance on a second tier retarder and just shift traffic to one of the other eight sets of track (which then break out in to eight more tracks each).
 
LoudMusic said:
I can only imagine what it would cost to build something like the NLR hump yard in HO scale. Not even counting all the surrounding track, it's probably thousands of dollars in track alone. I estimate about 1500' of flex track and 128 custom turnouts. Shiza ... The real problem is, it would be more than 10' wide. Probably 12' or more, so you better get that track right or have a plan of how you're going to reach the middle with an over-head crane or something! :D
Click to expand...

I'd bet that if anyone did (successfully) make one it'd be an instant hit at all the train shows! :)
 
Speaking of what might be popular at shows, here are a couple of pictures of a model hump yard that was exhibited at the Springfield show for a few years. I'd describe it as "looked great, ran awful". The yard is still part of that group's layout, but at some point they tore the hump out and made it into a flat yard.

http://files.myopera.com/John98wbr/albums/661338/dryhill2.jpg
http://files.myopera.com/John98wbr/albums/661338/dryhill1.jpg

I wonder if that's Mom holding the control for the air jets. She's doing her best, but she doesn't seem too confident.
 
humping w/o retarder control -- works so far

I've spent some time seeing what I could do with the hump yard before resorting to a control system and retarders

only room for 4 tracks at the moment -- one Y switch and 2 number 6 switches --

So far, it seems to be working pretty well with the following set up:

I used a long piece of thin flexible Masonite as the base for the track with shims underneath so I could adjust and vary the grade to make the bowl curve in the vertical as needed to get the slowest possible speed at each point along the bowl --

I started from the bottom of the bowl, working back toward the hump and adjusted the slope / height of each short 6-12 inch section of track so that a properly weighted car with free rolling metal wheels will just barely start moving and keep moving at a fairly steady slow speed down the rest of the bowl --

the slope gets ever-so-slightly steeper toward the top of the hump where the switches are -- the cars keep moving at a nearly constant slow speed -- because there is very little net force down the hill -- friction is very nearly balanced by gravity parallel to the hill-- it even looks realistically close to walking speed -- almost stopping, but not stopping -- almost want to push, but don't need to -- the acceleration is slow enough not to be noticeable -- the cars are moving slow enough to couple without a huge collision anywhere along the gentle slope --

the bowl is relatively short so far -- only about 9 feet of space to play with yet -- and the hill is very short -- no underpass -- can't say what the exact slope is yet -- somewhere under 1% -- the shims make up for an uneven surface underneath -- (since the floor isn't level and the "benchwork" is modular) --
 
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