Configuring reversing loops in a balloon staging yard

[GaryHinshaw]

Thanks for the feedback gents.  I hope to follow up on this soon but I realize this discussion is hampered by the lack of a valid image.  Alas I'm away on a work trip now and probably won't be able to fix it for a few days, so this topic will probably lie dormant until then.

-gfh

[peteski]

Thanks for the feedback gents.  I hope to follow up on this soon but I realize this discussion is hampered by the lack of a valid image.  Alas I'm away on a work trip now and probably won't be able to fix it for a few days, so this topic will probably lie dormant until then.

-gfh

Gary, with all this hullabaloo about the image not being visible, why not simply upload the image directly the TRW?!  I know the space here is at a premium, but with all the crap you went through, it would make your life easier and entire thread much clearer.

[GaryHinshaw]

Good point.  I actually forgot about that feature...    Done.

Now, to Martin's question: there could be up to 4 trains or loco sets crossing gaps at any given time, so 4 AR's seems correct.  There are only two mainline trains coming or going at a time, but there could be one or two loco sets tying on to their trains at the same time.  (I have not shown the loco service tracks on the schematic, but they hang off the two inner ladders, and I think this violates one of jb's assumptions.)

Since I have 4 AR boards available, I am not especially worried about reducing the number further than that.  I am mainly worried that I am introducing an operational restriction compared to having 8 independent AR's, but I don't think I do.

Gary, I'm going to assert that with your new track plan you only need 3 ARs:  one each for the outside throats, and one for the two middle throats,

Don't I still have the "short block" problem with this scheme?

[John]

Gary .. I'd like to see your upstream track layout before I can comment further .. but I'm a believer in keeping as simple as possible .. if you can give us a diagram showing the approaches, that will help

[jagged ben]

Gary, after seeing your image in the first post, and finally grasping your proposal, I think that's a very elegant solution.  There's two potential operational constraints I can think of, but they both seem very minor.  First is that if you bring in a train with rear-end helpers onto a staging track, and then wish to move both sets of power to the engine terminals, the lashups will have to take turns leaving the track.  But unless you have an overabundance of eager hostlers, I see that problem hardly ever popping up in an actual ops session.  The second constraint is that if you ever decided to try to use one track for two trains facing opposite directions, (e.g. passenger and/or locals) they'd again have to take turns.  But that seems outside your planned staging scheme and not likely to crop up often even if you changed the scheme. 

So at least for your outside 4 tracks, I won't say I can think of a better solution. 

I do want to speak to this, though, for the inside half...

Don't I still have the "short block" problem with this scheme?

...because actually this issue is easily solved with X-blocks.  And not only did I promise you an X-block circuit diagram a long time ago in your build thread, but I actually drew it up last night before I revisited this thread and thought through the above.  So here goes...

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You could put these on your inner yard leads like this (one X-block on each side), and have one AR for the entire inner yard beyond those crossovers.

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 When the turnout is closed it the X-block section would be part of the AR.  When it is thrown, it would be part of the unreversed mainline.   If it were my layout, I'd be inclined to go with this on the inside of the yard.  And not because it lessens the number of ARs required, but rather because it 100% eliminates all polarity related operating constraints.   For example, if you ended up running a train that was a bit too long for your staging track, you could overrun into the yard ladders and then remove the power, even if you had rear-end helpers.  Since these are your shorter yard tracks that might be an actual advantage.

[GaryHinshaw]

Ok, I finally had a chance to think this through and I really like jb's X-block proposal!  Now, let me make sure I understand it correctly. 

Here is a redraw of my original proposal, with some more trackage added, per John's request, and a new colour coding for the AR sections:



Here each colour represents one of four AR sections, and solid and dashed lines indicate opposite relative polarity.  This has the operational restriction that one cannot cross gaps at both ends of a given yard track simultaneously.  As noted before, this is not a serious limitation, but it does require some care.  The opposite polarity of neighbouring tracks does allow one to cross gaps onto, e.g. track 8 on the top and track 7 on the bottom simultaneously, while cutting the number of AR blocks in half.

Now, if I understand jb correctly, he is proposing the following blocking:



where now the inner yard is under one AR and there are two X-blocks, A and B. When crossover A is closed, X-block A is fed by the green AR bus, and when crossover A is thrown, it's fed by the fixed mainline bus.  Similarly for X-block B.  The only move that could ever cause a polarity problem in the inner yard is when the gaps on the left side of blocks A and B are crossed at the same time, but this is precluded because it would be a fouling move.  Very elegant!

Comments and/or further suggestions are welcome.  And thanks for the valuable feedback!

-gfh

P.S. For reference, I have compiled the clear lengths of the 8 staging tracks from the inner to the outer.  In general, there won't be many trains exceeding 14', but there may be some. The X-block scheme accommodates those cases better.

BNSF arrival / UP departure:
1 - 14' 4"
2 - 14' 1"
3 - 14' 6"
4 - 15' 5"
UP arrival / BNSF departure:
5 - 16' 4"
6 - 16' 1"
7 - 16' 5"
8 - 17' 2"

Jan 2020 - repaired broken image links -gfh

[GaryHinshaw]

By the way, does anyone have a favourite 2-pole relay they could recommend?

[Cajonpassfan]

My head hurts
With the brilliant X-block idea, isn't there a simpler way to do the reversing on the approaches rather than the balloon tracks?
Otto

[GaryHinshaw]

Not that I am smart enough to figure out...   (And recall that I want to avoid less-than-train-length AR sections.)  How did you configure the reversing sections in your yard Otto?

-gfh

P.S. @jagged ben, shouldn't one of the DC leads be connected to pin 4 on the Tortoise, rather than 2 or 3?

[Cajonpassfan]

Gary, both of my staging yards have a single AR section on approach, but the approaches are long enough to accommodate  a "long" train. Barstow was easy, it's a one way staging yard, and the AR block is the last one before the yard is entered. (Pic below, before it was finished. The track on the left is the E\B inbound main/AR block).

LA is more complex, in that it has three two directional tracks going in, but again there is enough length for a train in the AR approach blocks. Two of the three tracks require reversal but for now I only have one AR for both, see sketch. I suspect I may need to add another AR for the 2nd District main if it turns out to be an operational problem; not there yet. The last shot is of the LA Jct. crossovers where the AR block starts (marked with black ink).

The thought I had was that you could minimize the number of AR blocks (there is always fewer approaches than staging tracks) if there was a way to use the X block to get around the crossover/short block issue. My gut is telling me there is, but my brain isn't cooperating at the moment...
Otto K.

[Cajonpassfan]

The thought I had was that you could minimize the number of AR blocks (there is always fewer approaches than staging tracks) if there was a way to use the X block to get around the crossover/short block issue. My gut is telling me there is, but my brain isn't cooperating at the moment...
Otto K.

Well Gary, instead of working on my own layout, like i should have, I didled and doodled around with yours, and it turns out I'm not smart enough either. Too many crossovers within your design train length, and to overcome that, with multiple possible routings, would complicate and not simplify the problem. My gut led me astray again.
Never mind then
Otto

[eric220]

@GaryHinshaw for the second plan with the X blocks, I'm having a hard time seeing what advantage the X blocks have over just wiring blocks A and B outside the reversing section (make them black track). It doesn't seem possible to enter both sides of the inner yard simultaneously, since both tracks come off of one turnout, so just a simple reversing section covering the yard should do it.

Put another way, under what scenario do blocks A and B need to be part of the AR section, as opposed to fixed polarity?

[GaryHinshaw]

Thanks for trying Otto, and for posting your approach to the problem!   

Put another way, under what scenario do blocks A and B need to be part of the AR section, as opposed to fixed polarity?

Good question Eric.  The scenario I had in mind was loco hostling: the inner stub tracks are loco service, and the X-blocks are long enough to hold a loco consist between the turnouts.  So a loco set coming out of the BNSF (upper) stub could occupy X-block A, then back into the departure (upper) yard via crossover A.  At the same time, a UP train could depart the inner (lower) yard on track #1 through X-block B and there would be no polarity conflict.   The BNSF loco set would be contained within the reversing section while crossover A is closed, then the X-block will switch to fixed polarity when the crossover is thrown.  So if those two moves happen at the same time, the two trains never cross both ends of the AR block at the same time.  If the X-blocks were permanently fixed polarity or permanently under AR, that could happen (and you would have routes with short AR sections in the latter case).

So, for the price of a few relays and a bit of wire, you buy a fair amount of flexibility.  It's a really nice solution!

[eric220]

Fair enough! Carry on. 

[jagged ben]

Gary, glad you like the suggestion.      And yes, I was thinking about your loco hostling too or I might not have suggested the X-blocks as being so worthwhile.

Note that the X-block circuit is similar to what can be applied to your Mojave staging as we discussed along time ago in your build thread.  For three tracks you need to nest one X-block inside the other but we can re-visit that whenever you want. 

...

P.S. @jagged ben, shouldn't one of the DC leads be connected to pin 4 on the Tortoise, rather than 2 or 3?

Yes, that's correct.  Show's how long it's been since I actually wired a Tortoise.     I'll try to correct the drawing when I have a bit more time.