Double slip switch workings?

[train2]

I have not spent a lot of quality time around a double slip switch to watch them in operation. I have always been curious how these things work differently from a normal turnout? How many switch machines are needed? In photos they look like 4 sets of points. Do any other parts move? Do they have anything like a movable frog that requires a switch machine?

And from the dispatchers/tower operators point of view does the switch have more than two positions: normal and reverse?

[Jersey_Mike]

I have not spent a lot of quality time around a double slip switch to watch them in operation. I have always been curious how these things work differently from a normal turnout? How many switch machines are needed? In photos they look like 4 sets of points. Do any other parts move? Do they have anything like a movable frog that requires a switch machine?

There are 4 sets of points, but they are connected to the point machines in sets of two (a pair on each end) and move in unison. You can see in the picture there that the throw and detection bar arrangement are more complex than a normal set of points, but still work in the same Normal/Reverse fashion.

Double slip switches only need two point machines to work, but usually have three with the center machine attached to a movable point frog. Movable Point Frogs are equipped anywhere trains move faster than slow speed.

The action of the Movable Point frog is different from normal point machines as there is a simultaneous push and pull movement to normal one set of rails and reverse the crossing set.

And from the dispatchers/tower operators point of view does the switch have more than two positions: normal and reverse?

Double slip switches are levered as two sets of points just as if one had two turnouts back to back in a ladder formation. Doubleslips serve the same function, just in a more compact setup. For example you can see the numbering of the doubleslip ladder at PENN interlocking on a diagram. A better example is the model board in PAOLI tower where the 15/17 and 17/19 double slips were converted to single turnouts with no modification to the model board or interlocking machine being necessary.

[train2]

Jersey Mike,

Thanks for the photos, they help but I would like to understand a few things:

In reference to the normal and reverse: are there not 4 routes through the plant? So would the DS have to make two reverse line ups to get both sets lined for the diverging moves?

And to further that point when in reverse is the switch set so that both sides of the diverging routes can be used? (based on which way the DS has lined the signals) without any additional lining of the points?

What I am trying to understand when the routes conflict within the switch?

Got two photos of one of these set to normal and then reverse from the save prespective?

[krispy]

Last tower that had a switch to throw a slip (for a tower operator) was Nassau's old strong-arm machine. Crossing a Bay from 2 track in Mineola station was a flurry of activity, as you had to throw the 3 unlocks in sequence, (big blue levers that had additional mechanisims mounted to the side that buzzed if they weren't happy with the indication) then you tossed 3 black switch levers, 23 switch (No 1 OYB to ML 1), 27 slip (IIRC) and then 25 switch (both these were for the switch to go from ML 2 to OYB 2), then you threw back the switch locks to lock up the route and then you'd go for the signal. If you were a brand new op poster scared @#$%less of screwing up, it was a great way of blowing off steam. Throw them too hard and the Maintainer would speak up with some choice words. New machine combined all of that with just 2 buttons. Rest of the machines do the same thing, just use 1 button/lever for a combination - Normal or reverse. If one part of that combination did not have "correspondence", it would not let you get "full" indication, so you call the maintainer and they would figure it out.

Jay and Hall have some interesting frog/slip/switch combinations, but they would be controlled by 1 lever. You had no idea what switch had frogs/slips or whatever until switch inspection, when the fellas had to test each mechanism, so testing certain levers would be endless ordeals of tempting carpal tunnel.

[Jersey_Mike]

In reference to the normal and reverse: are there not 4 routes through the plant? So would the DS have to make two reverse line ups to get both sets lined for the diverging moves?

Reversing both levers would line the DS for the "diagonal" move. As I said, a single doubleslip has the same logical function as two normal turnouts in a ladder configuration.

And to further that point when in reverse is the switch set so that both sides of the diverging routes can be used? (based on which way the DS has lined the signals) without any additional lining of the points?

I don't know what your trying to ask there.

What I am trying to understand when the routes conflict within the switch?

All 4 point blades on a given double slip end are attached to the same point machine and move in unison. As you can see in this picture there is only ever one valid route through a double slip at a time, even if there aren't MPF's. If the ladder route is set straight through both main routes are set to diverge into a set of points set against it. Again, just think of two single turnouts back to back in a ladder configuration. How many valid routes can you set through those? Just one at a time with two "sets" of points being normal or reverse. Double slips works the same way.

Got two photos of one of these set to normal and then reverse from the save prespective?

I don't believe so.

[ex-tc driver]

Bayridge Yard had hand thrown slip switches when the float bridges were active. I dont believe Nassau ever had a slip switch ,the switch thats is there now is a movable point diamond frog on Mainline # 1 connecting to Oyster Bay # 2 .

[nyandw]

http://www.trainsarefun.com/lirr/jamaica/jam1970.gif
Jamaica Diagram with 1970 slip switch indications

[train2]

Look at this photo for an example of my question: are both diverging routes usable at the same time?

http://www.railpictures.net/viewphoto.p ... 74&nseq=49

What still has me confused is IF the switch only has two positions -- normal and reverse positions -- look at the points in this photo which is lined diverging from the track the train is on to the right. Now look at the opposite diverging route on the opposite side of the switch. I am thinking of a move that would be coming toward the camera on the track this train is on (but not at the same time) and diverging to camera left. This move would have a train coming toward the camera and turning to the opposite direction from the direction this train will end on on the track it is now routed toward. However the points on the opposite side of the switch don't make a through route with the switch set in what I would call reverse. Almost looks like the switch needs a position called reverse-reverse.

So in my mind the dispatcher looks like he has 3 different moves the switch has to make to line up each possible route. Normal and reverse would be only two.

What I was beginning to think based on some of the responses so far was with only two positions when normal you could move through the switch straight on either straight move (like crossing on a diamond) and when in reverse both of the diverging points would move so that trains would make both diverging routes possible. However this photo doesn't seem to support that theory.

Looks like the DS board needs a minimum three positions if not four. I am afraid I can't see the model board photo well enough to understand the options.

[Jersey_Mike]

Look at this photo for an example of my question: are both diverging routes usable at the same time?

Ha, that's another one of my pictures and no both diverging routes are not usable at the same time. The points on each side of the doubleslip are all connected to the same motor and move in unison so that when the straight route for one track is set the other track is set to diverge.

What still has me confused is IF the switch only has two positions.

A doubleslip switch is TWO switches, each with a normal and reverse, that is 4 positions for each of the 4 routes through a double slip. Each point machine is thrown by a separate "lever" (with the optional MPF having its own logic).

What I was beginning to think based on some of the responses so far was with only two positions when normal you could move through the switch straight on either straight move (like crossing on a diamond) and when in reverse both of the diverging points would move so that trains would make both diverging routes possible.

I have said plainly that only one route is possible through a doubleslip at a time. The points on either end are connected in such a way that precludes multiple valid routes being set, even without an MPF. The 4 blades are thrown in unison. Look at the clseup of the point rodding in my initial reply to see how it works.

[train2]

Making some progress.

In this photo would you say the near points are normal or reverse?

http://acm.jhu.edu/~sthurmovik/Railpics ... Ladder.jpg

To me looks normal for the train you are riding and reverse for the track at right at the same time?

The may be a major point but the points on each end throw separate from the points on the opposite end of the switch. I was thinking of conventional CTC crossover, say a crossover between two mains, where both points at each end of crossover throw in unison. I see the two close points are on the same push/pull bar in your first photo example.

The more I study all the photos it looks like the switch is half thrown for a diverging route at all times when normal? Then it only takes one set of points to throw and not both (meaning points on opposite ends together) to make a diverging route?

From the model board it would be just two switches with N and R that just happen to be close together?

[Gerry6309]

Double Slips are vital for routing trains into a major terminal, but are a major no-no on a main line. Because of the number of moving parts the straight moves operate at restricted speed and the diverging moves even slower. Only one train can operate through a double slip at the same time. Otherwise you get a train wreck of major porportions. If you move the switches outside the diamond crossing, you can then operate opposing diverging moves since the connecting rails are totally seperate. This type of connection is more of a quarter grand union, since all switches are seperate

[pennsy]

Well, you all have the general idea of how the double slip switch works, and why they are needed. At Los Angeles Union Station, you come into the station through a series of double slip switches. Spoke to one Metrolink engineman once and he called them "Puzzle Switches", because they have so many parts to them. In any event, if you needed to get the train from track 12, all the way over to track 3, you would need to traverse several Puzzle Switches. And at a speed less than 20 mph. The train would wend its way through the maze like a snake, and eventually get to the proper track. These "fancy" switches are used extremely frequently, daily. I will venture a guess that you cannot enter LAUS without traversing one of these Puzzle switches, at least.

[train2]

I realize two trains can't use one switch at the same. I hope my examples didn't give anyone that idea.

If you have no experience with them, they take a few studies to understand how they move.

[Jersey_Mike]

In this photo would you say the near points are normal or reverse?

http://acm.jhu.edu/~sthurmovik/Railpics ... Ladder.jpg

To me looks normal for the train you are riding and reverse for the track at right at the same time?

Normal and reverse are terms only defined for the switch's frame of reference. You can't just look at a switch and know which direction is "Normal" (although it is usually intuitive which is which). In the case of the K ladder at ZOO you first look at the diagram. You see that the first double slip is controlled by levers 69 and 71 and the second double slip by levers 71 and 73. To route a train straight down the K Ladder you reverse 69, 71 and 73. Trains going straight down the 36th St connector would see those 3 levers set normal. Any move between the lines would see one lever normal and the other reverse.

I was thinking of conventional CTC crossover, say a crossover between two mains, where both points at each end of crossover throw in unison.

A double slip represents two adjacent crossovers, not the same one. On the K ladder the 71 switch is part of two different double slips.

The more I study all the photos it looks like the switch is half thrown for a diverging route at all times when normal?

I wouldn't necessarily call it being "half thrown", but a double slip is two switches in one. To switch a train from one route to the other requires one half of the double slip being normal and the other reverse.

Then it only takes one set of points to throw and not both (meaning points on opposite ends together) to make a diverging route?

Well you need to make sure that the second set of points aren't set against the movement. On the K-ladder if you normal 69 trains will diverge onto the 36th St connector, but if you leave 71 normal a train would run through the other set of points so you need to reverse 71 to have a valid route.

From the model board it would be just two switches with N and R that just happen to be close together?

Yes exactly. You have seen how double slips are diagrammed on model boards and track charts, right?

[RearOfSignal]

To me looks normal for the train you are riding and reverse for the track at right at the same time?

Puzzle switches, double slip switches, butterfly switches etc. you can only be lined for one route at a time. If you're lined straight through a puzzle switch, all the other routings through the switch not cocked. At least one of the points through the switch are not lined properly. You cannot have two clear routings through a single puzzle switch at the same time.