Single and Double Slip - Difference?

[petejones]

What's the difference between a single and a double slip?

 

Cheers

Pete

[Butler Henderson]

A double slip allows a train entering on either side of, say, its left end to leave by either exit route. A single slip allows a train from one of the entry routes to do the same but from the other entry route it only has one exit route.

['CHARD]

Acknowledgements to Track-Shack for these images:

[jpendle]

A single slip has 3 routes, 2 straight and 1 curved, a double slip has 4, 2 straight and 2 curved.

 

Or looking at it with the slip horizontal. There are 4 tracks Top Left, Top Right, Bottom Left, and Bottom Right.

 

A single slip has 3 routes, TL to BR, BL to TR, and TL to TR (or BL to BR) depending on which way up it is.

A double slip allows all four routes to be set.

 

Regards,

 

John P

[imt]

Just think of a double slip as two points pushed together toe to toe (i.e. the part at which the switch blades direct movement ).  Hence entering a double slip you have 2 possible exits - and there are two possible entrances.

[Phil Himsworth]

2 hours ago, imt said:

Just think of a double slip as two points pushed together toe to toe

I find it weird that a double slip is similar to an arrangement of two points, but the single slip - the lesser of the two in terms of complexity - can only be represented by two points *and* a crossover...

[wasdavetheroad]

Not a difference between a single and double slip is BOTH need 2 point motors but a difference is a single slip needs I peco switch and a double slip needs 2

[Free At Last]

1 hour ago, wasdavetheroad said:

Not a difference between a single and double slip is BOTH need 2 point motors but a difference is a single slip needs I peco switch and a double slip needs 2

Are you saying you can switch both point motors at the same time from one switch?

This will not work with electrofrog single slips, they need to be operated like a double slip for correct frog polarity.

[Butler Henderson]

31 minutes ago, Free At Last said:

Are you saying you can switch both point motors at the same time from one switch?

This will not work with electrofrog single slips, they need to be operated like a double slip for correct frog polarity.

Um… I had a single slip on a layout where I changed the points by a diode matrix so set the route rather than the point and I do not remember any issues with the throw of the single slip when a route that required both motors to be activated was set . Frog polarity can be take care of by a switch on the motor itself or Gaugemaster DCC80s etc.

Edited February 23, 2020 by Butler Henderson

[Titanius Anglesmith]

2 hours ago, Butler Henderson said:

Um… I had a single slip on a layout where I changed the points by a diode matrix so set the route rather than the point and I do not remember any issues with the throw of the single slip when a route that required both motors to be activated was set . Frog polarity can be take care of by a switch on the motor itself or Gaugemaster DCC80s etc.

 

It depends how you’re using the slip, but a polarity issue can exist, as I recently learnt the hard way. 

 

Let’s say the switch toes at end A control the crossing polarity at end B. Therefore end A has to be in the appropriate position to give the correct polarity at crossing B, even for a train traversing the straight route through B (which therefore doesn’t touch the switch rails at A and otherwise wouldn’t care what position they’re in). This would probably be easier to explain with the aid of a diagram. 

 

When the slip is used in its most typical layout as part of a crossover this issue doesn’t arise, but it does when used in other more unusual formations. 

[Joseph_Pestell]

We have been here before on other threads.

 

A slip, whether single or double, is rarely found in isolation. One or both ends will form part of a crossover. So by linking the switching of the polarity simultaneously with that of the other turnout (or end of slip), you should be able to find a simple enough solution - either with accessory switches on the turnout mechanism or by using a multi-pole switch on your control panel.

[Grovenor]

A single slip can be set so that the two routes set form a diamond crossing. Just like any diamond crossing using live frogs the polarity can only be correct for one  the two routes. To avoid this problem the two sets of switches should never be set like that, if used prototypically it will never arise as the interlocking will prevent it.

Rgds

[The Stationmaster]

21 hours ago, Grovenor said:

A single slip can be set so that the two routes set form a diamond crossing. Just like any diamond crossing using live frogs the polarity can only be correct for one  the two routes. To avoid this problem the two sets of switches should never be set like that, if used prototypically it will never arise as the interlocking will prevent it.

Rgds

And equally on a model the controls can be easily arranged to do it prototypically (and thus correctly control the polarity of the frogs crossings)

[Titanius Anglesmith]

My layout is loosely based on Bromley North which has this unusual slip arrangement:

 

 

(diagram from the S-R-S website - https://www.s-r-s.org.uk/html/sra/R1633.htm )

 

The normal lay of the right-hand end of the slip is for the straight route into Platform 1. Unfortunately this sets the wrong polarity for the left-hand crossing when the crossover is reversed (plat 1 to up line). On my layout I’ve got around this by making the normal lay of the R/H slip the other way, towards platform 2 (the home signals are equal height suggesting that both routes have equal status anyway). There were other ways of fixing the problem but this was the easiest for me to implement. 

Edited February 24, 2020 by Titanius Anglesmith
Mixed up the platform numbers

[clachnaharry]

If that layout wasn't real, I would have said it was most unlikely!

[meil]

15 minutes ago, Titanius Anglesmith said:

My layout is loosely based on Bromley North which has this unusual slip arrangement:

 

 

(diagram from the S-R-S website - https://www.s-r-s.org.uk/html/sra/R1633.htm )

 

The normal lay of the right-hand end of the slip is for the straight route into Platform 1. Unfortunately this sets the wrong polarity for the left-hand crossing when the crossover is reversed (plat 1 to up line). On my layout I’ve got around this by making the normal lay of the R/H slip the other way, towards platform 2 (the home signals are equal height suggesting that both routes have equal status anyway). There were other ways of fixing the problem but this was the easiest for me to implement. 

The polarity is set by how you wired it up not its "Normal Lay".

[Titanius Anglesmith]

2 minutes ago, meil said:

The polarity is set by how you wired it up not its "Normal Lay".

 

The polarity of the L/H crossing is set by the R/H switch rail position, and vice versa (obviously). In a true model of Bromley North, the r/h slip would have to be in the reverse position in order to give the correct polarity on the l/h crossing when the l/h slip is also reversed. In the real world conventional interlocking will not allow both ends to be reversed at the same time (or rather there’s no logical reason for doing so). The easiest way for me to satisfy the interlocking was to “flip” the normal and reverse positions of the r/h slip. 

 

(I’ve just realised I’ve been using the word “polarity” rather erroneously, but I’m sure you all know what I meant)

[Flying Pig]

23 hours ago, Titanius Anglesmith said:

Unfortunately this sets the wrong polarity for the left-hand crossing when the crossover is reversed (plat 1 to up line).

 

Do you mean platform 2 to up line via crossover 12? The position of crossover 16 should not affect the polarity of the single slip as you should have an insulated joint between them.

 

22 hours ago, Titanius Anglesmith said:

The polarity of the L/H crossing is set by the R/H switch rail position, and vice versa (obviously).

 

I can see that with crossover 12 reversed and switches 11 normal the polarity of the L/H common crossing of the slip will be wrong, if you change it based solely on the position of 11, feeding from the toe end of each switch.

 

I think you would need to implement a slightly more sophisticated power switching scheme to get the correct polarity with both sets of switches in the straight through position, so your compromise seems sensible, though now of course you need to ensure that 11 and 12 aren't reversed at the same time.

[Titanius Anglesmith]

7 hours ago, Flying Pig said:

 

Do you mean platform 2 to up line via crossover 12? The position of crossover 16 should not affect the polarity of the single slip as you should have an insulated joint between them.

 

You are absolutely right, I did mean  platform 2 and crossover 12.  

 

7 hours ago, Flying Pig said:

 

I can see that with crossover 12 reversed and switches 11 normal the polarity of the L/H common crossing of the slip will be wrong, if you change it based solely on the position of 11, feeding from the toe end of each switch.

 

I think you would need to implement a slightly more sophisticated power switching scheme to get the correct polarity with both sets of switches in the straight through position, so your compromise seems sensible, though now of course you need to ensure that 11 and 12 aren't reversed at the same time.

 

When you say 11, do you mean the other end of the slip? The numbers on the drawing aren’t very clear (at least not to me), but it looks to me like 11 is the trap points on the up siding (loco release). I can’t make out the number on the slip. In any case, yes I’ve interlocked both ends of the slip. 

[Flying Pig]

2 hours ago, Titanius Anglesmith said:

When you say 11, do you mean the other end of the slip? The numbers on the drawing aren’t very clear (at least not to me), but it looks to me like 11 is the trap points on the up siding (loco release). I can’t make out the number on the slip.

 

Yes I do. The numbers aren't clear to me either and I misread that one.  These online plans are only really thumbnails anyway.