Delayed (or Delay) Action Tension Lock Uncoupling Solutions

Tension lock coupling is very common in model railroad rolling stock for the simple fact that the vast majority of locomotives, wagons, trucks and carriages come equipped with a tension lock coupling of one type or another.

The simple tension lock is easy enough to understand - each coupling has a little hinged hook that pops up and over the bar of the coupling on the opposite number. In this way, each coupling links to the other in a secure fashion.

Before exploring the world of delayed action (or delay action) tension lock uncoupling, it's worth taking a quick refresher in standard manual and semi-automated tension lock uncoupling techniques.

Tension Lock Manual Uncoupling

The trouble is that when it comes to separating the rolling stock, a manual approach must be taken. The little hooks need to be lifted up, at the same time, and the locomotive driven away to separate it from the rake.

Many model railway enthusiasts have come up with a variety of ingenious hooks and bars that can be used to decouple the tension locks, but most of them require some kind of unprototypical intervention.

Model railway manufacturers have also added their own solutions - usually taking the shape of decoupling ramps or between the rails devices to aid uncoupling in a semi-automated way. 

Tension Lock Auto-Uncoupling

For many, though this isn't enough. Automating the tension lock uncoupling process has become a preoccupation of many model railroad operators. 

For example, Brian Kirby (see Brian Kirby Uncoupler Variations) has developed a fairly sophisticated do-it-yourself magnetic decoupling solution, that can be enhanced using movable and electro- magnets.

This technique requires that non-metallic (or at least, non-magnetic) tension lock couplers are used, ruling out the many owners of Hornby rolling stock. Even there, though there is a solution (see How do I Convert Old Hornby Couplings to New Type) but it requires changing the couplings themselves.

If you're going to do that, some might argue, why not go the whole way to fully automated, delayed action tension lock uncoupling solutions?

Delayed or Delay Action Tension Lock Uncoupling

Delayed action (or sometimes delay action) tension lock uncoupling is a way of automating the uncoupling process such that the uncoupling doesn't actually take place until the direction of the rake is reversed, allowing the loco to separate.

Imagine an Inglenook switching puzzle. With regular uncoupling, some kind of uncoupling device has to be placed at each fork so that trucks (wagons, or carriages) can be spotted on any one of the sidings.

As the article Inglenook Kadee Magnet Placement Advice points out, delayed action uncoupling allows a single uncoupling device to be placed at the throat of the Inglenook, and rolling stock spotted in any of the sidings.

To achieve all of this, the most common solution is to use something called a knuckle coupling. The most popular manufacturer is Kadee (see the blog post on adding Kadee couplings to rolling stock.)

There are other solutions, which we will examine in future posts. On a personal note, I have used Kadee and the Brian Kirby alternative, and have found that both have their uses, with a slight preference to the simplicity (and cheapness!) of the Kirby magnet uncoupling solution.

Inglenook Kadee Magnet Placement Advice

Many of us, especially those of us with a shelf switching layout, have an Inglenook. Kadee magnet auto-coupling/decoupling makes operating an Inglenook much easier (when it works) but is a real pain when it doesn't, or if the magnets are put in the wrong place.


First off, what exactly is an Inglenook? Figure 1 shows the basic layout (adapted, with many thanks, from the Model Railways Shunting Puzzle Web Site) and can be adapted to any scale, with a couple of points (switches) and 7 or so bits of track.

Figure 1: Basic Inglenook

The operating fun to be had with the Inglenook relies on being able to pull wagons off trains (rakes) which are parked on the ends of the Inglenook, and swapping them with others, in a kind of Towers of Hanoi style puzzle.


While decoupling using the paintbrush-with-a-loop-of-wire-on-the-end solution is all well and good, for the ultimate in operating action, many enthusiasts like to implement some kind of automatic decoupling solution. Kadee manufacture such a solution, using magnets and knuckle couplers to provide a reliable shunting experience.


Due to the way that they work, on an Inglebook, Kadee magnet based auto-decouplers  are a great solution for one simple reason : delayed decoupling. For layouts using electromagnetic decoupling (in my opinion, the next best thing to Kadee's solution), magnets are needed at each place where a wagon (truck) can be uncoupled.


Wagons can be uncoupled  from other wagons, or from the loco (shunter), and Figure 2 shows where the placements should be (or could be) for an Inglenook using only electromagnetic automatic decoupling.

Figure 2: Inglenook Magnet Placement

There are other places that magnets might be appropriate or desirable, but Figure 2 serves to illustrate the point - 3 separate magnets, with three separate buttons, are required to be able to spot trucks (wagons) on each of the three sidings of the Inglenook. 


Kadee magnet based uncoupling changes this, as seen in Figure 3.

Figure 3: Inglenook Kadee Magnet Placement

The reason only a single magnet is required is that once decoupling has been activated the remaining rake (train, or wagon) can be shunted into place, and remains decoupled. When the loco pulls away, the decoupled wagon or rake is left in place - delayed decoupling.


There is a drawback, however. In order to decouple a relatively long rake, the track in front (to the left of) the magnet needs to be long enough to accommodate it. However, if this proves to be a problem, more magnets can be added on the sidings themselves, this allowing decoupling with some, or most, of the train over the points.