Briefly on the AAR Coupler Part 2

Last week, we've identified the Janney coupler and briefly looked at its elegant design. This week, let's, again, very briefly, look at the different types of Janney coupler that are widely used today. I will only talk about the head of the coupler, and ignore anything that the general public may need to trespass onto railroad property and get in a unsafe situation in order to have a good look at.

As far as coupler heads are concerned, there are 3 types in used today. Type E, F, and H. Types E and F are used on freight, and H used on passenger equipment. Since the withdrawal of passenger service in North America by private railroads, the Type H standard is no longer maintained by the Association of American Railroads, a trade group formed of major freight railroads, but is under the control of the APTA, the American Public Transportation Association.

Now let me introduce another term, slack. Slack is an allowed gap between two coupled up couplers. In other words, when most AAR couplers are engaged, they are not fully snug against each other and allow some movement in the longitudinal direction (i.e. parallel to the track).

Coupled Type E couplers, note the slack between the two
Type E couplers heads are further devided into an ordinary coupler head, a bottom shelved head, and a double shelved head. The shelves provide protection against the coupler pin falling out of the coupler in case of failure and cause damage to the car body. They are usually seen on tank cars. In fact, newer tank cars are mandated to have double shelved couplers.

A double shelf coupler... the car doesn't look in very good shape
Type F couplers have a higher tensile strength than Type E couplers and have larger knuckles (Type E knuckle will however fit in a Type F head but not the other way around). They are bottom shelved and can have a top shelf as well. They can be identified by the interlocking feature to prevent couplers from disengaging during a derailment.

Type F Couplers viewed from the side, note the interlocking feature
Another view of the Type F coupler
Type H couplers look like Type F couplers without the bottom shelf and are used on passenger equipment only.

Type H coupler, look real closely and compare with the F to see the difference
Type H coupler on British Rail Class 321 EMU
Other than geometrical differences, Type H couplers have virtually no slack, and Type E couplers have the greatest slack.


Andy_in_Germany said…
"I will only talk about the head of the coupler, and ignore anything that the general public may need to trespass onto railroad property and get in a unsafe situation in order to have a good look at."

Good for you. It amazes me how irresponsible people can get looking for the perfect picture of some railway detail.

It seems odd that our very effecient German railway network has almost no buckeye couplers except for some heavy ore trains in the north west and a few private systems running railcars with them. A number of Deutsche Bahn railcars have Scharfenberg couplers, as do a lot of narrow gauge systems.

We do have a sort of hybrid coupler used on shunting locomotives that can be folded down and engages with a normal hook on a screw link coupling DB are fitting these to their new B-B shunters so I think they expect screw couplings to be around for a while.

I do wonder if one reason is that trains aren't usually that heavy: they have to be fairly light to scoot between the fast passenger trains on our very heavily used network.
Andy, thank you very much for your continual support of my blog.

I agree with your hypothesis there. The AAR coupler is advantageous when a railroad switches (I guess the European term would be shunts) a lot of cars and runs heavy trains. The Swedish opted for the Soviet automatic coupler for the first reason, however they don't need the capacity of the AAR coupler. My understanding is that the Soviet coupler is even easier to maintain and have fewer parts but I'll have to look more into it.

In Britain however (experience from my trips there), I noticed the increased use of AAR couplers on freight equipment. In fact, I even saw a train with mixed screw and AAR couplers with a transition car in the mist. On the passenger side though, Britain was a heavy user of the AAR type coupler under British Rail, but has switched to Scharfenberg on equipment purchased since privatisation.

Anonymous said…
Andy, you are correct that many trains in Germany (and most other European countries) are lighter. But that is not just about speed, it is also about the maximum possible length of a train, which is dictated by the lengths of sidings, axle load (Germany: 21t on most main lines, USA: in excess of 30t on main freight lines) and details of track construction such as grades and radii. Also add to this that a complete replacement of the chain coupler with an automatic coupler would require a pan-European effort -- well, good luck with that... ;)
Anonymous said…
For passenger services, Scharfenberg couplers have the advantage of also connecting cables and air lines automatically. AAR couplers still need a worker to connect the cables and air lines. AAR is a stronger coupler, but this is irrelevant for most passenger services.

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