Questions about Screw-link/Buffer and chain couplings

L

littleshunter060

New member
Hello everyone, I have a couple of questions about screw-link/buffer and chain couplings, commonly found on British and other European rolling stock.

1. By the nature of the coupling, each vehicle has a chain, often with an adjustable screw to tighten the coupling. So when two vehicles are coupled together, does it matter which vehicle's chain is used, or does it not matter which chain the shunter uses to connect them?

2. Different rolling stock had different kinds of buffers. Some had oval-shaped buffers, some had square or rectangular buffers, and some had circular buffers. How was the kind of buffer that would be used on the vehicle determined?

3. Early DMUs and some EMUs had standard screw-link couplers, but they changed to other designs later on. Could one of these early DMUs or EMUs theoretically pull non-multiple-unit stock, like a goods van or a standard passenger coach?
 
littleshunter060 said:
Hello everyone, I have a couple of questions about screw-link/buffer and chain couplings, commonly found on British and other European rolling stock.

1. By the nature of the coupling, each vehicle has a chain, often with an adjustable screw to tighten the coupling. So when two vehicles are coupled together, does it matter which vehicle's chain is used, or does it not matter which chain the shunter uses to connect them?

2. Different rolling stock had different kinds of buffers. Some had oval-shaped buffers, some had square or rectangular buffers, and some had circular buffers. How was the kind of buffer that would be used on the vehicle determined?

3. Early DMUs and some EMUs had standard screw-link couplers, but they changed to other designs later on. Could one of these early DMUs or EMUs theoretically pull non-multiple-unit stock, like a goods van or a standard passenger coach?
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1) It doesn't matter if the couplings are the same, although if one coupler was a three link and the other a screw then you would choose the most appropriate coupling for the train and the vehicles position in it.

2) The buffer shape is basically cosmetic, although some designs had the shape designed to clear the bodywork when the buffers were retracted so the knuckle coupler could be used.

3) Early DMUs could often be seen with a single goods or parcel van on branch lines.
 
edh6 said:
1) It doesn't matter if the couplings are the same, although if one coupler was a three link and the other a screw then you would choose the most appropriate coupling for the train and the vehicles position in it.

2) The buffer shape is basically cosmetic, although some designs had the shape designed to clear the bodywork when the buffers were retracted so the knuckle coupler could be used.

3) Early DMUs could often be seen with a single goods or parcel van on branch lines.
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Thank you, I really appreciate your help with this, edh, especially with the last question; I'm making a route where I have some DMUs pulling freight wagons. As a sort of addendum to the first question, if a chain were to break, like say as the train was starting away, I assume that the stock could be re-coupled using the other vehicle's chain, correct?
 
littleshunter060 said:
3. Early DMUs and some EMUs had standard screw-link couplers, but they changed to other designs later on. Could one of these early DMUs or EMUs theoretically pull non-multiple-unit stock, like a goods van or a standard passenger coach?
Click to expand...

As long as DMU/EMUs had standard couplers (modern ones are almost all equipped with automatic couplers) it was a rare but not exceptional occurrence.

Pulling conventional rolling stock with DMU/EMU usually occurred when using a locomotive to run an extra train would be impractical: typically, when a single through coach or a freight car must be forwarded to its final destination. Since most DMU/EMU have limited power, being designed to pull a single trailer, it was unlikely to see more than one extra car pulled by them.

The practice was far more common on secondary private or non-state railways, which had fleets consisting almost exclusively of DMU/EMUs with very few (if any) locomotives for freight traffic, and is still a standard practice on most narrow-gauge lines.
 
edh6 said:
Either that or spare couplings were often carried in the guard's van.
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Yes, I remember seeing an old British Rail training video where it described coupling a Class 415/416 EMU in an emergency, and it had a red screw-link coupling in the guard's compartment. I assume that on goods trains, these couplings probably would have been carried in the brakevan.
 
Pendolino said:
As long as DMU/EMUs had standard couplers (modern ones are almost all equipped with automatic couplers) it was a rare but not exceptional occurrence.

Pulling conventional rolling stock with DMU/EMU usually occurred when using a locomotive to run an extra train would be impractical: typically, when a single through coach or a freight car must be forwarded to its final destination. Since most DMU/EMU have limited power, being designed to pull a single trailer, it was unlikely to see more than one extra car pulled by them.

The practice was far more common on secondary private or non-state railways, which had fleets consisting almost exclusively of DMU/EMUs with very few (if any) locomotives for freight traffic, and is still a standard practice on most narrow-gauge lines.
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I see. Would the power even be limited in the case of a single railcar unit, such as a SNCF X-2800, or a BR class 121? I know that most older DMUs and EMUs only had one or two vehicles, AKA a motor coach or power car like the class 455s and Class 43 HSTs, to actually power the train, but those trains are 4 cars long or more in the case of the HST.
 
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edh6 said:
2) The buffer shape is basically cosmetic, although some designs had the shape designed to clear the bodywork when the buffers were retracted so the knuckle coupler could be used.
Click to expand...

Some were also designed so that it would be very difficult or impossible for buffers to "lock up" with each other due to some combination of turning, braking and buffer run-in.
 
X-2800s are a peculiar case, since they were among the most powerful railcar ever built (800+ HP), and were designed to pull multiple trailers; BR 121's are a more typical European railcar design (300 HP). The HST Class 43 is a normal Diesel locomotive, just like the ones you find at both ends of many HS trains (TGV, ICE, ETR500...). In most cases, for normal use, the powered car/trailer ratio is 1:1 (of course, this also depends on the grades the train will meet).


Besides the small amount of engine power, another factor limiting the pulling power of DMUs is their lightweight construction (since they are mostly used on branch lines, they rarely exceed 40 tons), which means their tractive effort is limited. Doodlebugs managed to pull several freight cars, but they were much more heavier (and slower) than European DMUs.
 
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