Quiet commuter rail couplers?

Question:

Why is it that MBTA commuter trains can start and stop so quick without slack creating loud bangs, like with freight trains? Do they use a special coupler?

JD

I would tend to think they do, but also since we are talking passenger cars that we can walk from car to car that all that connected area also keeps the cars from making that racking sound like freight cars. Just a guess

Different types of couplers are used and these have a lot less slack than the typical freight coupler. That's about all I know.

Here is a link to a newsgroup post about the history of couplers.

http://groups-beta.google.com/group/rec ... 8c4259b291

Passenger car couplers are different than freight couplers and are also designed not to separate in a derailment. When braking the locomotive brakes are usually not used and many times the engineer also power brakes( some loco traction power is on at same time passenger car brakes are applied) to ensure there is no slack. This pertains to loco pulling but I think that while pushing there is also loco brake control from the cab car so that when pushing the slack remains pushed in when braking.

i remember asking an engineer about this before, and i was told that the passenger car couplers are the same, but the way that they are attached to the cars is different, freight train couplers can slide more because they will have the tendency to break, but on the pass. cars, the couplers are stuck, and don't move

MBTA F40PH-2C 1050, I'm not so sure you have that right. Some freight cars have cushion drawbars that allow extra front-to-back motion of the couplers, but the draft gear on passenger cars does pivot side-to-side on curves (otherwise you'd have a serious problem). If you're only talking about the front-to-back motion, though, they it's true that passenger draft gear is fixed in that direction.

Almost all passenger cars have Type H tightlock couplers, which have extra tabs on the side that slide into a pocket on the mating coupler. These help keep the couplers locked tightly together even in the case of a derailment. Some freight cars also have this type of coupler, and there are similar Type F couplers for tank cars, but the average freight car will have a regular Type E coupler with no special locking features.

Remember that slack also varies with train length. If you were running only a 7-car freight train, you wouldn't have to worry too much about the slack either, but if you have a mile of freight cars behind you, then you need to be pretty aware of what's going on throughout the train. Car weight is yet another issue, since for example having several heavy cars on the rear of your train would result in more slack action.

I would not expect that the rubber diaphragms in between cars have any effect on the slack action. The reason they are spring-loaded and compressible is to keep their striker plates pressed together so there's no gap that a person could fall through - they are not actually designed to absorb any loads being transmitted from car to car.

astrosa wrote:MBTA F40PH-2C 1050, I'm not so sure you have that right. Some freight cars have cushion drawbars that allow extra front-to-back motion of the couplers, but the draft gear on passenger cars does pivot side-to-side on curves (otherwise you'd have a serious problem). If you're only talking about the front-to-back motion, though, they it's true that passenger draft gear is fixed in that direction.

yea, thats what i was trying to explain, but i couldn't remember, and i wasn't as in detail, i just said what i knew, thanks for filling the rest in

Even on a 7 car freight train you could get slack.

A major difference between freight and passenger trains is the difference in the air brakes. The standard passenger Brake pipe pressure is 110/psi, where as freights are using 90/psi (pounds per square inch).

Also, there is only one brake on the control cars, it is a "blended brake" which is a combination of the trains air brakes and the locomotives independent brake, I beleive. Whereas on a normal train with a locomotive pulling, whether it is passenger or freight, there would be 3 brakes (the locomotives independent brake, dynamic brake, and last but not least the train's air brakes).

I hear what you are all saying, but it is hard to visualize. It just seems odd that a T train can stop and start so solidly. Are coach brakes that much better than freight car brakes? I assume coaches have discs?

NellsChoo wrote: Are coach brakes that much better than freight car brakes? I assume coaches have discs?

Yes Nells, passenger coaches do have bigger and better brake shoes, in most casess. Also, many coaches, such as AmFleet coaches do have disc brakes.