Coupling Question

[M60lad]

Recently (not to sure if it was yesterday or the day before) a 4 car 142 decided to uncouple itself while in service at Liverpool Lime Street causing the emergency brakes to kick in and I have the following queries:

1> How can a train uncouple itself as I always thought once their coupled together there's no way they can uncouple without driver intervention

2> Whats the procedure for this kind of thing considering the fact the conductor would have been in the rear unit and the driver in the front unit, I'm guessing the driver would have had to release the doors on the front unit to let people off

 

[A-driver]

It won't just uncouple itself, it is either a fault with the equipment or an error from staff in coupling it up.

There have been (rare) examples of the couplers failing leading to one of the jaws opening allowing the unit to break free. As said, if the driver or shunter hasn't put it together correctly then there is also a chance it could split once it starts moving.

The procedure would be along the lines of...driver gets the emergancy break application and looses interlock. Driver will fault find, part of which should involve looking out of the window to check the train is complete. There is of course a chance that the units havnt come apart far enough for the driver to notice from the looking back but at some point the driver will become aware of the division. The driver will let the signaller know and check that no one has fallen between units (only really applicable to corridor stock rather than block-enders).

The rest depends. Technically they can get permission from the signaller and try to re-attach the units. That is more use on the running lines though to clear the line. In reality I doubt they would authorise that and just let the train carry on in service, especially if it is still in the platforms at a terminal station. They would most likely cancel the train pending investigation. They would investigate weather the units were banged together correctly in the first place using things like data recorders, CCTV and staff statements (when we attach units in a platform we often give "one to the cameras" by over dramatically looking between to check the pins are out so if anything goes wrong and they check the CCTV they can see that we did properly look). They would then test the units to see if that's asset fault, they will have coupling testing equipment which they will use.

The driver wouldn't need to open the doors to let people off straight away, that wouldn't be a priority at that stage. Once they had realised what had happened and decided weather or not to re-attach and run the service they would make arrangements for getting punters off.

 

[edwin_m]

There was an incident with 158s in Glasgow Queen Street a few years back when I believe the uncouple button was pressed but the units weren't separated. I presume the electrical and air connections were still made but the mechanical connection wasn't. When the whole train started away it travelled a short distance before dividing (was the interlock also bypassed?). Hence the label on the buttons which says that the units must be separated if they are pressed.

 

[A-driver]

There was an incident with 158s in Glasgow Queen Street a few years back when I believe the uncouple button was pressed but the units weren't separated. I presume the electrical and air connections were still made but the mechanical connection wasn't. When the whole train started away it travelled a short distance before dividing (was the interlock also bypassed?). Hence the label on the buttons which says that the units must be separated if they are pressed.

I have heard of that happening in a London terminal one evening when the attaching driver accidentally caught the uncouple button whilst trying to press the couple button. Instead of re- coupling it he just pressed the couple button and did the brake test which worked so assumed it was ok. Electrically the units were couples so interlock could be gained and the brakes could come off as the drum switches were set but it wasn't properly attached mechanically so the movement of the train caused it to come apart after a few feet.

 

[156441]

M60lad. Did the units actually detach themselves or just come to a stand. We (Northern) seem to have regular problems with the electrical connections between units so when you go over a curve or set of points the brakes jam on.

This would involve the units having to be uncoupled and reattached. (Although it's likely it would run as one set after that sort of incident as not to recreate the fault).

 

[455driver]

I have heard of problems when a 14x is coupled to a 153 and the train goes over some points and the interlock is lost bringing the brake in but in the few seconds it takes the train to stop the fault has rectified itself.

 

[Eng274]

This is a problem that comes round in cycles, usually what happens is:

1 - spate of UBAs caused by coupled sets travelling over snaking points
2 - coupler timer relays adjusted up to allow enough time for coupler electrical circuits to drop out and come back in over said points
3 - problem goes away, relays adjusted down to original setting
4 - autumn/winter arrives, seasonal disruption means trains are stopped at the bigger junctions more often, traverse points at slower speeds causing UBAs.

Sometimes NR are generous enough to increase speed limits over certain points (within safety margins of course) to minimise the risk of delays caused by coupler electrical breaks. The 6 car 156s tend to be the worst for it at Glasgow central.

 

[TEW]

I have heard of problems when a 14x is coupled to a 153 and the train goes over some points and the interlock is lost bringing the brake in but in the few seconds it takes the train to stop the fault has rectified itself.

142+153 combos on FGW used to be terrible for randomly losing interlock, but I haven't experienced it in a while now with the 143+153 combos.

 

[455driver]

142+153 combos on FGW used to be terrible for randomly losing interlock, but I haven't experienced it in a while now with the 143+153 combos.

I have seen 2 sets do it at Exeter this month, both going North out of P3.

 

[Qwerty133]

the two 170s on the 17:16 to Birmingham uncoupled when leaving Leicester one day a few months ago, driver drove front unit back to the rear unit, re coupled them and then left 8 mins late.

 

[Dieseldriver]

I have a specific unit which every time I drive it in multiple with another unit I get at least one spurious brake application... Always makes my day when it rolls in to the platform...

 

[M60lad]

Unfortunately 156441 I can't help any more with what actually happened as I wasn't there myself, I got the info from a Facebook friend of mine who took photo's of the incident after it had happened