Consist uncouples in green line tunnel on Wed 1/6/2016

[MCL1981]

https://www.washingtonpost.com/news/dr- ... navy-yard/" onclick="window.open(this.href);return false;

Apparently this morning a train was traveling between Anacostia and Navy Yard in a tunnel when the last two cars came uncoupled from the consist. Word is that both the main consist and the lost cars came to a stop immediately. Another piece of equipment had to enter the tunnel, push the consist back together, then push the whole thing out to Waterfront.

Questions for those familiar:
1) What connections are there between married pairs? I assume there are electrical connections for electronics and controls. Is there high voltage between pairs? Is there air between pairs?
2) When said things disconnect, does the whole thing (both the consist and disconnected cars) go into emergency or just B4?
3) What scenarios, other than equipment failure, could allow this to happen?

On a plus note for WMATA, they didn't kill anyone this time.

[srepetsk]

https://www.washingtonpost.com/news/dr- ... navy-yard/

Apparently this morning a train was traveling between Anacostia and Navy Yard in a tunnel when the last two cars came uncoupled from the consist. Word is that both the main consist and the lost cars came to a stop immediately. Another piece of equipment had to enter the tunnel, push the consist back together, then push the whole thing out to Waterfront.

Questions for those familiar:
1) What connections are there between married pairs? I assume there are electrical connections for electronics and controls. Is there high voltage between pairs? Is there air between pairs?
2) When said things disconnect, does the whole thing (both the consist and disconnected cars) go into emergency or just B4?
3) What scenarios, other than equipment failure, could allow this to happen?

On a plus note for WMATA, they didn't kill anyone this time.

The 2nd and 3rd cars decoupled, not a married pair. Part of the coupling includes brake piping, so when that disconnects all brakes go into BIE and the train doesn't move.
I'm thinking either some sort of coupler metal fatigue or a missing locking pin or similar wasn't completed in the yard before revenue service. Pure speculation, though.

[MCL1981]

Wouldn't that be the front married pair disconnecting from the rest of the consist?

[srepetsk]

Wouldn't that be the front married pair disconnecting from the rest of the consist?

Yes. My apologies; I read your question as asking what the connections are between two cars that are part of the same married pair.

[MCL1981]

What connections go between pairs?

[Sand Box John]

"MCL1981"
What connections go between pairs?

The married pairs are connected using a draw bar. Air hoses I believe are connected using a quick disconnect similar to a air tool connector, com cables are connected with multi pin bayonet connector.

[dcmike]

Just so everyone's clear, the uncoupling happened between two cab ends; in other words, the couplers normally used to reconfigure trains (not the interface between two elements of a married pair). As others have noted, the separation of the coupler faces results in the brake pipe venting to atmosphere and therefore an irrevocable automatic emergency brake application on all cars.

What connections go between pairs?

As John noted, with the exception of the 4000 series, all cars use a drawbar to connect the individual cars of a married pair. There are two pneumatic lines (one main reservoir and one brake pipe) fixed using threaded fittings and 6-8 bundles (depending on the series) of low voltage cables fixed using what is commonly referred to as Cannon plugs. There is no 700VDC connection between cars on any series. The 5000 and 6000 series cars do have a 230VAC auxiliary power "crossover" circuit that can be used to provide AC power to the air compressor, propulsion cooling fans, and part of the HVAC system should one car in a pair lose its APS (auxiliary inverter). The 4000 series uses traditional couplers just like those on the front (cab end) of the cars to connect the married pairs, but there is still other cabling and pneumatic lines that would physically break if the cars somehow became separated unintentionally.

[MCL1981]

Just so everyone's clear, the uncoupling happened between two cab ends; in other words, the couplers normally used to reconfigure trains (not the interface between two elements of a married pair).

This is what I've been trying to ask about. When you couple two pairs together, what connections are there between the the two pairs and how? I don't see a bunch of air and electrical lines dangling like you see on conventional rail cars.

[dcmike]

There's a mechanical coupler with a hook and line-up pins, plus a pneumatic fitting that carries the brake pipe. On either side of the mechanical coupler are two electrical coupler heads with spring loaded pins that make the electrical connections. Unfortunately I don't have access to good pictures right now but I do have some examples from my cell phone.

The first is from a 7000 series, but the mechanical coupler is nearly identical across all the fleets. Notice the brass ring under the hook with the black rubber seal. That's the brake pipe connection.



This is the electrical coupler head used on all the other car series, but this one is damaged (obviously). Each spring-loaded pin carries a discreet electrical (trainline) signal that matches up with the coupler head on another car.

[MCL1981]

Neat. So it's all mechanically lined up, pulled together, and locked. No actual human needs to pull pins and plug stuff in? It seems like an control/mechanical failure is the only thing that could cause a coupling to release like that?

[Sand Box John]

"MCL1981"
Neat. So it's all mechanically lined up, pulled together, and locked. No actual human needs to pull pins and plug stuff in?

Yes and no. The couplers are self centering. The pin is pneumatically controlled from inside the cab. Train line brake valve need to be manually opened or closed, also in the cab. Com line connections and disconnections are totally automatic.

[MCL1981]

Cool. If someone doesn't open the valve for the train line, will it be electronically detected as a brake failure and prevent the train from operating?

[Sand Box John]

MCL1981"

Cool. If someone doesn't open the valve for the train line, will it be electronically detected as a brake failure and prevent the train from operating?

That's an interesting question. I think we can safely believe the answer is yes.

[litz]

Regular trains (both freight and passenger) have been able to do this for decades ... either an actual brakeman at the back end of the train looking at a gauge, or an electronic device reporting brake pressure telemetry.

Either way, the concept is simple : if you reduce brake pipe pressure at the front end of the train, you'd better see the same pressure reduction at the back end of the train. If you don't, something is wrong.

With all the electronics and telemetry in a Metrorail train, if it's not capable of effectively the same thing ... something is seriously lacking in the engineering and design of the equipment.

[MCL1981]

Regular trains (both freight and passenger) have been able to do this for decades ... either an actual brakeman at the back end of the train looking at a gauge, or an electronic device reporting brake pressure telemetry.

Either way, the concept is simple : if you reduce brake pipe pressure at the front end of the train, you'd better see the same pressure reduction at the back end of the train. If you don't, something is wrong.

With all the electronics and telemetry in a Metrorail train, if it's not capable of effectively the same thing ... something is seriously lacking in the engineering and design of the equipment.

I understand how it works on any other normal railroad. Unfortunately WMATA makes it necessary to question what should be otherwise obvious.