Emergency Fuel Cutoff

Is this mechanism used when the train goes into emergency? Does it activate for another purpose at any other time?

No. When the train goes into emergency (braking) the brake pipe pressure goes sharply down (or the train gets "dumped" in the parlance).

The emergency fuel cutoff switch(es) is(are) used to cut off fuel supply in case of engine fire, or whatever. That's why two of these switches are on the outside of the engine, where the crew or first responders can reach them without actually climbing into the cab.

When a train goes to emergency the brake pipe pressure goes rapidly and uncontrolled to zero. The PCS switch then activates not shutting down the engine, but in very basic terms, cutting off the power output. The engine still is running.
The EFCO buttons completely shut down the engine. Most EMDs have 3 buttons, one in the cab behind the engineer and two ouside ones on the frame. Two other ways to shut down the engine are by holding out the layshaft or moving the throttle to the "STOP" position, which is on the other side of idle.

The EFCO buttons are in series with the coil of the fuel pump relay, hence when the button is pushed, it breaks the circuit, drops out the relay and shuts off the main fuel transfer pump. Also, the dropping out of the fuel pump relay activates the DV solenoid in the governor to go to shut down.

Older locomotives have a pull cord (instead of a EFCO button) located on both sides of the platform. This pull cord activated a mechanical valve which shut off the fuel supply to the diesel engine. For those of us in the business of preserving locomotives, this pull cord mechanism is a nuisance, as it gets rusty and binds up. In this case, its better to retrofit the locomotive with the now standard EFCO buttons.

Newer locomotives that have EFI diesel engines do not have a layshaft, so that's not an option. Other way to shut down an engine is to press the MU stop switch on the control stand, which not only shuts down the lead engine, but also the trailing units in consist via the MU trainline.

In the event that you find the working cable operated shutdown device, its not guaranteed that the locomotive will die immediately as I've seen them run 5 to 10 minutes after pulling the cord.

There's alot of fuel still under pressure between the injector pumps and the cutoff valve.

TxBritt

the emergency fuel cut off switchs are just engine off switches. we use them all the time just to kill the engines once we don't need them running anymore. the efi engines have 4 of them [one on each side, one in the cab, one by the start station]. governor engine have the standard 3 [all minus start station one]

and they don't work on older [governor] units if the battery knife switch has been pulled....

The buttons don't really disable the engines. They just shutdown the engine by tripping the low lube switch in the governor.

TxBritt

txbritt wrote:The buttons don't really disable the engines. They just shutdown the engine by tripping the low lube switch in the governor.

TxBritt

the governor button doesn't pop, it just activates the "D" solenoid in the governor