Putting the brake handle in the big hole opens the brake pipe to atmosphere through the largest port on the valve, so pressure drops to zero and every car's control valve goes into emergency using its full reservoir charge. The brakes cannot be released until the train has stopped and the brake pipe recharges. Engineers use it for collisions, obstructions and anything else where stopping distance matters more than the risk of slack damage, and a break-in-two or burst hose does the same thing with nobody touching the handle.
Truck was hung up on the crossing, I put it in the big hole a quarter mile out and we stopped thirty feet short.
When a train goes into emergency on its own, the crew broadcasts the word emergency three times with its location, and the conductor walks back to find the cause before anyone moves.
Also heard as
- emergency application
- dump the air
- wipe the clock
Related terms
Brake pipe
The air line running the full length of a train that charges and controls every car's brakes.
Kicker
A car whose brake valve throws the whole train into emergency when only a normal service application was made.
Slack
The free play in couplers and draft gear that lets cars move a little toward or away from each other.
EOT
End-of-train device: a unit hung on the last car's coupler that reports rear brake pipe pressure and motion to the head end.