Train splits

[NW Mailing List]

Recent comments on the Mailing List about slack action causing a coupler pin to rise and cause an uncoupling provides an opening for a little "Techno Talk" on the interesting anti-creep features built into a coupler and into the articulated locklift that the uncoupling rod hooks into.  The common Type E bottom-operated freight car coupler will be used as an example.

As shown on the attachment "AntiCreep," Figure 1, the "Connector" of the articulated locklift has an extension aimed at the bottom of the coupler body.  If the slack runs in sufficiently to cause the uncoupling lever handle to swing forward, the locklift assembly will normally swing forward also, causing the Connector extension to contact the underside of the coupler, as shown in Figure 2, preventing the lock (aka "pin") from moving upward (As shown in these figures the bottom end of the lock has the diagonal slot into which a pin on the locklift "Toggle" is engaged.).  In contrast to the preceding slack action result, normal operation of the uncoupling lever against the bottom of the Connector rotates it so that the extension on the upper end of the connector clears the bottom of the coupler body as connector rises, as shown in Figure 4 (Figure 3 is omitted here).

There is another anti-creep feature intended to prevent a lock from working upward due to vibration or bouncing on rough track (the latter should not be a problem on NS's good track!).  As shown on the attachment "Locklift" the Toggle has a projecting horizontal ledge at its upper end, and near the pin that engages the slot in the lock.  In the normal position of the locklift and lock, the toggle ledge in directly underneath a mating ledge in the coupler body (see the note in the upper left of attachment "AntiCreep" referred to above).  If the lock tries to move upward on its own, the Toggle will be pulled upward with its pin in the bottom of the lock slot until the two ledges come into contact preventing further upward movement.  Again, normal operation of the uncoupling lever nullifies the anti-creep by causing the Toggle pin to move upward in the diagonal slot in the bottom end of the lock moving the Toggle ledge back far enough to clear the ledge in the coupler body.

Incidentally, the Type F coupler for freight service has an additional anti-creep feature, making a total of three for that coupler.

So, why do uncouplings occur in service?  One possibility is that the carman or trainman making the coupling does not ascertain that the lock dropped fully.  As shown in the attachment "TypeE Coupler," it should be evident if the lock on a rare top-operated coupler is not down fully, and a little experience should reveal if the articulated locklift on a bottom operated lock is not in pin-down configuration.  Incidentally, the Type F coupler has a "tell tale" hole that is only visible when the lock is fully down.  I recall a similar telltale hole in the Type H tightlock coupler for passenger service.  Anyone can imagine the importance of insuring that a passenger car coupler does not uncouple while passengers are crossing from one car to another!

Although a drooping coupler mated to a high coupler can lead to an unintended separation, particularly on rough bouncy track, the  most probable cause of undesired uncouplings is wear in the mating parts.  There are gages to check such wear when a coupler body is reconditioned, but excessive wear could occur before a coupler goes through reconditioning.  For example, if the wall in the coupler body back of the bottom end of the lock wears excessively, it could allow the bottom end of the lock to move  back far enough to nullify both anti-creep features.  A prescribed procedure to check a coupler's anticreep involves the use of a large screwdriver inserted through the lock hole in the bottom of the coupler to pry the bottom of the lock backwards (away from the coupler face) while a pry bar inserted through the opening in the coupler face is used to try to pry the lock upwards.  The lock should not rise if the anticreep is effective.

[The three attachments came from the "AAR Manual of Standards and Recommended Practices" in the N&WHS Archives.]

Gordon Hamilton

----- Original Message ----- 
  From: NW Mailing List 
  To: NW Mailing List 
  Sent: Saturday, October 23, 2010 8:02 AM
  Subject: Re: Train splits


      In regard to the OWL "BROKE IN TWO!". One thing that hasn't been mentioned is that sometimes lockpins will get shaken up. Slack action would be a good cause of this. Slack runs in and the cut lever swings up lifting the pin. The pin now stays up and when the slack comes out , the train separates. POW!  You are now in emergency.
      The cause of the break-in-two on the recording is unclear. It definately wasn't a drawhead or the car would have been set out. 
      A broken knuckle might seem the most likely cause, however, nothing was ever said about a knuckle or repairing one. A pin coming up is the only other likely cause. However, there is just not enough information provided in the narrative to know for sure.

  Jimmy Lisle


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