[PRCo] Re: Derail

[Phillip Clark Campbell]

The derail worked similarly to any track switch in that it was controlled by the operator through a contactor in the overhead.   For Prc it was coast through the contactor to set/maintain the straight through or draw current through the contactor to set/maintain a diverge movement at turnouts on the system.

The Derail was a special situation - it was a diverge movement to derail and a straight through movement into the tunnel when set properly but it was necessary to draw current through the contactor to set for this straight through movement.    This was a spot for crew changes wasn't it and if a car rolled when the operator was not present it would coast under the contactor and not set the point to travel into the tunnel - the car would technically derail but there was a block there to prevent this and stop the car instead.

On the old cars the operator could use a combination of power and brake simultaneously to draw the current through the contactor; on Prc Pccs there was a toggle on the dash which drew current through a resistor to set points for diverge.  It was forbidden on Prc Pccs to set points by using the power pedal.   Thus the operator had to take specific action to set the point straight at the derail.

The derail had a time delay feature as well  --  the track point would not set immediately upon passage through the contactor.  This could possibly catch a car with slack brakes.

After the car passes through the derail successfully there is a simple contactor in the overhead (like those used to activate Nachod signals) that resets the point for the derail position.  It doesn't matter if the car coasts or draws power through this contactor.

This junction and derail were interlocked with outbound movements.  If a 44 or 48 car had already set its point and proceeded through the turnout it prevented operation of the interurban derail until the 44 car cleared.

As originally built the derail was a RR point and possibly operated by the man in the tower  --  but this would not catch equipment with slack brakes would it.  Don't remember when Prc first used electric turnouts; believe it was in the 1920s but don't have my notes.

I have often wondered why there weren't derails in the outbound tracks as well since crew changes happened in this direction; a car could roll backward into the tunnel.    Such a derail is a simple sprung point.

Prc had derails at other locations and some reverse derails for cars that would roll backward.  There were derails on the 46 aka 49 on New Arlington but being single track they have to be for rollbacks in one direction.  Didn't the 21 Fineview also have derails to prevent rollbacks?

Phil


----- Original Message ----
From: ROBERT R ROCKWELL <w3syt1 at msn.com>
To: pittsburgh-railways at dementia.org
Sent: Tuesday, September 25, 2007 11:07:40 AM
Subject: [PRCo] Re: Derail

I see it, how did it work ?

Robert Rockwell
w3syt1 at msn.com<mailto:w3syt1 at msn.com>


http://lists.dementia.org/files/pittsburgh-railways/1200-42-ob-shj-09-04-1951.jpg<http://lists.dementia.org/files/pittsburgh-railways/1200-42-ob-shj-09-04-1951.jpg>





       
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