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Hop off for a spot of cable car history.
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Author:  Sloan [ Mon Jul 20, 2009 4:35 pm ]
Post subject:  Hop off for a spot of cable car history.
http://www.stuff.co.nz/travel/internati ... ar-history

The writer describes the process of going around curves in which the grip must let go of the cable and "drift" past the shive before taking up the next cable. It was my understanding that most curves have baffles on the shives to allow the grip to hold onto the cable. This is called a "pull curve." Am I right or off on my perception?

Sloan
Author:  PJS [ Mon Jul 20, 2009 8:32 pm ]
Post subject:  Re: Hop off for a spot of cable car history.
As I understand it, there are both types. Curves on down grades are designed for coasting. The gripman lets go of the rope, coasts around the curve, then picks up the rope again at a dip in the tracks provided for that purpose, or more likely coasts to the end of the down grade.

Curves on the level or upgrades are designed as pull curves. The pulleys (sheaves) are located so that the rope is normally slightly toward the center of the curve from the plow slot. The plow pulls the rope away from each pulley as it passes.

The one thing that may not be possible is to release the grip halfway through a pull curve, which can be a problem if someone or something fouls the track, since in this case the cars can't stop or slow down while in the pull curve. There apparently was a long reverse pull curve in New York which was known as "dead man's curve" for that very reason
Author:  JimBoylan [ Tue Jul 21, 2009 11:12 am ]
Post subject:  Re: Hop off for a spot of cable car history.
One of the Pittsburgh, Pa. cable car lines had to deal with long pull curves on twisty hills. It used a "top grip" (San Francisco uses a "bottom grip" today) which could not drop the cable when it tried to let go, so the cars could go around those curves in "partial release" at less than the speed of the cable. Other cities that used this grip found it unsatisfactory because it was too complicated to get the cable in and out of the grip. Pittsburgh had a special need which made it worthwhile to endure it until electrification.
Source: Prof. Hilton's "Cable Car in America".
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