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rail-interlock.com • View topic - Facing Points Lock - FPL

Facing Points Lock - FPL

Specifies the different types of track formation used to set the path of a train.

Facing Points Lock - FPL

Postby admin » Sun Jun 05, 2011 10:43 am

A facing points lock, typically abbreviated as FPL, is a device used to lock the moveable elements of a turnout/switch in one of their running states. For most turnouts, the only moveable elements are the point blades, but some have a swinging nose at the common crossing (frog).

For locking point blades, a common arrangement is to provide notches in the stretcher bar (joining the point blades together) into which a plunger may be inserted. While the plunger is engaged, the point blades cannot move. The lock may be operated separately, for example by a lever in a lever frame, or in conjunction with the points themselves. In the latter case if operated by a mechanical lever, then the actions of the lever are firstly to release the lock, then to change the points, and finally to lock the points. In the case of motor-operated points, the locking is usually a combined action.

The name derives from the fact that trains are particularly susceptible to derailment when making a facing movement through points. (A facing movement means that a train encounters the point blades first.) Because of this vulnerability, in British practice it was legislated very early in railway history that any passenger-carrying movements through facing points must require that the points be locked for the route set.

A locking bar is often linked with an FPL. This is a long bar lying just inside one of the running rails in the vicinity of the points. It is set at a height such that its upper surface is just clear of the wheel flanges. To unlock the points, it is necessary to simultaneously rock the locking bar up and then back down in order to prove that no vehicle is adjacent to or moving through the points. The bar is of a length that is greater than the greatest gap between adjacent wheels of any vehicles that may traverse the points.

Locking bars are not required if track circuits are used in order to detect the presence of a train and in turn electrically lock any device that may operate the points.
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