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GWR Route: Banbury to Wolverhampton
GWR Route: North Warwickshire Line
Birmingham Snow Hill Station: gwrbsh1672
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One of the Siemens electrically powered point machines
installed on one of the facing switches (lever 46) of the relief line scissors
crossover at the north end of Birmingham Snow Hill. The cast iron cover of the
point machine has been hinged open to reveal the internal workings. The point
machine contains an electrical motor to drive a geared wheel, which is coupled
at high level to a rod operating a rocking shaft. This rocking shaft travels
under the rail and lifts or lowers the plunger bolt and operates the locking
bar. Also connected to the geared wheel at a lower level is the rodding linked
to the point tongues, which operate the point movement. This is mechanically
interlocked, such that it can only operate once the plunger bolt and locking
bar have been disengaged by the high level operating mechanism and this
mechanism also re-engages the plunger bolt and locking bar following the
operation. A smaller second box attached to one of the sleepers behind the
point machine, contains the electric detector circuitry which identifies that
the point tongues are correctly positioned and that the plunger bolt is fully
home.
Robert Ferris
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