This gate opening and closing mechanism is fixed into a trench in the ground, directly under the tracks of two sideways sliding gates. It consists of a horizontal shaft with square profile left- and right-hand screw-threads. Two threaded bronze collars are mounted on the shaft, one connected to the left-hand gate and the other to the right, so that the gates move in opposite directions when the shaft is rotated. The shaft is driven by a chain. The latter runs around a sprocket on the centre of the shaft and another runs on the output of a 10:1 reduction gearbox. The reversible 1/3 h.p., 1400 r.p.m. electric motor which drives the gearbox is controlled by a pushbutton via a relay and gate end-stop switches. For safety reasons the relay is powered by 12 volts obtained from the mains via a transformer.
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