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MIDLAND JUNCTION "B"
Western Australia Government Railways

by John Hinson

Photograph from the collection of Dr J W F Scrimgeour, 1969

Apart from the locomotive, there is little in this view that was not manufactured by McKenzie & Holland. The all-timber cabin and the somersault signals with revolving discs are all from their workshops and are of typical design. Notice how the signal on the right has been modified after insects have eaten away at the base.

Photograph from the collection of Dr J W F Scrimgeour, 1969

This view shows the McKenzie & Holland lever frame, together with the signalling instruments and the layout diagram.

The block instrument on the left is of considerable interest, being of the Dowson's three-position type. Harold Dowson was the Signal Engineer of the WAGR from 1898 to 1926, and later worked for the Bombay, Baroda & Central India Railway. He invented this instrument as an improvement on Winter's blocks, having three indications and extra security in the provision of a treadle release to confirm that trains have left the section. They were manufactured in the WAGR workshops.

Photograph from the collection of Dr J W F Scrimgeour, 2/69

The Dowson's three-position block instrument controlled the double-line section between Midland Junction "B" and Bellvue.

The left dial was the red needle, used for trains approaching the box. The right dial had a black needle and applied to departing trains. The Black Button was used in conjunction with the Red Switch, whilst the Red Button and the White Button were used for cancelling and for clearing in the event of treadle failure. The Red Switch was normally free, but became locked when at ON LINE and remained so until the arrival of the train was detected by a treadle release.

Operation was as follows:

• Box "A" sends Is Line Clear? to Box "B"
• Box "B" turns the Red Switch to CLEAR, presses Black Button, and acknowledges Is Line Clear?
• Box "A" turns Black Switch to CLEAR, which places black (right) needle at Box "A" and red needle at Box "B" to LINE CLEAR
• Box "A" sends Train Departure and turns Black Switch to ON LINE, in which position it becomes locked
• Box "B" acknowledges Train Departure and turns Red Switch to ON LINE, in which position it becomes locked. Turning of the switch also places black (right) needle at Box "A" and red needle at Box "B" to TRAIN ON LINE
• After arrival of the train at Box "B", operating the release treadle which releases the Red Switch, the signalman turns the Red Switch to CLOSED, gives Train Arrival to Box "A" and presses the Black Button
• Box "A" turns Black Switch to CLOSED, which replaces both needles to CLOSED, and acknowledges Train Arrival.

At the time these pictures were taken, this section was the last to be signalled with Dowson's blocks. They are now long-gone, in fact there is not even any nechanical signalling now remaining in Western Australia.