Preece's 1-Wire Block Instrument

This photograph shows the Preece 1-wire 2-position block instrument inside Templecombe No 2 Junction signal-box on the former Somerset & Dorset Joint Railway. This instrument controlled the block working of trains on the double-track spur which connected the S&DJR line to the former London & South Western Railway main line at Templecombe (Upper) station. Although this photograph was taken on 3rd June 1957 in British Railways days, it will be noted that the indentification plates still read "SR Box" (for Southern Railway).

The instrument itself has the block bell on its top and at the front is the block indicator, in the form of a semaphore signal. This indicator would be worked by the signalman in the main line box at the Upper station to indicate to the signalman at No 2 Junction that it was clear for a Down train to proceed into the section. To the right of the instrument is the associated switch handle (plated 'Up Line'), which worked the corresponding block indicator for Up trains in the signal-box at the far end of the section.

The switch handle was locked by an electro-magnetic lock contained in the wooden casing immediately behind the handle. Situated below the switch handle is the brass plunger which worked the block bell on the instrument in the box at the Upper station. To the left, sunk into the front of the shelf and surrounded by a brass ring, is a push-button which released the electric lock on the switch handle. The large round indicator (numbered '9') on the left was a signal arm repeater and is not connected with the Preece equipment. Also visible in the picture is part of the large signal-box diagram.

© Chris Osment 2002
Photo by Ian Scrimgeour, courtesy of Signalling Record Society