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Resources > Whitaker apparatus
Compiled by Dr Peter Cattermole. Monochrome pictures from Alfred Whitaker's personal album.
Colour picture of No. 88 at Washford exchanging the tablet 8 April 2006 by © Murray Lewis
Download a video clip 6MB MPEG
The SDJR consisted of several sections of single line. It was essential that only one train could be in the same single-line section at the same time. In 1878, Edward Tyer patented a design of tablet instrument for the control of single lines of railway. In 1886, Tyer's instruments began to be installed on the S&D.
For further detailed information, see Chris Osment's site.
A tablet instrument would be placed in each of the signalboxes at either end of the single-line section and the instruments connected electrically by means of a line wire and an earth return. In each instrument there would be a number of round discs or tablets which bore the names of the signalboxes controlling the section. The tablets were secured in the instrument by a lock which could be released electromagnetically. To obtain a tablet, the signalmen would exchange bell signals, and the signalman in advance would then send a current down his line wire to release the lock securing the tablet. Once at tablet had been removed from an instrument no further tablets could be removed from an instrument until the first had been replaced.
The driver of the train had strict instructions not to proceed into the single line section until he possessed the tablet for that section. The signalman would hand the tablet to the driver in a stout leather pouch attached to a large metal hoop clad in leather and of a diameter ranging from ten to eighteen inches. The driver would give up the hoop and tablet to the signalman at the end of the section. Railway regulations prevented the exchanging of tablets by the big pouch at speeds in excess of 10mph in daylight and 4 mph at night.
The requirement for trains to slow down when exchanging tablets meant that fast running of expresses was impossible. At the turn of the century, Alfred Whitaker, Locomotive Superintendent of the SDJR, began to examine possible improvements in tablet exchanging by using a mechanical apparatus. After a number of patterns had been tried out at Highbridge and elsewhere, nine mainline and seventy-one locomotives were equipped with the new apparatus in 1904 at the modest cost of £245. A year of successful trials followed, leading to Whitaker's patent of 1905.
The apparatus allowed the exchange of tablets at speeds of up to 60mph. On the S&D, journey times of the fastest trains were reduced by 7 minute as a result of the installation of the automatic tablet exchanger.
The apparatus consists of a combined receiver and deliverer on the locomotive or tender. 2-8-0 No. 88 has been fitted with this. At the lineside, there is a deliverer at the beginning of the single line section, such as stands opposite the station at Washford.
A receiving apparatus would have been placed at the end of the single line section. A pair of tablet instruments in the signalbox and museum complete the equipment needed to re-enact the automatic exchange at Washford sidings.
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© SDRT 2006 All material contained herein is subject to copyright and may not be reproduced, copied, held in an electronic repository system (particularly on another web site) without seeking permission. Every effort has been made to identify the holders of copyright material included within this website. If any material has been used inadvertently without permission or attribution the Trustees of the Somerset & Dorset Railway Trust will be pleased to receive information with a view to correcting this in further updates. |