Acton Yard was a curious mixture of the mechanical and the electrical as it interfaced with Acton panel - a lot of electrical control circuits were required for the colour light signals it controlled or released and a lot of conditional mechanical locking was required as a large number of signals read over multiple routes. Several dog charts may be downloaded, the first dog chart shows the position in February 1958 following testing of the newly installed frame. At this stage levers 6, 7, 8, 9, 56, 57 and 58 are spare and levers 27,28 and 29 spares or spaces and the mechanical locking table shows this. A minor change to the locking on 18 lever is illustrated in the dog chart and mechanical locking table at amenment B in December 1958.
Acton Yard opened on 1 February 1959 when Acton East closed. The other drawings for Acton Yard show the locking provided in 1968 after most of the layout controlled by Acton panel had been transferred to Old Oak Common panel. The signalling and controls for the Goods Lines were not transferred to Old Oak Common though,and these were controlled by Acton Yard and a new box at Acton West - the connections to and from the Main and Relief Lines were controlled both from the panel and the relevant box using electrical releases and slots. The box had block instruments for the Up and Down Goods lines to Acton West and for the Up and Down Poplar lines to Acton Wells Junction as well as communication with the panel by bell and train describers.
The dog chart at amendment L shows the position in 1967 with levers 6, 7, 8, 9, 56, 57 and 58 in use and the mechanical locking table and lever leads now include much more conditional locking, lever 7 in the upper tier having a condition piece on no less than eight of the nine channels.
A further change in 1969 was implemented as the pointwork was remodelled, affecting points 31 to 34, with lever 32 becoming spare and lever 29 brought into use to operate a spring point - this is shown in the dog chart and mechanical locking table at amendment M.
The frame from Acton Yard was extended from 58 to 62 levers and now controls Kidderminster Station (S.V.R.). The box diagram is available from the Signalling Record Society.
A simple demonstration of how mechanical locking operates may be viewed - click here to see the diagrammatic 'dog chart' moving as a simple sequence of shunting takes place. Alternatively click here to see the actual locking being assembled and then moving as the same shunting manoeuvres are repeated.
Acton Yard is an example of a mechanical frame in which the mechanical locking principles have been applied to a layout where most of the main running signals are colour light and for some of these a single lever operates all of the available routes. The electrical control table ran to eleven pages and is too complicated to describe here but ensures that the correct aspect is displayed, amongst other things.
Where there are many multi-routed signals, the conditional locking will become complicated and there are two trays, each of nine channels, to contain the locking. One lever has no less than ten conditions (lever 7) and several levers have six or more conditions attached to the tappet. Most of this is to provide signal to signal locking depending whether the route is set so that the signals read towards each other.