Yellow Diamond Electrical Control System
Engine Shut-Down Solenoid
1. Engine shut down solenoid
2. Solenoid trip lever
3. Throttle control motor
4. Stop lever
5. Throttle control rod
6. Fuel-injection pump
Description
From the BUT A Series Service Manual:
The engine shut down solenoid is connected by linkage to the fuel-injection pump stop lever.
When the water level switch is closed, it energises the solenoid which operates the trip lever and shuts off the fuel supply to the injectors.
Schematics
Schematics showing the electrical connections, as shown in the BUT A series maintenance manual.
On yellow diamond vehicles were two methods of stopping the engines: via the throttle motor by only energising the throttle 1 circuit, this put the fuel pump into the cut fuel position; and with a stop solenoid which was directly connected to the fuel pump stop lever. The solenoid option was needed for when an engine needed to be shut down while in motion, as energising throttle 1 would not be effective if other throttle circuits were active.
On Derby Lightweights (the first diagram) the water level switch was the only item that controlled the shut down solenoid and simply connected the train + to the solenoid (the side of which was connected to the train - cricuit).
On the Met-Camm Lighweights (second diagram) the + feed to the solenoid could also come from the engine stop buttons on the underframe.