Blue Square Electrical Control System
Electro-Pneumatic Valves
Each power car had boxes containing E.P. Valves located on the underframe.
Electro-pneumatic valves for gearbox
1. First Speed Gearbox E.P. Valve
2. Second Speed Gearbox E.P. Valve
3. Third Speed Gearbox E.P. Valve
4. Fourth Speed Gearbox E.P. Valve
Electro-pneumatic valves for engine and final drive
1. Throttle Motor E.P. Valve - No. 1
2. Throttle Motor E.P. Valve - No. 2
3. Throttle Motor E.P. Valve - No. 3
4. Throttle Motor E.P. Valve - No. 4
5. Final Drive E.P. Valve - Forward Speed
6. Final Drive E.P. Valve - Reverse Speed
7. Hand-Testing Button
Description
From the BUT 50000 Series Service Manual:
Each car is provided with a number of E.P. valves; these control the supply of compressed air to the actuating mechanism for gear selection and engagement, the engine throttle control motors and the engagement of forward or reverse gears in the final drive units.
These valves are of the "ON" type and will pass air when the solenoid is energised.
A push button is provided on the underside of the valve to enable the valve to be tested by hand.
Each E.P. valve embodies a needle valve which opens a short passage connecting an air feed to a delivery pipe which leads to the actuating mechanism concerned. The needle valve is operated by a loosely fitted plunger inside the core of a solenoid whenever the latter is energised, and works against the pressure on the air line in addition to that exerted by a small coil spring. The design of the connecting passage and the plunger top is such that any air leaking past the valve is discharged to atmosphere.
Schematic
Schematic showing the electrical connections, as shown in the BUT 50000 series manual.
Circuit 52 is the "Local -", this provides a common negative feed to all the valves. The positive feed to each indivdual valve comes from the "Local +" (circuit 51) when the matching relay is operated on the "EP Control Relay Panel", via wires 90-3 for the gears, 94-97 for the throttle and 99/100 for forward/reverse.
Exploded View
Taken from the AEC Spare Parts Catalogue.
