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The Speedbrake Hydraulic Control Unit is designed with a four way-three position selector valve driven by two solenoids valves.
– The selector valve alternatively connects the supply pressure and return pressure to the extension and retraction chamber of the Speedbrake Actuator.
– The two solenoid valves control the position of the selector valve.
The two solenoid valves receive an energizing power signal from the SECU.
In de-energized condition, the selector valve blocks both the controlled ports. When Extension solenoid is energized, supply port is connected with Extension control port and Retraction control port is connected with return port.
When Retraction solenoid is energized supply port shall be connected with Retraction control port and Extension control port shall be connected with return port.
The retraction solenoid is dual coil type in order to assure actuator retraction capability also in case of main electrical power absence. In fact, one coil of this solenoid is powered by A/C main electrical bar while the other is supplied by A/C essential electrical bar. In case of main electrical bar failure, second coil can power retraction solenoid allowing SBA retraction.