(a) Initial stowed position (Ref. Fig. 027) In the initial stowed position with the reverse stow control selected in the cockpit, the hydraulic pressure is applied to the input of the HCU. All reverser hydraulic systems are connected to the return line as long as the aircraft is in flight and, no signal is sent to open the pressurizing valve solenoid.
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 Stow Configuration
 Figure 027

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 1 When reverse thrust is selected in the cockpit, the ECU
_ controls that deploying conditions are achieved. In that case, the electrical power (28VDC) is sent to the pressurizing valve solenoid and to the directional valve solenoid. The SEC and the static relay open the SOV. (Ref. Fig. 028)
 2 When the pressurizing valve is opened and the directional
_ solenoid energized, high pressure (HP about 3000 psi) is routed to the hydraulic actuator rod side. Actuators overstow, relieving loads on hydraulic door latches. Pressure signal is sent to the EIU. Pressure from directional valve causes door primary latches to unlock in sequence.
 3 When the last latch is opened, the pressure drives the
_ directional valve which enables to supply hydraulic actuator heads with pressure. Actuator secondary locks release. (Ref. Fig. 029)
 4 As soon as one blocker door is at more than one percent of
_ angular travel, its stow switch changes over and sends a "1 or 2 or 3 unstowed doors" signal to the ECU. In the cockpit an amber REV indication is displayed in the middle of the N1 dial. The "unstowed doors" signal will not be send to the ECU until all blockers doors are at more than one percent of their angular travel. (Ref. Fig. 029)
 5 Each blocker door arriving at 95 percent of its travel is
_ slowed down until completely deployed through hydraulic actuator inner restriction: at this moment the switch is also activated. When the four blocker doors are deployed the ECU receives the "deployed doors" information and stops pressurizing valve solenoid supply. REV indication changes to green. Latches remain in door stowed position. (Ref. Fig. 029)
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 Deployed Position Selected - Latch Unlocking
 Figure 028
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 Blocker Door to Deployed Configuration Figure 029 (SHEET 1)
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 Blocker Door to Deployed Configuration Figure 029 (SHEET 2)
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 Blocker Door to Deployed Configuration Figure 029 (SHEET 3)
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 (c) Stow sequence
 (Ref. Fig. 030)

 1 When blocker doors stowage is selected, the ECU controls that
_ stowing conditions are achieved. In this case, the ECU reverses the electrical power supplies of the end of deploy sequence. Pressurizing valve solenoid is energized, directional valve solenoid de-energized. When one door is at less than 95% of his travel, REV indication changes to amber color.
 2 Pressurizing valve opens and hydraulic actuators rod are
_ supplied. Hydraulic actuator heads are connected to return. A flow limiter controls hydraulic actuator retraction speed.
 3 When all blocker doors are at one percent from their stowed
_ position they activate the switches which send the "stowed door" information to the ECU. The REV indication disappears. (Ref. Fig. 030)
 4 The ECU maintains pressurizing valve solenoid in energized
_ conditions for one second after receipt of "doors stowed" signal from stow switches. This permits hydraulic pressure supply to actuators to ensure full retraction of doors and re-engagement of the latches.
 5 HCU in de-energized condition connects all circuits to return.
_ The pressure switch transmits a "without pressure" signal to the ECU.
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 Blocker Door to Stowed Configuration Figure 030 (SHEET 1)
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