pushing the crank assembly aft and rotating theshaft. The rotation of the shaft extends theoperating gear linkage and raises the panelassemblies. Fluid from port B of the piston isdirected through the 4-way valve assembly andback to the gravity tank.To lower the JBD (fig. 12-11), solenoid A ofthe 4-way control valve assembly is energized. Thespools of the 4-way valve assembly shift, allowmedium-pressure hydraulic fluid to flow into portB of the hydraulic cylinder. The cylinders retract,pulling the crank assembly forward and rotatingthe shaft. The rotation of the shaft retracts theoperating gear linkage and lowers the panelassemblies. Fluid from port A of the piston isdirected through the 4-way valve assembly andback to the gravity tank.To lower the JBD in the event of hydrauliccontrol failure, each JBD panel is equipped witha manual bypass valve, which allows bypassingthe 4-way control valve. This allows venting thehydraulic pressure from the “raise” side of thecylinder back to the gravity tank.The three lines to port A of the hydrauliccylinders have orifice assemblies in them. Theseorifice assemblies control the flow of hydraulicfluid in both the raise and lower operations.12-13
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