aft doors’ cylinders and the shuttle valve on thenose gear cylinder to close off the normal portand operate these cylinders. The nose gear cylinderextends; this unlocks the uplock and extends thenose gear. The nitrogen flowing into the aft doorcylinders opens the aft doors. Fluid on the closeside of the door cylinder is vented to returnthrough the actuated dump valves. Nitrogen fromanother bottle actuates the shuttle valves on theuplock cylinders. Nitrogen flows into the uplockcylinders and causes them to disengage theuplocks. As soon as the uplocks are disengaged,the main gear extends by the force of gravity.Fluid on the up side of the main gear cylindersis vented to return through the actuated dumpvalves, preventing a fluid lock.JET BLAST DEFLECTORSJet blast deflectors (JBD) onboard aircraftcarriers are raised and lowered by hydrauliccylinders through mechanical linkage. Twohydraulic cylinders are attached to each JBD panelshaft by crank assemblies. (See fig. 12-9.) Theshaft is rotated by the push and pull operationof the hydraulic cylinders. Shaft rotation extendsor retracts the linkage to raise or lower the JBDpanels. This operation is designed so that in theevent of a failure of one of the hydraulic cylinders,the other one will raise or lower the panels.Figure 12-10 is a diagram of the hydrauliccontrol system of a JBD during the raise cycle.Hydraulic fluid from the catapult hydraulic supplysystem is supplied to the JBD hydraulic systemthrough an isolation valve and a filter to the 4-waycontrol valve assembly. (The 4-way control valveassembly consists of a pilot-operated controlvalve, a direct- or solenoid-operated control valve,and a sequence valve, which is not shown.)To raise the JBD, solenoid B of the 4-waycontrol valve assembly is energized. The spoolsof the 4-way valve assembly shift, allowingmedium-pressure hydraulic fluid to flow into portA of the hydraulic cylinder. The cylinders extend,Figure 12-9.—Operating gear assembly (panels raised).12-10
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