WARNING Before performing any maintenance procedures behind a JBD panel in the raised position, install three supports to prevent the panel from lowering. Failure to do this could result in serious injury to personnel. To ensure dependable operation of the JBD equipment, proper lubrication of the mechanical linkage is essential. Lubrication is part of the preoperational checks given in an MRC. Extension tubes are provided on trunnion bearings and hydraulic cylinder bracket assemblies so that all lube fittings can be reached from the deck. PROTECTING OPEN EQUIPMENT. —When removing a component from the hydraulic system, cap or plug all openings to prevent entry of foreign matter. Use tape to protect pipe threads. CLEANING. —Hydraulic system components must be disassembled, cleaned, repaired, and reassembled as specified in the operation, maintenance, and overhaul instructions manual for the specific type of JBD installation on your ship. WARNING Before repairing or removing any components connected to hydraulic or water lines, make sure the lines are repressurized. Also, before repairing or removing any electrical component, de-energize the electrical circuit and attach an out-of-service tag. HOSES, SEALS, AND O-RINGS. —Hoses, seals, and O-rings are selected on the basis of their compatibility with the hydraulic fluid. Therefore, replacement parts should be of the same material as original parts. O-rings must be removed and replaced with care to avoid damage to the O-ring and O-ring sealing surfaces of the various parts. O-rings must be free of cuts and not deformed. New O-rings must be installed at every reassembly of components.   Before assembly, all O-rings must be lightly lubricated with the system hydraulic fluid. Hoses are subject to wear and require periodic replacement. When installing hoses, take care to avoid unnecessary bends and overstressing. To restore the JBD system to operating condition after a down period that required draining of fluid, perform preoperational inspection procedures given in the applicable MRC. For most repairs to the hydraulic system, only portions of the system need be drained. Isolation valves in each of the hydraulic cylinder lines, manifold shutoff valves, and a shutoff valve between the filter and the catapult pumps permit isolation of portions of the JBD hydraulic system. The entire JBD system can be drained, if necessary, by closing only the shutoff valve, venting the high points, setting the four-way valves at UP or DOWN, and draining at the filter. Drive Mechanism Maintenance If drive mechanism mechanical parts are damaged or require replacement because of wear, proceed as follows: 1. Relieve hydraulic system pressure. 2. Support or block the link, arm assembly, hydraulic cylinder, and all other components that may fall free when unfastened or when pins are removed. 3. Support the panel with three supports. 4. Remove the pin that connects link and arm assembly. Examine the bushing of the arm assembly for wear, and replace it if necessary. 5. Remove the pin that connects the panel and link. Examine the bushing of the panel lug assembly for wear, and replace it if necessary. 6. Remove the pin that connects the clevis and crank assembly. Examine the bushing for wear, and replace it if necessary. 7. Disassemble the crank assembly and remove it from the trunnion shaft. Examine the key and key slots for wear, and replace the worn parts if necessary. 8. Disassemble the arm assembly and remove it from the trunnion shaft. Examine the key and key slots for wear, and replace the worn parts if necessary. 5-10