(d) Plug-retainer assembly. This assembly consists of a metal rod and chain which hang from the plug and prevent accidental loss of the plug when filling or inspecting.
b. Removal of plugs.
(1) Before removing the filling plug, the safety-head plug, or an unbroken safety head, operate the fuel valve until any pressure which may have accumulated in the fuel tanks is eliminated. If the coupling plug is in the tank coupling, very slightly loosen the threads of either the filling plug or the safety-head plug, using the 1-3/4-inch wrench, to eliminate pressure in the fuel tanks. Keep face and eyes away from the threads.
(2) The plug-retainer assemblies should not be lifted completely out of the tanks unless required.
(3) If either the rod or the rod and chain breaks from one of the plugs and falls into the tank, upend the tank group to permit removal of the parts.
(4) To replace burst safety head, unscrew lock nut and deflector tube. ([Fig 11]) Using wrench ([Fig 41]), unscrew safety head. Never disassemble the safety head.
c. Installation of plugs. The filling plug, safety-head plug, and safety head are screwed in by hand and then tightened with wrenches. No substitution will be made for the safety head, which is manufactured to burst at the safe limit of pressure. The plug threads and seats should be cleaned with a cloth ([Fig 29]) before installing plugs. Screw in deflector tube, using hand pressure. The tube outlet should face to the rear and at a 45-degree angle to operator’s left shoulder. ([Fig 18]) Replace lock nut and tighten with wrench. (Use wrench on lock nut, not on deflector tube.)
d. Maintenance of plugs. Replace safety head if damaged or blown. Never repair safety head or use an improvised head.