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Single Shank Centering Devices Single shank-type arresting hook assemblies are held in the centerline position for retraction into their fuselage recesses. The centering devices prevent side movement of the assembly during carrier-arrested approaches. LIQUID SPRING. The representative arresting gear mechanism, shown in figure 12-56, uses a liquid spring for this purpose. The spring is located within a recess of the hook shank, and the keyed end presses against the centering cam. On installation, shim the spring until the thickness of the spacer and shims is approximately 0.125 inch. Install the spring in the shank, and then secure the shank to the drag link. Check the hook point for excessive side play. If side play exceeds 0.24 inch, add more shims to the spring. The total thickness of shims must not exceed 0.185 inch. Anytime shim thickness exceeds 0.150 inch, move the hook laterally several times in each direction to make sure that the hook can move 40 degrees left and right without bottoming out the liquid spring.While liquids are normally thought of as incompressible, the action of the liquid spring is based
1. Cap Figure 12-57.Liquid spring shock assembly. on the slight compressibility of liquids. Figure 12-57 illustrates the disassembled spring assembly. Most of the internal parts are classified as nonrepairable, and damage will require replacement of the parts at the depot level of maintenance. The spring assembly contains 19 cubic centimeters of oil, MIL-S-21568. The oil is confined within the piston cylinder assembly, and any side movement of the arresting hook shank must be against the compressibility of the oil. The maximum travel or compressibility of the overall liquid spring assembly is 0.68 inch. The operating pressure within the assembly, when bottomed out, will be as high as 20,000 psi. In the static condition, the oil trapped within the spring assembly is under a return preload pressure of 350 pounds, which is created by the reassembly of the close tolerance parts that confine the liquid. The tolerances of parts within the liquid spring and the necessity to subject certain parts to approximately 110F for varying lengths of time during the disassembly and assembly process make it impractical for it to be overhauled at the lower levels of mainte-nance. |
 
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