Chapter 4—REDUCTION GEARS AND RELATED EQUIPMENTfrom the shafting to the hub assembly. The hubis secured to the tailshaft by flange bolts. Thesebolts are not designed to take torque from the tailshaft. The hub to tailshaft joint is sealed byO-rings located between the hub and the tailshaft,and between the tailshaft and the tailshaft spigot.Each blade is attached to a crank pin ring by bladebolts. The crank pin ring fits over and rotatesabout a center post which is physically a part ofthe hub body. The crank pin ring is retained inthe hub by the bearing ring. The area under eachblade is sealed by the blade port cover and by twoO-rings in the blade seal base ring. Each bladeseal base ring is spring-loaded against the under-side of the blade port cover to provide a sealingsurface under all loading conditions.The blade turning mechanism in the hub con-sists of a single crosshead, attached to the end ofa piston rod. Several sliding blocks are fittedinto the machined chambers of the crosshead. Aneccentric pin on the underside of each crank pinring fits into a hole machined into each slidingblock. The hub servomotor is attached to the afterend of the crosshead. A piston rod carries the linesfor the regulating valve pin which is attached tothe end of the valve rod. This assembly forms apassage for hydraulic power oil flow and returnoil flow to and from the hub.class and DD 963 class ships, is mounted to theforward end of the main reduction gear and isflange-connected to the main reduction gear shaftcoupling. The other type, used on the LST1179-1198 class ships, is called the Bird-JohnsonKamewa Unit; it is manufactured of steel, is castin two sections, and is line-bored for installationover the intermediate shaft. The OD box providesa direct hydraulic oil connection to the main pro-pulsion shaft and also translates to the valve rodin response to hydraulic control oil commands.High pressure oil from the hydraulic oil powermodule (HOPM) is introduced through the ODbox to the internal bore of the valve rod and tothe hub. The oil returns from the propeller hubto the hydraulic oil sump tank by way of the an-nulus between the valve rod and the internal boreof the shafting, through the OD box.Hydraulic SystemValve Rod AssemblyThe valve rod assembly is composed offabricated sections of seamless steel tubingjoined by couplings to provide a mechanical linkbetween the oil distribution (OD) box and the hubservomotor through the internal bore of thepropeller shaft. The valve rod assembly providesa passage for high pressure hydraulic oil from theoil distribution box to the hub. Each valve sec-tion is supported at the center of the propellershaft bore by guides. The after end of the valverod assembly supports a regulating valve pinwhich operates in the valve pin liner of the hubservomotor. The forward end of the valve rodassembly is mechanically linked to the OD boxshaft, so that the valve rod assembly turns withthe shaft.The hydraulic system consists of a self-contained HOPM, a standby hydraulic pumpdriven by the main reduction gear, the pitch con-trol valves manifold block assembly, and all theassociated connecting piping, fittings, and valves.The hydraulic oil is supplied to the hydraulic oilpumps from a separate sump tank. To maintaina static head pressure when the hydraulic systemis shut down, a gravity head tank is connected tothe OD box.Oil Distribution BoxPresently there are two types of OD boxesbeing used in the Navy. One type, used on FFG-7HYDRAULIC OIL POWER MODULE.—The HOPM is located adjacent to the main reduc-tion gear. It is a RESILIENT mounted, weldedstructural assembly, consisting of a base plate withstructural ANGLE bar, flat bar, and mountingplates. The HOPM contains the major com-ponents of the hydraulic system, including (1)either the motor-driven hydraulic screw or thevane pump, coupling, and AC motor; (2) a suc-tion strainer for the motor-driven pump; (3) two40 micron duplex discharge filters; (4) the pressurecontrol assembly operating valves, which consistof a pressure reducing valve, an auxiliary reliefvalve, a check valve, an unloading and checkvalve, and a relief and sequence valve; (5) one 10micron duplex control oil filter; (6) a gauge panelassembly and associated instrumentation; (7) amanual bypass valve; and (8) the interconnectingpiping and fittings.4-13
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business