The valve rod assembly is composed of fabricated sections of seamless steel tubing joined by couplings to provide a mechanical link between the oil distribution (OD) box and the hub servomotor through the internal bore of the propeller shaft. The valve rod assembly provides a passage for high pressure hydraulic oil from the oil distribution box to the hub. Each valve sec-tion is supported at the center of the propeller shaft bore by guides. The after end of the valve rod assembly supports a regulating valve pin which operates in the valve pin liner of the hub servomotor. The forward end of the valve rod assembly is mechanically linked to the OD box shaft, so that the valve rod assembly turns with the shaft.

Oil Distribution Box

Presently there are two types of OD boxes being used in the Navy. One type, used on FFG-7 class and DD 963 class ships, is mounted to the forward end of the main reduction gear and is flange-connected to the main reduction gear shaft coupling. The other type, used on the LST 1179-1198 class ships, is called the Bird-Johnson Kamewa Unit; it is manufactured of steel, is cast in two sections, and is line-bored for installation over the intermediate shaft. The OD box provides a direct hydraulic oil connection to the main propulsion shaft and also translates to the valve rod in response to hydraulic control oil commands. High pressure oil from the hydraulic oil power module (HOPM) is introduced through the OD box to the internal bore of the valve rod and to the hub. The oil returns from the propeller hub to the hydraulic oil sump tank by way of the annulus between the valve rod and the internal bore of the shafting, through the OD box.

Hydraulic System

The hydraulic system consists of a self-contained HOPM, a standby hydraulic pump driven by the main reduction gear, the pitch con-trol valves manifold block assembly, and all the associated connecting piping, fittings, and valves. The hydraulic oil is supplied to the hydraulic oil pumps from a separate sump tank. To maintain a static head pressure when the hydraulic system is shut down, a gravity head tank is connected to the OD box.

HYDRAULIC OIL POWER MODULE. The HOPM is located adjacent to the main reduction gear. It is a RESILIENT mounted, welded structural assembly, consisting of a base plate with structural ANGLE bar, flat bar, and mounting plates. The HOPM contains the major components of the hydraulic system, including (1) either the motor-driven hydraulic screw or the vane pump, coupling, and AC motor; (2) a suction strainer for the motor-driven pump; (3) two 40 micron duplex discharge filters; (4) the pressure control assembly operating valves, which consist of a pressure reducing valve, an auxiliary relief valve, a check valve, an unloading and check valve, and a relief and sequence valve; (5) one 10 micron duplex control oil filter; (6) a gauge panel assembly and associated instrumentation; (7) a manual bypass valve; and (8) the interconnecting piping and fittings.

STANDBY PUMP.The standby pump is of the same type as the main hydraulic pump, but it is mounted at the forward end of the main reduction gear housing and is driven through a disconnect coupling. The suction strainer and suction gauge for this pump are mounted separately. The primary function of the standby pump is to assist the main pump in effecting pitch changes. When the control pitch (C/P) unit is in the holding pitch position, the standby pump discharge oil is unloaded back to the sump through the hydraulic block. But, whenever a pitch change is ordered, the pump discharge oil is directed to the hydraulic block high pressure passage.

LOWER OIL TANK.The lower (sump) oil tank is usually located aft and below the OD box assembly. The oil capacity of the sump varies depending on the type and class of ship. Two pumps, the main and standby hydraulic pumps, take suction on the lower oil tank through a foot valve, which permits the oil to flow from the tank but does not allow it to return through the suction line.

UPPER GRAVITY OIL TANK.This tank is located above the maximum draft line. Its main purpose is to maintain hub oil pressure above that of the surrounding seawater when the C/P unit is secured. In the Kamewa installation, the upper gravity oil tank serves an additional purpose. During C/P unit operation the tank assists in maintaining the sliding ring chamber pressure.