MOISTURE SEPARATION SYSTEM.— The moisture separation system includes the

inlet louvers and the demister panels. The inlet louvers are arranged in sections. They are located in the sides of the high hat assembly. The design and arrangement of the louvers aresuch that they will shed sea spray. The louvers are electrically heated to prevent icing. These heaters type and are located on the back of the louver surface. The heaters are controlled from the engine control consoles. The demisters are the two-stage, mesh-pad type and are mounted vertically behind the louvers. Water, separated from the inlet air as it passes through the demisters, is collected in scuppers and drained overboard. The demisters will remove 70 percent of the particles that are 1.7 to 5 microns in size and 90 percent of the particles that are 5 microns and larger.

BLOW-IN DOORS.—The blow-in doors are located just below the inlet louver Then function is to bypass the moisture seperation system. They provide an unrestricted inlet airflow to the engines if the moisture separation system becomes blocked. They are designed to open by solenoid-operated latch mechanisms, and will open if the inlet airflow becomes too restricted for normal engine operation.

On the DD-class ships, a controller is located in each engine room to provide for manual or automatic operation of the doors. This is done by a selector switch and a push button on the controller door. On the CG-class ship this controller is in the helo hangar. The push button on the CG-class is located on the high hat assembly. In manual operation, you can only open the doors by depressing the push button. In automatic operation the doors open by operation of a pressure switch. The switch operates on low duct pressure. This pressure switch also provides a DUCT PRESSURE LOW signal to propulsion auxiliary machinery control equipment (PAMCE) and propulsion local control equipment (PLOE). The pressure switch operates when duct pressure falls below 8 inches of water. If the doors open, the doors must be manually reset closed.

Ducting

See figure 2-12 as we discuss the ducting. It allows the air to travel from the high hat assembly to the inlet of the compressor. The components of the ducting include the silencers, the anti-icing piping, the cooling air duct, and the engine removal system.

SILENCERS. —The main engine intake duct silencers are located about halfway clown the duct. The silencers are vertical vane assemblies constructed of sound-deadening material. The intake ducts are encased in perforated stainless steel sheet. The vane assemblies are arranged in modules which are removable to aid in the removal of the GTEs through the intake duct.

ANTI-ICING SYSTEM.—This system pre- vents the formation of ice in the intake duct. High-temperature bleed air from the GTEs is piped to a manifold. This manifold is located inside the duct between the cooling air extraction port and the silencers. From the manifold the bleed air is discharged into the inlet airstream. The bleed air is mixed with the inlet air, raising the temperature enough to prevent the formation of ice. When enabled from the PAMCE or the PLOE, an electromechanical control system regulates bleed air flow to maintain the inlet air temperature at about 38°F. This prevents the formation of ice. A temperature sensor in the stack provides an ANTI-ICING INSUFFICIENT signal. This alarm activates when the anti-icing system has been enabled and the temperature drops below 36°F.

COOLING AIR DUCT.—Main engine cooling air is extracted from the main intake duct. It is taken at a point between the blow-in doors and the main duct silencers. It is then ducted to the engine enclosure. The cooling air duct contains a silencer and a cooling air fan. The cooling system will be discussed in more depth later in this chapter.

ENGINE REMOVAL SYSTEM.—Sometimes a main propulsion GTE must be removed from the ship for maintenance/overhaul. At the time of engine removal, a set of channel-shaped maintenance rails is installed in the engine enclosure. These are put adjacent to each side of the engine. A set of rollers, which fit into the rails, is attached to each side of the engine. The removable maintenance rails extend into the enclosure inlet plenum. They then turn 90 degrees, from horizontal to vertical attitude. They mate with permanently installed rails that extend up the intake duct. In the FFG-class ship, the uptake rails must be installed each time the engine is removed. The engine is removed through the intake duct. In the inlet plenum, three sets of maintenance rails interface with three sets of permanently installed rails in the ship’s intake

Figure 2-14.—FFG air intake system.

duct. The permanently installed rails extend through the high hat section. These serve to guide the engine as it is lifted vertically from the ship. Removal of the engine is accomplished in two operations due to space constraints. The GG is separated from the PT while still in the enclosure. Then it is removed from the ship, followed by removal of the PT.