LEARNING OBJECTIVES: Describe the hydraulic system and components used in the Mk 45 gun mount. Explain the mechanics of pneumatic systems used in ordnance equipment.

The MK 45 hydraulic system is divided into two components: stationary and rotating (fig. 4-55). The stationary gun-loading system components are in the loader room and in the ammunition-handling room-a compartment one or more decks below the loader room. The stationary components are a loader drum, the fuze setter, a hydraulic power source (lower accumulator), and a lower hoist (if required). 'The rotating hydraulic components are a cradle and rammer, a breech mechanism, an empty case ejector, an empty case tray, recoil-counterrecoil system, some components of the slide, and a hydraulic power source (upper accumulator). The slide itself is primarily a supporting structure and a counterbalance for the gun barrel. .

LOWER ACCUMULATOR SYSTEM

The lower accumulator system (fig. 4-56), mounted in the loader room, provides the hydraulic power for operating the lower hoist, the loader drum, the fuze setter, and the upper hoist. The major components of the system include a main supply tank, a header tank, a

Figure 4-56.-Lower accumulator system.

main motor and pump, an exercise and emergency power drive, hydraulic controls, and an accumulator.

Lower Hoist

The lower hoist (fig. 4-57) provides a means for ammunition handlers (members of the gun mount crew)

Figure 4-57.-Lower hoist.

Figure 4-58.-Loader drum.

Figure 4-59.-Fuze setter.

to onload 5-inch 54-caliber ammunition into the loader drum from a remote station. It also provides a means for striking down ammunition into the ship's ammunition room.

Loader Drum

The loader drum (fig. 4-58) receives and stows ready service ammunition, positions the rounds for fuze setting, and ejects them-one by one-into the upper hoist. A rotating drum indexes as a unit within the cagelike support structure of the loader drum.

Fuze Setter

The fuze setter (fig. 4-59), an electrohydraulic device mounted atop the support structure for the loader drum, sets mechanical time (MT) or control variable time (CVT) fuzes on projectiles positioned for mechanical fuze setting in the transfer station. The coil assembly, at the base of the fuze setter, energizes to set the ESFs electronically (electronically settable fuzes).