Quantcast Basic Mechanisms

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The purpose of this chapter is to explain some of the fundamentals of mechaniccs and hydraulics to help you better understand the ordnance equipment that you will be working within the fleet. We will also introduce you to the air and power supplies that are used by a shipboard GMLS and gun system. The control mechanisms of GMLS and gun systems involve a combination of mechanical, hydraulic, electrical, and electronic devices. By studying this chapter and the chapter that follows (on electricity and electronics), you should become familiar with most of the principles of how these devices operate. Understanding how these devices operate is the first step in becoming a good technician. Pay particular attention to the References listed throughout the text, which describe sources of more detailed information on each topic. These textbooks are included on the bibliography list for GM3 through GMC (from which advancement examination questions are referenced).


LEARNING OBJECTIVE: Discuss the operating principles of the mechanical devices used in ordnance equipment.

The movement and functioning of major systems (directors, launchers, and gun mounts) are accomplished, in part, using one or more basic mechanical devices. Our discussion centers on the functioning principles and applications of cams, gear trains, levers and linkages, couplings, and bearings.


A cam is an irregularly shaped device used to transmit motion through a follower. The cam surface contours are determined by the needs of the device the cam serves. The follower may be used to operate any number of other mechanisms.

In figure 4-1, we show a face cam being used in a cutout device for a gun firing circuit. The cam face is contoured to correspond to the ship's firing and nonfiring zones. Each position on the cam plate corresponds to a specific position of gun train and elevation. The low area corresponds to the positions in which the gun may be safely fired; the raised area corresponds to the areas where firing would endanger permanent ship's structure. The cam is geared to the train drive to rotate as the gun moves in train. The follower is linked to move across the face of the cam as the gun is moved in elevation. The follower is linked to a switch in the firing circuit that opens when the follower is raised by the high portions of the cam.

The face cam is one of many different styles. There are also barrel cams and edge cams. The barrel cam is similar to the face cam but is cylindrical in shape with the cam surface on the inside or outside. Both face and barrel cams are used in firing cutout mechanisms.

Figure 4-1.-A face cam used in a firing cutout mechanism. 4-1

Figure 4-2.-A. A barrel cam used as a firing cutout device in a 5"/54 gun; B. An edge cam positioning a hydraulic valve.

An edge cam is one that has the irregular surface machined around its outer edge. It may be stationary with the follower attached to a nearby moving component, or rotary. Edge cams are used to shift valves, to make or break switch contacts, and to position other mechanical devices. Figure 4-2 shows some of the uses of cams in ordnance equipment.


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