The roller bearing assemblies just described can be disassembled for replacement of parts, for cleaning, and for examination. Ball bearings, on the other hand, usually are assembled by the manufacturer and installed as a unit. Like roller bearings, the ball bearings reduce friction and, in some applications, prevent unwanted movement.

Sometimes maintenance publications refer to roller-and-ball bearings as being either radial or thrust

Figure 4-12.-Ball bearings: A. Radial type; B. Thrust type.

bearings. The difference between the two depends upon the angle of intersection between the direction of the load and the axis of rotation of the bearing. Figure 4-12, view A, shows a radial ball bearing assembly. The load here is pressing outward along the radius of the shaft. Now suppose a strong thrust is exerted on the right end of the shaft, tending to move it to the left. The radial bearing is not designed to support this axial thrust. Even putting a shoulder between the load and the inner race would not do. It would just pop the bearings out of their races. The answer is to arrange the races differently, as shown in view B. Here is a thrust bearing. With a shoulder under the lower race and another between the load and the upper race, it will handle any axial load up to its design limit.

The horizontal bearings shown in figure 4-11, view A, are another example of a roller thrust bearing assembly. The vertical roller bearings in the illustration are called radial bearings. Sometimes bearings are designed to support both thrust and radial loads, thus the term radial thrust bearings. For an example of such bearings, see the tapered roller bearings in figure 4-11, view B.

HYDRAULIC MACHINES

LEARNING OBJECTIVE: Discuss the principles of hydraulics and the application of hydraulics in ordnance equipment.

Hydraulic machines are used throughout ordnance equipment. They provide smooth and accurate train and elevation movement for gun mounts and missile launchers and operate the loading systems. To appreciate the usefulness of hydraulics, we need to understand some basic characteristics and definitions. In the practical sense, hydraulics is concerned with the uses of a fluid-filled system in transmitting applied forces and producing (or controlling) mechanical motion.

FLUID CHARACTERISTICS

Let's deal first with the transmission of applied force. There are two qualities of fluid that make them useful as a means to transmit force. They are (1) they take the shape of their containers and (2) they are not compressible. Therefore, pressure applied to a fluid in a closed container will be felt equally against the entire inside surface of the container. The force is transmitted equally in all directions, as shown in figure 4-13. This is true regardless of the shape of the container. This means that it is not necessary for the tube connecting the two pistons to be as large as the pistons throughout.

Figure 4-13--Force transmitted through fluid.

A connection of any size, shape, or length will do, as shown in figure 4-14. The size of the line, however, will determine the volume of fluid flow, which, in turn, affects operating speed.

In figures 4-13 and 4-14, the systems contain pistons with the same area. This makes the output force equal to the input force. Remember what we said earlier-the force applied is transmitted to all surfaces in the container equally. Now consider figure 4-15. The input piston is much smaller than the output piston. Assume the area of the input piston is 2 square inches. With a force of 20 pounds applied to it, a pressure of 10 pounds per square inch (psi) will be felt throughout the container, including the output piston. The upward force on the output piston is therefore 10 pounds for each of its 20 square inches, or 200 pounds. We have effectively multiplied the applied force.

The system works the same in reverse. Consider piston (2) the input piston and piston (1) the output. The output force will be one tenth of the input force.

You should now have a basic understanding of hydraulic principles. More information on hydraulic principles and theory can be found in the Navy training manual Fluid Power, NAVEDTRA 12964. This manual has a wealth of information that will be very useful to you as a Gunner's Mate.