Nearly all hydraulic component manufacturers and users agree that dirt is responsible for a majority of malfunctions, unsatisfactory component performance, and degradation. Dirt is introduced into hydraulic systems at the time of fabrication of the components and during the manufacture of the system. Contamination that enters the oil from the environment surrounding the hydraulic system can do so by following several paths. These entry points include air breathers, access plates, and seals. The awareness of the sources, the effect on the system, and control of contamination will develop habits within the maintenance people that are conducive to minimizing the introduction of dirt by shop activities. It is well known that contaminant particles are of all shapes and sizes, and that the finer they are, the more difficult it is to count them and to determine the material of which they are composed.