Downloaded from https://www.everyspec.com FM 1-509 An example of how to apply the mechanical advantage is illustrated in Figure 1-5. It shows how big the large piston must be to raise an 800-pound weight. The 800-pound weight must be raised by applying a 40-pound force to the 4-square-inch piston. The mechanical advantage in this case is 20 (800 pounds divided by 40 pounds) and is expressed as a 20-to-l ratio. By multiplying 20 times 4 square inches (area of the small piston), the area of the large piston should be 80 square inches. The mechanical advantage also applies to the distance the piston moves--length of stroke.
Assuming that the large piston must move 10 inches, multiplying this factor by 20 gives 200 inches as the length of stroke for the small piston. Of course, the small piston moving that far on a single stroke would not be feasible; therefore, the small piston must move through a series of short repeated strokes. Contamination. Contamination of fluids in a hydraulic system occurs when any material is present other than the hydraulic fluid being used. This includes water, metal, dust, and other solids. Contamination sources may be internal or external. Internal contamination can cause normal wear of the pump or other components.
When filters are used too long (especially the paper-element type), particles may begin breaking off from the filter element. Moving seals and backup rings also add contamination to the system. External contamination is generally caused by poor maintenance practices. Examples include leaving hydraulic lines open after removing a part; wiping fittings with dirty rags; leaving valves, tubing, and so forth uncovered on workbenches; changing fluid with dirty test equipment; and installing new or rebuilt parts that have not been properly cleaned. 1-8