Gear sets operate under such varied conditions that it is
difficult to give general suggestions for prevention of contamination of the
gear lubricant. The two contaminants most often encountered are water and dust.
In the latter are included large particles such as scale in steel mills. Less
trouble is encountered where a circulating system provides the lubricant rather than a splash system, since the former can be supplied with settling tanks or filters. Even here regular
inspection is necessary and accumulated water should be drawn off whenever
noted. Such accumulations may be
quite large in the case of gear oils for ship propellers or in oils servicing paper mill machinery or steel mill gears.
Where gear
cases are vented, the location of the vent or a pipe connection to the same should be so located that the least dirt possible can enter. One automobile manufacturer reduced contamination in differential cases by extending a line from the vent and securing it forward under the car frame with the opening toward the side of the vehicle.
Prevention of contamination of lubricants by chemicals
must have individual consideration. In extreme cases it may be necessary to provide pressure on gear cases to prevent entry of contaminants.
