The concept of purifying oils to be used for electrical insulating purposes, such as dielectric oils used in transformers, circuit breakers, and the like by removing water therefrom, which water is absorbed by water absorption, is well known in the art. For example, Roberts et al, in their U.S. Pat. No. 2,067,345 teaches placing in the oil a finely divided absorbent material, such as activated carbon, silica, and the like. The water containing oil may be subjected to a filtration step to remove the water therein. After water removal, the oil is used for its intended purposes.
The U.S. Pat. No. 2,233,093, issued to Carman et al discloses an oil filter for use with an internal combustion engine. It comprises an oil filter cartridge having a homogeneous filter bed of discrete particles in combination with a fibrous mat to direct the oil to be filtered and distribute it uniformly into the filter bed. Moisture may be released from the filter bed when the oil becomes heated because the engine has operated for sometime.