A filter system for filtering cleaning solvents includes a first filter unit having mechanical filters such as paper or the like, through which the fluid is first pumped, and a second filter unit having adsorption chemicals, such as clays and charcoal, through which at least a portion of the fluid from...http://www.google.com/patents/US4277336?utm_source=gb-gplus-sharePatent US4277336 - Multiple by-pass filter system
