It is interesting that Donaldson gives proper procedures to "wash" and dry a filter. What interests me is that talking to any mechanic or equipment manufacturer and they will recomend against it - yet the people that MADE the filter - who you would assume should know something about filter maintence - say you can.

I can see in a situation like you describe, where filter costs might really add up, it might be aceptable. For us at our replacement interval and the recomendation on replacement by age it would not be worth the hassle. Most manuals recomend to replace every year regardless of hours or cleanings. We strech that to two because we only put 4-600 hrs/ year on most of our tractors. Our utility tractors that work in the turkey barn dust get them every year and the combines usually do. Vibration can cause filter failure by vibrating holes in the media where the paper rubs against the wire. I think that is why they recomend annual replacement. If we were putting 1000-1200 hours a year on them like Dutch or other southern farmers I would replace every year.

John