Keller Products was founded in 1990 as a supplier of engineered filtration products for the industrial market. The major initial product line was a series of cartridge filters utilizing the unique Keller plastic stacked disc washable filter element. To meet customer requirements, cartridge filters with replaceable filter elements and bag filters were added to the line. Keller industrial filters continue to enjoy a substantial market in filtration of cooling water, municipal water supplies, and pond and well water.

In marketing filters to industrial users and machine shops, the Keller salesmen received numerous requests for rugged and practical oil/water separators, particularly for the removal of tramp oil from water-base machine tool coolant. Keller management recognized that a modification of the stacked disc filter element could be the basis for a compact, efficient, and rugged oil/water separating (coalescing) element. Intensive development work led to the inroduction in 1994 of the first Keller pump/separator units based on the stacked disc separator element. U.S. Patent 5,401,404, issued in 1995, covers the unique Keller oil/water separator design. Another patent is pending.

Keller has continuously improved and simplified the pump/separator units since they were first introduced. There are now over 5000 units in shops, and Keller introduces new separator models and related products for machine shops based on continuing discussions with present and potential shop users.