Dual element, dual valve filter assembly

Claim 1

A FILTER UNIT FOR AN ENGINE LUBRICATING SYSTEM COMPRISING A CASING HAVING A SINGLE INLET OPENING AND A SINGLE OUTLET OPENING CONCENTRIC TO SAID INLET OPENING FOR THE LUBRICANT BEING FILTERED, MEANS FORMING A BYPASS DIRECTLY BETWEEN SAID SINGLE INLET AND SAID SINGLE OUTLET, A VALVE IN SAID BYPASS ADAPTED TO OPEN AT A PREDETERMINED PRESSURE DIFFERENTIAL, AN ANNULAR BODY OF FINE FILTERING MEDIUM IN SAID CASING, A CENTRAL BORE OF COARSE FILTERING MEDIUM WITHIN SAID ANNULAR BODY, IMPERVIOUS TUBULAR MEANS SEALED BETWEEN ONE END OF SAID CORE AND THE CORRESPONDING END OF SAID ANNULAR BODY, SAID TUBULR MEANS FORMING SEPARATE PASSAGEWAYS FOR CONVEYING FILTERED LUBRICANT FROM SAID ANNULAR BODY AND SAID CENTRAL CORE TO SAID SINGLE OUTLET, MEANS FORMING A PASSAGEWAY FROM SAID CASING TO A SURFACE OF SAID CENTRAL CORE THROUGH SAID SEALED END OF SAID TUBULAR MEANS, AND ANOTHER VALVE FOR CONTROLLING PASSAGE OF LUBRICANT THROUGH SAID PASSAGEWAY TO SAID CENTRAL CORE, SAID OTHER VALVE BEING ADAPTED TO OPEN AT A LOWER PRESSURE DIFFERENTIAL THAN SAID BYPASS VALVE, WHEREBY LUBRICANT IS ADMITTED TO SAID COARSE FILTER MEDIUM FROM SAID INLET ONLY AFTER SAID FINE FILTERING MEDIUM IMPOSED A PREDETERMINED PRESSURE DIFFERENTIAL TO THE FLOW OF LUBRICANT THERETHROUG.