Dual element, dual valve filter

Claim 1

A MULTISTAGE FILTER UNIT COMPRISING A HOLLOW, SUBSTANTIALLY CYLINDRICAL, CASING HAVING ONE CLOSED END AND THE OTHER END PORTION CLOSED EXCEPT FOR A PAIR OF PORTS PROVIDING RESPECTIVELY FLUID INLET AND OUTLET PORTS FOR THE CASING, A FIRST, SUBSTANTIALLY CYLINDRICAL, HOLLOW, FILTER ELEMENT, MOUNTED CONCENTRICALLY WITHIN AND SPACED FROM THE INTERIOR WALLS OF SAID CASING WITH THE BORE OF SAID FIRST FILTER ELEMENT EXTENDING LONGITUDINALLY OF THE CASING AND SUBSTANTIALLY ALIGNED WITH AND CONNECTED TO THE CASING OUTLET PORT, SAID FIRST FILTER ELEMENT PROVIDING A FIRST STAGE OF FILTERING ACTION, A SECOND PRE-FORMED, SUBSTANTIALLY BAR-SHAPED, FIBROUS, FILTER ELEMENT MOUNTED IN AND ARRANGED FOR MOVEMENT LONGITUDINALLY OF THE BORE IN SAID FIRST FILTER ELEMENT, AND A FIRST PRESSURE FLUID RESPONSIVE VALVE MEANS CARRIED BY THE UPPER END OF SAID SECOND FILTER ELEMENT TO CONTROL FLUID FLOW THROUGH A FIRST PORTION OF SAID BORE AND THROUGH SAID SECOND FILTER ELEMENT TO PROVIDE A SECOND STAGE OF FILTERING ACTION, AND A SECOND PRESSURE FLUID RESPONSIVE VALVE MEANS CARRIED BY SAID SECOND FILTER ELEMENT TO CONTROL FLUID FLOW THROUGH A SECOND PORTION OF SAID BORE FOR BY-PASSING SAID SECOND FILTER ELEMENT.