Dual, alternately operating, interlocked liquid filters

Claim 1

A LIQUID FILTER COMPRISING A HOUSING HAVING THEREIN TWO CYLINDERS AND AN INTAKE PORT AND A DISCHARGE PORT COMMUNICATING WITH EACH CYLINDER, A SLEEVE PISTON IN EACH OF THE CYLINDERS HAVING AN ADVANCED AND A RETRACTED POSITION, SUCH SLEEVE PISTONS PREVENTING COMMUNICATION WITH THE DISCHARGE PORT WHEN IN AN ADVANCED POSITION AND PERMITTING SUCH COMMUNICATION WHEN IN A RETRACTED POSITION, MEANS INTERLOCKING THE TWO SLEEVE PISTONS SO THAT WHEN ONE IS IN AN ADVANCED POSITION THE OTHER IS IN A RETRACTED POSITION, A FILTER CARTRIDGE IN EACH SLEEVE PISTON HAVING THEREIN A RAISED AND A LOWERED POSITION, SUCH FILTER CARTRIDGE FURTHER HAVING AN INNER AND OUTER FACE THEREON AND A TOP AND A BOTTOM OPENING, A SMALL CYLINDER ADJACENT THE UPPER END OF EACH SLEEVE PISTON, A CAP OVER THE TOP OPENING IN THE FILTER CARTRIDGE HAVING A SLEEVE SLIDABLE ON THE SMALL CYLINDER, LOCKING MEMBERS SLIDABLY CARRIED BY THE SMALL CYLINDER, A PISTON IN THE SMALL CYLINDER FOR MOVING THE LOCKING MEMBERS INTO HOLDING ENGAGEMENT WITH THE SLEEVE, MEANS PROVIDING COMMUNICATION BETWEEN THE OUTER FACE OF THE FILTER CARTRIDGE AND THE UPPER SURFACE ON THE SMALL PISTON WHEN THE FILTER CARTRIDGE IS IN A LOWER POSITION, AN AXIAL ROD FIXED IN THE PISTON AND PROJECTING DOWNWARD THROUGH THE CAP, AN ADJUSTABLE RESILIENT MEMBER ON THE AXIAL ROD URGING THE PISTON DOWNWARD SO AS YIELDABLY TO HOLD THE LOCKING MEMBERS IN ENGAGEMENT WITH THE SLEEVES WHEN THE FILTER CARTRIDGE IS IN THE LOWERED POSITION, A CLOSURE DISC OVER THE BOTTOM OPENING IN THE FILTER CARTRIDGE SLIDABLE IN THE SLEEVE PISTON, AND HAVING THEREIN A PLURALITY OF OPENING, A SPRING IN EACH CYLINDER YIELDABLY URGING THE FILTER CARTRIDGE AND THE MEMBERS THEREON TO A RAISED POSITION, AND MEANS IN THE SLEEVE PISTONS FOR OPERATIVELY ENGAGING THE UPPER SIDE OF THE CLOSURE DISC.