Back pressure valve

Claim 1

IMPROVED ASSEMBLY FOR POSITIONING IN A BOREHOLE TO MAINTAIN BACK PRESSURE IN SAID BOREHOLE WHICH COMPRISES AN OUTWARDLY AND DOWNWARDLY FLARED CONICAL STRUCTURE THUS DEFINING A FRUSTO-CONICAL VALVE STRUCTURE, AN OPENING IN THE UPPER AREA OF SAID STRUCTURE PERMITTING COMMUNICATION FROM WITHOUT SAID STRUCTURE TO WITHIN SAID STRUCTURE, A CIRCULAR CUP ATTACHED TO THE BOTTOM OF SAID STRUCTURE, THE BASE OF SAID CUP BEING FRANGIBLE, A GUIDE EXTENDING UPWARDLY FROM SAID BASE, AND A BALL POSITIONED IN THE AREA DEFINED BY SAID GUIDE, SAID BASE AND THE WALLS OF SAID CUP WHEREBY SAID BALL IS LOCKED INTO A RELATIVELY FIXED POSITION, THE DENSITY OF SAID BALL BEING LESS THAN THE DENSITY OF BOREHOLE FLUD, MEANS FOR FACTURING SAID BASE THEREBY PERMITTING MOVEMENT OF SAID BALL WITHIN SAID STRUCTURE, WHEREBY AS FLUID FLOWS DOWNWARDLY THROUGH SAID OPENING FREE PASSAGE OF THE SAME IS PERMITTED; BUT ON BACK FLOW OF FLUID SAID BALL SEATS IN SAID STRUCTURE THEREBY PREVENTING BACK FLOW OF SAID FLUID.