Apparatus for measuring the difference between hydrostatic and formation pressure ina borehole

Claim 1

APPARATUS FOR MEASURING THE PRESSURE DIFFERENTIAL BETWEEN THE HYDROSTATIC PRESSURE OF THE MUD COLUMN EXISTING IN A BOREHOLE ANNULUS AND THE FORMATION PORE PRESSURE AT THE SAME DEPTH COMPRISING: (A) A DRILL STRING; (B) A TUBULAR MEMBER CONNECTED IN SAID DRILL STRING AND FORMING A PORTION THEREOF, SAID TUBULAR MEMBER HAVING A TRANVERSE CAVITY FORMED IN THE WALL THEREOF WHICH IS OPEN TO THE ANNULUS OF THE WELL AND COMMUNICATES WITH THE INTERIOR OF SAID TUBULAR MEMBER THROUGH AN APERTURE; (C) MEANS MOUNTED WITHIN SAID TUBULAR MEMBER FOR SELECTIVELY OPENING AND CLOSING SAID APERTURE; (D) A CYLINDER HAVING ONE CLOSED END SLIDABLY MOUNTED IN A FLUID-TIGHT MANNER WITHIN SAID TRANSVERSE CAVITY, THE END OF SAID CYLINDER ADJACENT THE WALL OF SAID BOREHOLE FORMING AN OPEN FUNNEL SHAPED CHAMBER;