Lubricant sealing means for rotary positive displacement pump

Claim 1

IN A ROTARY POSITIVE DISPLACEMENT VACUUM PUMP HAVING A CASING FORMING A PUMPING CHAMBER, A FLUID INLET AND A FLUID OUTLET IN COMMUNICATION WITH SAID CHAMBER, A PAIR OF MULTILOBED INTERFITTING IMPELLERS MOUNTED WITHIN SAID CHAMBER ON SPACED PARALLEL SHAFTS GEARED TOGETHER FOR ROTATION IN OPPOSITE DIRECTIONS SO AS TO DISPLACE FLUID FROM SAID INLET TO SAID OUTLET, BEARING MEANS SUPPORTING EACH OF SAID SHAFTS AT THE OPPOSITE ENDS THEREOF, AND MEANS FOR SUPPLYING LUBRICATING OIL TO SAID BEARING MEANS, THE IMPROVEMENT COMPRISING SEALING MEANS FOR PREVENTING OIL FROM PASSING FROM SAID BEARING MEANS INTO SAID CHAMBER, SAID SEALING MEANS BEING DISPOSED BETWEEN SAID BEARING MEANS AND SAID CHAMBER AND INCLUDING A ROTATABLE MEMBER CARRIED BY EACH OF SAID SHAFTS, SAID MEMBER HAVING A SLINGER ELEMENT AT THE END THEREOF ADJACENT SAID BEARING MEANS, A FIXED SLEEVE MEMBER DISPOSED ABOUT AND SPACED FROM EACH OF SAID ROTATABLE MEMBERS AND HAVING AT LEAST ONE ANNULAR GROOVE IN THE INNER SURFACE THEREOF, SAID GROOVE FORMING A POCKET FOR TRAPPING OIL WHEN THE PUMP IS SHUT DOWN, A DRAINAGE PASSAGE IN SAID FIXED SLEEVE MEMBER LEADING FROM SAID GROOVE TO A POSITION ADJACENT SAID SLINGER ELEMENT, WHEREBY TRAPPED OIL IS PUMPED OUT OF SAID POCKET THROUGH SAID DRAINAGE PASSAGE PON ROTATION OF SAID SLINGER ELEMENT AND MEANS FOR PREVENTING A DIFFERENTIAL PRESSURE BUILD UP ACROSS SAID SEALING MEANS INCLUDING A PLURALITY OF PASSAGES, EACH PASSAGE HAVING ONE END DISPOSED IN COMMON COMMUNICATION AND THE OTHER DISPOSED IN COMMUNICATION WITH ONE SIDE OF SAID SEALING MEANS SUCH THAT THE PRESSURE ACROSS SAID SEALING MEANS IS EQUALIZED.