1. A MECHANICAL VACUUM PUMP OF THE ROTARY, FLUIDSEALED, INTERNAL VANE TYPE MOUNTED WITHIN A HOUSING AND HAVING INTAKE AND EXHAUST CONNECTIONS ON SAID HOUSING AND COMPRISING, (A) A STATIONARY PUMP ASSEMBLY ON THE INTERIOR OF THE HOUSING AND INCLUDING A CENTRAL STATOR AND END PLATES AND A CYLINDRICAL BORE WITHIN THE STATOR, (B) AN ECCENTRICALLY MOUNTED CYLINDRICAL ROTOR JOURNALLED FOR ROTATION WITHIN THE STATOR AND FORMING A CRESCENT PUMPING CHAMBER IN SAID BORE AND HAVING A PLURALITY OF SLOTS AND A VANE IN EACH SLOT, THE VANES ADAPTED TO RECIPROCATE WITHIN THE RESPECTIVE SLOTS DURING ROTATION OF THE ROTOR AND ENGAGE THE INNER CYLINDRICAL WALL OF THE BORE TO SWEEP THE CRESCENT CHAMBER, (C) AN INTAKE PORT AND AN EXHAUST PORT IN THE ASSEMBLY ON OPPOSITE SIDES OF THE PERIGEE POINT OF ENGAGEMENT OF THE VANES WITH THE BORE, ROTATION OF THE ROTOR ACTING TO DECREASE THE PRESSURE OF THE INTAKE PORT BY ACTION OF THE VANES MOVING THROUGH THE CRESCENT CHAMBER,