Dispensing piston can

Claim 1

IN A CONTAINER FOR DISPENSING A FLUID PRODUCT FROM ITS UPPER END UNDER PRESSURE, THE IMPROVEMENT COMPRISING: AN ELONGATED SEAMLESS METAL CYLINDRICAL HAVING AN INSIDE WALL SURFACE, AN ANNULAR METAL PISTON SLIDABLY MOVABLE LONGITUDINALLY THROUGH SAID CYLINDER SNUGLY, SAID CYLINDER WALL SURFACE HAVING A LARGER DIAMETER IN ITS UPPER PORTION THAN IN ITS LOWER PORTION, FOR REDUCING THE FRICTION BETWEEN SAID PISTON AND WALL SURFACE IN ORDER TO COMPENSATE FOR DECREASED PROPELLENT PRESSURE AND TO ASSURE COMPLETE PRODUCT EVACUATION, A BOTTOM COVER FOR SAID CYLINDER INCLUDING MEANS FOR INTRODUCING A PROPELLANT TO CAUSE SAID PISTON TO MOVE UPWARDLY IN SAID CYLINDER, SAID PROPELLANT BEING OF THE TYPE WHICH EFFECTS DECREASING PRESSURE ON SAID PISTON AS THE PISTON MOVES UPWARDLY AS AFORESAID, AND SAID PISTON HAVING AN OUTER LONGITUDINALLY EXTENDING SURFACE INTERNALLY PRESSURIZED BY SAID PROPELLANT AND CONVERGING DOWNWARDLY WITH SAID WALL SURFACE TOWARD THE BOTTOM EDGE OF SAID OUTER SURFACE TO CREATE A CONVERGING FLUID PRODUCE WEDGE IN THE AREA OF SAID EDGE AS THE PISTON MOVES UPWARDLY, AS AFORESAID, SO AS TO INCREASE THE FILM PRESSURE DEVELOPED BY THE SLIDING OF SAID SURFACES AND CAUSE AN EFFECTIVE SEAL AND WIPING CONTACT THEREBETWEEN, SAID BOTTOM EDGE OF THE PISTON ENGAGING THE WALL SURFACE OF SAID CONTAINER AND REMAINING IN FRICTIONAL CONTACT WITH SAID WALL SURFACE.