Syringe piston

Claim 1

IN A SYRINGE, IN COMBINATION, A CYLINDER HAVING A CLOSED END FORMED WITH A BORE THERETHROUGH; A PISTON SLIDABLY LOCATED IN THE CYLINDER AND HAVING A FRONT END PORTION OF REDUCED DIAMETER FACING SAID CLOSED END AND A MAIN PORTION HAVING A DIAMETER LARGER THAN SAID FRONT END PORTION BUT SMALLER THAN THAT OF SAID CYLINDER SO AS TO FORM A SHOULDER FACE REARWARDLY OF SAID FRONT END PORTION; AND A PISTON HEAD FORMED FROM ELASTICALLY DEFORMABLE MATERIAL LOCATED BETWEEN SAID MAIN PORTION OF SAID CENTRAL PORTION ENGAGED BY SAID FRONT END PORTION OF SAID PISTON AND AN ANNULAR LIP PORTION SURROUNDING SAID CENTRAL PORTION SPACED THEREFROM AND BEING CONNECTED AT A FRONT END THEREOF TO SAID CENTRAL PORTION, SAID LIP PORTION CURVING CONVEXLY AND REARWARDLY FROM SAID FRONT END AND ENGAGING INTERMEDIATE ITS ENDS THE INNER SURFACE OF SAID CYLINDER SUBSTANTIALLY ALONG A LINE CONTACT, SAID LIP PORTION HAVING A REAR FACE FACING SAID SHOULDER FACE AND BEING SLIGHTLY SPACED THEREFROM, WHEREBY UPON COMPRESSION OF FLUID BETWEEN SAID CLOSED END OF SAID CYLINDER AND SAID PISTON HEAD, PRESSURE EXERTED ON SAID PISTON HEAD WILL TEND TO BEND A PORTION OF SAID HEAD BETWEEN SAID LINE OF CONTACT AND SAID CENTRAL PORTION REARWARDLY SO AS TO PRESS SAID REAR FACE OF SAID LIP PORTION AGAINST SAID SHOULDER FACE TO CAUSE THEREBY SAID LIP PORTION TO BUCKLE AND TO PRESS PORTIONS OF SAID HEAD ADJACENT SAID LINE OF CONTACT WITH INCREASING FORCE AGAINST THE INNER SURFACE OF SAID CYLINDER.