edges of the passage 48 as best illustratedin fig1 and 8 the curling strips 28 and 32 are each made of two layers of silicone elastomer with the lower layer 70 made of a high tension set unvulcanized silicone elastomer and the top layer 72 being mase of a low tension set vulcanized silicone elastomer the lower layer 70 is placed in contact with the vulcanized layer 34 for bonding of the strips to the section 40 the placement of the curl strips that is on both sides of the passage 48 causes the passage section of the valve to curl along the longitudinal axis of the passage as illustrated in fig1 and to also curl in a direction perpendicular to the axis of the passage as illustrated in fig8 forcing the layers that define the passage 48 toward each other as illustrated in fig8 a cross sectional view of thesealing portion of the valve shows the passage 48 having a concave cross sectional configuration the curling strips are then vulcanized to the rectangular section 40 thereby forming the sealing portion of the valve 20 of the present invention stretching the section 40 thins out the layers forming the passage 48 thereby making the passage section more compliant than the passage sectionof.