Waterstop with provision for flexing

Claim 1

A WATERSTOP TO BE POSITIONED AT A JOINT BETWEEN ADJACENT CAST CONCRETE PANELS, THE WATERSTOP COMPRISING, IN CROSS-SECTION, A CENTRAL SECTION FOR BRIDGING THE JOINT BETWEEN THE PANELS AND A PAIR OF LATERALLY PROJECTING FLANGES INTEGRAL WITH THE CENTRAL SECTION AND ADAPTED TO BE IMBEDDED IN THE PANELS, RESPECTIVELY, THE CENTRAL SECTION BEING IN THE FORM OF A HOLLOW BULB LYING SUBSTANTIALLY TO ONE SIDE OF A MEDIAN PLANE TO THE FLANGES AND HAVING A RELATIVELY THIN RIP-MEMBRANE LYING SUBSTANTIALLY IN THE MEAN PLANE OF THE FLANGES, THE DIMENSION IN SAID MEAN PLANE DEFINING THE WIDTH OF SAID WATERSTOP, SAID WATER STOP BEING OF GREATER LENGTH THAN WIDTH AND OF GREATER WIDTH THAN HEIGHT, SAID CENTRAL SECTION AND SAID FLANGES BEING FORMED OF COMPATIBLE ELASTOMERIC MATERIAL OF SUBSTANTIALLY DIFFERING HARDNESSES, THE CENTRAL SECTION BEING SUBSTANTIALLY SOFTER AND MORE READILY DISTORTABLE THAN THE FLANGES IN ORDER TO ACCOMMODATE READY TEARING OF THE RIP-MEMBRANE AND STRETCHING AND DISTORTION OF THE CENTRAL PORTION AFTER TEARING WITHOUT DISTURBING THE RELATIVELY HARDER FLANGES UPON ATTEMPTED RELATIVE SEPARATION OF THE PANELS WHEN THE WATERSTOP IS INSTALLED SO THAT THE CENTRAL SECTION BRIDGES THE PANELS IN WHICH SAID FLANGES ARE EMBEDDED.