Gasket suitable for use in sealing exterior of sewer pipe to opening in manhole, and method and system employing same

Claim 1

In a manhole system comprising a manhole having a generally circular wall opening surrounding the outer surface of a generally cylindrical pipe extending through said opening, and a gnerally circular gasket ring of elastomeric material having a uniform cross-section along its circumferential length and comprising a radially-outward foot portion embedded in the wall of said manhole surrounding said opening, a head portion radially inward of said foot portion and bearing against the exterior of said pipe, and a neck portion between said head and foot portions of lesser width than either of them and also embedded in said wall, the radially inward tip of said head portion when undeflected defining a circle of lesser radius than that of the outer surface of said pipe so that when said pipe is inserted into said opening said gasket is deflected axially of said pipe and the side surface of said head portion bears sealingly against said outer surface of said pipe, said head portion tapering from a greater lateral thickness near said neck portion to a smaller thickness near said tip: the improvement wherein said head portion contains a first cavity and a second cavity each of circular cross-section and spaced radially from each other to define a transverse wall between them, each of said cavities extending completely around the circumference of said gasket, said first cavity being nearer said neck portion and a larger cross-sectional diameter than said second cavity.