Abstract: A manhole closure assembly primarily for preventing drainage and storm water from emptying into a manhole leading to a sewage system. The closure assembly includes a retaining ring secured within a manhole opening, and a removable closure plate seated within an internal opening through the retaining ring for sealing off the manhole opening. A valve assembly for relieving pressure inside a manhole includes a handle connected to the cover plate and spaced above its upper surface, a passageway extending through the cover plate in underlying relationship with the handle, a movable valve element extending through the passageway and having an enlarged, upper sealing member for seating against the upper surface of the cover plate to close the passageway and biasing means positioned between the handle and the enlarged upper sealing member of the movable valve element for normally biasing the sealing member in a downward direction to seal the valve passageway.