Abstract: Manhole closure assembly for preventing storm water from entering into manhole opening comprises cover section including downwardly depressed central portion. Circular mounting flange extends outwardly from depressed central portion and flange is adapted to rest upon inwardly directed manhole cover supporting flange of annular manhole frame. Downwardly depressed portion of cover section is depressed amount that exceeds path of spin of manhole cover resting upon supporting flange of annular manhole frame. First valve member is secured to cover section to relieve pressure inside manhole when pressure therein exceeds predetermined amount.

Abstract: Device for expanding ring-like support to increase diameter thereof comprises flexible expander band having overlapping end portions and forming closed loop of variable diameter. Expander band is positioned within ring-like support and functions to expand support. Motivating structure is fixed to one of overlapping end portions of flexible expander band and has rotatable pinion gear connected thereto. Gear rack is associated with other overlapping end portion of flexible expander band for movement therewith. Gear rack is in meshing engagement with rotatable pinion gear so that rotation of pinion gear shifts overlapping end portions of flexible expander band relative to one another to increase diameter of closed loop formed thereby.

Abstract: Combination includes manhole closure assembly for preventing storm water from entering into manhole opening and separate support ring for assembly. Support ring has lower closure supporting flange with upper flange spaced therefrom, and sealing material is provided on lower flange. Closure assembly includes substantially circular cover plate engaging sealing material, and cover plate comprises pair of semi-circular segments. Structure is provided for holding semi-circular segments of cover plate together at diametral edge portions thereof. Spaced apart biasing structure is located along arcuate edge portions of cover plate, and such structure extends between plate and upper flange of support ring for urging plate against sealing material. When pressure force acting upon underside of cover plate exceeds force of biasing structure, arcuate edge portions of cover plate lift away from sealing material to relieve such pressure force.