Patent ID: 7896574

Claim:
A self-locking manhole cover, comprising: a cover plate adapted to rest on a manhole cover support surface of a manhole frame so as to be substantially flush with a top portion of said manhole frame and a surrounding surface in which said manhole frame is situated; an anchor on said cover plate adapted to engage said manhole frame at a first location in a manner that resists lifting of said cover plate proximate to said first location; a locking member on said cover plate that is movable between a locked position in which said locking member is adapted to engage said manhole frame at a second location in a manner that resists lifting of said cover plate proximate to said second location, and an unlocked position in which said locking member is not adapted to engage said manhole frame; said locking member being biased by a biasing force toward said locked position; a locking mechanism adapted to drive said locking member to said unlocked position in response to actuation by a security key on an upper side of said cover plate; and said locking mechanism being further operable, without said security key, to maintain said locking member in said unlocked position against said biasing force when said cover plate is removed from said manhole frame, and being actuatable from said upper side of said cover plate to release said locking member from said locking position after said cover plate has been returned to said manhole.