Self-locking manhole cover

摘要

The cover (4) has a protruding locking boss (6) secured to a resilient arm (5) fixed to the cover underside. The underside is provided with stiffening ribs. The boss engages beneath a flange (2) of a manhole frame (1) and is elastically biassed into this position. A further locking boss on the cover underside also engages beneath the flange. The further boss is also secured to an associated resilient arm (9) which extends parallel to the plane of the cover on its underside. The arms, in the locking position, extend parallel to part of the cover periphery.