| 摘要 |
A manhole cover is secured to a support ring by means of a latch member which is rotatable in a cavity formed in the manhole cover between a pair of upper and lower walls having respective upper and lower throughgoing apertures. The latch member is rotatable and has a lower end projecting through the lower aperture and an upper end underneath the upper aperture and formed at the axis of rotation of the latch member with a socket opening toward the upper aperture. The socket in the upper aperture is of similar shape and of like radial extensions. The rim has a formation cooperating with the lower end of the latching member for locking of the cover and the support ring together in a locking angular position of the latching member relative to its rotation axis in permitting separation of the cover and the support ring in an angular offset freeing position. The radial extensions of the socket and upper aperture are axially aligned only in the locking position. The key has the tip of substantially the same cross-sectional shape as the upper aperture and the socket and is engageable through the upper aperture into the socket only in the locking position. The tip of the key is dimensioned so that it is possible to withdraw it from the manhole cover except when the latching member is in the locking position so that this key cannot accidently be taken away before the cover is locked in place.
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