| 摘要 |
<p>The manhole cover is secured inside a ring shaped frame so that their top surfaces are level and flush with the road surface. The cover has two rectangular lugs diametrically opposite, which locate in corresponding recesses in the ring. Each lug is hollow, and houses a locking pin with a head at the top with a slot across it which is engaged by a cross piece at the end of a special locking key used by maintenance personnel. This pin has a bar across the bottom, which after passing through a slot at the position of the recess in the ring, is rotated by the key so as to wedge against taper pads on the underside of the ring, locking the cover inside the ring.</p> |
