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So they don't fall in!
Manholes, which interconnect underground sewerage pipes, and serve as a point
of entry for cleaning the pipes, are located at every major sewer pipe junction,
and are capped with round manhole covers. The reason for the circular
construction of these covers is, quite simply, that covers of any other shape
would fall through the manholes by virtue of their varying diameters. Circular
manhole covers do not vary in width, or in diameter, as is the case with these
other shapes, thus remaining in place despite the street traffic running
roughshod over them.
Manufacturers craft the manhole covers together with the smaller sized lip,
upon which they rest, at the same time to ensure a tightly sealed fit.
Additionally, the manufacture of circular manhole covers is easier and more
accurate than the manufacture of covers of any other shape. Lastly, round
manhole covers, once removed, require less lifting and less manpower, as their
shape allows them to be rolled. |
