You’d have to rotate the cover precisely the right way. Therefore, many manhole covers are round and don’t need to be rotated. There are no corners to deal with. Also, a round manhole cover won’t fall into a hole because it was turned incorrectly, so it’s safer.
Why Are Sewer Lids Round?
Most of us take it for granted that sewer lids are round and give it no further thought. Many have probably assumed that it must be some industrial or engineering standard. But the reason why sewer lids are round is much simpler than that.
Sewer lids are round for safety; round lids are less likely to be a hazard to passersby than other shapes. Sewer lids often have embedded metal hardware, which could easily be a tripping hazard if the lids were square or rectangular. Round sewer lids are much less likely to cause injury due to their curved edges.
Another benefit of round sewer lids is that they are sturdier than other shapes. Round shapes have the ability to disperse pressure more evenly, meaning they are less likely to crack, warp, or take damage from heavy use. This helps protect sewer lids from accidental damage and vandalism and keeps them functioning for much longer.
Finally, round sewer lids are just easier to move and maneuver. Round shapes are symmetrical and fit into each other nicely, meaning that they can be rolled out of the way or increased in diameter relatively quickly. This makes moving or replacing sewer lids a much more efficient task.