There is no law that requires a manhole cover to be rounded, but why is it round then?
Some duct covers are square or rectangular, but these types are rare and are commonly found only when heavy equipment is required to pass through them. The answer to the question of why a manhole cover is round is relatively simple, but you need to understand its purpose and history.
Manholes appeared in the mid-19th century to provide access to sewerage systems that began to be built underground to accommodate the growth of sewerage systems. Originally, the access point to the sewer was only big enough to shed light through the hole to make sure the sewer was flowing properly. But in the end, humans had to be able to get into the sewers.
What exactly is the reason why the manhole cover is round and not square today? Is there a manufacturing reason why round manhole covers are more popular than square covers? Did the first inventor of the manhole cover have a grudge against a right angle?
If you've ever thought you needed logic, you're right. After all, it was the engineer who was in charge of the original design!
Why is the MANHOLE COVER round
There are actually many reasons why the manhole cover is circular. It's all about structure, safety and efficiency.
There is the geometric fact that the round manhole cover cannot fall out of its own opening. For example, if you have a square cover, the total diagonal distance of the square is 1.414 times the length of the side. Therefore, if you drop the square cover diagonally into the opening, it can easily fall off. For a more visual thinker, imagine a children's toy with an array of shapes such as triangles, rectangles, squares, circles, and a bucket with the same shape punched up. The square shape could not only be aligned in the corners, but could also be tilted to fit the square box. However, in order to match the shape of the circle, the shape of the circle must be aligned at the edges.
2. Ease of movement
The round cover is relatively easy to roll.
3. Easy installation
When replacing the manhole cover, you don't have to worry about the orientation of the round cover. Unlike other shaped covers, it can be continued at any angle. Another factor behind the circular manhole covers is that they are most likely to return to their original position when bounced off by the force of a passing heavy vehicle.
Believe it or not, there is also the economic reason that the manhole cover is round. A circular duct cover has less surface area than a square cover of the same size, so less material is required to make a circular cover.
5. Other Shapes
Another geometric reason is that the circular cover provides the strongest shape. Especially because the cover rests only on the flat lips around the hole. Each point on that edge is at the same distance from the centre of the cover. Each of these dots is, in many respects, as strong as the corners of a square or rectangular cover.
The cylinder is the most powerful shape of the hole because it can withstand the compression of the surrounding earth. Therefore, it is easier to dig and maintain a round hole. However, not all manhole covers connect directly to the round holes. Many underground structures are square or rectangular because they touch the intersections of pipes, making it easier to have straighter, flat sides than circular ones.
Geometry and history play the major role in manhole cover design. Although round manholes aren't the only tradition-there are many practical reasons manufacturers make round manhole covers. The next time you look down on the sidewalk in your neighbourhood, pay attention to the manhole cover.