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Why are manhole covers round?
...and other trivia about the drain covers |
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Manholes, are chambers providing access to underground utilities such as sewerage, gas, telephone, electricity, storm drains etc. for maintenance equipment, and, in some cases, for operatives to enter the system itself. Manholes are generally found in urban areas, in streets and occasionally under sidewalks and are capped with manhole covers.
A manhole cover is normally a circular plate, forming the lid over the opening of a manhole to prevent someone from falling in and to keep unauthorized persons out. A manhole cover usually weighs more than one hundred pounds, partly because the weight keeps them in place when traffic passes over them, and partly because they are usually made out of cast iron, which is inexpensive and strong, but heavy.
WHY ARE MANHOLE COVERS ROUND?
These are some of the answers posted by our website visitors. If you have anything further to add, you can send us an e-mail and if your point will be relevant we will try to put it up here!
It's true that MOST are round but square, rectangular and some triangular ones are also seen. Manhole covers are very heavy and made of Cast Iron or steel which are extremely durable materials since their placement exposes them to wear.
1. Manhole covers are round so that is doesn’t get dropped accidentally into the manhole. Manhole covers are round because round is the only shape that can never fall into the manhole and hurt someone (with the hole of the same shape, but slightly smaller size than the cover). 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 other shapes, thus remaining in place despite the street traffic running roughshod over them.
2. The manufacture of circular manhole covers is easier and more accurate than the manufacture of covers of any other shape.
3. You can roll round manhole covers, which makes them easy to lift and carry around. The round shape requires less space than a square and makes handling easier. Once removed, the cover can be transported by rolling.
4. The hole below the cover is round because a cylinder is the strongest shape against the compression of the earth around it. Also, the term "manhole" implies a passage big enough for a man, and a human being climbing down a ladder is roughly circular in cross-section. So a cylindrical pipe is the natural shape for manholes. The covers are simply the shape needed to cover up a cylinder.
5. Round covers don't have corners to bend, break off or that can puncture car tires.
6. Round covers can cover holes no matter how they are oriented vis-à-vis the hole. Square covers fit only when they are positioned in one of four orientations. With round covers, you don't have to line up the covers' edges before putting them into place. With what the government spends on road repair, the few seconds it takes a worker to align a cover's edges could cost dearly.
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