Repair 

Why hatch. Why are sewer manholes round and not square? Why was this form chosen?

Have you ever wondered why, sewer manholes are everywhere round and not square? Manhole covers are made of cast iron, it happens that of concrete. This is to ensure that the lid is heavy and cannot open spontaneously. If we talk about cable ducts, then most often there are two shut-off and protective ones. The first weighs much lighter, it is usually made of steel and is needed in order to protect the cable from theft. They place it, just under the protective one, and on the lid itself they simply write the purpose of the hatch.

The simplest and most logical explanation

The square-shaped cover can easily fall into the hatch, for example, slip through the corner. This may be because the diagonal of the square is larger than its sides, that is, the lid can fall into the hole. And the circle has the same diameter, no matter how you turn it. And since the diameter of the upper surface of the hatch is always larger than the bottom, the cover will never fall inside the hatch, no matter what position it is in. The round cover is safer than other forms of cover, as it will not fall on the head of workers who are inside the hatch.

The most frivolous explanation

There is an explanation, which, of course, seems ridiculous. Hatches are round because the holes are round. Although, on the other hand, it is easier to dig a round hole than to align the corners of a square or rectangular or triangular hole. And in general, for example, it makes no sense to make a sewer well square, because you have to spend extra effort and extra time. In addition, round holes are more technologically advanced, they have a longer service life, they are resistant to temperature changes and transformation.

So, there is some truth in this statement too.

The fact is that round hatches are easier to transport. That is, the square cover only needs to be carried, and one person is unlikely to cope with this, because the hatch cover is very heavy. You will have to take at least two men to carry the manhole cover to the right place. A round one can be rolled, which is within the power of one adult man. Moreover, without experiencing any particular difficulties. Moreover, when closing the hatch with a round lid, there is no need to rotate it, combining it with the hatch opening. There is also some truth in this, round hatches are much more convenient. And yet, they are also convenient to manufacture, because again, you will have to tinker with square hatches, their corners may suffer during transportation, for example, fight back.

By the way, the question “Why are hatches round” is asked by recruiters to candidates. They say that the answer to this question allows you to assess the general level of intelligence, how capable it is of solving problems and tasks. By asking this question, experts want to see if the candidate for employees has the readiness and ability to enter into discussions and how the applicant solves the task or refuses to solve it. It is also very important how the candidate answers the question, seriously or with jokes. By the way, the world-famous company Microsoft has long been using this question when testing specialists who are going to be hired.

To summarize, it is easiest to say that The lid is supposed to be round., including manhole covers!

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In each country, the development of sewerage systems took place in different ways, but the only common feature has always been the need to install sewer manholes.

The first manholes appeared together with the emergence of public utilities back in the 30s of the 19th century: then manhole covers had different shapes, but preference was most often given to round-shaped covers. Currently released, sewer manholes are round, and not of a different shape. This feature, in spite of everything, remained unchanged. But why exactly round?

Manhole covers are subdivided depending on their purpose. All of them have different drawings and embossing. On the old hatches you can see already outdated images of coats of arms, all kinds of drawings and inscriptions.

Modern manhole covers carry information about the manufacturer, serial number and date of manufacture. Some companies intentionally replace old sunroofs with new ("decorative") ones near their offices, and usually put their logos on the covers.

Why was the round shape chosen for the hatches?

There are a lot of answers to the question why the hatches are round, but the following assumptions are the most reasonable:

  1. In our country, well tunnels and sections sewer pipes round, so it makes no sense to make covers of other shapes. However, Foreign experience knows many exceptions: for example, square manhole covers can be found in some cities of the Czech Republic and China, although they do not correspond to the shape of the wells they cover.
  2. Round sewer manholes will never fall into the well, which means they are best suited to perform their protective function. And all because the diameter of the covering circle is always greater than the diameter of the well itself, and square covers can enter it, for example, at an angle.
  3. Hatches are made round in order to reduce the cost of their production. This is due to the specifics of the equipment: in order to make a round cap, less material is needed. The standard hatch width norms are 600 mm, for a circle it will be a diameter, and for a square it will be a side, so the square hatch area will be 0.36 square meters, and round - 30% less.
  4. The manhole cover is round because it is convenient to carry. In most cases, sewer manhole covers are made from a grill (grey cast iron), which is obtained by melting various scrap metal. The weight of one cover varies from 50 to 110 kg. It is quite difficult for one person to transfer the manhole cover from one place to another, and thanks to its round shape it can be rolled.
  5. It is convenient to mount and dismantle not square, namely round hatches, since the load concentration points go along the entire circumference of the cover, while for square or rectangular shape only corners will be such points. That is why the necks and, accordingly, the lids for the jars are made round.

In fact, discussions about the shape of manholes may seem meaningless to many. However, few people know that such an unimportant question can take anyone by surprise when ... applying for a job! And this shouldn't be surprising.

This type of interview question is not uncommon. Eychars among themselves refer it to "cases", that is, keys with which you can give a more accurate assessment of some qualities and abilities of applicants.

This practice is used mainly during interviews for applicants applying for high positions. In this way, the fact of how a person behaves in case of force majeure, what speed of thinking he has, whether he knows how to use non-standard approaches, and so on, is evaluated.

Quite often, when applying for a job, a candidate for a position is interested in why manholes are round. This is a very unexpected question that takes a person by surprise, and he begins to think about it. So you can quickly determine the thinking of a person, assess his level of intelligence and the ability to get out of difficult situations. If a person hesitates, thinks about it for a long time and gives a completely illogical and incorrect answer, then one can judge his inability to think creatively and quickly. But it's actually interesting why sewer manholes are round and not square. There are different theories and answers. Let's try to figure them out.

manhole cover

The lid is component manhole hatch, which must be present. In addition, it should be comfortable and ergonomic, should not rattle when a car wheel hits it. It also has a small hole through which you can check the gas content of the well.

With all this, the cover is most often made of cast iron and is very heavy. Its large weight is justified by the difficulty of theft, but it is precisely because of such a large weight that it is often stolen for subsequent scrapping. And although the Law prohibits accepting sewer manholes at scrap metal collection points, this does not stop thieves. Someone generally uses them in everyday life for various purposes.

However, now is not about that. In most countries, the lids are indeed made in a round shape, but there are exceptions. In some US states and even in India, they are made in the form of squares and triangles. Therefore, it cannot be argued that all manhole covers are round. Why is the round shape most common? As mentioned above, there are different versions.

logical version

The very first version explains the shape of the lids with economy. The fact is that it is the round shape with minimal cost allows you to create a hole in which a person could easily crawl through. For example, for a person to freely enter the well through a square hatch, the hole would have to be made a little larger in area. Consequently, in the manufacture of a hatch for such an opening, more metal would be spent, and this is economically unprofitable. It is believed that the production of round hatches is 40% more profitable compared to the production of square ones, and on a large scale this is a fairly solid figure.

Due to the round shape, the lids do not fall down

The second version, which explains why sewer manholes are round, is that such a shape prevents the manhole from falling down. That is, under no circumstances, no matter how hard someone tries, he will not be able to push the lid into the well itself. But the square manhole cover can fall into the well if you try to shove it with an edge along the diagonal of the hole.

It is also believed that the round shape has a good feature - it distributes loads more evenly when a car hits it. Therefore, this allows to slightly reduce the size of the section (thickness), which ultimately contributes to additional savings funds.

On a round well - a round cover

However, it is strange to ask at all why sewer manholes are round, because the well itself is round, so when designing covers, no one even thought about using a square shape. Moreover, if necessary, you can quickly move the cover of the round hatch from the well, you can simply roll it with an edge, which even one person can handle. But rolling a square hatch will not work - it must either be transported or carried by two or even three. However, some lids have special "antennae" that make it impossible to roll them edgewise.

It is also believed that opening a round sewer manhole cover is easier due to the fact that any point on its circumference is also a point of stress concentration. As for square covers, there are only two similar points - the corners of one of the sides.

It just so happened

In general, no one knows why sewer manholes are round. Few think about it, but looking for an answer to this question is simply stupid. It's like asking why curbs are rectangular. There is no single answer to this question, because when the first sewer wells appeared, no one even thought about making them of other forms. It just so happened, and all attempts to explain why the hatches are round are, to put it mildly, far-fetched. The only more or less logical option is the inability to drop the hatch into the well itself. This is possible with a square lid, since the length of the diagonal of the lid itself will be greater than the length of the side. This makes sense, but even this explanation does not suit many.

Other forms

Note that hatches are not always round. AT different countries forms may be different. In India, triangular shapes are common, and in some countries they may represent a generally indefinite geometric figure. Square shapes are not uncommon in the US and elsewhere in the Americas. There are even hatches with eight corners and very rarely there are models in the form of a rhombus, semicircles.

But it is worth recognizing that most often they are round. This form is the most popular, comfortable and ergonomic.

Conclusion

So, we figured out why the hatches are round. You can answer this question in different ways. If you really become a bore, then you can calculate how much metal is needed to make a square cover for a hole into which a person would freely crawl. The resulting value must then be compared with the weight of the metal required to make the cover for round hole. With the same cross section of the metal, it turns out that more metal will go to the square hatch due to the presence of corners in the square.

You can also calculate how evenly the forces are distributed when a car wheel hits the sunroof. It turns out that the loads are distributed more evenly around the entire perimeter of the circle. In the case of a square or a triangle, this is not the case.

In general, now you know why manholes are usually round, and you understand what you need to answer if you are suddenly asked about this at an interview. Most likely, this is the only case when such information can help. However, if we are talking about the interview, it is not at all necessary to answer correctly. You can answer with a joke, or even say that manholes from sewer wells are not always round, it's just customary in our country. Sometimes even the person who asks such a stupid question doesn't know why hatches are round at all. However, you now know the answer for sure. Despite many good versions, the most logical and plausible seems to be the version with the shape of the lid, because of which it simply cannot pass into the sewer hole.

The development of sewer systems in each state took place in its own way. the only common feature in all cities - this is the need to install hatches. Sewer manholes first appeared in the middle of the 19th century. Then they were made in a variety of shapes - from round to square. AT last years only round models are made. Why?

What is a sewer hatch?

A manhole is a hole in concrete or ground that provides access to underground utilities. This hole is always closed with a lid, hatch, to avoid accidents. The hatch has another function - to prevent illegal entry into the underground communications system.

Types of manholes

Covers are divided into types. On them there are different embossing, patterns. So, for example, on the first sewer manholes depicted the coat of arms of the state, propaganda slogans. Now the covers display the serial number, date and initials of the manufacturer. Sewer people emit:

  • plastic;
  • iron;
  • rubber;
  • cast iron;

India is considered the leader in the manufacture of sewer manholes.

Why are manholes round?

For many years in a row, exclusively round hatches have been produced. There are several reasons for this:

  1. The cost of manufacturing a case for a round hatch is lower than any other shape (triangular, diamond-shaped, rectangular);
  2. Ease of travel. The round hatch is much easier to move: you just need to put it on its edge and roll it in the right direction;
  3. The round hatch is easier to open. He has any point of the circle is the concentration of stress. For example, all lids for jars are also only round;
  4. The round manhole will not fall into the sewer system. Any other form has a high probability of subsidence below the established level;
  5. The cross section of the pipes of the system is round. It is logical to make the same shape and cover that closes the sewer systems.
  6. An object of a square (triangular, rectangular) shape cannot be taken out through a round manhole cover.

In some countries, triangular sewer manholes are used. In Nashua (a city in the USA), underground systems are still covered with triangular lids. The sharp corners of the triangle indicate the direction of the current to the repair team Wastewater. However, such hatches were recognized as hazardous to health, and their dismantling began.

The choice of a round shape of sewer covers is dictated by elementary practicality. Such hatches last longer, they are resistant to influence environment. Less material is used to manufacture, they are cheaper. Convenient to work if you need to get inside sewer system are safe. The probability of subsidence of the round hatch is very small.

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And involuntarily wondered - why is it round? And often hatches are never made square. What is this standard? Or a conspiracy of plumbers and electricians? With this question, I turned to a professional master, it turns out that this question is almost the very first for beginners in this field. It turns out everything is quite prosaic ...


To begin with, the guys propose to put everything on the shelves, and tell what these covers are, which actually close various wells. Do not worry, the answer will be lower, it will definitely be - read to the end.

Types of hatches

It is a mistake to think that the hatches that close the wells embedded in the ground are of the same type. A fairly large infrastructure is laid out underground, so there are different types:

  • Hatches for drainage systems
  • For storm systems
  • For electrical networks
  • Contact

Initially, hatches were made of very durable materials, usually steel or black cast iron. Thus, it was very difficult to remove and carry it away, and the cars that ran into it could not turn it over either. However, with the era of "perestroika", metal variants still began to be stolen and sold for metal (and they were simply smashed),

therefore, it was not uncommon for wells to be open (oh, it was a terrible time), therefore, in those days, they began to close wells with concrete round (as I call them) “under-fills”. It was even more difficult to carry such things away, and there was no need to, because you can’t hand over concrete!

Now, of course, new polymer or sand-polymer options are appearing, they are also durable - they can withstand a load of up to 3 tons, they are also resistant to high and low temperatures, do not rot - do not rust, and practically do not steal them, because again you will not pass!

However, all these types make invariably round! But why - everything is trite simple.

Cause and effect

Any mine consists of several parts:

  • This is top part the lid itself (the main purpose is to protect the internal components from dirt, sediment and other debris).
  • Medium shaft - usually made in a round size with a diameter of 70 cm, a recess of up to 3 meters.
  • The last is the lower part, there can be different sizes and shapes, for example, in some communication wells they have a square shape.

But the main question is why is the lid round? Guys, this is a safety requirement.

The fact is that the round hatch cannot fall into the well shaft, no matter how you twist it. Try it at your leisure, whatever one may say - but everywhere is a circle. But if the covers were square, or triangular, etc., then at a certain angle they could fall down, but if this well is a sewer, how to get it back? Complicated!

Yes, and children, and large equipment will not be able to somehow overturn or push such a hatch down, everything is done wisely. It is worth noting that the weight of the metal options is 50 kg, so no traffic flow can overturn it. That's actually the answer.

It is also worth noting the side "ears" - special branches from the circle, they are made so that the lid does not "walk", but sits tightly in place.

Interesting facts about "well covers"

It should be noted that they were not always made round - there were square options and triangular and polygonal ones.

But they were all dangerous and often just failed, leaving an open shaft.

However, triangular covers were valued to the last, all because the corners of the structure showed the direction of pipes or communications. Therefore, when the repairmen descended, they were already aware.

Also, hatches on hinges, a kind of “down” door, were not rare before. Also, the loops protected a little from theft. However, with large traffic flows, they were often broken and the covers fell through, so over time they were also replaced with round ones.

Here is such an article turned out, now watch a cool video.

I will finish on this, read our construction site, there will be a lot of interesting things.