Have you ever wondered why, there are sewer manholes all over round, not square? Manhole covers are made of cast iron, sometimes of concrete. This is so 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 one 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 cover 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 diameter of the circle is the same, no matter how you turn it. And since the diameter of the upper surface of the hatch is always greater than the lower one, 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, since it does not get on the head of workers who are inside the hatch.

Most Frivolous Explanation

There is an explanation that, of course, seems ridiculous. The 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 energy and extra time. In addition, round holes are more technological, they have a longer service life, they are resistant to temperature extremes and transformation.

So, there is some truth in this statement too.

The point 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 it, because the hatch cover is very heavy. We'll have to take at least two men to carry the hatch cover to the right place. And you can roll a round one, 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, aligning it with the hatch hole. There is some truth in this, too, round hatches are much more convenient. And yet, they are also convenient in manufacturing, because, again, you will have to tinker with square hatches, their corners may suffer during transportation, for example, to fight back.

By the way, the question "Why are the hatches round" is asked by the recruiting specialists to the candidates. It is said that the answer to this question allows you to assess the general level of intelligence, how much he is capable of solving problems and tasks. By asking this question, specialists want to see if the candidate for employees has the willingness and ability to enter into discussions and how the applicant solves the problem or refuses to solve it. It is also very important how the candidate answers the question, seriously or jokingly. 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, the easiest way is to say that the lid in theory should be round, including manhole covers!

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Hello always, dear friend!

There is a type of question that is generally considered to be a smart question. Sometimes this is true. But more often such questions are asked at once with several purposes.Why hatches round is an interview question just one of this series. Although it is found less and less, for it has already lost its former originality and the effect of surprise.

Let's remember that at the interview they want to evaluate not so much “Who are you?” As “What are you?”.

1. How do you respond to this question? - the first goal of your interlocutor.

He wants to understand the degree of your emotional maturity.

2. Will you be looking for an answer to this question? - the second goal.

Let's remember that the employer is interested in several key questions that he never asks directly. One of them: will you solve the problems that will inevitably arise in the course of your work.

Either you will look for reasons why the problem cannot be solved, or you will pass problems onto other people, including the leader.

3. The very content of the answer - the third goal.

Can you solve problems that require ingenuity and analytical thinking, logic?

If instead of answering you say “I don’t know” or “I’m at a loss to answer,” this means that when faced with a difficult task, you will most likely fold.

How to react?

Let's agree right away that we define this question “why are hatches round” as constructive, not manipulative and not tough. Therefore, we answer constructively.

The worst thing you can do is puff out your cheeks and freeze something like this:

"Listen, what does this have to do with the subject of our meeting?"

After that, consider that you have not passed the test, although in fact you are right. The reason - you did not accept the rules of the game that are offered to you. I repeat, this question is constructive and is not an attack on your personality. Therefore, it should be answered constructively.

Let's remember the principles of answering constructive interview questions:

1. If you get asked questions, that's fine. If you are not asked about anything, how will they know that you are the best candidate?
2. As a consequence of point # 1: Just give the interlocutor the right to ask any questions. Any question is your opportunity to be better than other candidates. You will answer confidently and calmly, and there is no reason to be afraid or nervous.
3. Most of the questions are asked to get to know you better, and not then to hear the correct answer. That's why you came so that they would know what a wonderful candidate you are.

How to answer?

1. Listen to the end.
2. The verbal reaction is a smile with the eyes and the tips of the lips (teeth are closed!), A slight nod.
3. A short pause.
4. Answer.

The simplest and most logical answer to this question:

Round hatch - cannot fall into a well. No matter how hard you try and twist it. The square has a diagonal longer than its sides, and when raised, it can slide down into the well. Drown or even injure someone. Besides -the diameter of the top of a round hatch is usually larger than that of the bottom, and it cannot slide inward under any circumstances.

In addition, round hatches are easier to move - they can be rolled.

A couple more questions from the same series

About cake

Myself Question: How to divide the cake into eight identical pieces using 3 cuts?

Answer: First, you should make a cross-to-cross cut, thereby dividing the cake into 4 equal parts. Next, make one cut horizontally in half along the entire diameter. The pieces are lower, but the problem is solved - you have 8 equal pieces.

Second option: after your two cuts, we have 4 pieces. We can put them on top of each other. Then split all four pieces in half with one cut.

About light bulbs

There are three light bulbs in the room. There are three switches in the hallway leading to the room.

Question: How many times do you need to open the door to determine which light bulb corresponds to which switch?

Answer: It is enough to open the door once. We turn on 2 switches at the same time, then turn off one. We enter the room: we see that one lamp is on. She is from the first switch. We place our palm on each of the remaining two bulbs. Which is warm from the second switch, respectively cold from the third.

In the event that, if any intelligible answer does not come to mind, start thinking out loud. Trying to find a suitable answer is much better than a nervous reaction or a “hard to answer” answer. Keep in mind that some of these questions don't have a definite answer at all.

Your attempts to find an answer, a train of thought, options for solutions are often more important than the answer itself.

Thank you for your interest in this article. I would be grateful for your comment (at the bottom of the page).

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Have a good day and good mood!

A familiar familiar detail of the urban landscape is the cover of sewer manholes, almost everywhere, in all countries of the world, having a round shape.

Why exactly round - we will try to answer this question in detail.

Security

The manhole cover of the sewer well is a massive cast iron product. It weighs more than 50 kilograms, and the weight of the hatches on the carriageway exceeds 78 kilograms.

This is not surprising, since the hatch cover on the sidewalk of the street must withstand a load of 12 tons, and the cover lying on the road - as much as 25 tons. This weight is due to the thickness of the cover, calculated taking into account the given load and the strength of the cast iron.

Now imagine the following situation: the hatch cover is open and lies next to the hatch, and people are working in the well below. If someone accidentally moves the round lid, in the worst case, it will simply close the hatch. In this case, a rectangular or square lid can fall into the hole right on the workers' heads, because the diagonal of a square or rectangle is always larger than either side of it. Therefore, the round shape of the lid is the safest in this case.

Strength

It has long been known to engineers that round objects are much more durable than square ones. The sewer hatch is not only round, but also slightly convex towards the middle: this shape provides the greatest resistance to mechanical stress from above.

Internal stresses in a hatch of this shape are evenly distributed over the metal, while in square, rectangular and any other covers under the action of load, the stresses are distributed unevenly, which leads to faster wear and, therefore, more frequent replacement of the covers.

In addition, one should not forget that cast iron is a rather fragile material, and if you drop a rectangular lid, a corner may well break off from it. It takes a lot more effort to crack the round manhole cover.


Judging by the fact that almost all lids are safe and sound for decades (and some for more than a hundred years), it is almost impossible to damage the round lid under normal conditions.

Saving metal

Why is the round shape of the hatches more optimal from the point of view of metal saving? With the same length of the perimeter of the round and rectangular hatches, the area of ​​the circle is always larger than the area of ​​the rectangle or any other geometric figure.

If we translate this into economic indicators, it turns out that the circle is the most advantageous shape of the hatch, since it requires much less cast iron on the cover (saving up to forty percent) than on a rectangular cover.

The optimal ratio of the length of the perimeter to the area makes it necessary to make round hatches not only for sewer wells, but also in much more serious structures - for example, between the compartments of submarines or spaceships. Round hatches are more economical and can handle heavy loads than any other shape.

Convenience of work

The round manhole cover is much more convenient when carrying out repair or maintenance work. If the rectangular lid needs to be lifted in order to move it a certain distance, which will require at least two adult men, then the round lid can be safely rolled over, placing it on its edge, and this task can be done alone.

And in order to fit the heavy cover in place, you do not need to rotate it, adjusting it to the hole configuration. The round lid will snap into place anyway, whichever side you install it.


So, there are more than enough reasons why you need to make the manhole cover round.

Modern public utilities emerged around the world in the 1830s. Despite the variety of shapes, more preference was given to round lids. Currently, manufacturers of manholes for sewer systems produce an exceptionally round shape.

Manhole covers: weight and maximum load

Despite the fact that modern sewer systems in different countries appeared at different time intervals, the only similarity was the need to install sewer manholes. The urgent need for cast-iron hatches arose primarily in large cities with asphalt roads for safety reasons. Still, moving the cover weighing from 45 to 160 kg is several times heavier than the wooden flooring and barriers that were used earlier.

Note! In recent years, along with cast-iron lids, cheaper analogs made of polymer materials have appeared on sale, the minimum weight of which is 15 kg, the maximum - 48 kg.

Sewer cover shape

The main reason why the manhole cover is round is due to the following considerations.

1. The triangular shape is not suitable based on the characteristics of the human structure. Otherwise, the size of the hatches would be much larger than modern round ones. And this entails unnecessary trouble in the form of an increase in the required raw materials for the production of the lid, therefore, its cost increases.
2. A square-shaped hatch can eventually fall into the well. Moreover, the shape of the well is round. Changing the transitions of the manhole shaft to the surface from a round to a square shape is not an easy task, it requires an increase in the financial costs of manufacturing and replacement.

The round shape of the lid does not have a one-sided nuance: it is convenient to carry such a lid - i.e. roll, as opposed to square or triangular. But with an increase in the number of thefts in and the nearest CIS countries for the sake of profit, the authorities began to look for a way out of this situation by producing from other materials.

In the United States, slotted or bolted covers are made as "anti-theft" measures. European countries use a combined material for the manufacture of the lid - they combine concrete with cast iron. This avoids theft because hybrid material is not accepted in scrap collection centers.

Interesting fact! Enthusiasts are not discouraged, and on the Internet, users arrange exhibitions of discovered samples with an unusual design with a postscript of the city. The art of molded lids traces its history for about 150 years, every day the world public gallery is replenished with new unusual samples of modern and antique products.

Modern and antique manhole covers are externally different. If on old ones you can find engraved coats of arms, various inscriptions and drawings, then modern counterparts are designed in a serious style: production number, name of the manufacturer, date of manufacture. Some organizations request “unique” copies to order, which contain detailed information: the company logo, a short list of services provided, and more.

The main reasons why the manhole cover is round

1. In Russia and neighboring countries, wells and sewer pipes have a circular cross-section. This is the main factor that influences the shape of the lid. In some European and Asian countries, square options are found. However, these are rather exceptions to the rule than the norm, because in the Czech Republic or China, where people found square-shaped covers, the cross-sections of pipes and wells of the sewer system are also round.
2. Reduced cost. Unlike a round one, the manufacture of a square manhole cover will require 30% more raw materials.
3. Convenience. To install a manhole cover of any other shape will require more costs: incl. human effort and time for its installation: the cover does not have to be moved (given the minimum weight of a cast-iron specimen of 65 kg, a square one based on an increase in raw material costs by about 30% will be heavier - that is, about 85 kg).
4. The round-shaped sewer hatch will not fall into the well due to the increased diameter in comparison with the section of the well.
5. Mounting and dismantling of round covers is faster and there are a number of reasons for this:
   no need for more installers to move the hatch;
   the time spent on its transfer is reduced - a round hatch is easier to roll, this method will not work with a square or triangular cover.
6. Distribution of load concentration. With a round lid, distribution is made over the entire area. Angular covers do not boast of such - it is the corners that will serve as the main points of the load.
7. It is more difficult to damage the edges of a round hatch than an angular one. In the process of transportation, you can put a chip. Considering that it is the corners that act as the main reference point for the distribution of the load, the chipped piece, regardless of its size, violates the system and the load is already distributed to the other corners.
8. Wear resistance. The value of the service life directly depends on the integrity of the hatch cover. If a part of the angular caps breaks off, the load distribution is uneven. Over time, this will damage other anchor corners.

Quite often, when hiring a candidate for a position, they are interested in why the sewer 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 a person's thinking, 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 what is really interesting is why the manholes are round and not square. There are different theories and answers. Let's try to figure them out.

Manhole cover

The cover is an integral part of the manhole cover, which must be present. In addition, it should be comfortable and ergonomic, and should not crash when hit by a car wheel. 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 complexity of theft, however, it is precisely because of such a great weight that it is often stolen for subsequent delivery for scrap. And although it is prohibited by law to accept sewer manholes at scrap metal collection points, this does not stop thieves. Someone generally uses them in everyday life for different purposes.

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

Logical version

The very first version explains the shape of the caps by economy. The fact is that it is the round shape with minimal cost that allows you to create such a hole into which a person would easily crawl. For example, for a person to freely penetrate to the well through a square hatch, the hole would have to be made slightly larger in area. Consequently, in the manufacture of a hatch for such a hole, 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 covers do not fall down

The second version, which explains why the sewer hatches are round, is that this shape does not allow the hatch to fall down. That is, under no circumstances, no matter how anyone tries, he will not be able to push the lid into the well itself. But the square cover of the sewer manhole 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 the loads more evenly when a car hits it. Therefore, this allows a slight reduction in the cross-sectional size (thickness), which ultimately leads to additional cost savings.

Round well - round cover

However, it is strange to ask at all why the sewer hatches are round, because the well itself is round, so when developing the covers, no one even thought about using a square shape. Moreover, if it is necessary to 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 "tendrils" that prevent them from rolling with an edge.

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

It just happened so

In general, no one knows why the sewer hatches are round. Very few people think about it, but looking for an answer to this question is simply stupid. It's like asking why the curbs are rectangular. There is no unequivocal answer to this question, because when the first sewer wells appeared, no one at all thought about making them in other forms. It just happened that way, 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 diagonal length 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. Different countries may have their own forms. In India, triangular shapes are often found, and in some countries they can represent a generally indefinite geometric figure. Square shapes are not uncommon in the United States and other countries in America. There are even hatches with eight corners and models in the shape of a rhombus, semicircles are very rare.

But we must admit that most often they are just 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. Then the resulting value must be compared with the weight of the metal required to make the cover for the round hole. With the same metal cross-section, 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 hatch. It turns out that the loads are distributed more evenly around the entire perimeter of the circle. In the case of a square or 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 suddenly asked about it during an interview. This is most likely the only case where such information can help. However, if we are talking about an interview, then it is not at all necessary to answer correctly. You can answer with a joke, or even say that the hatches from sewer wells are not always round, it is just that it is customary in our country. Sometimes even the person who asks such a stupid question does not know himself why the hatches are round at all. However, you now know the answer for sure. Despite the many good versions, the most logical and plausible version seems to be with the shape of the lid, because of which it simply cannot go into the sewer hole.