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 patterns 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 On the old hatches you can see already outdated images of coats of arms, all kinds of drawings and inscriptions.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 images of 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:
- In our country, well tunnels and sewer pipe sections are round, so it makes no sense to make covers of other shapes. At the same time, 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.
- Round sewer manholes will never fall into a 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.
- 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 area of a square hatch will be 0.36 square meters, and a round one will be 30% less.
- 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.
- It is convenient to mount and dismantle hatches that are not square, namely round hatches, since load concentration points go along the entire circumference of the cover, while for square or rectangular hatches, only corners will have 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.
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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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 durable - they can withstand a load of up to 3 tons, they are also resistant to high and low temperatures, they do not rot - they do not rust, and they 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 the upper part of 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.
In fact, at first they differed: in many countries other shapes were used, but the “winner” was still round. They are used throughout the world to this day.
What is the difference between manhole covers? Everything but the form. On top of them at the dawn of their mass use, images of various coats of arms, motives for events, memorable dates could flaunt. Today, everything is much simpler: a simple pattern and information about the manufacturer of the caps and the customer who made them. “Decorative” ones are sometimes placed near their offices by large companies.
So why are hatches round?
- Because the tunnels of wells and the cross section of sewer pipes are also round. Therefore, it simply does not make sense to use a different shape, round is the most convenient.
- Because round manhole covers never fall into a well. But square ones, for example, can do it without problems.
- Because it's cheaper that way. To cover a round "hole" with a diameter of 60 centimeters with a square lid, the area of such a lid should be 0.36 square meters. At the same time, this task can be completed using a round hatch with an area of 0.28 sq.m. Noticeable difference?
Because it's easier to carry them. Or roll, because the weight is not small - from 50 to 110 kg: one person may not be able to cope. What if they were still square?
Because round hatches are more convenient for installation and dismantling. They have load concentration points around the entire perimeter, and in square ones - only in the corners.
However…
“Who cares why manholes are round,” you ask? I would like to answer that no one is interested in this, but there are precedents. And they happened at very serious events, in the offices of reputable companies. The fact is that sometimes HR managers like to ask unexpected questions at interviews to see how a person behaves in force majeure situations. Now ask someone unexpectedly why the hatches are round? Do you think you will immediately hear a clear answer? Not! So they torment applicants for high positions in the private sector with insidious and at the same time stupid questions.
Logical tasks are given to job candidates to assess their analytical skills. Anyone can face such questions. But even if this does not happen to you, it will be simply interesting to study them for preparation.
Job seekers who encounter puzzles during the interview process should not panic and get lost. As a rule, in most cases it is enough to show the course of your thoughts and ways to solve the problem. It may well be that the problem does not have a correct solution or an unambiguous answer. In no case should you say “I don’t know” or “I find it difficult to answer”, just think out loud.
So that you know what to be prepared for and not get confused, we have collected the most popular puzzle questions and prepared answers and recommendations for them. Who knows, maybe you will come across exactly these tasks.
sewer manholes
This is perhaps the most common question among all puzzles.
Question: Why are sewer manholes round?
Answer: There are several options. Since the diameter of the circle is the same, no matter how you twist it, the round hatch cannot fall into the well. A square, for example, has a diagonal larger than its sides, so the lid could fall off. You can also answer that round hatches are easier to transport and move.
light bulbs
Question: There are 3 light bulbs in the closed room and 3 switches in the hallway. What is the minimum door opening required to determine which switch belongs to which bulb?
Answer: For one discovery. We turn on 2 switches at the same time, after a while we turn off the second one. We go into the room: one of the bulbs remained on - this is the first switch, then we feel the remaining bulbs - warm and will be the second switch, and cold, respectively, the third.
Cake
Question: How to divide the cake into 8 equal parts with three cuts?
Answer: First you need to make 2 cuts crosswise, dividing the cake into 4 equal parts. Then cut the cake horizontally in half. So what if the pieces have become low, but you have 8 equal parts. You can also, after the first two cuts, put the pieces on top of each other and halve them in one cut.
Dead man and match
Question: A dead man was found in the middle of the field with a match in his hands, there are no traces. What did he die of and under what circumstances?
Answer: A man died from a fall from an airplane that began to lose altitude, and an accident was inevitable. One parachute was not enough for all the passengers and they drew lots. He got a short match, and he was forced to jump without a parachute.
Bus and balls
Question: How many tennis balls will fit on the bus?
Answer: The recruiter himself does not know the exact correct answer, since it does not specify what kind of balls and bus - their sizes are not known, and no one has checked this thoroughly. Therefore, the course of your thoughts is important here, you can only guess. Name the approximate length, width and height of the bus, the dimensions of one ball. Calculate the volume of the bus and the ball - this way you will know how many balls will fit in an empty bus. Decrease approximately this value, taking into account the seats and other details of the bus, make allowance for the fact that the balls are not square and give an answer. In this case, the process of finding an answer is more important than the answer itself. The options for the question can be different: footballs - footballs, instead of a bus - a room, etc.
Pills
Question: The doctor gave the patient 4 tablets of two types - 2 tablets of each, which cannot be distinguished by their appearance. Tablets should be drunk in two doses: in the morning, one tablet of each type and in the same evening. If you violate the dosage or do not take the pills, the patient will die. So it turned out that the pills were mixed. How to get treatment and survive?
Answer: Of course, we can say that it is better to go to the doctor and ask for more, it's still a matter of life and death. But these may be the only pills on Earth, the doctor may disappear under mysterious circumstances, etc. So you still have to answer. In addition, everything is quite simple: you need to divide each tablet into 2 parts and drink half of each tablet in the morning and evening.
Finally
Remember that, first of all, such tasks and puzzles are designed to test the candidate's behavior in non-standard situations, to assess the ability to think, creative and logical approach. Alas, there are often cases when the interviewer cannot correctly interpret the results of such questions, or does not understand their purpose at all. But even in this situation, confident behavior and the desire to come to an answer will show you from the best side and increase the chances of getting a job.
