home · On a note · Why are all the hatches round? Why are the hatches round? Unexpected interview question. Also, hatches with existing holes into which you can insert a hook and thus pull out the lid have long been put into production

Why are all the hatches round? Why are the hatches round? Unexpected interview question. Also, hatches with existing holes into which you can insert a hook and thus pull out the lid have long been put into production

Have you ever wondered why, there are sewer manholes everywhere? round, and not square? Manhole covers are made of cast iron, sometimes 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 of them: shut-off and protective. The first one weighs much lighter, it is usually made of steel and is needed to protect the cable from theft. They place it just under the protective cover, and on the cover itself they simply write the purpose of the hatch.

The simplest and most logical explanation

A square-shaped lid can easily fall into a hatch, for example, slip through at an angle. This may be because the diagonal of the square is larger than its sides, that is, the lid may fall into the hole. And a 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 lower one, the cover will never fall inside the hatch, no matter what position it is in. The round lid is safer than other types of lids, since they will not fall on the heads of workers who are inside the hatch.

The most frivolous explanation

There is an explanation that, of course, seems funny. 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 will have to spend extra effort and extra time. In addition, round holes are more technologically advanced, they have a longer service life, and 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. It will take at least two men to carry the manhole cover to the right place. And the round one can be rolled, which is something one adult man can do. 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 opening. There is some truth in this too; round hatches are much more convenient. Moreover, they are easy to manufacture, because again, you will have to tinker with square hatches; their corners may be damaged during transportation, for example, knocked off.

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 problems. By asking this question, experts want to see whether the candidate employee has the willingness and ability to enter into discussions and how the candidate solves the task 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 used this question when testing specialists who are going to be hired.

To sum it up, it is easiest to say that The lid should be round, including manhole covers!

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The eternal question: “Why is the hatch round?”

Almost all manholes in the city are covered with special round covers. If you carefully study such objects, it turns out that they are the same all over the world. This involuntarily prompts the question: “Why are the covers on sewer manholes round? Why do the technical objects themselves have exactly this shape, and, for example, not square?” It turns out that the answers lie on the surface.

Some details about sewer manholes

The described items are made of cast iron or concrete. They are specially made heavy and unbearable, so that no one would have the desire to take a “useful” thing with them. Opening a technical hole on your own is not so easy, and this is specially provided for in the design for the safety of passers-by.

Sewer hatches have a conditional classification. They are divided according to the material of manufacture and the type of communications passing under the launch shafts. Therefore, experts highlight:

  1. Drainage systems.
  2. Storm drains.
  3. Electrical networks.

Hatches are made from high-strength cast iron and plastic, a special polymer-sand mixture, composite materials and reinforced concrete. But they are all invariably round in shape. Why, let's find out.

Logical explanation

So why is a manhole round? The described technical object consists of several parts - a round shaft, an inspection room and a lid.

The viewing room can have different shapes. It all depends on what communications are laid in the well. Dimensions are chosen taking into account the ease of their maintenance. But the mines are invariably made round. The diameter of the oval is 0.7 meters. They are assembled from brick and additionally equipped with a ladder that helps the service worker to go down without hindrance.

The top of such a hatch must be closed with a lid. It prevents various types of foreign objects from entering sewer systems that could cause accidents. Almost everywhere the lid has a round shape. Why not square? Because in any position, such a lid will never fall inside and hit the person located there.

A square lid can easily fall inside under the influence of vehicles, slipping through at an angle. After all, the diagonal of a square is always greater than any of its sides. A circle has the same radius, no matter how you look at it.

Typically, manufacturers produce lids that weigh more than 50 kg. This is done so that no heavy traffic of cars could move them.

Other explanations for the shape of the hatches

It is very rare to find such a form

There are several more explanations to help understand why manhole covers are round:

  • Firstly, a circle has a higher ratio of cross-sectional area to circumference than a square or rectangle. This allows the lid production process to reduce material costs and save on product production.
  • Secondly, the round shape reduces the internal forces that invariably occur when installing any cover on an object. And this also provides savings on the production of the product, since in this case it is possible to produce lids of smaller thickness.
  • Thirdly, the round shape helps reduce the production of defective products. By reducing the number of reference lengths, the likelihood of errors leading to the appearance of uneven protrusions and other characteristic defects is reduced.

And further. The round lid is much easier to transport for one person. He can just roll her to the place. A square or rectangular one will have to be carried in several hands.

The above arguments show that the choice of form is explained by elementary practicality.

Fun facts

There are known cases around the world of using lids of other shapes. For example, in the American city of Nashua you can still see sewer wells covered with triangular covers. Their sharp corners indicate the direction of wastewater flow, and until recently this helped repair crews to navigate well. But today their use is considered unsafe, so the prefecture is dismantling them and replacing the triangles with circles.

Other forms are also found

Now you know why sewer manholes are made round. But why they are made so massive and heavy is also an interesting question. Although the explanation lies on the surface. The weight ensures relative safety from theft and delivery of the described products to metal collection points. About 10 years ago, a wave of characteristic crimes swept across the country. Lids began to disappear en masse, so the designers came up with an interesting solution.

Most modern sewer wells are not simply covered on top with a massive object that one person cannot carry away. The lids were placed on strong hinges, and they turned into real doors, which were additionally locked.

There is no way to leave wells open, especially those that contain storm drainage and water supply. Their depth sometimes reaches 6 meters, and at the bottom of the technical room there are many protruding pipes and pieces of fittings. If a person falls there in the dark, it will end in death. Therefore, those who are responsible for the sewer hatches - and this is the district administration - are entrusted with great responsibility for the safe use of this technical structure.

Who else could be responsible for the hatches?

But the Russian people are still accustomed to seeing such a hatch

There are wells that are not municipally owned, but belong to the property of an apartment building or to the property of a certain legal entity.

All ownerless objects are first registered by the body that registers the right to property. This happens at the request of the local government. Then, through the court, everyone can challenge their own right. If there are no volunteers within a year, all ownerless objects are transferred to the departments of specialized companies.

Generalization on the topic

The round shape of sewer manholes is more practical than all other types. Over many years of operation of sewerage structures, it has been proven that round holes are more technologically advanced and have a longer service life. And all because such a hatch is more resistant to temperature changes.

Many people have come across the question of why sewer manholes are round in shape. Most have heard it during job interviews. In this way, “cunning” HR managers test the general erudition and ability for creative thinking of potential employees.

This question is also often used in various competitions and quizzes. If you study the design of sewer hatches, the answer to the question will become obvious and quite understandable. This is what we'll do.

Sewer hatch installation

A sewer well usually consists of a shaft and a working room, and the hatch serves as a cover. The workroom is equipped and located depending on the type of communications being served and the requirements for their operation. The depth of the shaft and the size of the room also depend on this.

  • Typically the height of the room is 1.8 meters, but it can be more or less. The main criterion for its determination is the depth of communications. The length of the shaft directly depends on the depth of the room. Typically the shaft is round in shape and has a diameter of 0.7 meters. The shaft must have a ladder so that the worker can go down into the room. The material used for shaft construction is usually brick or concrete.
  • A cover on the sewer hatch is necessary to prevent foreign objects and people from entering the mine. The round shape prevents the lid from falling into the shaft if someone steps on it, which means it protects against accidents. This is the most important reason why the shape of sewer manholes is made round.
  • Also, the lids have quite a large mass, and sometimes this also raises questions. This fact can also be easily explained. Very often, sewer manholes are located on the roadway and when driving, the car's wheels hit the cover. If the lid were light, it would easily flip over, opening the shaft and creating the possibility of accidents. To avoid this, the lids are cast from cast iron, which is considered one of the heaviest metals.
  • The surface of the lid usually has raised stripes, letters, or other designs or images. This was also not done by chance. The ribbed surface prevents slipping and increases the adhesion strength of car tires and pedestrian soles to the surface of the hatch. There are flat lids, and sometimes they are curved in the middle, but you will never see concave ones anywhere.

Cable duct wells usually have two covers at once - a protective cover and a shut-off cover.

The protective one is on top. There is an additional lock on the locking cover, which prevents unauthorized persons from entering the shaft to steal the cable. These lids are lighter than regular ones because they are made of steel.

Also, sewer hatches can be installed in wells of gas, heat, water supply and other utility networks, as well as storm sewers.

Each of them is designed to ensure that no unauthorized person or animal accidentally or deliberately enters a sewer well or mine or gains unhindered access to underground utilities.

Types of sewer manholes

Sewer hatches can be divided into several types depending on the design, the material from which the hatch is made, and the type of communications that it covers. Sewer hatches can cover drainage systems, cable (electrical or telephone), and storm drainage systems.

Depending on the material used in manufacturing, we can distinguish cast iron, plastic, composite, concrete, reinforced concrete and rubber hatches, as well as hatches made of a polymer-sand mixture.

Helpful information! Each material has its own pros and cons, taking into account which you can choose the best option for a particular situation. But still, the traditional option is a sewer manhole made of gray or high-strength cast iron. This material has high strength, is resistant to mechanical stress of various types, is independent of weather conditions, and its service life exceeds the shelf life of all other materials.

Safety of sewer manholes

The main purpose of making a sewer manhole round is to ensure the safety of the population. Unfortunately, cases of an adult or child falling into an open sewer shaft are not that rare. If the mine is shallow, then this can result in one or more fractures, but greater depth can even lead to death.

A common cause of such falls is theft of a manhole cover.

Nowadays, many people, walking down the street, are distracted by talking on a mobile phone or writing SMS messages, sometimes so carried away that they forget to look at their feet. This kind of absent-mindedness leads to accidents.

Also, a car can get caught in an open hatch, which at best will lead to minor damage to the car, and at worst, to injuries to passengers. Those who like to ride other types of transport - scooters, motorcycles, mopeds, bicycles, rollerblades or skateboards - are also at risk. Falling into a hatch at high speed can result in serious injury.

Fun facts about sewer manholes

If the manhole was installed long ago, opening it can be a serious problem. In this case, specialists weld a metal handle to the hatch from above, open the hatch, perform the necessary operations, close it, and then cut off the handle.

Also, hatches with existing holes into which you can insert a hook and thus pull out the cover have long been put into production.

But such hatches cannot be used when closing electrical, telephone and cable networks. This is because water can get into the holes due to rain or melting snow, which can damage the network and negatively affect the operation of the entire system.

The issue regarding the excessive mass of sewer manholes should also be explained.

This weight is given to the lids specifically in order to make it difficult and sometimes even prevent their theft. The fact is that free metal has always attracted those who like to make money at the expense of the state. Thus, in the last decade of the twentieth century, several thousand sewer manhole covers were stolen on the territory of the Soviet Union. Thieves sold them for scrap metal, thereby earning significant money.

Helpful information! To avoid theft, wooden shields, plastic hatches or concrete circles are currently used to cover the main cover on top. Lids fastened with metal hinges have also become widespread. They cannot simply be removed and carried away; special equipment will have to be used, which will complicate the theft process.

Also, the hatches are made so massive that teenagers do not play in the sewers or use them for other, less decent things.

There are several other explanations for why sewer manholes are round.

  • Firstly, this shape makes it easier to transport. The hatches are quite heavy and to move a lid, for example, a square one, you need to use the strength of one or even two adult men. The round lid can easily be rolled along the ground by any teenager and over any distance.
  • Secondly, there are no problems when installing the cover. It is unlikely that anyone will have questions about its location in the well hatch. The only mistake here could be installing it the wrong way up, but this is not very critical for operation.
  • Well, and thirdly, less material is used for the production of round products.

Why are the hatches round? Those that close and open the entrance to the sewer system. Those that have to be bypassed so that misfortune does not happen. They have become so commonplace in everyday life that many people do not notice a foreign object in their path and automatically step over the dangerous place.

There are also car owners who diligently drive around the places where the sewage system exits to the surface in order to maintain the suspension. For this reason, the question of the shape of the lid may concern a fairly large number of people.

Why was this form chosen?

Man is a being of a higher order, thanks to his ability and desire to discover the world, seek and find answers to questions of interest. And people are curious about a lot of things. Why are huge elephants afraid of mice? Where do fallen stars go? How to make a magic wand? Why is the manhole cover without corners and extra hinges?

Of course, there are squares, stars, and triangles on the asphalt. But this happens so rarely that it can be classified as an exception. And the pattern is a hatch in the shape of a circle. And there are several reasons for this:

1. The ideal shape for sewer wells is round. They are easier to maintain. The likelihood of blockages is minimal. It is clear that to cover wells it is most rational to use covers of the same shape, but with a slightly increased diameter.

2. The production of round lids costs factories less than the production of other shapes. This is mainly due to material savings. What is a circle? This is a pretty good geometric figure. With a limited amount of material, choosing just this shape will allow you to get the maximum area (compared to other shapes). After all, the ratio of the cross-sectional area of ​​a circle to the circumference is greater than that of squares or rectangles.

3. You can also save on thickness if you choose the right hatch shape. The resulting load is evenly distributed, reducing internal pressure, only in a circle. Therefore, the lid can be thinner, even while maintaining its strength and reliability.

4. A sewer hatch covering a circular well will not fall inside. Not from any position. And these are additional safety measures for performing plumbing work.

5. Each point on the circumference of the hatch is a stress concentration point. The even distribution of the load, which was already mentioned above, has another advantage. It is this shape that makes it easier to open the well by moving the heavy lid to the side.

With rectangular hatches it’s a little different. There the tension is concentrated in the corners. You will have to tinker with such covers.

6. Round options are easier to move not only due to load distribution, but also simply due to the absence of corners. Typically, sewer covers are made of cast iron. This is very heavy material. And any product made from it is almost unbearable. The circle can be placed on its edge and rolled.

In addition to the above reasons, one more important point should be mentioned. There is such a production pattern: the fewer protrusions and corners a part has, the less rejects will come out of the machine. Therefore, the production of round hatches is more than justified.

The development of sewer systems in each state took place in its own way. The only common feature in all cities is the need to install hatches. Sewage hatches first appeared in the middle of the 19th century. Then they were made in a variety of shapes - from round to square. In recent years, only round models have been produced. Why?

What is a manhole?

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

Types of sewer manholes

Lids are divided into types. There are different embossing and patterns on them. For example, on the first sewer manholes they depicted the state emblem and propaganda slogans. Now the covers display the serial number, date and initials of the manufacturer. Sewer people highlight:

  • Plastic;
  • Iron;
  • Rubber;
  • Cast iron;

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

Why are sewer manholes round?

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

  1. The cost of manufacturing a housing for a round hatch is lower than any other shape (triangular, diamond-shaped, rectangular);
  2. Ease of movement. A round hatch is much easier to move: you just need to place it on its edge and roll it in the desired direction;
  3. The round hatch is easier to open. For him, any point on the circle is a stress concentration. For example, all lids for jars are also only round;
  4. The round hatch 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 system pipes is round. It would be logical to make the same shape as the lid that covers the sewer system.
  6. It is impossible to remove a square (triangular, rectangular) object through a round hatch cover.

In some countries, triangular sewer manholes are used. In Nashua (a city in the USA), underground systems are still covered with triangular-shaped covers. The sharp corners of the triangle indicate to the maintenance crew the direction in which the wastewater flows. However, such hatches were recognized as hazardous to health, and their dismantling began.

The choice of the round shape of sewer covers is dictated by elementary practicality. Such hatches last longer and are resistant to environmental influences. Less material goes into production and they are cheaper. Convenient to work with if you need to get inside the sewer system, safe. The likelihood of a round hatch sagging is very low.

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