17 why sewer manholes are made round. Why are manhole covers round? Sewer cover shape
Quite often, when hiring a candidate for a position, they ask why sewer hatches round. This is a very unexpected question that takes a person by surprise and he begins to think about it. This way you can quickly determine a person’s thinking, assess his level of intelligence and ability to get out of trouble. 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's really interesting is why the 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 hatch manhole, which must be present. In addition, it should be comfortable and ergonomic, and should not rattle when a car wheel hits it. It also has a small hole through which you can check the gas contamination of the well.
With all this, the lid 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 scrap metal. And although the law prohibits the acceptance of sewer manholes at scrap metal collection points, this does not stop thieves. Some people use them in everyday life for various purposes.
However, this is not about that now. 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 said 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 by economy. The fact is that it is the round shape with minimal costs allows you to create a hole that a person can 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, when making a hatch for such a hole, more metal would be spent, and this is not economically viable. 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 respectable figure.
Due to the round shape, the lids do not fall down
The second version, which explains why sewer manholes are round, is that this shape prevents the manhole from falling down. That is, under no circumstances, no matter how hard anyone tries, will he be able to push the lid into the well itself. But a square manhole cover can fall into the well if you try to insert it with its edge diagonally across the hole.
It is also believed that the round shape has a good feature - it more evenly distributes the load when a car hits it. Consequently, this allows the section size (thickness) to be slightly reduced, which ultimately leads to additional cost savings.
For a round well - a round lid
However, it is strange to even ask why sewer manholes are round, because the well itself is round, so when developing the covers, no one even thought about using a square shape. Moreover, if you need to quickly move the round hatch cover from the well, you can simply roll it on its edge, which can be done even by one person. But rolling a square hatch will not work - it must either be transported or carried by two or even three people. However, some lids have special “antennae” that prevent them from being rolled on edge.
It is also believed that opening a round manhole cover is easier due to the fact that any point on its circumference is also a point of stress concentration. As for square lids, there are only two similar points - the corners of one of the sides.
It just happened that way
In general, no one knows why sewer manholes are round. Few people think about this, but looking for an answer to this question is simply stupid. This is like asking why curbs have rectangular section. There is no definite answer to this question, because when the first sewer wells appeared, no one thought about making them in other shapes. 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. IN different countries forms can be different. Often found in India triangular shapes, and in some countries they may represent a generally indefinite geometric figure. Square shapes are not uncommon in the USA and other American countries. There are even hatches with eight corners, and very rarely there are models in the shape of a diamond or 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 want to get really boring, you can calculate how much metal is needed to make a square lid for a hole that a person could easily fit into. The resulting value must then be compared with the weight of metal required to make the cover for the round hole. With the same cross-section of metal, it turns out that more metal will be needed for a 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 along the entire perimeter of the circle. This is not the case with a square or triangle.
In general, now you know why sewer 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 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 are from sewer wells not always round, it’s just the way it is in our country. Sometimes even the person who asks such a stupid question doesn’t know why hatches are round in the first place. However, you now know the answer for sure. Despite many good versions, the most logical and plausible version seems to be the one with the shape of the lid, because of which it simply cannot fit into the sewer hole.
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. Besides, round holes They 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. 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 us to evaluate general level intelligence, how capable he is of solving problems and tasks. 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, worldwide famous company Microsoft has long used this question when testing specialists they are going to hire.
To sum it up, it is easiest to say that The lid should be round, including manhole covers!
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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. Workroom are arranged 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 main reason, according to which the shape of sewer manholes is made round.
- Also, the lids have a fairly 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 most heavy 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 manholes can be installed in gas, heat, water and other wells utility networks, as well as storm drains.
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. Sewage hatches can be closed drainage systems, cable (electrical or telephone), storm drainage systems.
Depending on the material used in manufacturing, cast iron, plastic, composite, concrete, reinforced concrete and rubber hatches, as well as hatches made of a polymer-sand mixture, can be distinguished.
Helpful information ! Each material has its own pros and cons, taking into account which you can choose best option for a certain situation. But anyway 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 public. 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 in the territory Soviet Union Several thousand manhole covers were stolen. Thieves sold them for scrap metal, thereby earning significant money.
Helpful information! To avoid theft, they are currently used wooden boards, plastic hatches or concrete circles that 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.
And I couldn’t help but wonder – why is it round? And often hatches are never made square. What is this standard? Or a conspiracy of plumbers and electricians? I addressed this question to to a professional master, it turns out that this question is almost the very first one for newcomers in this field. It turns out everything is quite prosaic...
To begin with, guys, I suggest you put everything on the shelves and tell us what these lids are, which actually close various wells. Don’t worry, the answer will be below, it will definitely be – read to the end.
Types of hatches
It is a mistake to think that the hatches that cover wells embedded in the ground are of the same type. There is quite a large infrastructure laid out underground, so there are different types:
- Hatches for drainage systems
- For storm systems
- For electrical networks
- For 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 over it could not turn it over. However, with the era of “perestroika”, metal versions still began to be stolen and sold for metal (and they were simply broken),
therefore, wells were often open (oh, it was a terrible time), so in those days they began to cover the wells with concrete round (as I call them) “short-holes.” It was even more difficult to carry them away, and there was no need, because you can’t hand over concrete!
Now, of course, new polymer or sand-polymer options are appearing, they are durable - they can withstand loads of up to 3 tons, they are also resistant to high and low temperatures, they don’t rot, they don’t rust, and they practically don’t steal them, because again, you can’t hand them over!
However, all these types are invariably round! But why - everything is banally simple.
Causes and Effects
Any mine consists of several parts:
- This top part the lid itself (the main purpose is to protect the internal components from dirt, sediment and other debris).
- Middle shaft - usually done round size diameter 70 cm, recess up to 3 meters.
- The last one is the lower part, there may be various 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 a round hatch cannot fall into the well shaft, no matter how hard you twist it. Try it at your leisure, whatever one may say, but there is a circle everywhere. But if the covers were square, or triangular, etc., then at a certain angle they could fall down, and if this is a sewer well, how can you get it back? Difficult!
Yes, both children and large equipment will not be able to somehow overturn or push such a hatch down, everything was done wisely. It is worth noting the weight metal options, is 50 kg, so no traffic flow can tip it over. 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 move”, but sits tightly in place.
Interesting facts about “well covers”
It should be noted that they were not always made round - there were also square, triangular and polygonal options.
But they were all dangerous and often simply fell through, 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 came down, they were already aware.
Also, hatches on hinges and some kind of “down” door were not uncommon in the past. The hinges also provided some protection against theft. However, during large traffic flows they were often broken and the lids fell through, so over time they were also replaced with round ones.
This is how the article turned out, now watch the cool video.
I’ll finish here, read our construction site, there will be a lot of interesting things.
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:
- Drainage systems.
- Storm drains.
- 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 it from entering sewer systems. various kinds third party objects that can 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 flow Wastewater, and until recently this helped repair teams 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 the well open, especially those in which storm drain and plumbing. Their depth sometimes reaches 6 meters, and at the bottom technical room a lot of 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 sewer hatches - and this is the district administration - have a great responsibility for 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 in municipal ownership, but are part of the property apartment building or to the property of a specific 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. Long-term service life 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.
