Why are sewer manholes round? Why are round sewer manholes a necessity or a tradition? Why are sewer covers round?

A familiar, familiar detail of the urban landscape are sewer manhole covers, which are round in shape almost everywhere, in all countries of the world.

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

Safety

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

This is not surprising, because a manhole cover located on the sidewalk of the street must withstand a load of 12 tons, and a manhole cover lying on the road must withstand a load of 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 manhole cover is open and lies next to the hatch, and below, people are working in the well. If someone accidentally moves the round lid, then in the worst case they will simply close the hatch. In this case, a rectangular or square lid can fall into a hole directly on the heads of the workers, because the diagonal of a square or rectangle is always larger than any of its sides. Therefore, the round shape of the lid is the safest in in this case.

Strength

Engineers have long known that round objects are much stronger than square ones. The sewer hatch is not only round, but also slightly convex in the middle: this shape provides the greatest resistance to mechanical load directed from above.

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

In addition, we should not forget that cast iron is a rather fragile material, and if you drop a rectangular lid, a corner may well break off. To crack a round manhole cover, you will have to put in a lot more effort.


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

Metal saving

Why is the round shape of hatches more optimal in terms of saving metal? With the same length of the perimeter of round and rectangular hatches, the area of ​​the circle is always more area rectangle or any other geometric shape.

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

Optimal ratio the length of the perimeter to the area forces us 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 withstand greater loads than any other shape.

Convenience of work

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

And in order to fit the heavy cover into place, you do not need to rotate it, adjusting it to the configuration of the hole. The round lid will fall into place in any case, no matter which side you lay it on.


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

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 propose to put everything on the shelves and tell you 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 different types are distinguished:

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

Initially, hatches were made from very durable materials, usually it was 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 scary time), so in those days they began to cover wells with concrete round (as I call them) “underholes.” 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 is the upper part of 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.
• Last thing - Bottom part, there may be various sizes and shapes, for example, in some connection wells they have 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 overturn or push such a hatch down in any way, everything is 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.

Quite often, when hiring a candidate for a position, they ask why sewer hatches round. This is quite unexpected this question, which 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. Eat different theories and answer options. 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 great weight is justified by the difficulty of theft, but it is precisely thanks to such heavy weight it is often stolen to be sold as 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, it would cost more metal, and it 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 uncertain 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're talking about about an interview, it is not at all necessary to answer correctly. You can answer with a joke or generally 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 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.

Modern enterprises public services appeared in the world in the 30s of the 19th century. Despite the variety of shapes, greater preference was given to round lids. Currently, manufacturers of manholes for sewer systems produce exclusively round shape.

Covers for manholes: weight and maximum load

Although sewer systems modern type appeared in different countries at different times, the only similarity was the need to install sewer manholes. The urgent need for cast iron hatches arose primarily in major cities with asphalt roads for safety reasons. Still, moving a lid weighing from 45 to 160 kg is many times harder wooden flooring and barriers that were previously used.

Note! Last years Along with cast iron lids, cheaper analogues from polymer materials, minimum weight which is considered 15 kg, the maximum is 48 kg.

Sewer cover shape

The main reason why the manhole cover is round comes from the following considerations.

1. The triangular shape is not suitable based on the structural features of the human body. Otherwise, the size of the hatches would be much larger than modern round ones. And this entails extra hassle in the form of an increase in the necessary raw materials for the production of the lid, therefore, its cost increases.
2. A square-shaped hatch may eventually fall into a well. Moreover, the shape of the well is round. Changing the transitions of sewer manhole shafts to the surface from a round to a square shape is not an easy task; it requires increased financial costs for manufacturing and replacement.

The round shape of the lid has a more than one-sided nuance: such a lid is convenient to carry – i.e. roll, as opposed to square or triangular. But with the increase in the number of thefts in and nearby countries CIS for the sake of profit, the authorities began to look for a way out of the current situation through production from other materials.

In the United States, lids with grooves or latches are made as “anti-theft” measures. European countries use combined material To make the lid, concrete is combined with cast iron. This helps prevent theft because scrap metal collection centers do not accept hybrid material.

Interesting fact! Enthusiasts do not lose heart and on the Internet users are organizing exhibitions of discovered samples with unusual design with the addition of the city. The art of cast lids dates back about 150 years; every day the global public gallery is replenished with new unusual examples of modern and ancient products.

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

The main reasons why the manhole cover is round

1. In Russia and neighboring countries, wells and sewer pipes have round section. This is the main factor influencing the shape of the lid. In some European and Asian countries, square versions are found. However, these are exceptions to the rule rather than the norm, because in the same Czech Republic or China, where people discovered covers in the shape of a square, sections of pipes and wells sewer system also have a round shape.
2. Cost reduction. Unlike a round one, the manufacture of a square manhole cover will require 30% more raw materials.
3. Convenience. To install a hatch cover of any other shape will require more costs: incl. human effort and time to install it: the lid will not have to be moved (taking into account the minimum weight of a cast iron specimen of 65 kg, a square one, based on the increase in raw material costs, will be approximately 30% heavier - i.e. about 85 kg).
4. A round-shaped sewer manhole will not fall into the well due to its increased diameter compared to the cross-section of the well.
5. Installation and dismantling of round covers is faster and there are a number of reasons for this:
   no need for more installers for moving the hatch;
   the time spent on moving it is reduced - it is easier to roll a round hatch; this method will not work with a square or triangular cover.
6. Load concentration distribution. For a round lid, distribution is carried out over the entire area. Angular lids cannot boast of this - it is the corners that will act as the main load points.
7. It is more difficult to damage the edges of a round hatch than an angular one. During transportation, it can be chipped. Considering that it is the corners that act as the main reference point for distributing the load, a broken piece, regardless of its size, breaks the system and the load is distributed to the remaining corners.
8. Wear resistance. The service life directly depends on the integrity of the manhole cover. If a part breaks off on angular lids, the load is distributed unevenly. Over time, this will cause damage to other supporting corners.

Logic problems are given to job candidates to evaluate their analytical skills. Anyone can face similar questions. But even if this doesn’t 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 or become confused. As a rule, in most cases it is enough to show your thoughts and ways to solve the problem. It may well be that the task does not have the right decision or a clear answer. Under no circumstances should you say “I don’t know” or “I don’t know,” just think out loud.

So that you know what to be prepared for and don’t 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.

Sewage hatches

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, a 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 a closed room, and 3 switches in the hallway. For what minimum opening of the doors can you determine which switch belongs to which light 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 light bulbs remains on - this is the first switch, then we feel the remaining light bulbs - the warm one will be the second switch, and the cold one will be the third, respectively.

Cake

Question: How to divide a cake by 8 equal parts three cuts?

Answer: First you need to make 2 crosswise cuts, dividing the cake into 4 equal parts. And then cut the cake in half horizontally. So what if the pieces are not tall, but you have 8 equal parts. You can also, after the first two cuts, stack the pieces on top of each other and halve them with one cut.

Dead man and match

Question: Found among the field dead man with a match in his hands, no traces. Why did he die and under what circumstances?

Answer: A man died from a fall from a plane that began to lose altitude, and an accident was inevitable. There was not enough one parachute for all the passengers and they drew lots. He got a short match and was forced to jump without a parachute.

Bus and balls

Question: How many tennis balls can fit on a bus?

Answer: The recruiter himself does not know the exact correct answer, since it is not specified what kind of balls and bus they are - their sizes are not known, and no one has thoroughly checked this. Therefore, your train of thought is important here, you can only guess. Give the approximate length, width and height of the bus, and the dimensions of one ball. Calculate the volume of the bus and the ball - this way you will find out how many balls will fit into the empty bus. Reduce approximately this value taking into account the seats and other parts of the bus, make allowances for the fact that the balls are not square and give your answer. In this case, the process of finding an answer is more important than the answer itself. The question options may be different: the balls are soccer balls, instead of a bus there is a room, etc.

Pills

Question: The doctor gave the patient 4 tablets of two types - 2 tablets of each, which cannot be distinguished by appearance. The tablets should be taken in two doses: one tablet of each type in the morning and the same in the evening. If the dosage is violated or the pills are not taken, the patient will die. It so happened that the tablets were mixed. How to undergo treatment and survive?

Answer: Of course, we can say that it is better to go to the doctor and ask for more, after all, it is a matter of life and death. But these may be the only pills on Earth, the doctor may disappear with 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 primarily such tasks and puzzles are designed to test the candidate's behavior in non-standard situations, assess the ability to think, creatively and logically. Unfortunately, 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 with the best side and increase your chances of getting a position.