In each country, the development of sewerage systems took place differently, but the only common feature There has always been a need to install sewer hatches.
The first hatches appeared along with the emergence of public utilities back in the 30s of the 19th century: then the manhole covers had different shapes, however, preference was most often given to lids round shape. Currently produced, sewer manholes are round, and not of any other shape. This feature, despite everything, has remained unchanged. But why exactly round?
Manhole covers are divided depending on their purpose. They all have different drawings and embossing. On old hatches you can see outdated images of coats of arms, all kinds of drawings and inscriptions.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 deliberately replace old hatches with new (“decorative”) ones near their offices and, as a rule, put images of their logos on the covers.
Why did you choose a round shape for the hatches?
There are quite a lot of answers to the question of why hatches are round, but the most reasonable assumptions are the following:
- In our country, well tunnels and sections sewer pipes round, so there is no point in making lids 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 the well, which means they are best suited for fulfilling their purpose. 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 fit into 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 produce a round lid, it is necessary less material. The standard norm for the width of the hatch is 600 mm, for a circle this will be the diameter, and for a square it will be the side, so the area of the square hatch will be 0.36 square meters, and round - 30% less.
- The manhole cover is round because it is easy to carry. In most cases, manhole covers are made from scrap (gray cast iron), which is obtained by melting various scrap metals. The weight of one cover varies from 50 to 110 kg. It is quite difficult for one person to move the manhole cover from one place to another, but thanks to its round shape it can be rolled.
- Not square, but round hatches are convenient to install and dismantle, since load concentration points run along the entire circumference of the cover, while for square or rectangular hatches such points will only be at the corners. That is why the necks and, accordingly, the lids of the jars are made round.
In fact, discussions about the shape of sewer manholes may seem pointless to many. However, few people know that such a question of no particular importance can take anyone by surprise when... applying for a job! And you shouldn't be surprised by this.
This kind of interview question is not uncommon. HR managers among themselves refer it to “cases,” that is, keys with the help of which one can give a more accurate assessment of certain qualities and abilities of applicants.
This practice is used mainly during interviews for applicants applying for high positions. In this way, the fact is assessed how a person behaves in the event of force majeure circumstances, what speed of thinking he has, whether he knows how to use non-standard approaches, etc.
Quite often, when hiring a candidate for a position, they ask why sewer manholes are 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 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 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 manhole hatch, 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 make it impossible to roll them edgewise.
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. It's like asking why curbs have a rectangular cross-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 longer sides. 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. In India, triangular shapes are common, and in some countries they can be a generally vague geometric figure. Square shapes- 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 the metal required to make the lid for 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, when 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.
Round? What else could they be? Theoretically, the hatch can be square or rectangular. But this design is rather an exception to the rule. A hatch is not a simple hole; it must be securely closed. It must be easy to maintain and safe to use.
If convenience is not an acquired taste, then the round design of the lid can ensure reliability at the level of standard loads. The configuration of the base, which, in fact, is the sewer hatch, depends on its shape.
Waste system
Sewer networks are a set of structures designed to collect and drain from users to treatment facilities. The easiest way to do this is by digging a trench and laying pipes in it through which the wastewater will be drained.
In order to be able to service the system over a certain distance, inspection shafts are required. In urban infrastructure with dense buildings, it is possible to install sewer networks only along roads or directly under them. In this case, during heavy traffic, the hatches must be securely closed. But why are sewer manholes round? They must have sufficient strength to withstand the maximum possible transport loads.
In a large city, the number of inspection hatches and various shafts can number in the hundreds of thousands. After all, this is not only a sewer system, it is also a communications network: water supply, heating networks, electricity, gas, telephony, etc.
Manholes
For ease of access to communications, the well shaft is usually made in a round shape. The sewer rings used for the construction of such structures are most often made of reinforced concrete.
The cylindrical shape of the well is most suitable for maintenance. It is more convenient to carry out work in such mines. They are suitable for ventilation, since air circulation in a cylindrical object occurs more intensively.
Cover size, base area and internal diameter are selected in accordance with the purpose of the inspection shaft. In this case, all elements of the system will correspond to each other as much as possible. The location, possible loads, and traffic intensity are taken into account.
It depends on the shape of the lid. On the one side, service personnel must have easy access to underground communications. On the other hand, the well must be securely closed to prevent foreign objects from getting inside, to ensure the safe movement of pedestrians and vehicles. A round lid is best suited for this, which means the hatch itself should be of this shape.
Depending on their purpose, they are divided according to the type of communications laid under them: engineering cable networks, water supply, gas mains, heating mains, storm and sewerage. The size of the sewer manhole varies from country to country. In Russia they are most often used standard dimensions(645 and 800 mm). Hatches manufactured not in accordance with GOST are designed and developed by manufacturers in accordance with the order and specific technical conditions.
This configuration has a number of advantages. Previously, hatches were made in various shapes. They could be square, rectangular, oval, or even triangular to indicate the direction of water flow. However, the round shape of the lid turned out to be the most suitable.
It will never fall inside the well, no matter how much it is turned. A round lid is easier to open, since the point of application of force anywhere on the circle will be the same. It can be rolled by placing it on its edge. This design is more economical to manufacture.
The round shape of the lid is less susceptible to sagging. It can withstand greater loads with the same thickness, which means it can be made thinner without losing quality. During production, round castings produce a lower percentage of defects (shells, pores, cavities).
Material
The base and manhole covers for those in charge are most often made of cast iron. This material has strength, which makes it possible to withstand heavy loads, and corrosion resistance for a long time. The weight of the structures is sufficient so that passing traffic cannot accidentally lift and move the cover. They are made by melting down recycled materials and are cheaper than their steel counterparts.
In places where there is no heavy traffic, it is not practical to install heavy and powerful structures. Recently, hatches made of plastic, polymers and composite material. They are lighter, cheaper, have a sufficient margin of safety, long term operation.
In private houses, sewer rings made of reinforced concrete are used to install sewage systems, equip inspection wells and septic tanks. In this case, it is quite justified to install the same base for the hatch on top of them. The lid is also made of concrete. It is made of a larger diameter, does not fit into the groove, but simply covers the hatch hole. The massive structure is quite heavy and cannot be accidentally moved. This provides the necessary safety during operation.
Specification and marking
For increased loads on roads, heavy hatches (class T) are used. They can have a weight of over 100 kg and a thickness of over 100 mm. Where vehicular traffic is not provided, lightweight hatches (class L) are used. Structures for gardens, lawns and other areas (class A) have a diameter of 540 mm and a thickness of 50 mm.
Why are sewer manholes round and marked? This was done for the convenience of recognizing their belonging to. On their covers there are letters: GS - gas network, MG - main gas pipeline, PG - fire hydrant, etc.
Why are the hatches round? Those that close and open the entrance to 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 creature higher order, thanks to his ability and desire to discover the world, search 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 do 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 pretty lucky geometric figure. With a limited amount of material, choosing exactly this form will allow you to get maximum area(compared to other figures). 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. Sewer hatch covering the well round section, will not fall inside. Not from any position. And this additional measures safety 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.
Many people are interested in why sewer manholes are made round, but not everyone knows that this shape is considered the most practical. It is safer to use round lids, and at the production stage of products, metal is saved. Of course, in addition to round ones, there are hatches of other shapes on city streets, for example, square ones, but they are quite rare. This is explained by a whole series of factors.
Security Considerations
Despite their small dimensions, the lids weigh about 50 kilograms, because they are made of cast iron. And the weight of products located on the roadway exceeds 78 kilograms - after all, they must withstand the weight of passing cars. According to the rules, hatches located on sidewalks must carry loads of up to 12 tons, and those intended for installation on the road - up to 25 tons.
Given the significant weight of the covers, it is very important to follow safety rules when working in a sewer well. If the product falls through the hatch onto the heads of the workers, tragedy cannot be avoided. Fortunately, the round lids are designed to never fall down the well. Products shaped like a square or rectangle can easily fall off, because their diagonals are always larger than any of the sides.
Ease of use
Considering the large weight of cast iron covers, dismantling them is quite difficult, especially if they are square. To move such hatches from place to place, you will need several adults. Round lids are much easier to handle because they can be rolled on an edge. You can cope with this task even alone.
There is no need to rotate the round lid, trying to adjust it to the shape of the hole. It will take the desired position no matter which side you place it on.
Increased strength
Since the covers that are used to protect engineering systems, are subjected to heavy loads during operation, care must be taken to ensure that these products have improved strength indicators. The easiest way to achieve this is to make the hatch round, because products of this shape have improved strength compared to square ones.
Photo: standard sewer manhole
In addition, if you carefully examine the structure of the hatch, you will notice that towards the middle of the circle it is slightly convex. This is not an accident: this shape ensures the most uniform distribution of internal stress in the product. Rectangular covers do not have this property; the loads in them are distributed unevenly and lead to increased wear of the metal.
Cast iron is a brittle material, so as a result mechanical influences Cracks and chips may appear on its surface. Round hatches are made in such a way as to prevent the destruction of the metal: it is much more difficult to break off a piece from them than from square or rectangular-shaped products.
The load concentration points of a round hatch are evenly distributed around the entire circumference. With square products, stress is concentrated only in the corners, and this is very risky, because you cannot transfer the entire load to just one part of the part.
Economic feasibility
In addition to improved consumer properties, the round shape saves metal. With the same perimeter length, a circle always has an area greater than that of a rectangle. Thus, the production of round hatches is economically feasible, because savings on materials can reach 30%. It turns out that instead of three square lids, four round ones can be made at the same cast iron consumption.
Considering the low cost of round manholes, on a city scale, the savings on the installation of sewer wells look impressive. In addition, round covers are widely used to protect other communication systems, such as waste pipelines, gas pipes or underground electrical networks.
The advantages of round hatches include not only metal savings, but also a very small percentage of rejection. Reducing the number of reference lengths is the key to a low probability of errors leading to the appearance of various defects.
Photo: open sewer manhole operating on the principle of doors Who is responsible for the hatches
Sometimes hatches are equipped with hinges - this is done in order to avoid theft, which has become especially noticeable in the last two decades. Cast iron products are in demand at metal collection points. Additionally, the hatches can be locked - in this case they resemble a door.
Most sewer wells, including their covers, are municipally owned, although some may be owned by legal entities And apartment buildings. If the object is ownerless, at the request of representatives local government registered with the authority that registers property rights. Then, if the owner is not found, the hatch is transferred to the balance of one of the specialized companies.
