In each country, the development of sewerage systems took place in different ways, but the only common feature has always been the need to install sewer manholes.
The first manholes appeared together with the emergence of public utilities back in the 30s of the 19th century: then manhole covers had different shapes, but preference was most often given to round-shaped covers. Currently released, sewer manholes are round, and not of a different shape. This feature, in spite of everything, remained unchanged. But why exactly round?
Manhole covers are subdivided depending on their purpose. All of them have different patterns and embossing. On the old hatches you can see already outdated images of coats of arms, all kinds of drawings and inscriptions.
Modern manhole covers carry information about the manufacturer, serial number and date of manufacture. Some companies intentionally replace old sunroofs with new ("decorative") ones near their offices, and usually put their logos on the covers.
There are a lot of answers to the question why the hatches are round, but the following assumptions are the most reasonable:
In fact, discussions about the shape of manholes may seem meaningless to many. However, few people know that such an unimportant question can take anyone by surprise when ... applying for a job! And this shouldn't be surprising.
This type of interview question is not uncommon. Eychars among themselves refer it to "cases", that is, keys with which you can give a more accurate assessment of some qualities and abilities of applicants.
This practice is used mainly during interviews for applicants applying for high positions. Thus, the fact of how a person behaves in case of force majeure, what his speed of thinking is, whether he knows how to use non-standard approaches, and so on is evaluated.
Why are hatches round? Those that close-open the entrance to the sewer system. Those that have to be bypassed so that misfortune does not happen. They are so habitually included in everyday life that many people do not notice a foreign object in their path and automatically step over a dangerous place.
There are also car owners who diligently go around the sewer outlets to the surface in order to save the suspension. For this reason, the question of the shape of the lid can excite a fairly large number of people.
Man is a being of a higher order, thanks to his ability and desire to discover the world, to seek and find answers to questions of interest. And people are very curious. Why are giant elephants afraid of mice? Where do the fallen stars go? How to make a magic wand? Why is the manhole cover without corners and extra loops?
Of course, there are squares, stars, triangles on the pavement. 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 clogging is minimal. It is clear that for closing wells it is most rational to use covers of the same shape, but in a slightly increased diameter.
2. The production of round caps is cheaper for factories than the production of other forms. 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 such a shape will allow you to get the maximum area (compared to other figures). After all, the ratio of the cross-sectional area of \u200b\u200bthe 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 the internal pressure, only in a circle. Therefore, the lid can be thinner, even while maintaining its strength and reliability.
4. The sewer hatch covering the circular well will not fall inside. From no position. And these are additional safety measures for performing plumbing work.
5. Each point on the circumference of the hatch is a point of stress concentration. The uniform distribution of the load, which has already been mentioned above, has another advantage. It is this form that makes it easier to open the well by shifting the heavy cover to the side.
With rectangular hatches, it's a little different. There tension is concentrated in the corners. With such covers you have to tinker.
6. Round options are easier to move, not only because of the distribution of the load, but also simply because of the absence of corners. As a rule, sewer covers are made of cast iron. This is very heavy material. And any product from it is almost unbearable. The circle can be put on edge and rolled.
In addition to the above reasons, one more important point should be mentioned. There is such a production pattern: the less protrusions and corners a part has, the less marriage will come out from under the machine. Therefore, the production of round hatches is more than justified.
Round? And what else can they be? Theoretically, the hatch can be square or rectangular. But such a design, rather, is an exception to the rule. The hatch is not a simple manhole, it must be securely closed. It should be easy to maintain and safe to operate.
If convenience is an amateur, then reliability at the level of standard loads can be ensured precisely by the round design of the cover. The configuration of the base, which, in fact, is a sewer hatch, depends on its shape.
Sewer networks are a complex of structures designed to collect and divert from users to treatment facilities. The easiest way to do this is to dig a trench, lay pipes in it, through which drains will be discharged.
To be able to service the system after a certain distance, inspection shafts are required. In the conditions of urban infrastructure with dense buildings, it is possible to conduct sewer networks only along roads or directly under them. In this case, with heavy traffic, the hatches must be securely closed. But why are sewer manholes round? They must have sufficient strength to withstand the maximum possible traffic loads.
In a large city, the number of inspection hatches and all kinds of mines can be in the hundreds of thousands. After all, this is not only sewerage, it is also a network of communications: water supply, heating networks, electricity, gas, telephony, and so on.
For ease of access to communications, the well shaft is usually made in a round shape. 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 work in such mines. They are suitable for ventilation, as the air circulation in a cylindrical object is more intensive.
The 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, traffic intensity are taken into account.
It depends on the shape of the lid. On the one hand, maintenance personnel should have convenient access to underground utilities. On the other hand, the well must be securely closed to exclude the possibility of foreign objects getting inside, to ensure the safe movement of pedestrians and vehicles. A round lid is best suited for this, which means that the hatch itself should be of this shape.
Depending on the 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, standard dimensions are most often used (645 and 800 mm). Hatches not manufactured 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, and even triangular to indicate the direction of water flow. However, the round shape of the lid proved to be the most suitable.
She will never fall into the well, no matter how she is turned. A round lid is easier to open, so the point of application of force in any place of the circle will be the same. It can be rolled by placing it on edge. In the manufacture of such a design is economically more profitable.
The round shape of the lid is less prone to sagging. It withstands a large load with the same thickness, which means that it can be made thinner without losing quality. In the production of round castings, they give a smaller percentage of rejects (shells, pores, cavities).
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 vehicles cannot accidentally lift and move the cover. are made during the remelting of secondary raw materials, they are cheaper than steel counterparts.
In places where there is no heavy traffic, it is not advisable to install heavy and powerful structures. Recently, hatches made of plastic, polymers and composite material have appeared. They are lighter, cheaper, have a sufficient margin of safety, long service life.
In private houses, reinforced concrete sewer rings are used to equip sewage, manholes and septic tanks. In this case, it is quite justified to install the same base for the hatch on top of them. The cover is also made of concrete. It is made of a larger diameter, does not enter the groove, but simply covers the hatch opening. The massive structure is heavy enough that it cannot be accidentally moved. This provides the necessary safety during operation.
For increased loads on the roads, heavy hatches (class T) are used. They may have a weight of over 100 kg and a thickness of over 100 mm. Where vehicular traffic is not provided, light hatches (class L) are used. Constructions for the garden, lawn 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 is done for the convenience of recognizing their affiliation. On their covers there are letters: GS - gas network, MG - main gas pipeline, PG - fire hydrant, etc.
Modern public utilities emerged in the world in the 30s of the XIX century. Despite the variety of shapes, round lids were more preferred. Currently, manufacturers of manholes for sewer systems produce exclusively round shapes.
Despite the fact that the sewer systems of the modern type in different countries appeared at different time intervals, the only similarity was the need to install sewer manholes. The urgent need for cast-iron hatches arose primarily in large cities with paved roads for safety reasons. Still, moving the lid weighing from 45 up to 160 kg is several times heavier than the wooden flooring and barriers that were previously used.
Note! In recent years, along with cast-iron covers, cheaper analogues made of polymeric materials have appeared on sale, the minimum weight of which is considered to be 15 kg, the maximum - 48 kg.
The main reason why the manhole cover is round comes from the following considerations.
The round shape of the lid has a non-unilateral nuance: it is convenient to carry such a lid - i.e. roll, as opposed to square or triangular. But with an increase in the number of thefts in and nearby CIS countries for the sake of profit, the authorities began to look for a way out of this situation through production from other materials.
In the United States, slotted or latched covers are made as "anti-theft" measures. European countries use a combined material for the manufacture of covers - they combine concrete with cast iron. This avoids theft, because scrap metal recycling centers do not accept hybrid material.
Interesting fact! Enthusiasts do not lose heart, and on the Internet, users organize exhibitions of discovered samples with an unusual design with a postscript of the city. The art of cast lids has a history of about 150 years; daily, the world public gallery is replenished with new unusual examples of modern and ancient products.
Modern and antique manhole covers look different. 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 manufacturer, date of manufacture. Some organizations request “unique” copies on order, on which detailed information is located: the company logo, a short list of services provided, and more.
Access to underground utilities is reliably protected with manhole covers. Made of cast iron, they are not such a tasty prey for thieves, and special holes do not allow them to be opened. To understand why the hatches are round, you need to have the mind of a practitioner.
A manhole cover that opens the way down can be called a means of prevention. It is heavy circles that prevent many injuries and deaths. You can safely stand on them without fear of falling. Only those hatches are dangerous if the cover is missing or has a shape that does not look like a circle.
Currently, caps of a different shape are extremely rare.
The main advantages of this form:
And another plus in the treasury of the economy of production - there are few defective products. This is due to the smaller number of reference lengths for the circle.
In addition, the round shape reacts less to temperature changes and therefore lasts longer.
In the absence of a cover, the hatch must be fenced and marked with warning signs. Imagine that a manhole cover is square, triangular, or rectangular. Now let's try to move this cast-iron product from place to place. The circle will roll like a wheel, which is not the case with angled shapes.
A square cover is only safe when its side length exceeds the diameter of the round hole. This entails an increase in the consumption of material for manufacturing, which is inappropriate. If the well itself is square, then you just need to turn the lid a little - and it will fall inward, losing its protective functions. Therefore, it is not difficult to guess why hatches are made round and not square.
Manhole covers usually weigh 50 kg or more so that they cannot be moved from the manhole even in heavy traffic. In the US city of Nashua, New Hampshire, there are triangular manhole covers. They indicate the direction of flow in the sewer. Now these covers are being eliminated, as they do not meet modern safety standards.
The question is not always idle, even when it comes to hatches underfoot. Only by thinking about it, you can get new knowledge and use it in practice.
