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.
What are sewer manholes for?
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.
Why are they round
The main advantages of this form:
- safety - the circle does not fall inward, no matter how you turn it, it will not hit the one below and will not drop the one standing above;
- savings - less cast iron is used for a round shape than for a square one, since the moment of stress under load on the circle is less and the cover can be made thinner;
- convenience - it is physically easier to open such a lid, this property is also used in the form of cans for canned food.
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. If only they had a different shape
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.
Many have faced the question of why sewer manholes have a round shape. Most have heard it in job interviews. In this way, "insidious" HR managers test the general erudition and ability for creative thinking of potential employees.
Also often this question is used in various competitions and quizzes. If you study the device of sewer manholes, then the answer to the question will become obvious and quite understandable. This is what we'll do.
Manhole device
A sewer well usually consists of a shaft and a working room, and the hatch serves as a cover. work space equip and dispose depending on the type of serviced communications and the requirements for their operation. The depth of the shaft and the size of the room also depend on this.
- Usually 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. Usually the mine is round and 0.7 meters in diameter. There must be a ladder in the mine so that the worker can go down to the room. The material for the construction of the mine is usually brick or concrete.
- The cover on the sewer manhole is necessary to prevent entry into the mine foreign objects and people. The round shape prevents the cover 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 the sewer manholes is made round.
- Also, the covers 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 the car wheels are moving, they fall on the cover. If the cover were light, it would easily turn 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.
- On the surface of the lid, there are usually raised stripes, letters, or other patterns and images. This is 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 sunroof. There are flat covers, and there are ones that are curved in the middle, but you will never find those that are concave inside.
On the wells of cable ducts, two covers are usually located at once - protective and locking.
The protective one is on top. A lock is additionally located on the locking cover, which prevents unauthorized persons from entering the shaft in order to steal the cable. These lids are lighter than conventional lids because they are made of steel.
Also, sewer hatches can be installed in the wells of gas, heat, water and other engineering networks, as well as storm sewers.
Each of them is designed to ensure that no unauthorized person or animal accidentally or specifically enters the sewer well, mine and does not get unhindered access to underground utilities.
Varieties 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 closes. Sewer hatches can close drainage systems, cable (electrical or telephone), storm drain systems.
Depending on the material used in the manufacture, cast iron, plastic, composite, concrete, reinforced concrete and rubber manholes, as well as manholes made of a polymer-sand mixture, can be distinguished.
Helpful information ! Each material has its pros and cons, taking into account which you can choose best option for a certain situation. But still, the traditional option is a gray or ductile iron manhole. This material has high strength, is resistant to mechanical influences of various nature, is independent of weather conditions, and its service life exceeds the shelf life of all other materials.
Manhole safety
The main purpose of giving the sewer manhole a round shape is to ensure the safety of the population. Unfortunately, cases of an adult or child falling into an open sewer shaft are not uncommon. If the mine is shallow, then this can result in one or more fractures, but a great depth can even threaten death.
Common causes such a fall is the theft of a manhole cover.
Now many people, walking down the street, are distracted by talking on a mobile phone or writing SMS messages, sometimes getting so carried away that they forget to look under their feet. This distraction leads to accidents.
Also, a car can get into an open hatch, which at best will lead to minor damage to the car, and at worst, to injury to passengers. Fans of riding other modes of transport are also in danger - scooters, motorcycles, mopeds, bicycles, roller skates or skateboards. Hitting the hatch at high speed is fraught with serious injury.
Fun Facts About Manholes
If the sewer hatch was installed a long time ago, then 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 have long been launched into production, into which a hook can be inserted and thus the cover pulled out.
But such hatches cannot be used when closing electrical, telephone and cable networks. This is due to the fact that water can get into the holes due to rain or snow melt, which can damage the networks and adversely affect the operation of the entire system.
The issue of the excess mass of sewer manholes should also be explained.
This weight is given to the lids specifically to make it difficult and sometimes prevent their theft. The fact is that free metal has always attracted fans to profit at the expense of the state. So, in the last decade of the twentieth century, several thousand manhole covers were stolen on the territory of the Soviet Union. Thieves rented them for scrap, thereby earning substantial money.
Helpful information! To avoid theft, wooden shields, plastic hatches or concrete circles are currently used, which cover the main cover from above. Covers attached with the help of metal hinges. They cannot be simply removed and carried away; special equipment will have to be used, which will complicate the process of theft.
Also, the hatches are made so massive that teenagers do not play games in the sewers or use them for other, less decent things.
There are several other explanations for why sewer manholes are round.
- Firstly, this form facilitates transportation. The hatches are quite heavy and in order to move the cover, for example, a square one, you need to use the strength of one or even two adult men. The round lid can be easily rolled on the ground by any teenager and for any distance.
- Secondly, there are no problems when installing the cover. It is unlikely that anyone will have questions about its location in the hatch of the well. The only mistake here may be to install it on the wrong side up, but this is not very critical for operation.
- Well, and thirdly, less material is used for the production of round products.
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.
Manhole covers: weight and maximum load
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 used previously.
Note! In recent years, along with cast-iron lids, 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 shape of the cover of sewer systems
The main reason why the manhole cover is round comes from the following considerations.
- The triangular shape is not suitable based on the structural features of the human. 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.
- A square-shaped hatch can eventually fall into a well. Moreover, the shape of the well is round. Engaging in changing the transitions of the sewer manhole shaft to the surface from a round to a square shape is not an easy task, it requires an increase in financial costs for manufacturing and replacement.
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 arrange exhibitions of discovered samples with unusual design with the 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.
The main reasons why the manhole cover is round
- In Russia and neighboring countries, wells and sewer pipes have a round section. This is the main factor influencing the shape of the lid. In some European and Asian countries, square options are found. However, these are more exceptions to the rule than the norm, because in the same Czech Republic or China, where people found covers in the shape of a square, sections of pipes and wells sewer system also have a round shape.
- Cost reduction. Unlike a round one, the manufacture of a square manhole cover will require 30% more raw materials.
- Convenience. To install a manhole cover of any other shape will require more costs: incl. human effort and time for its installation: the cover does not have to be moved (given the minimum weight of a cast-iron specimen of 65 kg, a square one, based on an increase in raw material costs by approximately 30%, will be heavier - i.e. about 85 kg).
- A round sewer hatch will not fall into the well due to the increased diameter compared to the cross section of the well.
- Mounting and dismantling of round covers is faster and there are a number of reasons for this:
no need for more installers to move the sunroof;
the time spent on its transfer is reduced - a round hatch is easier to roll, with a square or triangular cover this method will not work. - Load concentration distribution. With a round cover, the distribution is made over the entire area. Angular covers cannot boast of this - it is the corners that will play the role of the main load points.
- It is more difficult to damage the edges of a round hatch than an angular one. In the process of transportation, you can put a chip. Given that it is the corners that act as the main reference point for load distribution, a chipped piece, regardless of its size, violates the system and the load is already distributed to the remaining corners.
- Wear resistance. The value of the service life directly depends on the integrity of the manhole cover. If a part of the angular covers breaks off, the load distribution is uneven. Over time, this will cause damage to other support corners.
Have you ever wondered why, sewer manholes are everywhere round and not square? Manhole covers are made of cast iron, it happens that of concrete. This is to ensure that the lid is heavy and cannot open spontaneously. If we talk about cable ducts, then most often there are two shut-off and protective ones. The first weighs much lighter, it is usually made of steel and is needed in order to protect the cable from theft. They place it, just under the protective one, and on the lid itself they simply write the purpose of the hatch.
The simplest and most logical explanation
The square-shaped cover can easily fall into the hatch, for example, slip through the corner. This may be because the diagonal of the square is larger than its sides, that is, the lid can fall into the hole. And the 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 bottom, the cover will never fall inside the hatch, no matter what position it is in. The round cover is safer than other forms of cover, as it will not fall on the head of workers who are inside the hatch.
The most frivolous explanation
There is an explanation, which, of course, seems ridiculous. 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 have to spend extra effort and extra time. Besides, round holes 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. You will have to take at least two men to carry the manhole cover to the right place. A round one can be rolled, which is within the power of one adult man. Moreover, without experiencing any particular difficulties. Moreover, when closing the hatch with a round lid, there is no need to rotate it, combining it with the hatch opening. There is also some truth in this, round hatches are much more convenient. And yet, they are also convenient to manufacture, because again, you will have to tinker with square hatches, their corners may suffer during transportation, for example, fight back.
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 tasks. By asking this question, experts want to see if the candidate for employees has the readiness and ability to enter into discussions and how the applicant solves the task or refuses to solve it. It is also very important how the candidate answers the question, seriously or with jokes. Incidentally, the world famous Microsoft company has long been using this question when testing specialists who are going to be hired.
To summarize, it is easiest to say that The lid is supposed to be round., including manhole covers!
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Many are interested in why sewer manholes are made round, but not everyone knows that this form is considered the most practical. It is safer to use round lids, and at the stage of production of products, metal is saved. Of course, in addition to round ones, there are hatches of a different shape on the streets of cities, for example, square ones, but they are quite rare. This is due to a series of factors.
Security Considerations
Despite their small dimensions, the covers 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 the 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 while working in the sewer well. If the product falls into the hatch on the heads of the workers, tragedy cannot be avoided. Luckily, the round lids are designed to never fall down the well. Products that have the shape of a square or rectangle can easily fall off, because their diagonals are always larger than either side.
Ease of use
Given the heavy weight of cast iron covers, it is quite difficult to dismantle them, especially if they are square. To move such hatches from place to place, you will need several adults. It is much easier to handle round lids because they can be rolled on edge. This task can be done even alone.
The round cover does not need to be rotated, trying to fit the shape of the hole. It will take the right position regardless of 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 manhole
In addition, if you carefully study the structure of the hatch, you will notice that it is slightly convex towards the middle of the circle. This is no coincidence: this form provides 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 that as a result of 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 products.
Load concentration points at the round hatch are evenly distributed around the entire circumference. For square products, stress is concentrated only in the corners, and this is very risky, because you cannot transfer the entire load to only one part of the part.
Economic expediency
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 covers, four round ones can be made at the same cast iron consumption.
Considering the low cost of round manholes, on a city scale, savings on the arrangement sewer wells looks impressive. In addition, round covers are widely used to protect other utility systems, such as sewers, gas pipes or underground electrical networks.
The advantages of round hatches include not only metal savings, but also a very small rejection rate. 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, acting on the principle of doors Who is responsible for 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, hatches can be locked - in this case, they resemble a door.
Most sewer wells, including covers, are municipally owned, although some of them may be owned by legal entities and apartment buildings. If the object is ownerless, at the request of representatives of local self-government, it is registered with the body that registers the rights to property. Then, if the owner is not found, the hatch is transferred to the balance of one of the specialized companies.
