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.
Given the low cost of round manholes, on a city scale, the savings on the arrangement of sewer wells look 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 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.
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. The working room is equipped and arranged 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 foreign objects and people from entering the mine. 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 main reason why the shape of 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 manholes can close drain 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.
Useful information! Each material has its pros and cons, taking into account which you can choose the best option for a particular 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.
A common cause of such falls 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.
Useful information! To avoid theft, wooden shields, plastic hatches or concrete circles are currently used, which cover the main cover from above. Covers fastened with metal hinges have also become widespread. 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.
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.
Manhole covers are a familiar, familiar detail of the urban landscape, almost everywhere, in all countries of the world, having a round shape.
Why round - we will try to answer this question in detail.
Safety
The manhole cover of the sewer well is a massive product made of cast iron. It weighs more than 50 kilograms, and the weight of hatches located on the carriageway exceeds 78 kilograms.
This is not surprising, because the manhole cover located on the sidewalk of the street must withstand a load of 12 tons, and the cover lying on the road - 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 cover, then in the worst case, they will simply close the hatch. A rectangular or square lid in this case can fall into the pit right on the heads of the workers, because the diagonal of a square or rectangle is always greater than any of its sides. Therefore, the round shape of the lid is the safest in this case.
Strength
Engineers have long known that round objects are much more durable than square ones. The sewer manhole is not only round, but also slightly convex towards the middle: this shape provides the greatest resistance to the mechanical load directed from above.
Internal stresses in a hatch of this shape are evenly distributed over the metal, while in square, rectangular and any other covers, under the action of a load, the stresses are unevenly distributed, 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 cover, a corner may well break off from it. To split the round manhole cover, you will have to make a lot more effort. 
Judging by the fact that almost all lids have been lying 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 metal savings? With the same length of the perimeter of round and rectangular hatches, the area of the circle is always greater than the area of the rectangle or any other geometric figure.
If we translate this into economic indicators, it turns out that a circle is the most advantageous form of a hatch, since it requires much less cast iron per cover (saving up to forty percent) than a rectangular cover.
The optimal ratio of the length of the perimeter to the area makes it necessary to make hatches round not only for sewer wells, but also in much more serious structures - for example, between compartments of submarines or spaceships. Round hatches are more economical and can withstand greater loads than hatches of any other shape.
Ease of work
The round manhole cover is much more convenient when carrying out repair or maintenance work. If a rectangular lid needs to be lifted to move it some distance, which will require at least two adult men, then a round lid can be safely rolled on its edge, and this task can be done 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 snap into place no matter which side you put it on. 
So, there are more than enough reasons why you need to make the sewer manhole cover round.
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.
Why was this form chosen?
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.
