Modern public utilities emerged in the world in the 1930s. 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 V various countries appeared at different time periods, the only similarity was the need to install sewer hatches. 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.
- 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.
- A square-shaped hatch may eventually fall into a well. Moreover, the shape of the well is round. Engage in changing the transitions of the sewer manhole shaft to the surface from round to square shape– it’s not an easy task, it requires increasing financial costs for production 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 CIS countries for the sake of profit, the authorities began to look for a way out of the current situation by producing from other materials.
In the United States, lids with grooves or latches are made as “anti-theft” measures. European countries They use a combined material to make the lid - they combine concrete 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 order, which contain detailed information: 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 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.
- Cost reduction. Unlike a round one, the manufacture of a square manhole cover will require 30% more raw materials.
- 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).
- A round-shaped sewer manhole will not fall into the well due to its increased diameter compared to the cross-section of the well.
- Installation and dismantling of round covers is faster and there are a number of reasons for this:
no need for more installers to move 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. - 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.
- 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.
- 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 into 8 equal parts using 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 under 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.
Access to underground utilities is reliably protected using sewer 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 hatches are round, you need to have a practical mind.
What are sewer hatches for?
A manhole cover that opens the way down can be called a means of prevention. Heavy laps are what prevent many injuries and deaths. You can safely stand on them without fear of falling through. Only those hatches that are missing or have a non-circular shape are dangerous.
Currently, covers of other shapes 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 required for a round shape than for a square one, since the moment of stress under load on the circle is less and the lid 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 for production efficiency is that there are few defective products. This occurs due to the smaller number of reference lengths of the circle.
In addition, the round shape reacts less to temperature changes and therefore lasts longer.
If there is no cover, the hatch must be fenced and marked with warning signs If only they were of a different shape
Let's imagine that the manhole cover is square, triangular or rectangular. Now let's try to move this cast iron product from place to place. A circle will roll like a wheel, which cannot be said about shapes with corners.
A square lid is only safe when the length of its side exceeds the diameter of the round hole. This entails an increase in material consumption for manufacturing, which is impractical. If the well itself is square, then you just have to turn the lid a little - and it will fall inside, 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 dislodged from the manhole even by heavy traffic In the American city of Nashua (New Hampshire), there are triangular-shaped manhole covers. They indicate the direction of flow in the sewer. These covers are now being eliminated because they do not meet modern safety standards.
The question is not always idle, even if we are talking about hatches underfoot. Only by thinking about it, you can gain new knowledge and use it in practice.
The question of why sewer manholes are made round has already become a household word. It is asked in many academic quizzes and even when applying for jobs in relatively serious organizations. In search of an answer to this question, you should find out more about the design of hatches and the facts associated with them. So, first things first.
Sewer hatch installation
A sewer inspection well usually consists of a shaft, a working room and a cover. The type of workspace arrangement, as a rule, depends on the type of underground communications. The dimensions of the room are selected based on the requirements for servicing specific communications.
The depth of the room is selected based on the depth of their location. The height of the room is about 1.8 meters. The shaft is usually round in shape, its length depends on the depth of the working room, and its diameter is 0.7 m. Shafts are most often assembled from brick or cast from concrete. Equipped with a ladder for worker descent.
The sewer hatch is covered with a lid to prevent foreign objects from entering the system and to prevent accidents. In most cases, the lid has a round shape, which is caused by the following: in any position, the lid cannot fall into the hatch.
This is the first answer to the question “why are sewer manholes round?”
To prevent accidental opening during heavy vehicle traffic, hatch covers are made of cast iron, making them very heavy.
The surface of the cover is ribbed to increase the strength properties of the hatch, as well as the traction of the soles of pedestrians and car tires with its surface. There are lids either convex in the middle or flat - there are no concave ones.
Wells cable duct, as a rule, are equipped with two covers at the same time.
Namely:
- protective;
- constipated
Locking covers are made of steel, they are much lighter than usual and are equipped with a lock to prevent unauthorized persons from entering and stealing the cable. The locking cover is located under the protective cover.
Installation of sewer hatches is also carried out in wells engineering communications located underground: cable, gas, heating networks, sewerage and water supply.
Sewer hatches are designed to protect wells from damage, to prevent foreign objects or persons from entering the mines, to ensure unhindered movement of vehicles and pedestrians, and to provide access to communications located underground.
Types of sewer manholes
Sewage hatches are classified as follows:
- depending on the design of the product;
- by the type of communication networks passing under them;
- according to the material of manufacture.
In addition to the question of why sewer manhole covers are round, we will answer the question of what communication networks are covered with the help of such manholes.
This:
- drainage systems;
- cable - telephone and electrical networks.
The main materials for the manufacture of sewer manholes are the following:
- high-strength and gray cast iron;
- plastic;
- polymer-sand mixture;
- composite mixture;
- reinforced concrete or concrete mixture;
- rubber.
Advice! Each type of hatches has its own disadvantages and advantages, but still cast iron is considered the traditional material for making hatches. Hatches made of cast iron are reliable, durable, resistant to aggressive environments and durable.
Safety of sewer manholes
Why are sewer manholes made round? To protect the population from falling in them - this is one of those disasters that people begin to be warned about from childhood.
However, despite such warnings, such cases occur quite often. Previously, this was caused by absent-mindedness, but now it has been added to by distraction by talking on mobile phone or writing text messages.
The large number of thefts of manhole covers only aggravates the current situation. Falling down a hatch can lead not only to broken legs, but also to great depth hatch fatal.
The danger of open hatches is no less evident on highways. Colliding with a car on an open hatch can cause serious damage to the suspension and wheels, and also very dangerous accidents for cyclists and motorcyclists - even fatal.
Fun facts about sewer manholes
- If the installation of a sewer manhole was carried out many years ago, especially on the roadway, what to open such a manhole in the usual way(by prying) is often not possible.
Then a handle made of metal fittings, which is cut off after opening, or a small hole is drilled in the hatches, a hook is inserted from below and opened in this way.
Most manhole covers modern production(in addition to communication lines) are equipped with a factory hole, through which the hatch can be opened using a hook.
In many CIS countries, manhole covers also often have two slots on the sides. However, due to the water that penetrates through the slots during precipitation, holes are made only in water supply, sewer, storm, and drainage hatches. In the hatches electrical networks It is prohibited to make cuts for cable and telephone communications.
- In addition to the dilemma of why are sewer manholes round, you should be interested in another question: why are manholes so massive?
And so that the most active part of society - teenagers - does not physically have the opportunity to make shelters and the like from sewers. However, the mass of hatches does not stop lovers of relatively easy money. From the 1990s to the 2000s in all countries of the former Soviet Union There have been thousands of thefts of sewer manholes for the purpose of selling them for scrap.
In addition to standard cast iron manholes, steel manholes and storm grates were also stolen. For example, in the city of Kharkov in the Saltovsky district, in just one night, about 50 cast iron hatches were stolen by attackers using technology. And in 2009, more than 1,300 hatches were stolen in Kiev.
For this reason, in large cities, especially on their outskirts, sewer shafts are forced to be covered with concrete circles, wooden panels or plastic stationary hatches. Regarding the latter, their production is established in many regions.
- Now, the installation of a modern sewer hatch is carried out taking into account this feature - the hatches are equipped with hinges and open like a door with the impossibility of theft (except with the help of a cutter). Many hatches are also equipped with locks - this often applies to communication line hatches.
- The most dangerous from the point of view of injuries are stormwater wells, water supply and sewerage wells - their depth reaches 6 meters, and in addition, protruding fittings and pipes are usually located inside them.
A couple more explanations
Another reason why a manhole cover is round is because it is easy to transport.
For example, a square lid can only be transported by carrying it, which is often beyond the capabilities of one person. The round lid can be rolled, which an adult man can easily handle alone.
In addition, less material is required to make a round manhole cover. In addition, there is no need to rack your brains over how to install a round sewer hatch - just don’t install it upside down, otherwise there are no difficulties.
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, round lids made in such a way that they 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 cracks and chips may appear on its surface as a result of mechanical stress. 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 expediency
In addition to improved consumer properties, 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 hatches, on a city scale, savings on the arrangement sewer wells looks 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, along with their covers, are located in municipal property, although some of them may belong 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.