Why are sewer manholes round? Why are hatches round?

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 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.

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.

Quite often, when hiring a candidate for a position, they ask why sewer manholes are round. This is quite unexpected this question, which 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 trouble. 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 sewer 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 hatch manhole, 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 different 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, it would cost more metal, and it 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 covers no one even thought about using square shape. Moreover, if necessary, quickly move the cover round hatch you can simply roll from the well edgewise, which even one person can handle. 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 greater than the length of the side. 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 are 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 metal required to make the cover for the 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 where 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 the many good versions, the most logical and plausible version seems to be the one with the shape of the lid, due to which it simply cannot fit into the sewer hole.

Why are the hatches round? Those that close and open the entrance to the sewer system. Those that you have to bypass so that misfortune does not happen. They entered so habitually daily 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 can be quite worrying. a large number of 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, seek 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 make a 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 just this shape will allow you to get the maximum area (compared to other shapes). 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. A sewer hatch covering a circular well will not fall inside. Not from any position. And these are additional safety measures 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.

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 shapes.

Covers for manholes: weight and maximum load

Although sewer systems modern type appeared in different countries at different times, the only similarity was the need to install sewer manholes. 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 on a par with cast iron lids Cheaper analogues from polymer materials, the minimum weight of which is considered to be 15 kg, the maximum – 48 kg.

Sewer cover shape

The main reason why the manhole cover is round comes from the following considerations.

1. 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 unnecessary hassle in the form of an increase in the necessary raw materials for the production of the lid, therefore, its cost increases.
2. A square-shaped hatch may eventually fall into a well. Moreover, the shape of the well is round. Changing the transitions of sewer manhole shafts to the surface from a round to a square shape is not an easy task; it requires increased financial costs for manufacturing 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 which they contain detailed information: the company logo, short list services provided and more.

The main reasons why the manhole cover is round

1. 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.
2. Cost reduction. Unlike a round one, the manufacture of a square manhole cover will require 30% more raw materials.
3. 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).
4. A round-shaped sewer manhole will not fall into the well due to its increased diameter compared to the cross-section of the well.
5. Installation and dismantling of round covers is faster and there are a number of reasons for this:
   no need for more installers for moving 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.
6. 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.
7. 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.
8. 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.

And I couldn’t help but wonder – why is it round? And often hatches are never made square. What is this standard? Or a conspiracy of plumbers and electricians? I turned to a professional master with this question; it turns out that this question is almost the very first one for beginners in this field. It turns out everything is quite prosaic...

To begin with, guys, I suggest you put everything on the shelves and tell us what these lids are, which actually close various wells. Don’t worry, the answer will be below, it will definitely be – read to the end.

Types of hatches

It is a mistake to think that the hatches that cover wells embedded in the ground are of the same type. There is quite a large infrastructure laid out underground, so there are different types:

• Hatches for drainage systems
• For storm systems
• For electrical networks
• For contact

Initially, hatches were made of very durable materials, usually steel or black cast iron. Thus, it was very difficult to remove and carry it away, and the cars that ran over it could not turn it over. However, with the era of “perestroika”, metal versions still began to be stolen and sold for metal (and they were simply broken),

therefore, wells were often open (oh, it was a terrible time), so in those days they began to cover the wells with concrete round (as I call them) “short-holes.” It was even more difficult to carry them away, and there was no need, because you can’t hand over concrete!

Now, of course, new polymer or sand-polymer options are appearing, they are durable - they can withstand loads of up to 3 tons, they are also resistant to high and low temperatures, they don’t rot, they don’t rust, and they practically don’t steal them, because again, you can’t hand them over!

However, all these types are invariably round! But why - everything is banally simple.

Causes and Effects

Any mine consists of several parts:

• This is the upper part of the lid itself (the main purpose is to protect the internal components from dirt, sediment and other debris).
• Middle shaft - usually done round size diameter 70 cm, recess up to 3 meters.
• The last one is the lower part, here they can be of different sizes and shapes, for example, in some communication wells they have a square shape.

But the main question is why is the lid round? Guys, this is a safety requirement.

The fact is that a round hatch cannot fall into the well shaft, no matter how hard you twist it. Try it at your leisure, whatever one may say, but there is a circle everywhere. But if the covers were square, or triangular, etc., then at a certain angle they could fall down, and if this is a sewer well, how can you get it back? Difficult!

Yes, both children and large equipment will not be able to overturn or push such a hatch down in any way, everything is done wisely. It is worth noting that the weight of the metal options is 50 kg, so no traffic flow will be able to topple it. That's actually the answer.

It is also worth noting the side “ears” - special branches from the circle; they are made so that the lid “does not move”, but sits tightly in place.

Interesting facts about “well covers”

It should be noted that they were not always made round - there were also square, triangular and polygonal options.

But they were all dangerous and often simply fell through, leaving an open shaft.

However, triangular covers were valued to the last, all because the corners of the structure showed the direction of pipes or communications. Therefore, when the repairmen came down, they were already aware.

Also, hatches on hinges and some kind of “down” door were not uncommon in the past. The hinges also provided some protection against theft. However, during large traffic flows they were often broken and the lids fell through, so over time they were also replaced with round ones.

This is how the article turned out, now watch the cool video.

I’ll finish here, read our construction site, there will be a lot of interesting things.