Serious requirements are imposed on manhole covers - they must weigh at least 50 kilograms, have a surface with a relief from 2 to 6 mm, have special structural elements for easy removal and holes for checking the gas content of the sewer. However, there are no norms for the shape of the hatches, nevertheless, in most cases they are a circle.
Instructions
Step 1
The main reason manhole covers are made round is because they require less material to manufacture. The norm of the width of the sewer manhole is 600 mm, that is, the round manhole cover should have a diameter of 600 mm, and the square one - the side of 600 mm, with such dimensions, the area of the square manhole cover will be 0.36 m2, and the round one is only 0.25 m2, which 28% less.
Step 2
The round cover will not only be smaller in area, but also thinner, since the loads are evenly distributed in it, which means that the strength requirements are reduced.
Step 3
Rectangular or triangular covers can accidentally fall into the hatch, it will be problematic to get them due to their heavy weight, they can damage equipment or injure a person if they fall. The round cover will in no way fall into a hatch that fits its size. Sometimes manhole covers are made in the shape of a Reuleaux triangle, which is also called a round triangle, such a triangle also does not go into the hole, since it has a constant width.
Step 4
The round manhole cover is easier to install and always snaps into place. It does not need to be rotated correctly to fit the corners exactly as you would with any other lid shape.
Step 5
Round manhole covers have shorter support lengths than rectangular versions, which means that the risk of rejects is reduced. Lids with protrusions or grooves on the support parts break down and pop more quickly.
Step 6
It is controversial to say that manhole covers are round because they can be rolled and not carried. Round lids have special supporting protrusions, so it will still not work to roll them normally, on the other hand, it is really much easier to move such a lid a few tens of centimeters than a rectangular one.
Step 7
Round manhole covers almost never sag, but rectangular ones almost always sag. And finally, sewer shafts are often round in shape, so it is logical to make the lid for them round.
