A manhole allows one to access underground piping, meters, telephones lines, electrical cabling, storm drains, and facilities. It is an important element of any sewage or drainage network. It performs a wide array of functions. When the modification, cleaning, maintenance, or inspection of any underground utility is to be done, the manhole is the access point.
It also helps in joining the sewers or aligning them. They are covered with a lid that is perforated to allow the foul smell to pass and thus performs the function of ventilation.
A manhole has two important parts: the chamber and the pipe.
The chamber is what allows the professional to climb inside and inspect, while the pipe, circular in shape, helps one access the inspection joints. These pipes have a varied size, depth, and type and decide the design of the inspection chamber. Some inspection chambers have only a few feet of depth to allow seeing the pipe whereas some are very deep leading many meters into the ground.
Manholes serve an important role in the drainage and sewage system. This is why it is also important to maintain them and make sure that they are not blocked so that they are easily accessible at the time of inspection.
The opening of the manhole is covered by a lid called the manhole cover. It protects the manhole from being accessed by anyone other than an authorized professional. It also ensures that no one accidentally falls into the manhole. The manhole covers are available in a variety of shapes, including rectangular, square, and circular.
These covers are made of different material, depending on the purpose and location of the manhole.
Traditionally, the manhole covers were made of concrete and bricks. But in modern times, the manholes and their covers are made of newer material.
- Cast iron manhole covers: Cast iron is iron that is melted down and then molded. During the casting process, some minerals are added to make it more resilient and strong. These are also called ductile iron covers and can be coated to prevent corrosion. Cast iron covers are made of heavy duty material and can be placed in places which receive high traffic. The benefits of these covers include high durability and longer lifespan, firm structure that prevents accidents, and lower cost than steel.
- Plastic manhole covers: The use of plastic manhole covers has been on a rise. They are more preferable than concrete manhole covers. The advantages that plastic manhole covers provide include high resilience to water and chemicals, lighter weight, environment-friendliness, easy installation, and low maintenance. They are equally useful in commercial, residential and municipal projects. They are also available in different shapes and sizes. The most common ones are circular because unlike a square cover, it will not fall into the opening.
A manhole needs to be covered to not just prevent anyone from accessing it, but also for pedestrian safety as without a lid, anyone may accidentally fall into the hole. The cover needs to be placed correctly so that it doesn’t get removed when vehicles pass over it. The most popular manhole covers are made of concrete, casting iron, or plastic. The PVC manhole cover has one big advantage over the ductile iron one. Theft of manhole covers is very common in India. The iron or steel covers are sold to scrap dealers who pay a good sum for it, however the plastic manhole covers do not have the same scrap value and hence prevent stealing.