Sewer manholes are an essential part of any sewerage system. Their function is to maintain the smooth flow of fluid through the system. 

For what purpose are sewer manholes installed?

Sewer manholes are a commonly used component of sewerage systems. They are used in external gravity sewerage systems; in sanitary, rainwater, drainage, combined sewerage and industrial sewers, as we have written about here.

Manholes allow easy and quick access to the installation, not only in the event of an emergency, but also during inspection and maintenance. They also enable the flow of water or wastewater.

Concrete or plastic manhole?

The most well-known type is concrete wells, which have been used for decades. Recently, however, the following have become increasingly popular wells made of plastic. The construction and material of the manhole depend primarily on its intended use.

We distinguish between wells: 

–evil (inspection) manholes - these are large enough to allow you to get inside to inspect the installation or make any necessary repairs. Concrete manholes, which can be fitted with internal steps, are ideal here.

–unclassified (inspection) manholes - are much smaller in diameter than manholes and therefore only allow you to look inside. The extent of the work that can be carried out in them corresponds to the distance that a person can reach. If there is no need for a manhole step, plastic manholes are the ideal solution.

Differences between concrete and plastic wells?

The biggest difference between concrete and plastic manholes is their weight. Concrete manholes, although they appear very solid, have many disadvantages. Plastic manholes are lightweight and simple to install. Concrete manholes, on the other hand, require the use of specialised equipment, which significantly increases installation time and investment costs.

Plastic manholes are resistant to all chemical compounds. Concrete manholes suffer from so-called sulphate corrosion, which affects their durability.

Plastic manhole construction.

The basic element of a plastic manhole is the pipe corrugated molar. It has notches between which soil enters during burial. The well-prepared subsoil is intended to protect against soil subsidence around the manhole. The length of the pipe depends on the depth of the manhole to be constructed.

Another important element of the manhole is the kinet. The base of the manhole is equipped with connections for the flow-through sewer pipe and a main socket for the corrugated pipe.

Depending on the number of connections, we distinguish between kinettes:

–via- have two spigots ending in a socket

–cumulative- have several spigots ending in a socket

–through-feed with right or left-hand intake- have two spigots plus one

A manhole cover or manhole cover should be installed at the top of the manhole. If the manhole is being constructed in a pedestrian/bicycle access area, it is sufficient to install a manhole cover class A15. However, if there will be car traffic over the manhole, use manhole B125, C250 or D400. For higher load classes, it is necessary to fit a telescope to eliminate the loads acting on the base of the chamber.

Summary:

A manhole is an important part of the sewer network. It allows access to the installation in case of failure. Both concrete and plastic manholes are very popular. When it is not possible to use specialised equipment, a plastic manhole is recommended. There are many manhole models and manholes available on the market to suit specific manhole diameters.