In simple words, a manhole is an opening that gives workers and equipment access to sewer pipelines so that they can inspect, test, and clean, whether a part of their routine or in case of emergencies. You can expect to find a manhole wherever there is a change in a sewer pipe’s direction, elevation, slope, size, and junction.
A manhole is a small part of a sewer system, but it consists of various components and individual structures. It is easy for people to complain when it takes time for sewer cleaning professionals to cater to problems associated with manholes, not realizing what lies beneath. This post is an attempt to familiarize our readers with what lies beneath a manhole or utility hole.
Channel
A channel is a pipe or tube located right at the bottom of the manhole. Its purpose is to ensure gas and waste liquids flow through from their source to the destination without clogging the sewer system.
Invert
The lowest point of a channel is known as invert. It helps determine the flow and function of a pipeline. The distance between the top of the street where the manhole is located and the sewer pipe is known as invert elevation. For a sewer pipe to be installed successfully, it is critical first to measure the invert elevation.
Bench
A bench is another name for the concrete occupying the space between the sewer pipes and the manhole walls. The primary objective of constructing a bench is to direct the flow of wastewater back into the channel should a problem arise because of clogging. It also serves as a high ground for maintenance personnel when they enter a manhole to service the channel.
Steps
As the name suggests, steps inside a manhole act as a ladder for people to climb down for reasons varying from inspecting, repairing, or cleaning. They are usually constructed using plastic or concrete and are located along the walls.
Barrel Section
The widest point of a manhole is known as the Barrel section. You can also call it the body of the underground space that connects a manhole’s base to the cone.
Chimney
Yes. You guessed it. It is just like any other chimney in a house or factory. The only difference is that a manhole chimney is located below the ground. It connects the vertical barrel section to the casting frame you often see beneath the manhole cover.
Cone
The area lying between the chimney and the barrel section is known as the cone. It is named so because as you move upwards from the barrel to the chimney, the diameter keeps shrinking.
Lids or Covers
And finally, we reach outside. If you leave a manhole open, chances are you will find human beings inside along with dirt and debris. It is precisely to prevent such untoward incidents from happening that a manhole is covered with a lid. Lids are mostly carved out of cast iron and in a manner that ensures they stay flush to the surface, not an inch lower or higher. Manhole covers may be circular, square, or rectangular, but in the US, they are mainly circular.
Before We Bid Adieu
We are confident you now understand how complex even a regular manhole inspection job may turn out to be. The problem may lie anywhere; in fact, the problem may lie in more than one place. It needs time to conduct a thorough investigation so that the nail could be driven at the right spot. In other words, with so many structures beneath, it takes time to diagnose and treat the underlying problem. We hope you will be more patient and understanding the next time cleaning professionals or inspection personnel visit a manhole near you.
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