Plumbing System Vent – Simple But Vital
I don't believe the average person realizes the dynamics of the plumbing drainage system in their home. After all, the water flows out of the sink and disappears. As long as this happens each time, who really cares what is going on?
But I have come to believe that knowledge is power. The more you know the better you are equipped to handle problems. This holds true with many things in residential construction, including plumbing drain and vent systems.
Sanitation is the Goal
If you study the history of plumbing, or visit a third world country, you quickly begin to appreciate the advancements of modern plumbing. Turn the clocks or calendars back just 125 years ago and you discover that plumbers were treated with as much respect and reverence as doctors. The medical profession connected the dots after the Civil War and learned that the spread of many common diseases was linked to poor sanitation.
Doctors discovered that bacteria in plumbing systems could easily spread in a household if waste and contaminated water was not disposed of properly. A simple open pipe in a sink proved to be inferior. It allowed vermin as well as noxious fumes to enter the house through the pipe. It didn't take long for the simple plumbing trap to be invented. The water seal in the trap stopped small vermin and blocked fumes from entering the living space.
Before long, plumbers learned what happens when water flows down a pipe. They discovered that the water that flows into a pipe displaces and removes air from the pipe. They learned that flowing water can actually create a powerful vacuum. Vacuums are a bad thing in plumbing systems as they can remove water from traps. Shortly thereafter, plumbers determined that pipes must be connected to the system that allows air from the atmosphere to enter the piping system. This air stopped vacuums and helped to improve sanitation within a home.
Plumbing vent pipes are not much different than the drainage pipes. They typically are smaller than the drainage pipes for several reasons. First, they are designed to transport air. Air can be compressed and the quantity of air traveling in a vent pipe can be increased by simply boosting its velocity. Since water drains through a vent system by gravity, you generally can't increase its velocity. But a powerful vacuum within a drainage system that is created by a large volume of water can increase the velocity of the air entering the vent pipes.
It is not uncommon for all of the drainage pipes in your house to eventually join together and leave the house through a single pipe. Venting systems can be designed to do the same thing in reverse. I have plumbed many a house that had over ten fixtures that were served by a single 3 inch vent pipe that poked through the roof.
If you want to learn more about plumbing vent systems, you should get a few books on the subject. One of my favorites is a book titled Plumbing a House written by Peter Hemp. Peter has included some wonderful 3D diagrams and superb diagrams of all sorts of drain and vent combinations. This book is worth three times the purchase price.
Keep in mind that you must always follow the plumbing code. It is in place to protect you and your family. Be sure to read up on the subject and practice working with pipe materials before you started plumbing in earnest.