Plumbing System Vent - Simple But Vital

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By Tim Carter
©1993-2010 Tim Carter

Summary: Understanding your plumbing system vent and drainage systems can help you tackle problems that arise. Read and be forearmed.

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.

Venting Tips

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.

Awesome Books

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.





Comments:

Pat S.
21 May 2008, 13:09
I recently installed a new toilet on the second floor of my two story home. The original toilet worked fine. After installing the new one, I found that the toilet flushes fine, but after about 30 minutes, the bowl is empty of water. I removed the toilet and checked it to see if the bowl was defective. No leaks. I held my hand over the floor drain and could feel air being sucked into the drain. How do I locate and fix the vacuum that appears to be sucking the water out of the bowl?
Scott Stevenson
26 May 2008, 05:59
I had a plumbing leak in a main floor bathroom fixed. We had to turn the water main off to fix the leak. When we turned the water back on we have little to no water pressure. How do we get the water pressure back
Tom O
23 Jun 2008, 18:53
I installed a new toilet and when I sat on it I fell through the floor to the basement. Now I have to go to the basement to use the toilet! What do you think caused this?
P.S.- I weight 380 lbs
Randy Reed
21 Jul 2009, 07:14
The large house I stay in has three floors. The toilets run very slowly, sometimes not emptying the contents. The toilet on the second floor just started emptying slowly. By emptying slowly, I mean that the toilet bowl fills to the rim.


I removed the toilet on the top floor as it was the first to empty slowly first. I thought maybe on of the kids had put a toy in it and tried to flush it.

However, the toilet had no blockages.

Could the slow emptying toilets be caused by a clogged vent pipe? And if so, how does one go about getting the clog out of the vent?
Thanks


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