Common Plumbing Code
Violation
Drain Venting
Air Admittance Valves (AAV) and Mechanical Vents
Why do we need Venting on drain lines
and What is it?
Without venting, our drains would hardly work,
and they would make gulping noises due to negative air pressure in the
lines. When water moves down our drains
the empty space that was filled with air now needs to be replenished with more
air. Our drain system can be related to
a full bottle of water being emptied. If
we take the cap off of the bottle and turn it upside down to empty the bottle,
we will notice 2 reactions occurring.
1. The bottle creates a vacuum which
sucks air into the bottle to help drain the water more quickly. We will feel the bottle jump and make a
gulping noise while the water is draining.
2. We will notice the bottle being
pulled together at the top where the air is replacing the water.
v The reason the bottle starts to gulp
air inside is because we are creating negative pressure. By tipping the bottle completely upside down
we close off its only entrance for air or water to pass through. The bottle is trying to replace the area that
was once occupied with water for an exchange of air. The reason the bottle actually jumps and
gulps has to do with the amount of water that is trying to be released. We can
refer to the water pressure caused by the gravity as head pressure. The amount of head pressure blocking the
outlet of the bottle will determine how much velocity and force it takes to
make the bottle jump.
v The bottle is being squeezed together
at the top while draining because of negative air pressure in the bottle. Negative air pressure is created when a
closed room or container is being deprived of the air inside of it. Referring back to our plastic bottle example,
the plastic is ductile so it makes the bottle suck together where it is lacking
air.
Click here to check out what happens when you
improperly vent a tanker car, this is an extremely interesting example of what
kind of force negative pressure can have.
These are major concerns
with the venting of your drain pipes.
Another concern is the added pressure when drains tend to back up. Vents also allow for another place for drain
pressure to escape. Sometimes when a
home’s drain line backs up, it will push the water or sewage through the main
vent stack. This may cause the water to come
out of the stack opening on the roof.
This would be referred to as positive air pressure.
Venting allows for the
air in the line that is being filled with water to be replaced immediately with
more air. This will sustain a neutral
air pressure which will allow your drains to work properly. Properly working drains always keeps a
sufficient amount of water in the traps.
Drain traps are extremely important without them sewer gas would be
present in our home. The sewer gas is
terrible for anyone’s health and should not be breathed in. Without proper venting the water that is
supposed to be in the trap may be siphoned into the line in order to change the
negative air pressure back to neutral.
An absence in water leaves the line wide open to your homes main sewer
line, this is where the sewer gas will enter your home.
Air Admittance Valves (AAV) or Mechanical Vents
AAV’s or Mechanical vents
work on a spring loaded valve that will let air in. When positive pressure comes up through the
line it closes up tightly, not letting any water or air escape. These devices are basically check valves that
only allows air to be sucked into the system.
Most of the time we see
these devices underneath the sink in the vanity or buried in the wall. The technology has developed significantly
over the years. With new technology and
extensive testing, a more reliable product has been developed.
Mechanical Vent was the
original term for these devices. I feel
the term has been changed to AAV so that people will use them. Changing the name has confused many when
trying to decipher the plumbing codes. A
Mechanical vent is the same as an Air Admittance Valve in all code books.
Why someone might use a AAV?
Sometimes you may run
into a situation were the main vent stack or any branch vents are no were close
to where you want to put a sink, toilet, or shower. This makes it possible to vent your drains in
the hardest spots. You also may have
existing piping or HVAC Ducts in the ways of here you need to run your vent
pipe. AAV’s gives you a cost effective
solution to adding or moving your drains.
Some plumbers and home
owners find this to be an amazing product to complete their task. But the best plumbers will complete your job the right way the first time, so you will never
have any unexpected issues later down the line.
Are AAV Compliant to Code?
The simple answer to this
is “No”. In the state of Illinois, the code strictly
permits against the use of a mechanical vent or AAV. As far as code goes for Residential and
Commercial work you will want to check with your Local Municipal Inspectors. In
some cases, the village may allow the use of this device. You must know that every city is slightly
different with their codes but in most cases throughout the United States they
are not allowed and should not be allowed.
Let’s take a look at what venting systems are used by the best Plumbing Companies.
Difference between a dry and wet vent
A Dry vent
is a simple one drain system where the vent will not serve as another’s drain.
A wet vent
will tie into another fixtures drain, thus the term wet drain. A wet vent may share a common vent stack but
will tie in at different heights.
v A simple example of a wet vent would
be a bathroom were the main vent stack is offset to one side of the room. The toilets drain will run directly to the
main stack were it goes out to the sewer and is vent from the stack that goes
to the room. Now the sink will run a
vent branch up to the stack and the drain will tie into the toilets drain pipe
before the toilet vents in the stack.
Types Plumbing Venting
Common Vent/Drain System
Branch Venting
Is extremely common in homes it is
were drains share a branch vent pipe which ties into the main stack.
Loop Venting The vent goes up and loops back down and ties back
into the drain line for the fixture.
Commonly only used for sinks.
This system is normally allowed for single sink systems like in a
kitchen island where it is impossible to tie into a vertical stack. Some Municipalities allow one loop vent per
house. Before the loop vent ties back
into the drain it can either branch off to be properly vented or not.
Circuit Venting
