Oh we can really stir the pot talking about vents. Most have a hard time comprehending simple venting techniques. Lets through out Circuit Vents, Relief Vents, and Yoke Vents. Oh and do not forget the Mechanical Vents.. oh I am sorry the AAV crowd does not like to call a Air Admittance Valve a mechanical vent.
On another forum I had a guy trying to tell me AAV's are allowed in Illinois, that a AAV is not mechanical at all and do not fail. I had to point out two parts of the Illinois code that disallows these devices. Color bold added by me.
Section 890.1420 Stack Vents, Vent Stacks, Main Vents
a) Design. A properly designed and installed venting system, in conjunction with the soil or waste system, is essential to protect trap seals and prevent siphonage, aspiration, or back pressure. The venting system shall be designed and installed to permit the admission or emission of air so that under normal and intended use the seal of any fixture trap shall never be subjected to a pneumatic pressure differential of more than a one (1) inch water column. If a trap seal is subject to loss by evaporation, means shall be provided to prevent loss of the trap seal. (See Section 890.410(f).)
Section 890.1480 Types of Fixture Trap Vents
d) Mechanical Vents. Mechanical devices shall not be installed in lieu of vent piping.
The fact AAV by its own name is an Air
Admittance Valve, it does not allow any emission of air that disallows the use of them. Drainage systems do not only have negative pressures with in them they do happen to develop positive pressures as well which needs to be properly vented to prevent the drains from belching gas out of their trap seals.