Everyone understands that plumbing vents allow the stinky, obnoxious, & toxic sewer gasses to safely dissipate into the atmosphere however that is just the small part of what vents do.

As liquids pass through the drain and waste pipes it displaces the air, which is present in the line by pushing the air ahead as it moves. If a drain line is sized correctly a horizontal pipe should only be ½ full under full load. This keeps the upper half of the line open for the transfer of vent air over the liquid and into the space behind the moving liquid. In this manner the air pressure in the line will remain constant, however, there are conditions where the upper half of the line may also be obstructed by the moving liquid. Under these conditions as the liquid moves forward it leaves a partial vacuum behind the liquid which would then suck the water out of the fixture trap, thereby leaving the trap open for sewer gasses to enter you house once the liquid has moved on to the sewer.

In order to prevent that partial vacuum situation the Plumbing Codes are very specific about where and how vents are to be placed. In fact, ask any plumbing inspector and he or she will tell you that venting is the most important part of the plumbing system, and the part which gets the greatest scrutiny during a plumbing inspection.

Now to answer your question, the terms "Pro-vent, Studor Vent or Cheater Vent" are trade names for a device, which is properly called an "Air Admittance Valve or AAV). An air admittance valve is a device, which has an internal spring-loaded diaphragm that will open under negative pressure and allow additional vent air to enter the pipe. The singular drawback of the AAV is that they will allow additional air into the pipe to protect the water level in the trap seal, but they do not allow the sewer gasses in the pipe to safely escape to the atmosphere. For this reason the use of AAVÂs should be limited.

Under the International Residential Code (IRC) all structures are required to have one "Main Vent" which must run undiminished in size from the building main drain through the roof. After that is achieved you may terminate additional auxiliary vents in the attic space, through the wall under very limited circumstances or you may use an unlimited number of AAVÂs

Under the Uniform Plumbing Code (UPC) ALL VENTS must terminate through the roof, however the UPC will allow a maximum of one AAV per structure.

Based upon information presented in the original post this homeowner is under the UPC, and while it is legal to use the AAV or in their case "Pro-Vent" it is understood that this is the only one that may be used in the structure.

Caroline emailed me direct and asked if I would accept the "Pro Vent" I thought the question was important enough that i would like to share my response to all.....

I am sure that many people who read my reply are left wondering how did I conclude that you are under the Uniform Plumbing Code (UPC) rather than the International Residential Code (IRC).

The answer is that this is an island and it appears that your plumber originally intended to vent the island by means of an "Island Loop Vent" which is the preferred method of venting island fixtures.

Under the IRC to create an island loop vent we attach two parallel vertical risers on the upstream end of the drain line at the island sink. The sink drain is attached to one of the risers and both risers are interconnected at the top forming a loop from the drain below. (There is no vent line under the floor)

Under the UPC we also install two vertical risers as described above with the sink drain attached to one of the risers. On the top of each riser we then install a 1/8th bend (45deg sanitary elbow)and angle both pipes up at 45degress until they meet at the top where they are connected by means of a 1/4bend (90deg sanitary elbow). The UPC then requires that we install a vent on the riser opposite the sink connection and this vent line runs horizontal under the floor and back to a regular vent riser, which goes up and through the roof. This is the only situation in which the code will allow a horizontal vent below the flood level rim of the fixture served by that vent.

The IRC allows an unlimited number of AAVÂs therefore most plumbers simply use an AAV to vent an island rather that go to the expense and bother of making a proper loop vent.

The UPC only allows a maximum of one AAV per structure with the expressed consent of the local inspector therefore under the UPC it is common practice to install a proper island loop vent rather than the AAV.

As I am sure you will agree, everyone makes the occasional mistake and in this situation the mistake was forgetting to run the water line. The true measure of a tradesman is how well they can correct the mistake without causing additional problems on the job and when I read your plumbers solution to the problem of the missing water line I personally thought it was a rather ingenious. He, or she as the case may be, has opted to use the AAV to vent the island, which is fully code approved. Having done that, he or she is now free to use the horizontal vent line under the concrete as a conduit to pull in the missing water line thereby precluding the necessity to cut the concrete.

Under the circumstances I would give your plumber two thumbs up for a great recovery.