In Line Vents

Under what circumstances are “In Line Vents” ever allowed below the subfloor (In the crawlspace)?

What is an “in line vent”?

Vent for what please tell?

http://C:\Documents and Settings\Larry\My Documents\My Pictures\Kodak Pictures\6-27-2012\100-4477

DWV “In line Vent” as above. Hope the pic shows up???

No pic. Perhaps you mean and AAV or 'studor vent"?

vent under subfloor for vanity sink with p-trap DWV line.

An open vent is not allowed in the crawl space, or the attic, or anywhere else in the home. An AAV would be acceptable.

Thanks… all I needed. Just had a small brain f*rt!