Need help identifying this?

[SPB]

Was doing some handyman jobs for a client in London today. One of the problems related to a really bad smell coming from the area near washing machine in kitchen. This smell did not occur all the time, but when it did it was very, very strong. I checked that there were no obvious problems - leaks, blockages, but could find nothing wrong with the washing machine. On checking an inspection panel above the washing machine and in the corner of the kitchen (very close to cooker) I found what looks like an air vent, but I could be totally wrong. Could anyone tell me what this is? - see pictures.

 

[Spike295]

Looks like an Air Admitence Valve to me, what size pipe is it, its awkward to make out from photos.
I'm guessing 4" after a closer look.

 

[GQuigley67]

air admittance valve or "durgo" it basically lets air in to the waste pipe, but doesnt let air out. This one will be jammed open and letting air out. they are prone to failure that's why you must always fit an inspection hatch where one is fitted, you will be able to take that out(looks like a tricky number) and try fix or replace.

 

[GQuigley67]

its 4" by the way or 110mm diameter pipe