This stops a vacuum in the pipework and allows the waste to drain easily without letting smelly gasses out inside the property. I have also been doing some research on line and noticed the the Durgo Valve is below the waterline of the cistern which is not recommended. Air admittance valves, durgo valves, AAV’s or air inlet valves as they are sometimes known, allow air into the soil stack system without letting air (and thus smells) out.
The valve seemed to be mobile and free from restriction. I cleaned the waste from the inside of the pipe and put it back together. With the aid of a torch I could see there was a lot of sludge/waste in the (still attached) bend and a lot of crust on the inside of the pipe. I since installed a dual seal air admittance valve and no problems. On flushing the toilet, I noticed the AAV valve was making a rapid 'flapping' noise as the flap opened and closed - not sure if this is normal or if it should just open and close once I removed the valve (its a 'Ventapipe 100') and the toilet once again flushed no problem. It wasn't until I took the top of the valve and the top of the pipe apart that I realised what was going on. On the other hand if the problem is clogged drains outside the building you ought to. I have looked all over my bathroom for the source of the bad smells. This time it appears to be my Durgo Valve.
This is a cheaper, easier alternative to the traditional vents on the top of soil stack. They are designed to: Provide a means of ventilation to the drainage system under conditions of reduced pressure when ventilating pipes are terminated inside buildings in accordance with BS EN 12056-2:2000. When I hire builders to solve the problems they comment on how badly constructed the items are. Drainage Sales explains how and where to use an Air Admittance Valve. Air Admittance Valves (Ventapipe) 84 Ventapipe 100 and Ventapipe 50 Air Admittance Valves are for use in above ground drainage systems. I regularly come across things that are faulty or just not acceptable. You will only ever have consistent issues keeping it. I have bought a flat that has been built by total cowboys. I would advise getting rid of the Durgo and venting the waste another way if possible, either through the roof or out of a wall. Air Admittance Valves (AAV) for Drainage Systems.