Commonly called Durgo valves, air admittance valves are designed to decrease the number of pipes that need to penetrate the roof and walls of a property. They reduce the number of parts required to ventilate a soil system and do not compromise the performance.

A valve, D, which is under a light spring pressure, is held closed during times of non activity in the drainage system. The positive air pressure of the room holds the valve down as well as the spring. When the toilet is flushed, the turbulence and gravitational pull of the water to the manhole below causes a negative pressure within the pipework. This opens the Diaphragm A and valve B allowing fresh air to be sucked in through the side vents C and down into the system. The equalisation of pressure prevents the foul air from escaping and the water seals in the traps (bath, toilet and basin) from escaping.

Valve Closed

Valve Open

Air admittance valves, when installed, must finish above the highest flood level of the space the valve is in...I.E. If the valve is in the same room as a wash hand basin, it must be higher than the overflow of that basin. This is so the pressure equalisation can occur without breaking the water in the traps.

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Air admittance valves are easily fitted and slip onto the top of the soil and vent pipe. The use of air admittance valves are governed by building regulations and cannot be used in all cases. Please check these regulations before attempting an installation and see our guide to the building regulations, approved document H, in the projects section

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