Venting the drainage system correctly

The drainage system collects the effluent produced by human activities in buildings, and transports and empties it into the sewage system. The drainage process itself, which occurs by gravity, must not produce excessively high pressure differentials within the system. To ensure this, it is very important that the system is vented correctly, as in fact required by technical standard UNI EN 12056-2:2001, which defines the correct dimensions for drainage systems. Air is usually allowed into the drain system from an air inlet situated outside the building via the main drain stack or a specific air admittance line. If the system is correctly vented, this will ensure that the system itself drains effectively by maintaining the correct balance in the water levels in the traps connected to each sanitary fitting or utility. This water level in the traps (which must never drop below 50 mm) is crucial for the barrier effect which prevents the release of malodorous gases into interior spaces.

Technical standard for the correct dimensions of a drainage system

Calculating the correct quantity of air admitted to a drainage system in relation to the nominal drainage capacity of the building is crucial to prevent problems throughout the entire drainage system itself. By referring to the technical standard UNI EN 12056-2:2001 – considering the number of sanitary utilities and intended usage of the building – the designer can correctly calculate water drainage and air flow capacities and, as a result, define the correct diameter and layout of every element in the system, from the main drainage stacks and branches to traps and manifolds. This standard also identifies the correct technical solutions for venting the drain system, and expressly requires the use of EN 12380 certified air admission valves for both main drain stacks and branches. These valves include a specific membrane which only allows air into the system from the building when negative pressure is generated by active drainage, ensuring that no odours at all are released into the interior space.

MAXI-VENT valve: the ideal solution for venting the main drain stack

Patented and launched on the market in 1975, MAXI-VENT is a brilliant and effective solution ensuring the correct admission of air into the drainage system and preventing the need to extend the stack or any other line outside the building. The MAXI-VENT vent valve is simple and quick to install on the main drain stack, and is usable in a wide range of applications: in a service cavity, in an attic, outside the roof, on a balcony or built into the wall, with its own air intake grille. Complete with its own clamp, the MAXI-VENT valve may be installed, in a vertical position only, on 75, 90 and 110 millimetre diameter pipes. The air admission system has a capacity of 32 litres of air per second, and, once installed, requires no further maintenance. Installing the valve within the building prevents the need to extend pipes out of the building, which frequently release unpleasant odours and which, if situated near windows or balconies, can be an unhygienic nuisance.