Una red que lleva aguas sucias, con materia orgánica putrescible, genera gases malolientes y es necesario evitar que salgan olores de la red, en lugares que puedan molestar y muy especialmente en los locales interiores. Para ello se emplean dos dispositivos: los cierres inodoros, generalmente hidráulicos, y un complemento muy importante para su buen funcionamiento: un sistema de ventilación de la red, para facilitar el flujo del agua por los conductos y evacuar los gases a un lugar donde no molesten.
Odorless closures
There are two types of closures: hydraulic and mechanical. Although only hydraulic ones are usually used, the knowledge of mechanics is not to be neglected as they are used in dry climates to block the drains of walkable terraces.
The hydraulic seals, commonly known as siphons, consist of a tube shaped so that it retains a portion of clean water that is renewed in each drain cycle of the device, and prevents the passage of gases from the network to the premises. There are several types of siphon; The best known and oldest is the so-called S-siphon (in the figure) but there are also bottle, compact (very similar to the previous one, but made of plastic and smaller in size), etc. In any case, the one that works best is the S-siphon which, due to its hydraulic design, retains less solids (hair, for example) and is kept clean more easily.
There are also bell siphons, in which a half sphere or bell (now made of plastic) screwed to the closing grate of the drain, is placed with its lower edge below the level of the edge of the drain pipe, forming the closing pool. They are used on walkable terraces and in shower trays built on site.
There is also a device that serves as a siphon for several devices simultaneously, called siphon canister").
Mechanical closures, little known but widely used until half a century ago, consist of a sphere (in ancient times it was made of bronze or brass, hollow) that floats in the water and sits on a closing ring at the beginning of the downspout. When it rains, it floats, and leaves a free passage, but then it closes the passage to the gas outlet. In climates with warm and little rainy summers, the water from a siphon (on terraces one of the so-called bell ones is usually used) evaporates easily, so a mechanical one replaces it with advantage. In any case, if you have a hydraulic hood, you can avoid evaporation by placing a little vegetable oil on the surface of the retained water, which prevents evaporation.
Another mechanical device that has similar purposes is the aeration valve, which is placed at the upper end of the vents (a place where no water passes) and closes the odor outlet as long as there are no pressures or depressions in the pipes and opens when this occurs, to achieve pressure balance, avoiding desiphoning and gurgling in the siphons. They are used in ventilation outlets near inhabited areas, preventing odors except in the brief moments when they open to compensate for overpressure.
Network ventilation
For the correct functioning of the hydraulic seals, which ultimately mean a fairly efficient sealing of the network, it is necessary to have a ventilation system that prevents pressures and depressions in the ducts. Indeed, in the downpipes where toilets are discharged, a piston can form which, if the diameter is strict, will produce, when falling down the downpipe, an overpressure at the bottom and a depression at the top. These pressures can desiphon (empty water from) the hydraulic seals and, in the best of cases, produce gurgling and noises, which can be significant. Ventilation serves to balance pressures and avoid their effects.
There can be three types of ventilation:
• - Primary ventilation: it is the simplest; The idea is to extend the downspout upwards, at least above the ridge of the roof. It is usually sufficient in buildings of up to three or four floors, as long as there is at least more than one downspout.
• - Secondary ventilation: consists of a pipe parallel to the downspout, connected to it on each floor or two. By lowering the possible piston, the pressures are balanced by it. The secondary ventilation installation will be joined with the primary ventilation pipes.
• - Tertiary ventilation: consists of a tube that connects the outlets of each of the device siphons with the secondary ventilation. It is normally used in appliance batteries, in communal toilets, and in luxurious homes.
Primary ventilation is mandatory in Spain due to compliance with the Technical Building Code (CTE).