At times, there is such a situation when the smell from the sewer seeps into the bathroom or toilet. In the normal state, it is cut off by water locks. This is a certain amount of water that remains in the bend of the siphon and blocks the access to the apartment for gases from the sewer. Sometimes, with the simultaneous operation of several plumbing fixtures, these valves break off - there is a sharp change in pressure that pushes water out, sewer gases break into the room. To prevent such situations, put an air valve for the sewer. It neutralizes most of all air pressure drops in the system.
An air sewer valve is required in the system to equalize the rarefied (negative) pressure. It occurs when a large amount of water is suddenly released (descent, pouring a bucket of water, etc.), which takes a large amount of air with it. In the normal state, air is sucked in through the fan riser, the pressure stabilizes, no unpleasant odors are observed.
But situations arise when the amount of air entering through the fan riser is not enough for the water to leave freely. That's when the smell comes in. With a lack of air, the resulting negative pressure breaks the weakest water seal. This means that the water that is in the knee of the siphon (washbasin, sink, ladder under the bathroom) is partially sucked into the sewer, opening access to sewer gases. While you are not using this appliance, air from the sewer enters the bathroom/toilet. This is not only unpleasant, but also dangerous. The sewer atmosphere contains not only methane, which in itself is not a gift. There may be bacteria, spores of various fungi, microorganisms.
To prevent disruption of the water seal and put an air valve for sewage. It has several other names - a vacuum valve, a ventilation sewer valve and an aerator. In principle, it is the “aerator” that better reflects the purpose of this device, but this term is rarely used.
The principle of operation of the air valve for sewerage is simple. There is a diaphragm that, under normal or positive system pressure, is attached to the valve body. In this position, the system is sealed, the air from the sewer is blocked. When a negative pressure occurs in the pipe (when draining water), the membrane rises, air is sucked in from the room into the sewer (not vice versa), quickly neutralizing the resulting difference. Everything happens at lightning speed, the water seals on the sanitary equipment remain in place and continue to block access to sewer gases into the room.
Where to put
When installing the air valve for sewage, it must be placed 20-30 cm above the axis of the main sewer pipe. In two and three-story private houses, they put the device on the top floor.
It must be installed in a place where splashes or dirt will not get on the membrane. The quality of the device depends on how clean the membrane is. Salt, grains of sand, trash, etc. will appear on it, it will not be hermetically pressed against the body, the stench will begin to seep into the room. By the way, if you observe this, clean or change the membrane for now.
A place must be found such that air flows freely to the membrane. This is the basic condition for normal operation. When 1 liter of water falls into the sewer, it can carry 25 liters of air with it. Therefore, air access must be free.
If you decide to put a ventilation valve on the sewer, you need to know that sometimes during operation it can make “grunting” sounds - the membrane sucks in air when a slight vacuum occurs in the pipe. Not all models behave this way, but there are such complaints. So it is better to find a place where these sounds (if any) will not interfere.
In apartments
If we are talking about an apartment in a multi-storey building, then you can put an air valve on any vertical section of the pipeline. To do this, you can build a tee into the system, install a pipe vertically upwards into it, and put a ventilation sewer valve on it. Globally, this will not solve the problem of ventilation of the entire riser, but specifically your site will work without problems.
In a private house
If we are talking about a private house, then most often they want to put an air valve for the sewer so as not to bring the vent pipe through the roof. The correct passage of the pipe through the roof is a complicated thing, it is not easy to achieve its tightness. This is often the reason why people do not want to make holes in the roof. Many more do not like the pipes sticking out above the house. In principle, you can bring the ventilation pipe to the attic, put a ventilation sewer valve on top. In this case, the riser will be unventilated. But this is far from the best solution. At least that's what the plumbers say. They argue that ventilation is necessary for normal operation - to provide bacteria with oxygen.
If your wastewater treatment takes place in a septic tank, you cannot do without a fan riser, you will have to take it out through the roof. If the hydraulic locks periodically fail, it will be possible to install an air valve for sewage as an additional element of the system - on the highest floor (you can not put it in the attic).
If you have an autonomous sewage system based on it, you can try to make it non-ventilated - insert the pipe into the attic, and put a vacuum valve on top of it there. At the same time, the attic should be unexploited, large in volume, with good ventilation. The smell will be present and it will have to be somehow brought out into the street. If the attic is cold, the pipe must be insulated (but not the valve).
And anyway, plumbers and designers insist that in private houses an air valve for sewage should be installed only as an addition to the fan riser.
Installation
For the most part, plastic sewers are installed in private houses and apartments. Air valves are also selected from the same material - PVC or polypropylene. Like any sewer products, they have a bell with a sealing rubber at the end. The whole installation consists in putting the device on the prepared pipe. All.
For reliability, you can pre-lubricate the junction with a plumbing sealant, but even without this measure, the connection is tight (about the normal quality of the pipe and device).