Exhaust check valve in the ventilation system: basic types, device

The ventilation system is one of the main components in the general system of engineering support for the life of buildings. Its main purpose lies in the term itself, translated from Latin as "airing". Normal operation of ventilation should provide comfortable and sanitary and hygienic living conditions for the population, and for industrial enterprises - compliance with regulatory and design indicators for the content of harmful substances, gas pollution, permissible emissions, security.

The functions of ventilation systems include ensuring a balance of the volumes of incoming and outgoing air from compliance with the required air exchange rate, ensuring the required temperature, humidity, cleanliness air environment.

Classification of ventilation systems

Ventilation systems are classified both by purpose and by the way of organizing air exchange.

The following types of ventilation exist for their intended purpose:

1. Supply air, which supplies a certain amount of air to a building or room.
2. Exhaust, providing removal of exhaust air.
3. Supply and exhaust - a combined system, which includes elements of both types.

According to the method of organizing air exchange, ventilation is divided into:

• Natural, in which the degree of air exchange is determined by the difference in air pressure outside and inside the building. In this case, natural ventilation can be unorganized, in which air exchange is carried out through leaks or open doors, windows, vents, or organized - through a system of ventilation shafts, channels, openings.
• Mechanical, in which the pressure difference is created by the fan, and the operability is ensured by various devices and equipment - filters, noise dampers, regulators.

Reverse thrust problem

The development of new building technologies characteristic of the last decades, the emergence of new building materials and products, advanced and complex household appliances forced the population to expand their knowledge in the theoretical and practical terms of organizing the ventilation of their living space. The fight against "reverse thrust" has become relevant for the owners of apartments and private houses.

Reverse thrust - violation of the normal mode of air exchange, in which there is a decrease in the rate of air removal up to the return flow through the exhaust ducts into the room. The reasons may be design miscalculations, natural reasons (pressure drops both in the direction of rarefaction and in the direction of hurricane gusts), various defects in building elements (clogging, freezing, destruction of channels), as well as spontaneous changes in the design and design mode of operation systems.

An example of the latter reason is a standard high-rise building for which an organized natural type of ventilation has been established by the project. More than one generation is familiar with wooden doors and window frames with vents, seasonal campaigns for their insulation, puttying and gluing. The calculation of air exchange of entrances and risers was carried out taking into account the structural leakage of these elements. The massive installation of sealed plastic windows and metal doors that are denser in comparison with wooden doors has made adjustments to the established balance.

Another factor was the active installation of exhaust fans - on ventilation windows in bathrooms or as part of hoods above a gas a stove, the consequence of which was the mutual exchange of a bouquet of smells between neighbors, also indicating a disturbed balance air exchange.

Protection system

One of the most effective methods of dealing with backdraft is the installation of a check valve, which allows the medium to pass in one direction and does not allow it to move in the opposite direction. In technical terms, these devices refer to protective fittings and are used in hydraulic and pneumatic systems, which include ventilation systems.

Industrial ventilation systems are mandatory equipped with non-return valves, therefore, to meet the emerging needs of the population for these products, it was not necessary to reinvent wheel. The existing types of structures were taken as a basis and adapted for domestic needs, taking into account the required costs, dimensions and design requirements. The main structural designs used in industry turned out to be applicable for the household sphere:

• Petal, in which the working body is a disc fixed on the axis. The weight of the disc is designed to be opened by the air flow in normal mode and flopped in the event of reverse thrust.
• Louvers. Working lamellar sashes are mounted on axles, opening and closing occurs from the air movement in the forward or reverse direction.
• Diaphragm valves they work on the principle of a lattice, one or two membranes made of soft material (film, plastic, rubber), fixed on one side, serve as flaps.

The listed designs can be used in systems with both natural and supply and exhaust ventilation, and according to the mechanism of action, they are passive, in contrast to the following, which contains an active element.

• Butterfly check valve (butterfly type for industrial valves) - two-disc (equivalent to two-leaf, double-leaf) with springs that ensure tightness closing the sashes. To open, the springs are designed for a certain air flow pressure, as a rule, created by a fan, therefore butterfly valves are practically not used for natural ventilation.

The main characteristics of the check valve, which determine the possibility of its application, are the flow area, flow capacity and the tightness of the shutter at actuation.

The first two parameters must provide the standard air exchange rates determined by sanitary and building regulations. For living rooms, this figure is 3 cubic meters / hour per 1 square meter. area or 30 cubic meters / hour for 1 person, for a standard kitchen with a 4-burner gas stove at least 90 cubic meters / hour. For domestic ventilation systems, check valves with a diameter of 50 to 150 mm (or the corresponding size for a square or rectangular design) are mainly used.

Unfortunately, the flow rate or Ksv coefficient of valve manufacturers, produced for the population, are practically not indicated in passports, in contrast to manufacturers of industrial destination. It remains to either trust their professionalism and responsibility, or independently check the valve's performance.

Standard indicator for checking normal thrust in the ventilation duct there is a flame of a match or a lighter or a notebook sheet. The burning torch should deflect in the direction of the thrust, the sheet should be held by the vacuum force. If you lean against the ventilation opening of any type of non-butterfly valve, its flaps (louvers, membrane) should open. If you repeat the operation, turning the valve 180 °, the thrust should be enough to close it, and the tightness can be checked with the same lighter.

The specified method is suitable only for checking the exhaust check valve of ventilation as an independent product. For convenience and ease of installation, modular options are increasingly being offered - a ventilation grill with a reverse valve, they are with a fan, an air duct unit with them with a built-in filter, a temperature sensor, and so on.

Residential ventilation problems

As a rule, check valves are installed on exhaust ducts or ventilation openings, and much less often as supply ones. This is quite understandable, since initially it is meant that the house or apartment is clean and fresh. air, and protective devices must be installed on the side of removing contaminated or waste air.

In general, the ventilation device or the solution to the problems that have arisen must be approached in an integrated manner. Backdraft problems are most often the result of errors or irregularities during installation or operation. The lack of an integrated approach is again characteristic of the previously mentioned high-rise buildings. Unlike power supply, water supply and heating systems, the ventilation system is not under the control of any utilities or inspections and is not controlled by management companies. As a result, the tenants each solve problems in their own way, layering their mistakes on those of others, including "locking" the air movement with the help of fans and valves to both neighbors and themselves.

It is for this reason that the involvement of specialists is simply necessary for these works, from calculations and design to the commissioning of systems and devices.