Ventilation valve: functions and operating principle. Do-it-yourself check valve for a kitchen exhaust fan Ventilation shut-off valve

Residents of apartments in multi-storey buildings often encounter the fact that odors from their neighbors enter their premises through the ventilation ducts. An unpleasant situation that a ventilation check valve will help you cope with. We will discuss how it looks, how it works and where to put it.

Why do you need a check valve on ventilation?

During normal operation of exhaust ventilation, air moves from the room to the street. Exhaust vents are located “in dirty or damp” rooms - bathrooms, kitchens. The task of this part of the ventilation system is to remove odors and excess moisture to the street. But sometimes a situation arises when air flows through the exhaust ventilation in the opposite direction - into the premises. This moment is called thrust overturning and they try to fight this phenomenon.

Why do you need to fight backdraft? In the case of apartments, this is fraught with odors coming from neighbors, which is very unpleasant. If we consider private houses, portions of outside air in them reduce the temperature in winter. The second point is more dangerous and unpleasant - with reverse draft, the boiler may go out, and combustion products (and carbon monoxide too) may return to the room from the chimney. In any case, the reverse movement of air flow is an incorrect operation of the ventilation system and this phenomenon must be combated. A check valve is installed on the ventilation to block the movement of air in the wrong direction.

Design and principle of operation

A ventilation check valve is most often a piece of round or square pipe. In this segment, a piece of material (metal, plastic, mica) of a suitable shape is movably installed - usually on an axis. This is the valve itself. When closed, it completely covers the cross-section of the pipe; when open, it should create as little resistance as possible. For everything to work correctly, you need to install it so that when a backflow of air occurs, the valve closes.

For ventilation, not only valves are installed in the pipe - there are options for a ventilation grille and a fan. In the case of a vent grille, a thin plastic or mica membrane can be used, which is attached to the grille. There is also a butterfly valve and blind-type slats. The reverse air flow valve on an exhaust fan can be of the same type.

The operating principle of this device is simple: during normal air movement, the valve is open and creates slight resistance to air flow. When reverse draft occurs, it closes, preventing the entry of foreign odors or cold air from the street into the room.

Troubles that may arise

Everything seems clear and logical: foreign odors in the apartment are very unpleasant. Rollover in a private home is no less unpleasant, but also dangerous. In principle, with a correctly designed system, such phenomena should not occur and the causes of their occurrence must be dealt with. But not everyone has the opportunities and resources. It is easier to install a check valve for ventilation. This is true, but there are nuances that are worth knowing.

As you can see, installing a check valve on the ventilation does not mean solving the problem once and for all. You will have to monitor the state of the system and put up with the shortcomings of this solution.

Kinds

The ventilation check valve can be made of metal or plastic. The metal is most often galvanized, less often stainless steel. There is also a small group with a plastic body and a metal damper - most often called a “combined check valve for ventilation.”

How to choose on this basis? Just. Choose the material from which your air duct is made. There may be round or square models. Here again we choose the same form as the existing/planned ones. Fortunately, the dimensions correspond to standard pipes used for air ducts.

Opening method

Check valves can open in different ways:

• Manual. The dampers are opened or closed manually; for this they have a special lever. This is not very convenient; in addition, due to their design features, they are not airtight, so they cannot completely block the penetration of foreign odors.
• Electrically driven. They are forced to open simultaneously with the fan or hood being turned on. Suitable only for ventilation systems with forced air removal (without natural circulation).
• Mechanical. The most common type. They open and close according to air movements. They can be used in combination with a fan or hood, or for natural ventilation.

A manual check valve can be placed on a forced air exhaust pipe that goes outside. This is what they sometimes do - they take them out not into the ventilation duct, but through the wall into the street. In this case, it is better to have a damper that will open only while the hood is operating. You can, of course, install a normally closed valve, but in cold weather it will freeze and stop performing its functions. Therefore, manual opening is more reliable in this case.

The most common are mechanical check valves. They are installed in approximately 90% of cases. Structurally, they can be of different types. Let's talk about them in more detail.

Mechanical valve shapes

Various dampers can be installed in the check valve. The force at which it will move back largely depends on the shape of the damper. If the valve will work with a fan or hood, it is important that the weakest fan operating mode can open the damper. They say that the fan must push through the valve. If you want to maintain natural ventilation, it is necessary that the damper can “work” even from slight air movement.

The designs and shapes of mechanical check valves for ventilation ducts can be as follows:

Choosing a valve for ventilation is indeed not easy. If you are guided by what the majority uses, you will have to settle on a firecracker. Despite all its shortcomings, it works more reliably and opens even with natural ventilation. The most effective way to make the clapper quieter is to take silicone sealant and apply it to the thrust ring on the body (do not apply it to the disk, as it will become heavier, which means it will be more difficult to turn). Lubricate the valve disc with soapy water and press it against the sealant ring until polymerization begins. Then we move the valve away, we get an o-ring that dampens the pops. The result is an almost silent closing, and almost airtight.

Ventilation valve: where and how to install it

If made without the use of fans and hoods with motors, it is called natural. In order for everything to work, valves are installed immediately at the outlet of the channels to block the backdraft. To maintain normal circulation, it is advisable not to use grilles that block the valve. Yes, this option looks better, but ventilation suffers. Most likely, it simply will not work with little traction.

If you still want to install in front of the valve, you will have to put up with poorer ventilation, slower odor removal and excess moisture. Only installing a grille/valve with a larger diameter than calculated can help. In this case, air exchange will not be affected.

In the case of forced ventilation, the check valve can be placed either before or after the fan. This choice depends on the type of system and fan. Since ducted fan models are rarely used in private systems, it usually turns out that the damper is located after the fan in the pipe. How far is not important. The main criterion for choosing an installation location is ease of maintenance, since the damper will have to be periodically cleaned and checked.

Installation in the kitchen with a hood

When installing a forced-air hood in the kitchen, many people want to maintain natural ventilation. To do this, you will need to install a tee at the entrance to the ventilation duct. Connect a hood with a check valve to one of its inputs, and install only a check valve in the second. As you can see, the system is not too complicated, but it works.

How to connect a hood so that natural ventilation remains

Why should there also be a check valve on the hood? Because if it is not there, the reverse flow of air may pass through the hood. Yes, this will not happen every time, but with a strong flow it will.

When installing this unit, try to ensure that the check valve for ventilation is located as high as possible under the ceiling. As a result, the warmest and most humid part of the air will be removed, which is very important for the kitchen.

For bathroom and toilet

The ventilation of the bathroom can have its own exhaust duct - then everything is easy, simple and clear. Before entering the ventilation duct, we install a check valve to block the flow of air that will move into the room. But not all apartments can boast of individual shafts for the bathroom and toilet. In some old-style houses, the exhaust duct is only in the toilet. Ventilation of the bathroom is done by running a duct through the wall. In this case, we install a check valve for ventilation not only at the outlet to the ventilation duct, but also in the duct between the bathroom and the toilet. This will prevent unpleasant odors from entering the bathroom.

There is an even sadder situation: when there is only one exhaust duct and it is located in the kitchen. Actually, the installation logic does not change - the devices must be installed so that odors from one room do not enter another.

One check valve for ventilation is placed on the outlet to the dome hood (or on the channel that removes air from the kitchen), the second - on the pipe that comes from the bathroom. As you can see, if you understand the logic of operation, you can determine the most successful installation location yourself.

When trying to establish air exchange in a private house or apartment, we often make mistakes. For example, we install a ventilation check valve to get rid of unpleasant odors penetrating indoors through exhaust ducts. We are struggling with the consequences; the real cause of the phenomenon is the lack of air flow. It’s worth figuring out when you really need check ventilation valves, and considering the types and methods of installing return devices yourself.

What is a check valve for?

The main function of the valve is to allow air to flow in only one direction and to close immediately if reverse flow occurs. It is implemented quite simply: the flow area is blocked by a damper rotating on a transverse axis inside the channel. Second option: the passage is closed with thin polymer petals.

Reference. All check valves used in heating, plumbing and ventilation systems have a common property - high aerodynamic (hydraulic) resistance to the flow of gases (water). Hence the conclusion: you cannot install air distribution elements anywhere, risking disrupting the ventilation scheme of the rooms.

Before outlining the scope of application of valves, let us recall an important point: most domestic ventilation systems work naturally. The draft of a vertical pipe or shaft creates a vacuum and sucks out air; a fresh influx compensates for the losses. In what cases is a check valve used:

1. When connecting a kitchen hood to the shaft outlet. To maintain natural air exchange when the fan is turned off, the ventilation duct is connected to a tee with a return device.
2. If forced exhaust is organized using a horizontal air duct laid through the wall. After the fan stops, the valve will prevent cold air from outside from entering the room.
3. In supply and exhaust ventilation systems with forced impulse - for flow distribution.
4. When it is necessary to eliminate mistakes made by designers or installers of ventilation systems at the lowest cost.

A grille with a ventilation valve helps a lot against wind blowing on the upper floors of high-rise buildings. Another case: the end of the exhaust pipe is not raised high enough above the roof of a country house or is poorly protected from the wind. But inflow will still be needed, otherwise weak draft will not open the valve leaf.

Incorrect application of elements

A common mistake is installing a ventilation grille with a non-return air valve in the kitchen or toilet. Supposedly, it protects against odors from neighboring apartments in a multi-story building. Why this approach is wrong:

• the reason for the penetration of unpleasant odors is the overturning of the draft in the ventilation shaft;
• the draft overturns due to the lack of inflow, the shaft of a larger cross-section (in the kitchen) forces the smaller channel (in the bathroom) to work in the opposite direction, the air moves from top to bottom;
• if you install a compensating air supply device in a window or wall, both pipes will begin to draw out exhaust air, foreign odors will disappear;
• a ventilation grille with reverse petals will protect the apartment from “foreign” air by 90%, but the remaining 5–10% of gases will leak out - the flap does not fit hermetically;
• Natural ventilation will not work without inflow.

Note. As in a country house, read in a separate article.

1. According to the requirements of sanitary standards, the exhaust from the bathroom (bathroom, toilet) is prohibited from being combined into one channel with the kitchen ventilation.
2. With the fans turned off, toilet smells will leak into the kitchen.
3. When running two fans at the same time, it is difficult to predict the behavior of the air flows. Both valves will open, but the unit from the bathroom will “pass” the kitchen one, since it is installed on a straight section.

Clarification. If the kitchen hood fan is more powerful, it will “strangle” the bathroom unit and at least block the exhaust from the toilet.

Conclusion: each room needs a separate air duct, as required by the standards. Then check valves are installed at the outlets of horizontal pipes to keep the cold out from the street. Ventilation ducts from the shower and toilet are allowed to be combined, as shown in the drawing.

Types of return devices

The following types of check valves are used in room ventilation systems:

• air dampers - gravity and spring;
• petal (membrane);
• double-leaf butterfly type.

The elements are made of plastic, aluminum alloy, galvanized or stainless steel. Some manufacturers (for example, Vents) have combined models - a metal body, a plastic sash.

Galvanized dampers are used primarily in industrial ventilation systems. They are used to cut off the reverse flow or regulate the amount of air - manually or using an electric drive, shown in the photo. Plastic ventilation fittings are used indoors, stainless steel – outdoors.

Addition. Check valves also include ventilation grilles with horizontal rotating louvres. The principle of operation is similar - under the influence of gravity, the rectangular doors close, preventing outside air from entering the channel.

Let's give a short commentary on the video. Not all of the master’s words are true, but he does one thing right: he installs an external grille with gravity doors.

Design and principle of operation of dampers

A single-leaf check valve consists of the following parts:

• round or rectangular body;
• a damper is attached to the inside of the walls, which rotates freely on a transverse axis;
• in the closed position, the sash is held by a spring (not present in gravity models).

The axis of rotation of the spring-loaded damper coincides with the longitudinal axis of the pipeline, the normal position is closed. After the fan starts, the shutter opens under the pressure of the air flow, and when switched off, it automatically slams shut. Closing is accompanied by a characteristic sound, hence the second name of the valve – “clacker”.

The double-leaf “butterfly” is designed identically, but instead of one damper, 2 are used, the spring is installed in the middle. Both types of ventilation valves are capable of operating only in forced ventilation systems. The natural draft pressure is not enough to open the spring-loaded sash.

In single-leaf gravity dampers, the damper rotation axis is located eccentrically, that is, it is shifted above the axis of the air duct. Thanks to this, the larger half of the sash outweighs the smaller one, which is why it closes without any springs. Correct installation of the check valve plays a role here:

• if you insert the element into a horizontal pipe according to the instructions (the axis of rotation is above the center of the duct), the damper will close immediately;
• if you turn the ventilation valve upside down, the passage will remain open;
• when installed on a vertical channel, the closure of the sash also depends on the position of the element.

The firecracker for natural ventilation is placed in 2 ways: horizontally in a closed state or vertically, but with an upward flow. In other positions, the behavior of the valve is difficult to predict; if a reverse air flow occurs, the valve may not work.

Household "firecrackers" can be part of other ventilation accessories - connecting nipples, wall flanges. There are also exhaust fans with a check valve - “butterfly”.

Diaphragm Valves and Gravity Screens

In products of the first type, the function of the main shutter is performed by a membrane made of a thin polymer film adjacent to the body or the slots of the ventilation grille from the inside. The film is attached to the central axis of the valve, the edges remain free.

Under the influence of natural draft or fan pressure, the outer petals of the film bend, allowing air to pass through. When the gases move back, the lavsan membrane again adheres to the frame, blocking the passage. Leaf type valves can be included with exhaust fans and grilles.

Note. It’s easy to make just such an air valve with your own hands. It is enough to attach 2 film petals to a regular grille, pressing them with a cardboard spacer with cutouts. Manufacturing instructions are shown in the video below.

Multi-leaf grilles operate on the principle of dampers, which lower under their own weight. Scope of application: forced ventilation exhaust ducts ducted outside through walls. Natural draft does not occur in horizontal pipes.

The return element is selected depending on the ventilation scheme and installation location:

1. To connect a kitchen hood, use a gravity-action flapper that matches the shape of the air duct. The purpose of this valve is to maintain natural air exchange during fan inactivity.
2. A grille with a membrane valve (homemade or factory-made) is placed in the opening of the exhaust shaft if the draft is overturned by gusts of wind. It is better to get rid of odors using another method - install wall inlet valves for.
3. In private houses, the local exhaust duct is often laid directly through the external wall. To prevent cold air from being blown into the ventilation duct by the wind, install a multi-leaf exhaust grille outside.

In forced air mechanical ventilation systems, valves are used according to the design and specification drawn up by the designer. We do not recommend developing such an air exchange yourself - mistakes cannot be avoided, and the cost of alterations will be too high.

Advice. For installation inside rooms, buy inexpensive plastic products. Galvanization looks ugly; ventilation will have to be covered with plasterboard.

How to install a check valve

Installation of a multi-leaf grille and a membrane vent is not difficult and does not require a detailed description. The elements are attached to the wall and connected to the air ducts according to the factory instructions.

One addition: when installing an external grille, it is better to insulate the wall channel. From direct contact of the exhaust air with the cold walls, vapors will begin to condense. After the fan stops, the water will freeze and form ice.

If you decide to install a gravity check valve for your hood, consider the following nuances:

Advice. Before installing the check valve on silicone sealant, check the functionality of the circuit. Insert the firecracker into the tee, turn on/stop the hood 5-10 times, changing the performance. The damper should close and open 100%.

Conclusion

As you can see, a check valve is rarely used in home ventilation systems. If you take a thorough approach to organizing air exchange, then return elements will not be needed at all. A kitchen hood can be easily connected to an exhaust vent with a grille; the main thing is to ensure inflow. The exception is more complex circuits using 2-3 fans operating alternately or simultaneously. There, valves help direct flows or regulate the amount of air passing through.

A range hood is an essential component of any modern kitchen. Such equipment is necessary to maintain order in this area, as well as get rid of unpleasant odors. Most models are equipped with a so-called return valve, but the extent of its usefulness raises some doubts. An exhaust fan with a check valve is almost no different in appearance and design features from its analogues.

The key feature that distinguishes the hood of this type is the presence of a device for controlling the exhaust and intake of air. Nowadays there is a tendency to install the exhaust ventilation duct through load-bearing walls. The air goes directly into the atmosphere. In such a situation, the anti-return valve is a necessary component of the system.

At the same time, there is no consensus regarding the need for these valves. Experts assure that it should be installed if reverse draft often occurs in the ventilation system. The air flow from the mine carries with it various, not always pleasant, odors, and protection allows you to get rid of them. In general, this component can increase the comfort of living in a home.

A check valve for a kitchen hood is installed when a direct air duct is available. The fact is that the draft will be neutralized in the presence of a ventilation grille and various bends in the route. The specified element in such a system is superfluous.

Operating principle

This simple and inexpensive device allows you to get rid of unwanted odors. In this case, redevelopment of existing channels is not required. Also, the manipulation itself does not involve any significant financial investments. You can install a check valve on the kitchen hood directly into the ventilation and thus solve the existing problem.

Manual adjustment of air flows is irrelevant today due to the widespread use of exhaust devices. There are several ways to automatically prevent cravings. Each of them has its own advantages and disadvantages, which must be remembered when choosing one or another option. The classification involves the following types of valves:

1. Single-leaf, characterized by gravitational action.
2. Petal. In fact, these are mini-blinds.
3. Double leaf spring. This mechanism is called a butterfly.
4. Membrane with flexible structure.

Single door option

When the air flow leaves the room, it presses on the valve flap, which opens it. If there is a reverse thrust or no movement is observed, the sash does not experience any impact and therefore closes under the influence of gravity.

This model is often preferred because it is reliable and simple. One leaf is enough to solve the necessary problems. If it is installed correctly, you can resort to natural ventilation, since the resistance here will be small. There are two versions of such models:

1. With axis offset. The sash is fixed on it. The displacement is carried out regarding the cross-section of the air duct.
2. With a counterweight. The corresponding element is located outside or inside the device.

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To prevent air from moving in the wrong direction, a special device is used. A check valve for ventilation is installed in forced and natural systems. It can be purchased at the store, or created with your own hands. If necessary, installation is not difficult to complete without assistance. This article will help you solve the identified problems quickly, correctly and inexpensively.

Even such a light barrier is enough to prevent air from entering the room from the ventilation duct

Why do you need a check valve for ventilation: problems and ways to solve them

Signs of a violation of the normal operation of the system are foreign odors penetrating from other rooms (apartments in a multi-story building). The penetration of cold air in winter disrupts comfort and increases heating costs. Along with the reverse flow, various contaminants from the room enter the room. Some of them can cause harm to health.

It is clear that it is better to eliminate such shortcomings. But first we need to understand the reasons for their appearance. Some can be eliminated to improve the functional state of ventilation.

Sometimes problems arise after replacing old frames and installing double-glazed windows. New window blocks provide perfect tightness, completely blocking the access of fresh air to the room.

As a rule, these products are equipped with filters, which can become clogged over time. Regular inspection and cleaning will help restore lost functionality to full extent.

A change in the direction of the air flow can occur when several intake points are connected to one channel. Similar manifestations are not excluded in strong winds and frosty weather. It is especially difficult and even impossible to influence the actions of neighbors in an apartment building. Claims against them can only be made if the air duct is completely blocked. If odors come from someone else’s kitchen, where there is a powerful hood, you will have to solve the problem yourself.

Related article:

In our review, you will learn why a valve is needed, the principle of its operation, its design, advantages and disadvantages, an overview of ready-made models, independent production, and features of air duct installation.

Design and principles of operation of a check valve for ventilation

This industrial air valve for ventilation functions as follows:

• When air moves in the direction indicated by the arrow, the damper (1) opens slightly.
• It is fixed on a metal axis (3) installed in the holes of the housing (2).
• Under the influence of the force created by the load (5), the disk returns to its original position. Using the screw (6), this part can be positioned in the desired location of the auxiliary rod (7) to change the sensitivity of the device.
• In the lower position, the disc rests on the lock (4).

Using this ventilation check valve as an example, we can point out certain disadvantages in order to more accurately formulate the requirements for the parameters of high-quality equipment:

• There is an adjustment mechanism here. But it is not intended for installation in domestic ventilation ducts hidden inside building structures.
• There are no bearings in the central axle mounting unit. It is possible that during operation of this ventilation check valve, extraneous noise will appear. They will be difficult to eliminate with lubricant, even if the appropriate procedure is performed regularly.
• There are no seals here, so it will not be possible to completely block the air flow in the opposite direction. If you do not leave technological gaps, the risk of the damper jamming will increase.

This product is made of sheet steel, which increases strength (not necessary in this case) and increases weight. Conventional painting does not meet modern requirements for good corrosion protection. The listed facts must be taken into account when creating a design with your own hands, when choosing a suitable model in a retail chain.

Different types of check valves

In this article, the scope of the study is limited to household models. These products do not need to be connected to power sources. Their installation will not cause any difficulties for the average user.

Membrane design: simple and cheap

The principle of operation of a diaphragm check valve is not difficult to understand by studying this photo. The working hole is covered with a flexible polymer film that fits tightly to the base with the appropriate flow direction. Choose a material that is flexible but strong enough. By choosing the right stiffness, it is possible to set the required level of sensitivity. Such an overlay can be equipped with an existing system (fan, grille). There are no mechanical parts or complex mechanisms, which means reliability and durability.

This “butterfly” does not fly, but performs its functions flawlessly in any position

In this version, the main functions are performed by the petals attached to the central axis. They are pressed by springs, so significant force is required to open the channel. Such products are installed in forced ventilation systems. Some models are equipped with special devices for adjusting springs (increasing/decreasing action forces).

This modification is made of galvanized steel. It is resistant to corrosion processes and weighs little. A soft damper is attached to the surface of one plate, which prevents strong shocks and noise.

Features of reed valves

The simple design of the reed check valve for ventilation is one of the main advantages of products in this category. The sash moves downwards under the influence of gravity. Its relatively light weight does not create much resistance to air flow, so installation in natural ventilation systems is acceptable.

For your information! It should be noted that this model must be installed only in a horizontal channel. For vertical lines, products with springs (counterweights) are used, which ensure the forced return of the damper to its original state.

Using a check valve in the kitchen

With this installation with a check valve, ventilation operates continuously. If you turn on the desired fan speed, the speed of contaminant removal will be increased. Of course, we must not forget about creating a sufficient flow of fresh air.

For your information! To increase the efficiency of the system, the length of the channel is reduced, and the exit to the street is made directly in the wall of the room. In this case, it is equipped with an additional valve that blocks the flow of air from outside along this path.

Important! When choosing a suitable product, you should pay attention to models that are easy to clean, resistant to fats and other specific contaminants.

Correct operation of the valve in plumbing installations

For installation in these rooms, structures that are resistant to high humidity are used. We must not forget that potent agents are used to remove calcium and other persistent formations. The acids and other aggressive chemical compounds they contain are released into the air. They can damage decorative and protective layers, metal parts, and welded joints.

Ventilation devices equipped with a check valve

This section of the article discusses various combination products. They perform their functions in conjunction with a valve that prevents the reverse movement of air. In some cases, they are equipped with serial models to improve the original consumer characteristics.

Design of an exhaust fan with a check valve

The petals are pressed into place by built-in springs. The parameters of these return mechanisms are calculated at the design stage. They correspond to the performance of the equipment (force of air flow). If there is a need to replace a broken part, a new spring is selected with similar characteristics. This design with a large number of plastic elements is well suited for bathrooms. However, it will be useful to check the manufacturer’s recommendations, the protection class of the electrical device, taking into account the high humidity in the room.

For your information! Installation of a fan on a hood with a spring-type check valve is permissible in horizontal and vertical positions. This universal drive retains the same functionality in any position, at different angles of inclination.

Ventilation grille with non-return valve: affordable cost - excellent results

This ventilation grille with check valve has multiple petal elements. This solution is used when blocking large channels. Too large single parts have a lot of weight, which does not allow reducing sensitivity to a level that meets the requirements for natural exhaust. But when choosing such a model, it is necessary to clarify the tightness of the joints in the closed position of numerous dampers.

Operating principle of a tee with a check valve

The use of a tee for a hood with a check valve prevents air from flowing from the duct into the kitchen. Similar functions are performed by another device. It can be installed differently from the picture, but in combination with a fan.

Advantages of a check valve on an exhaust hood

Installing a check valve for exhaust prevents various contaminants from entering the engine from the ventilation duct. This extends the life of the equipment.

For your information! Some users are concerned that the spring drive and the weight of the dampers will reduce the performance of the air removal system. This is wrong. These loads are insignificant compared to the power of fans that are equipped with modern equipment of this class.

If such a device is not included in the kit from the manufacturer, you can install an anti-return valve for the hood yourself. What this is is not difficult to understand from the materials in the article. Below are instructions for creating functional products yourself and the specifics of installation operations.

The process of creating a check valve with your own hands

Photo	Step-by-step algorithm of actions with comments
	The author of the project is going to install a homemade check valve in a 125 mm wide channel under a standard plastic grille. There are no plans to install a forced fan. It was decided to use available materials to save money. The need for modernization arose due to the arrival of unpleasant odors from neighboring premises located on other floors of the house.
	This cover can be removed without any difficulty. It is attached to strips of tape (with two adhesive sides). Over time, they have ceased to perform their functions, so more reliable means will be used for new fixation.
	After removing the tape and dirt, a good basis was obtained for creating the necessary design.
	Cardboard, thin plywood, or a sheet of plastic are suitable for the valve frame. In this case, empty writing paper packaging was used. The corrugated lid has the necessary strength. An additional advantage is that damping sound vibrations is not useful here. But it can be used when creating a structure with a fan.
	To avoid damaging the workpiece, use a soft lining.
	The outline of the lattice is outlined with a pencil, and a rectangle is cut out from the lid along the marked lines.
	Next, measure the width and height of the ventilation hole. It turned out 125 x 170 mm.
	Using a ruler and pencil, the detail is drawn in the center of the rectangle. The distances from opposite edges to its perimeter should be the same.
	A vertical jumper 10-15 mm wide is placed in the central part. It will be useful for attaching the valve, which can be made from a suitable piece of thick polymer film. The author used the top part of a standard office folder (binder).
	First, cut out the central parts.
	Next, the valve flaps are created. They should converge in the closed state in the middle of the central bridge. If less rigid plastic is used, install an additional horizontal support bar in each hole.
	The valves are attached to the side parts of the frame using tape. Check the strength of the fastenings and the functioning of the mechanism.
	The multi-colored surface of the box will be visible through the cracks.
	To eliminate this drawback, the workpiece is covered with white paper.
	Using a practical experiment, you can test the functionality of the check valve for ventilation with your own hands. It is necessary to make sure that the petals move freely and reliably block the access of air when closed.
	To increase the test duration, the valve is mounted on self-tapping screws without tightening them completely. The locations of the holes are marked in accordance with the lattice parameters. If everything is in order, it is installed on top and attached with screws to the wall along with the valve.

A check valve for ventilation is an important element of the ventilation system and is widely used in exhaust and supply-exhaust installations. Using the device reliably protects the room from foreign odors and makes staying in it pleasant and comfortable.

Why does reverse draft occur?

The operating principle of supply and exhaust systems is based on the equality of incoming and outgoing air volumes. If the amount of incoming air masses decreases, a draft reversal effect occurs, as a result of which air from the exhaust ventilation duct enters back into the room. The reason for the disruption of flow circulation is often clogged ventilation openings, the installation of plastic windows, as well as breakdown or wear of the mechanisms responsible for the intensity of the inflow.

However, it can also be the other way around, when the cause is an increased outflow of air masses, which often occurs when smoke and fuel combustion products escape through the chimneys of stoves and fireplaces. If the chimney is in good working order, the hot mixture comes out very intensively, and the supply system may not be able to cope. As a result, the draft in the exhaust duct becomes overwhelmed, and the exhaust air rushes in the opposite direction.

Also, the reverse draft effect occurs when several air duct branches are connected to a common ventilation duct. In this case, an uneven pressure often forms, which leads to reverse flooding of the flows. There are often cases of connecting several intake points to one air duct, one of which is equipped with forced exhaust.

As a result of the operation of the fan, air pressure arises not only in the direction of the ventilation duct going outside, but also in the direction of other intake points that are not equipped with forced exhaust devices. This effect is often observed in old houses with common air ducts, when one of the neighbors installs a powerful hood. As a result, polluted air from the common channel is intensively driven into rooms that are not equipped with such devices.

Another reason for the appearance of reverse thrust may be a change in environmental conditions. For example, if the terrain is disrupted through the demolition or construction of nearby buildings, the wind may change its direction and begin to blow into the exhaust duct. Thus, whatever the cause of the overturned draft, at the first signs of its appearance it is necessary to equip the system with a check valve capable of neutralizing all the negative aspects of this effect.

What is it and what is it for?

A check valve is a device installed at the outlet of the air duct and consisting of a housing and a damper. The body, in turn, is equipped with a decorative grille that covers the internal parts and fastening elements of the structure. The damper has the ability to open under the influence of escaping air pressure and return to its original position in the absence of flow.

Check valves are available in standard sizes and are compatible with all types of air ducts. The material used to manufacture the devices is mainly plastic. There are also metal models, but their scope of application is often limited by the humidity levels of a particular room. Although galvanized and chrome-plated products have an anti-corrosion coating and, along with plastic ones, can be used in bathrooms, showers and kitchens.

The principle of operation of the check valve is as follows: polluted air leaves the room and, entering through the lining into the body of the device, presses on the damper and opens it. As soon as the pressure of the outgoing flow drops, the damper closes and begins to serve as a strong barrier to dust, foreign odors and small insects. In addition, the use of even the simplest reed valve significantly reduces the level of external noise coming from an adjacent room or from the street. The device is mounted on the internal or external end of the air duct, and when installed on systems with forced air circulation - behind the fan.

Varieties

The modern ventilation equipment market presents four types of check valves, each of which has its own design features, as well as strengths and weaknesses.

• Single-leaf gravity-type models. The devices consist of a body and one leaf, the opening of which occurs due to air pressure, and the closing is due to its own gravity. The gravity round valve is used in systems with natural air circulation, which is due to the low opening resistance of the valve.

Single-leaf models are available in two versions. The first type is represented by products with the position of the axis on which the bar is held offset relative to the center of the section, and the second is distinguished by the presence of a counterweight located inside or outside the device. The advantage of this type is the possibility of installation on systems that are not equipped with forced exhaust, but the disadvantages include the need to fix the device in a strictly vertical or horizontal position. Otherwise, the counterweight will sink and greater effort will be required to open the damper.

• Spring double-leaf “butterfly” models. Structurally, such valves consist of two curtains that can fold under strong mass pressure, and a spring that returns the valves to their original position in the absence of air circulation. “Butterflies” are used only in systems with forced exhaust, and are ineffective in natural ventilation conditions.

• Valve with shutter-blinds. The operating principle of this device is based on the force of gravity and is somewhat reminiscent of the principle of operation of single-leaf petal devices, with the only difference that instead of one leaf, several elements located one behind the other are used. Products of this type are made of metal, withstand negative temperatures well and are designed for installation on the outside of the ventilation duct.

Membrane-type valves are particularly sensitive structures and are able to open at the slightest air movement. They act as a valve with a thin membrane, which requires very little force to open. Membrane models are intended for installation in exhaust ventilation systems with natural draft and, when installed in systems with forced circulation, require the installation of additional stiffening ribs. Otherwise, under the influence of strong traction, the thin membrane will quickly deform and, due to a loose fit, will begin to let air through.

The next criterion for classifying devices is the material from which they are made. Based on this feature, there are two groups of devices: plastic and steel.

• The most common are plastic models. Such products are not subject to corrosion, are easy to install, have a long service life and low price. The disadvantages of plastic devices include low resistance to negative temperatures and insufficient structural strength.
• Galvanized steel appliances much more powerful than their plastic counterparts and are able to withstand low temperatures well. In addition, metal models have a long working life and are installed in powerful hoods with high pressure of passing air masses.

Another important feature by which anti-return valves are distinguished is the control method. According to this criterion, models are divided into manual and electric. The former are adjusted using a lever or valve, while the latter are equipped with an electric drive and require a nearby electrical power source.

The shape of the valves also varies. The devices are available in round and rectangular versions, which allows them to be easily combined with any type of air duct.

• Round household models have a cross-sectional size of 100, 120, 125, 150 or more millimeters, which corresponds to most diameters of ventilation ducts. Industrial devices used on powerful hoods in shopping centers and production workshops are produced with a diameter of up to 1000 mm.
• Rectangular and square models are more often used in high-performance installations of various enterprises and are also available in a wide variety of standard sizes.

In addition, check valves are distinguished by the installation method - devices can be mounted in both vertical and horizontal planes, as well as by throughput, which shows how much air the device can pass per unit of time. Devices also differ in safety class. Along with domestic and industrial models, there are explosion-proof or spark-proof valves. Such products are intended for ventilation systems in explosive zones of classes B1, B1A and B1B, in which the movement of explosive mixtures is expected. The devices are capable of withstanding a pressure of 1500 Pa at a flow speed reaching 6-20 m/sec.

How to do it yourself?

The modern market for exhaust and ventilation equipment offers a huge selection of inexpensive valves, so independent production of the device is justified only if the ventilation grille or ventilation duct has a non-standard shape and size. In such cases, it is faster and more profitable to make a device with your own hands rather than spending effort and money on making adapters. The easiest device to implement on your own is a single-leaf petal valve, where a rigid plate of plastic or thin metal, a sheet of thick cardboard or Mylar film is used as a damper.

• So, to make a check valve for an air duct with natural draft, you need to take a decorative ventilation grille, attach it to thick cardboard, trace it with a pencil and cut it out. Then you need to measure the height and width of the ventilation hole and draw the resulting rectangle in the center of the cardboard blank.
• Next, from the center of the upper side of the drawn figure, you should lower a perpendicular to its lower side, step back from it in both directions by 7 mm and draw two more lines through these points, parallel to the first. As a result, the rectangle will be divided into two halves by a vertical jumper, on which the free sides of both flaps will subsequently rest.

• Then you should cut out both parts of the rectangle without touching the jumper. The result should be a figure resembling the frame of a plastic window.
• Next, two rectangular pieces are cut out of the Mylar film, each half the size of a large cardboard blank. After which they are glued to the outer side parts of the frame so that when closed they rest on the central jumper. Externally, the design resembles a window with two sashes, the role of the frame in which is played by a cardboard blank, and the role of the sashes is performed by two rectangular films. You can attach the sashes to the frame using tape or a stapler.

• After the structure is ready, you should attach it with self-tapping screws to the wall at the end of the ventilation duct. The valve must be positioned in such a way that the glued flaps can open towards the air duct.
• Next, you need to open the window and check the operation of the valve. If everything is done correctly, the air flow will open both flaps of the “cardboard window” and flow freely into the air duct. After testing, the plastic grid is screwed on top of the cardboard flap using self-tapping screws.

There is an easier way. To do this, the film flaps are glued directly to the back side of the ventilation grille. However, with this design, the film is secured to the sides of the plastic grill using adhesive tape, which over time can lose its properties and come off. Therefore, gluing the flaps to the cardboard surface is a better option.

How is the installation carried out?

In order to equip a wall ventilation outlet with a check valve, it is necessary to ensure that the effect of an overturned draft does not occur with any combination of switched on bathroom, toilet and kitchen exhaust devices. Therefore, if a tee is installed in the ventilation system, collecting air from all intake points and discharging it into a common air duct, all outlets must be equipped with valves.

An important condition for placing check valves is to ensure free access to them. This requirement is dictated by the need to regularly clean devices from adhering grease and dust. If you rarely clean the devices or do not free them from dirt at all, then due to adhering deposits, the valves will no longer fit tightly to the valve, and the operation of the device will become ineffective.

The check valve is installed at the outlet of the ventilation duct using liquid nails or self-tapping screws. The second option is much more preferable from a practical point of view: if it is necessary to clean the device, it can be easily unscrewed, and after treatment it can just as easily be put back in place. When attaching the valve, it is necessary to ensure that the device completely covers the air duct opening.

When installing valves on systems with forced removal of contaminated air, the device is placed in the ventilation duct behind the fan.

• To do this, dismantle the fan, insert the valve into the air duct and mark the places for its attachment.
• Then the valve is removed again and holes for fasteners are drilled in the marked places.
• Next, the valve is again installed in the ventilation duct and the attachment points on the wall surface are marked through the drilled holes. Then, using a bolt, the marked places are drilled out and prepared for installing dowels.
• Then the anti-return valve is installed in the ventilation duct and fixed, while filling the gaps between the device and the surface of the duct with silicone sealant. Some models do not require additional sealing of the connections and are already equipped with a rubber sealing ring, which facilitates a tighter connection between the air duct and the valve.
• The final stage of installation will be to install the fan in its original place and test run the system.

Installation of external valves such as blinds is carried out according to the same principle. The only conditions for choosing such devices are the material of manufacture and the presence of additional functions. These include anti-vandal devices that prevent damage or breakage of blinds, as well as the presence of a heat recovery function. The last option is especially important for outdoor models: it prevents icing of the valve and promotes its correct operation during the winter period.

The correct choice, proper installation and timely maintenance of the check valve contribute to the effective protection of the apartment from unpleasant odors, extraneous noise and dust. This allows you to significantly improve the air quality in the room and leads to the creation of a comfortable microclimate inside it.