Check valve for ventilation: how to arrange ventilation with a check valve on the hood

Alexey Dedyulin
Checked by a specialist: Alexey Dedyulin
Author: Mikhail Yashin
Last update: April 2020

Are the smells of cooking food coming back again, instead of leaving the room forever? Agree, this is an extremely unpleasant situation, which I want to get rid of as soon as possible. Most likely the problem lies in the occurrence of reverse thrust. This is a common phenomenon that has many negative consequences.

We will help you get rid of unwanted aromas with a simple and inexpensive device. It will not require redevelopment of existing ventilation channels or significant financial investments. It will be enough to install a check valve on the ventilation, which will solve the problem.

For an optimal result, it is necessary to know the design options for the valves, their pros and cons, as well as the rules for placement and installation in exhaust systems. All information is given in our article. It also contains useful videos with step-by-step installation instructions and photos demonstrating the essence of the material presented.

Causes of Backdraft

In order to decide on the installation of a non-return valve, it is necessary to find out the possibility of back draft in the ventilation system of the house. Understanding this process will allow you to properly plan and implement indoor air exchange.

Operating principle supply and exhaust ventilation based on the law that at any given time, the volume of air entering and leaving the room is the same.

Checking the air flow direction
Using a burning match, you can easily check the direction of air movement in the ventilation hole and estimate the flow rate

Thus, the reverse draft in the hood occurs if the total flow at the other points of entry and exit of air is directed from the house. There are several main reasons for this effect to occur.

Often reverse thrust arises due to a significant reduction or termination of the flow entering the premises through the supply ventilation.

This can occur as a result of gradual clogging of the holes, and in the case of a forced circuit, wear or breakage of mechanisms responsible for air circulation. A sharp increase in the volume of air exiting through one of the exhaust devices can also contribute to the occurrence of back draft.

For example, when stove heating hot air with combustion products intensively exits through the chimney. If there is insufficient intake through the supply ventilation, the direction of flow in the hoods will change.

Check valve for ventilation and exhaust
The reason for the reverse movement of the air flow may be uneven pressure, formed when several branches are connected to one ventilation duct. In such situations, each line is equipped with a check valve.

In the case of using an air duct with several air intake points inside the house, a change in the direction of flow is possible if forced ventilation is included in one of them.

So, if the boxes from the kitchen and bathroom are connected to one system, then the inclusion cooker hood will lead to air pressure not only towards the street, but also towards the bathroom.

Changing environmental parameters outside the apartment or house can also cause reverse thrust. During construction work associated with a change in terrain, such as the erection or demolition of nearby buildings, a change in the direction of the wind towards the hood is possible.

In apartment buildings, when using common ventilation shafts to remove air, back draft in the apartment may occur due to the connection of powerful hoods by neighbors.

This problem is especially relevant for old houses, the common air ducts of which are designed without taking into account the possibility of using devices for forced ventilation.

Ventilation shaft of an old house
The capacity of the common ventilation shafts of old multi-storey buildings is not designed to allow the passage of a large amount of air generated by modern powerful hoods

Even if at the moment there are no conditions for the occurrence of reverse thrust, it is better to install a check valve when installing the air circulation system. Possible modifications, contamination of the supply ventilation or external factors can lead to a variable direction of air flow.

The cost of the finished devices is low, and the introduction of a valve into existing ducts is a laborious task. Those who wish to check the ventilation in the apartment will find detailed information in the next articleposted on our website.

Check Valve Types

Due to the widespread use of exhaust devices, the use of manual control to regulate the passage of air flow is no longer relevant.

There are four fundamentally different ways to automatically prevent back draft in a ventilation system. Each of them has its pros and cons, which must be considered when choosing the type of device.

Type # 1 - single-leaf gravitational action

The flow directed from the room exerts pressure on the valve leaf and opens it to allow air to pass through. In the absence of movement or in the event of a reverse thrust, there will be no pressure on the sash, and it will close under the action of gravity.

Gravity single leaf check valve
The use of just one sash for air passage and the use of gravity to close it make the gravity model of the valve simple and reliable.

When installed correctly, the gravity check valve can be used with natural ventilation, since its resistance to opening the sash is negligible.

There are two ways to perform this design:

  • axis offseton which the sash is fixed, relative to the middle section of the duct duct;
  • counterweightlocated inside or outside the device.

Considering that the principle of closing the sash is based on the action of gravity, it is necessary to place the valve strictly horizontally or vertically depending on the design using a level.

Otherwise, it may be either incomplete closure, or significant efforts will be required for the air flow in the ventilation system to open the sash, especially when using a counterweight.

Ways to install a check valve on ventilation
The installation scheme of the check valve on the ventilation duct is determined by the design features of the system. Devices are mounted so that their blades open in the direction of air flow

Type # 2 - double leaf using springs

The butterfly-type check valve is equipped with two shutters, which fold at the required pressure with excess pressure and are closed by means of springs in its absence. Since the closing process does not depend on the action of gravity, such a device, unlike the gravitational type, can be located at any angle.

As a rule, this option only works normally with forced ventilation using an exhaust hood.

Before purchasing a valve, it is necessary to check the sensitivity of the curtains to open to the air pressure characteristic of the duct on which it will be installed. Some modern butterfly-type devices can be adjusted according to the strength of the springs.

Butterfly Type Check Valve
The design of the “butterfly” type with the closing of the wings under the action of springs is used in ventilation systems with a strong air pressure, which creates hoods

Type # 3 - ventilation grille shutters

The grille that closes the exit to the street or into the ventilation shaft is often equipped with a valve that looks like window blinds. This device is detailed described here. The principle of its action is gravitational, similar to the single-wing version.

The use of several shutters instead of one is due to the compactness of the device in the open position, which is important for the external elements of the system.

The dimensions of the grilles are designed for standard parameters. ventilation ducts for hoods and air vents in the walls.

A ready-made solution for exhaust ventilation, organized using a plastic duct, is to place the valve in a shaped element - a connector of direct channels
Blinds are convenient to use, but it is preferable to install them in the outer part of the ventilation system. The combination of leaves provides excellent exhaust air

The valve to prevent backdraft can be installed on the entire grille or only on the hole for natural ventilation. On sale there are lattices with a backpressure valve of other design solutions.

However, options with a membrane or the use of springs will have serious problems with performance at low temperatures. Therefore, for a street grill, it is better to choose a device with a shutter of the “blinds” type.

Type # 4 - Flexible Membrane

The operating principle of the diaphragm check valve is based on the ability of the flow to reposition the flexible plate. Its placement allows you to open the ventilation hole in one direction of air movement, and to close it in the other, tightly fitting to the perimeter.

Diaphragm check valve
For the diaphragm check valve to open or close, a small force of the air flow is sufficient, therefore, such devices are successfully used for natural ventilation

In the case where there is a risk that a strong backward thrust deforms the membrane, additional stiffeners are required, on which it will rest when closing the ventilation hole.

This fact must be taken into account when acquiring a diaphragm valve; otherwise, the valve may be bent and subsequently loose, as a result of which the device will partially transmit reverse air flow.

Features of self-manufacturing

Given the low cost of check valves, self-manufacturing of the device is relevant only when using a ventilation grille or duct duct with non-standard geometric parameters. In this case, it is often cheaper and faster to make a valve for it than to switch to a standard shape and size.

The easiest way is to make a diaphragm or single-leaf valve yourself. A hard material, for example a plastic or metal plate, is used as a sash.

Particular attention should be paid to the following points:

  • the tightness of the plate against the walls of the valve body or the locking protrusion to prevent the formation of gaps and air passage;
  • exclusion of plate knocking, which is especially important in the case of frequent changes in the direction of air movement.

For a diaphragm valve, a sheet of thick paper or lavsan film of a larger diameter than the ventilation hole can be used. With strong reverse thrust, in order to avoid deformation of the membrane material, it is necessary to install a lattice on which it will rest.

Homemade diaphragm type check valve
As a membrane, a lavsan film is suitable. It does not lose its properties under the influence of moisture, as well as with repeated bending

Rules for placement and installation

For systems of any configuration, it is necessary to plan the placement of valves so that the return draft is blocked with any combination of fans and hoods turned on. The quality of ventilation depends on the proper installation of the devices themselves.

The location of the valve in the ventilation system

If exhaust system Since there is one place for air intake, which goes through the ventilation duct to the shaft or to the street, it is enough to install a single valve in the air duct to prevent back draft.

If the topology of the system is more complex due to the presence of several hoods or openings for natural ventilation, then the following rules for placing check valves are applied:

  1. A check valve is installed on each branch connecting the air intake point and the main air duct.This is necessary to prevent air from being redirected toward the hood when it is not turned on.
  2. Usually, another device is installed at the outlet of the ventilation system. Ideally, with a complete tightness of the channel, this is not necessary, but practice shows the feasibility of installing the valve in this place.

As a rule, the check valve is installed in places with the most convenient access to them. This is due to the fact that they must be periodically cleaned of adhering dust and fat deposits, otherwise the shutters will not be completely closed during reverse draft.

Valve location for natural ventilation
This arrangement of the valve for the organization of forced and natural ventilation provides good access to it for preventive maintenance.

When modeling the duct, remember that the manufacturer can install a check valve on the fan or exhaust hood. In this case, there is no need to install a separate backdraft protection.

Particular attention should be paid to installing the valve near the entrance to the mine shaft of apartment buildings.

The general ventilation system is a cavity protected from direct sunlight with a positive temperature, into which moist air periodically enters, which is an ideal medium for the propagation of various types of microorganisms. Also, insects, birds and rodents often live there.

Contaminated ventilation shaft of an apartment building
Management companies often do not perform cleaning work on public ventilation shafts on time, which leads to poor air quality

Air in such mines rarely meets sanitary and epidemiological requirements for residential premises. Therefore, even in the case of regular sanitization of ventilation shafts, it is necessary to prevent the possibility of back draft and air from it entering the apartment.

Nuances of installation and maintenance

To create household ventilation, round or rectangular ducts of standard sizes are used. For them, there are ready-made solutions containing a check valve that can be installed anywhere in the system. In this case, the installation process will be similar to connecting any other ventilation element.

Shaped box element with check valve
A ready-made solution for exhaust ventilation, organized using a plastic duct, is to place the valve in a shaped element - a connector of direct channels

If it is necessary to alternate the work of natural and forced ventilation, there are two typical solutions for installing a check valve, which makes this possible:

  • installation of a tee near the ventilation grill, with the installation of the valve on the outlets for natural ventilation;
  • purchase of a special design grille with two openings for both types of ventilation.

Installation of such a lattice can be carried out using self-tapping screws or liquid nails.

The first method is preferable, since the analysis of the ventilation system for cleaning, repairing or changing its configuration is easiest to do first by removing the grill. If it is decided to install the grill on the inside of the room, then it is necessary to carefully seal the joint of the grill and the wall.

Self-tapping ventilation grille on the wall
Fastening the grille to the wall is best done with self-tapping screws. In this case, it is easy to remove it for maintenance work on cleaning the air duct and check valve

One of the problems of outdoor grilles equipped with blinds is the freezing and icing of the wings in frost. The air leaving the bathroom, toilet or kitchen is saturated with moisture, which freezes at low temperatures.

In this case, two problems arise:

  • sashes stop tightly closing the ventilation hole, as a result of which, in the case of reverse draft, air enters the room, albeit to a lesser extent than in the absence of protection;
  • a significant reduction in the hole cross section occursAs a result, the throughput of the system is reduced, which reduces air circulation and increases the load on fans and cooker hoods.

In this regard, it is necessary to periodically check for the presence of ice on the grate and remove it. The easiest way to perform this procedure is mechanical, but there is a risk of damage to the body and curtains if they are made of plastic. Therefore, it is better to install a rigid lattice made of metal outside.

Conclusions and useful video on the topic

Mounting the valve in the ventilation grill in standard sizes:

Valve installation method for alternate operation of forced and natural ventilation:

Membrane Valve Fabrication:

Installing a non-return valve in the exhaust air system will ensure normal ventilation, eliminate the reverse movement of the air flow, and eliminate unpleasant odors and toxic volatile compounds.

This device can be installed independently if you purchase a finished structure that corresponds to the cross section of the ventilation duct in the house.

Those wishing to share their views on the information provided or to ask questions about the points of interest are welcome to leave comments. Please write in the block under the text of the article. Share useful information, post a photo on the topic.

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Visitors Comments
  1. Alexander

    Faced with the problem of poor-quality exhaust: from the bathroom to the toilet there is a standard hole in the wall as an exhaust, but this is not enough to completely eliminate condensation. Because of this, I encountered corrosion on the washing machine and mold on one of the walls. I plan to improve the exhaust system, based on the available material, in my opinion, the material.

    • Oh yes, there was such a problem in our bathroom. In general, similar situations are typical for rooms with high humidity. The ventilation we had in the old apartment, of course, worked disgustingly. On a washing machine, mold began to grow on rubber bands. I had to redo everything, because the condensate was tortured.

      In the kitchen there is a rectangular box with a check valve, it pulls normally.

    • Expert
      Alexey Dedyulin

      Alexander, in your case, a check valve is unlikely to help. You need to put the channel fan and think over the automation to turn it on. Usually the fan is paralleled with a light bulb so that they turn on simultaneously. But if it is very damp, you can additionally make the inclusion through a time relay. For example, every hour for five minutes. Then you will always have normal humidity in the bathroom.

  2. Irina

    I did not get that. And the check valve, that is, the second, is there an outlet in the opening? So that with a fume hood not working, odors from the ventilation duct do not come into the apartment.

    • Expert
      Alexey Dedyulin

      As I understand it, you are interested in a butterfly valve using springs (type 2 in the article). Yes, it really is located inside the ventilation duct. Only you must understand that the normal functioning of this type of valve is possible with forced exhaust.You will also need a preliminary adjustment of the springs to set the required resistance level.

      When the hood or fume hood will not work, the channel is blocked automatically, which prevents the smell from the kitchen from getting into another part of the ventilation. Once every few years, the springs will have to be adjusted.

  3. Boris Nikitin

    Everything is in theory. How is it put in practice? For example, check valve TU U V. 2.5-25-.2-30037114-004-2003? He himself is flat 14 mm, he has three plastic zazEpochki in the form of round teeth.

    Attached photos:
    • Expert
      Alexey Dedyulin

      And you definitely carefully read the article and watched all the attached materials? It seems to me that no. In the “Conclusion and useful on the topic” section, the first video clearly shows how to install a similar non-return valve.

      But I would highly recommend using a different type of check valve. The fact is that the option you are considering is the simplest, but it can hardly be called a full-fledged check valve. In fact, this is a membrane that bends when the hood is turned on, in addition, this membrane can detach. See for yourself video example. It is better to use a single-leaf valve of gravitational action.

      Attached photos:
  4. Sergei

    It is not a matter of valves and fans, but of providing an inflow into the apartment, if you have PVC windows installed, if there is no inflow, then, accordingly, the hood will work poorly.

  5. Victor

    Good afternoon! How to put the valve: vertically or axially? We have the 5th last floor, no technical floor. Thrust with rollover, and if it pulls, it is very weak.

    The ventilation duct is satellite. When he casts, it stinks, there is no other name! Maybe you advise?

    He set it along the axis: it seems to be pulling, (the shutter is about 45 degrees), but it has time to throw it. Set horizontally: almost all time is closed, i.e. about 5 degrees ajar. What to do, I can’t imagine.