What is a non-return valve exhaust fan, how it works and where it is used

When the neighbors smoke, or again someone has something burnt on the kitchen stove, all the smells are drawn through the ventilation in the apartment. To isolate the home or office from unpleasant odors from the outside, install an exhaust fan with a non-return valve. The system provides quality air exchange and closes the back draft when the fan is off.

What is an exhaust ventilation valve and how it works

An exhaust valve is an element of an exhaust system with a fan. When the blades work, a draft is created that moves air out of the room to the outside, replacing it with fresh air. The flow causes the flaps of the check valve to open, freeing a channel for air movement. When the fan is off, the flaps close it off.

Exhaust valve comes in several types according to the flap arrangement:

• Diaphragms made of flexible material deflect under the pressure of air. Under reverse pressure, they are pressed against the grille, and the passage into the ventilation is blocked.
• In the design of the butterfly exhaust valve, the blades work on the same principle as the wings of a butterfly. In this insect, they are spread during flight, and at other times they are folded. The check vent also has «wings» on its axis-two halves that close off the air inlet after the vent is turned off. When it starts running, the air flow opens the flaps of the valve.
• The petal vent has a similar design to the other models, only each flap has a separate rod.

Types of non-return ventilation valves:

• self-closing valve - when the air flow stops, the flaps close under the action of a spring;
• controlled dampers - flaps position is adjusted by electric actuator or manually;
• passive flaps - the flaps move solely by the action of the flow.

In domestic conditions in bathrooms and kitchens are often installed exhaust fans of the self-closing type. The flaps move silently. If the device is electrically powered, the motor makes noises. It is important to keep in mind that if there is a strong draft in the vent when the flaps close, a pop can be heard.

The design of a non-return valve differs:

• Horizontal or vertical according to the location of the fan;
• Round or square according to the shape of the duct;
• in the form of louvers.

The use of ventilation dampers

Non-return ventilation valve is used in industrial and domestic ventilation systems:

• In an apartment building, it keeps unpleasant smells of tobacco or burnt food from entering the apartment from the common shaft.
• In the kitchen and bathroom, the check valve allows steam and odors to escape with the air into the sump when the fan is on, preventing them from coming back in.
• In residential ventilation, it prevents cold air from getting in, which keeps the room temperature down. If plastic windows are installed, a non-return valve in the supply ventilation will provide sufficient ventilation, but without excessive heat leakage.
• In baths and saunas, to ventilate the rooms after use without excessive hypothermia.
• In manufacturing plants, to ventilate harmful vapors outdoors and prevent air from entering from the outside when it is not needed.
• In medical facilities to prevent foreign substances and contaminants from entering the rooms together with the air from the ventilation shaft, which is necessary for a high level of sanitation.

Check valve is used in all cases where it is necessary to isolate residential or office premises, warehouses or production halls from the flow of back-draught from the ventilation. Then foreign odors, contaminants and microorganisms do not get inside from there.