C100 check valve, also called a flap or shutter, designed for fans with a diameter of 100mm. It works by gravity. No power required.
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This valve acts as shutter, but it is much more practical and reliable.
It is mounted on a portion of the fan duct. When the fan starts to work the foil deviates allowing air flow.When the fan stops working, the foil under its own elasticity back to the previous position, stopping the flow of return air.
Some reasons for withdrawing air: 1. When the fan is running draws air from the room. The room creates a slight vacuum. After switching off the fan disappears string and vacuum formed in the room is sucked from the duct dirty air, which only just got rid of. 2. Fans often bought because of the lack of adequate natural ventilation. Natural ventilation is to himself that is variable depending on the temperature, the construction of the chimney and weather conditions. In the case of the fan assembly without the flap remains the problem of so-called "backair" or blowing air from the outside. The inclusion of the fan without flaps us solve this problem only for a moment. 3.The most common cause of establishment of the flap is the economic factor. In the winter, ventilation channels are a major cause of heat loss. In addition, backair followed by additional cooling of the rooms.
Why flap is better than shutter: Blinds in fans are controlled by actuators. The actuator except that significantly raises the price of a simple fan, not really fulfills its function. To be opened shutter actuator must heat up. This makes for about 30-40 seconds, the fan runs idly, i.e. without air flow. Only after heating the actuator shutters are opened. Unfortunately, even bigger downside is doing the opposite ie after switching off the fan. Shutter to shut needs about 30-40 seconds to cool down the servomotor. Only after cooling down the actuator, shutters gradually coming back to the previous position. Just those few seconds after stopping the fan is the most important in the correct functioning of the device, because then there is a backair. It should also be noted that the mechanisms of opening shutters are the most contingency elements in the fan, and their replacement is difficult and expensive.