Range hood check valve

The "check valve", also called "butterfly-valve", function is to allow air to one-way flow. Check valve is located in smoke lampblack machine turbofan (motor), before entering the exhaust duct, is wary of outdoor blowing winds, due to the instantaneous pressure difference between inside and outside, let outdoor air be "sucked" into the room. In theory, however, is "check valve", in a common case, it can only be "reduced valve" and not "check". Now a lot of people who live in multi-storey apartment buildings all complaints in their interior smell of other dishes.Reason is that at the bottom of the kitchen lampblack machine to lampblack to the vertical exhaust hole, because most of the building design and useless to the shaft caused "negative pressure", so the soot in the shaft up downstairs "squeeze", on the way will leak into other floors lampblack machine exhaust pipe.Because of the check valve can't be 100% sealing, the smoke nature can seep into the house.

(source:http://www.kg-machinery.com/news/range-hood-check-valve.html)