One: Because the outlet non-return valve of the ventilator and the drooping closing valve installed at the tobacco crossing are all structures that are opened by ventilator wind, the valve plate is closed by self-weight or booster spring. In order to ensure that the ventilator wind blows the valve plate open, its weight or spring force cannot be too large, so the valve closing force is small and not tight.

Two: There is an annular gap between the valve plate and the valve body of the outlet check valve of most range hoods. When neighbors turn on the range hood (discharge pollutants), the local pressure in the flue increases, and the polluted gas flows back from this annular gap nearby, which is the main reason for the backflow of oil smoke in the old flue.

Three: When the appropriate wind speed passes through the flue, it will produce an appropriate amount of negative pressure at the interface of the hood, so that the kitchen air will flow to the flue, so the lampblack will flow back.

Fourthly, when the exhaust pressure and air volume of the ventilator upstairs are large, wind resistance will be generated in the main flue, which will increase the local pressure of the flue downstairs and block the normal exhaust of the downstairs residents. This is the reason why cooking goes backwards upstairs and downstairs.

Extended data:

Precautions:

(1) The gas discharged from the range hood should not be discharged into the hot flue for discharging the flue gas burning gas or other fuels to prevent fire.

(2) The range hood shall be used when the stove consumes gas or other fuels, and the room must be well ventilated.

(3) It is forbidden to directly bake the range hood with fire.

(4) Reliable grounded power sockets must be used.

(5) If the power cord is damaged, it must be replaced with special wires or special parts purchased from its manufacturer or maintenance department.

(6) The range hood may catch fire if it is not cleaned according to the method specified in the manual.

(7) When replacing bulbs, please unplug the power supply first, and the power of each bulb shall not exceed 20W.

(8) When cleaning, please wear rubber gloves to prevent metal parts from hurting people, and the removed parts should be handled with care to avoid deformation.

(9) Special care should be taken when cleaning the wind wheel. Don't bump, deform or move the counterweight of the blade, otherwise the whole machine will vibrate and the noise will increase.

(10) Unplug the power cord when it is not used for a long time.

References:

Baidu encyclopedia-range hood

References:

Baidu encyclopedia-reverse flow