On-line oil fume reflux generally comes down to flue quality and design problems, hood quality problems and check valve quality problems. In addition, we often see that large air volume can prevent the backflow of lampblack. The subtext is that the oil fume reflux is the problem that the air volume of the range hood is too small.
In my opinion, the oil fume backflow has nothing to do with the air volume of flue, hood, check valve and hood. This is because for the same family, oil fume reflux is "intermittent" and rarely happens every day. If the poor quality of flue, hood and check valve will cause oil fume backflow, then oil fume backflow should happen every day, because the quality of installed flue, hood and check valve will never be good or bad. Oil fume reflux always occurs when the range hood is not used, and the air volume of the range hood with large and small air volume is zero when it is closed, so the air volume of the range hood has nothing to do with oil fume reflux.
Flue gas backflow can't be blamed on whether the flue design is correct or not, because the flue design only applies the specification, which is stipulated by the Ministry of Construction. What the designer does is to move the standard drawing to the design drawing. In addition, if it is really a design error or a flue quality problem, oil fume backflow should also happen every day, but there should be no such situation in real life.
At present, there are generally three lines of defense to prevent oil fume from flowing backwards in the kitchen:
1. Exhaust non-return valve on the hood body: The non-return valve on most hoods can block most areas of the ventilation pipeline, but there is still an annular gap between the valve body and the valve plate, which will cause a small amount of oil smoke leakage.
Second, the * * * flue in the building is variable pressure, main and auxiliary. The characteristic of these flues is that when the lampblack passes through the hood interface, it will theoretically generate negative pressure, which will suck the air in the kitchen into the flue to prevent the lampblack from leaking from the gap of the outlet check valve brought by the hood body.
Third, most kitchens are equipped with sealing valves at smoke outlets. This kind of sealing valve can play a good sealing role in theory when there is positive pressure in the flue. The greater the positive pressure, the better the seal.
The smoke outlet of the small smoke machine is set with three lines of defense, which should be said to prevent backflow. However, in fact, oil fume backflow occurs from time to time, indicating that the three lines of defense have both functions and failures. The failure shows that the three lines of defense are not targeted enough to prevent the backflow of lampblack, and the reason for the lack of targeting is that the mechanism of lampblack is not clear.
The reason for oil fume backflow should be that when a household discharges oil fume into the flue, the oil fume is under greater pressure than the atmospheric pressure and will expand in the flue. When the expanded pressure is still higher than the atmospheric pressure, it will move to generate airflow, which will be released from the smoke outlet on the roof when the fan valve of every household is closed. If you pass through an air valve that is not tight during the expansion movement, it will be released from the vicinity, which is the backflow of lampblack.
According to my own experience, there are four reasons for the occurrence of oil fume reflux:
One: Because the hood comes with a check valve and the closing valve installed at the smoke crossing adopts a structure that depends on the wind power of the hood, the valve plate is closed by its own weight or by adding a closing spring. In order to ensure that the valve plate can be blown open by the wind of the range hood, its weight or spring force should not be too large, so the valve closing force is small, and the valve plate is not in place after being stuck with oil, and the consequences of being out of place are poor exhaust and air volume attenuation; The consequence of not being closed in place is a large amount of oil fume backflow, which is a common phenomenon of oil fume backflow.
Two: the range hood comes with a check valve, and there is an annular gap between the valve plate and the valve body. When the neighbor turns on the hood (blowdown), 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 a proper amount of negative pressure at the interface of the hood, and there will be no oil fume backflow. However, if the negative pressure generated when the wind speed is too high, the valve plate will be sucked open, and if the valve plate is stuck by oil pollution, it cannot be effectively closed. When the negative pressure disappears, the lampblack will flow back. Because the hood in the flue design code is determined by 17 cubic meter, and now the air volume of hood mostly exceeds this value or even 17 cubic meter, the phenomenon of oil fume backflow caused by excessive air volume is also increasing gradually.
Fourthly, when the exhaust pressure and air volume of the smoke machine upstairs are large, wind resistance will be generated in the flue, which will hinder the rise of soot downstairs and increase the local pressure of the flue downstairs. After the local pressure increases, the dirty gas in the flue leaks from the check valve with poor sealing effect, which is the reason for the backflow of cooking upstairs and downstairs.
In addition, in the process of using the hood, it will be found that the smoke is not smooth. The reason is that the grease accumulated on the check valve increases the weight of the valve plate, and the opening resistance of the check valve increases after the valve plate is fitted with a spring, so the range hood needs to consume some air to overcome these resistances. However, the shut-off valves installed at the * * * smoke outlet are all opened downward, and the valve plate cannot be opened to the maximum position, which reduces the ventilation cross section, which will cause the attenuation of exhaust air volume and poor smoke discharge.
There are many reasons for oil fume backflow, but the solution is actually very simple. As long as a tightly closed valve is installed at the outlet of the range hood, the problems of oil fume backflow and poor smoke exhaust can be eliminated. Imagine: the door is closed tightly, how can the wind leak in? However, the traditional structure of "wind blowing and gravity closing" can't close the smoke exhaust valve tightly and open it in place, and it must be opened and closed by external force.
Three kinds of electric smoke exhaust valves can be found online, which have a good effect on completely solving the smoke exhaust problem:
I xingxi sanitary separator (electric flue) is not explained in detail. According to the name "electric flue", it should be judged that electric action should be adopted.
The second is the check valve of Chao Fu electric flue, which is closed by spring and opened by electromagnet. A square hole of 170× 185 is opened on the flue, which can be inserted into half of the flue for easy installation. The switch of the valve is automatically controlled by the switch of the hood.
The third type is Yu Chuang brand electric fume check valve, which is closed by a spring and slowly opened by a motor, and the switch of the valve is automatically controlled by the switch of the hood. Yu Chuang brand electric fume check valve has two forms, one is installed at the cigarette holder and needs to be fixed with four expansion screws, and the other is directly installed at the outlet of the hood and can be installed under the ceiling, which is more suitable for users who find that the fume can be poured after the decoration is completed.