1, backflow preventer is a device composed of non-return parts, which can prevent the backflow of water in water supply pipeline.
2. Check valve refers to the valve whose opening and closing parts are disks, which block the backflow of media by its own weight and media pressure.
Second, the classification:
1, backflow preventer is divided into LHS743X low-resistance backflow preventer and LHS743X backflow preventer according to the model. According to the connection mode, there are decompression backflow prevention valves and flange-connected low-resistance backflow prevention valves (there are two types of low-resistance backflow prevention valves: double diaphragm and single diaphragm); Threaded connection includes threaded low-resistance backflow preventer, miniature backflow preventer and water meter backflow preventer.
2. Check valves can be divided into three types according to their structures: lifting check valves, swing check valves and butterfly check valves. Cast iron check valves, brass check valves, stainless steel check valves, carbon steel check valves and forged steel check valves are classified according to materials. According to the function, it is divided into DRVZ silent check valve, DRVG silent check valve, NRVR silent check valve, FSCV rubber flap check valve and DDCV double flap check valve.
Third, the work:
1, the low-resistance backflow preventer consists of two independent spring-assisted elastic sealing check valves and an independent hydraulic differential drain valve located in the middle decompression chamber. The pressure chamber of the drain valve is connected with the upstream water supply pressure, and the three internal valves are not mechanically connected except the valve body (that is, related mechanical failures will not occur at the same time), so as to ensure their independent actions and strictly limit the pressure water in the pipeline to only flow in one direction.
2. Check valve The function of this type of valve is to only allow the medium to flow in one direction and prevent the medium from flowing in the opposite direction. Usually, this valve works automatically. Under the action of unidirectional fluid pressure, the disc opens. When the fluid flows in the opposite direction, the fluid pressure and the self-overlapping disc of the disc act on the valve seat, thus cutting off the flow.
Fourth, the principle:
1, countercurrent refers to the flow state of water flowing back to the upstream water inlet in the valve cavity. Reverse pollution is defined as: as long as backflow occurs, whether the backflow water is polluted or not, it is called backflow pollution. According to the working principle of backflow preventer, there are two important characteristics to ensure the realization of its function.
2. Check valves can also be used to supply air to auxiliary systems whose pressure may be higher than the system pressure. Check valves can be mainly divided into swing check valves (rotating according to the center of gravity) and lifting check valves (moving along the axis).
Extended data:
Principle and function of backflow preventer;
1, positive water supply
When the inlet pressure is greater than the outlet pressure, the two check valves open and the drainer closes. When the velocity is 2m/s, the loss of circulating water is less than 0.04Mpa
2. Reverse closing
When the inlet pressure is less than or equal to the outlet pressure, the two check valves are closed and the drainer is opened.
If there is no garbage jam, the two check valves are sealed and closed, the outlet of the drainer does not drain water, the middle cavity is communicated with the atmosphere, and the pressure of the middle cavity is zero.
3. Prevent backflow pollution
When the inlet pressure is less than the outlet pressure, the two check valves are closed and the drainer is open. If the valve port of one or two check valves is blocked by garbage, it will leak, and the leaked medium will flow to the middle cavity and be directly discharged from the valve through the drainer to prevent backflow from polluting the inlet end.
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