What is the specific difference between backflow preventer and check valve?

Simply put, the backflow preventer is a valve device consisting of two separate check valves and a safety drain valve. It has the characteristics of reasonable structure, difficult wear of parts, safety and reliability, long maintenance period and so on. When the pipe network pressure is normal, water can easily flow from the inlet to the outlet through two check valves. Due to the local resistance of the first check valve, the pressure in the valve cavity is slightly lower than the inlet pressure, while the water pressure under the diaphragm is the inlet pressure, so the water pressure under the diaphragm is higher than that on the diaphragm, and the safety drain valve remains closed. At this time, the water in the pipeline flows normally, as shown in figure 1. When all valves in the pipeline behind the backflow preventer are closed, the water flow is in a static state. At this time, if the pressure at the inlet is unchanged, the water pressure in the valve cavity is still slightly lower than that at the inlet, and the safety drain valve is still closed. When the pipeline pressure behind the backflow preventer rises above the water supply pressure, that is, the so-called back pressure, if the second check valve does not leak, high-pressure water will not flow back into the valve cavity, and the pressure will remain when the valve cavity flows normally, so the safety drain valve will not act to drain water; If the second check valve leaks, the pressure in the valve cavity will increase due to the leakage, and the safety drain valve will act to drain water. In this way, the pressure of high-pressure water flow on the first check valve is reduced, thus effectively preventing backwater from flowing back from the first check valve to the front pipeline. If the pressure of the water supply system continues to drop, the pressure at the lower part of the diaphragm that controls the action of the safety drain valve will also drop. When the inlet pressure drops to 0.02MPa, the control spring of the safety drain valve will be extended, and the safety drain valve will be opened for drainage. When the inlet pressure drops to zero or negative pressure, the safety drain valve will be completely opened, and air will enter the valve cavity, so that an air gap twice as large as the inlet diameter will be formed in the valve cavity, so that siphon backflow will not occur, and the water in the pipeline will stop flowing at this time. \x0d\ A check valve, one-way valve or check valve is a valve that does not allow (a large amount of) water to flow backwards. Generally, it is located between the pump outlet and the bypass pipe of the superimposed water supply device, and the bottom valve at the bottom of the water pump suction pipe also has the same function. -Simple, less head loss, but hard to leak. Anti-backflow valve, the specification stipulates that it must be installed in seven situations. The water leaked from the one-way valve will be drained, and an air partition will be formed between the upstream and downstream, so as to prevent the possibly polluted water from flowing back to the upstream-municipal pipe network. -It's very complicated, especially if it is used in places with large head loss, daily waste of electricity and insufficient water pressure, there will be no water. When buying, you should pay attention to whether you can really do it without backflow. There is a patented technology that can reduce the damage to tens of centimeters and reliably prevent backflow. It is under development. \x0d\ 1) Function \x0d\ backflow prevention valve is mainly used to prevent the backflow of water. Even if all possible internal seals fail, it can still ensure that backflow pollution accidents do not occur. It is a special technical measure to ensure water quality. \x0d\ check valve is mainly used to ensure one-way flow of water and prevent water from flowing backwards. However, it has no antifouling performance, and when the check sealing surface fails, it can not effectively prevent water from flowing back. \x0d\ For the pipe section with backflow prevention valve, there is no need to set a check valve; On the contrary, it is irreplaceable. \x0d\2) Structurally \x0d\ check valve only has single-stage check seal structure, which is short in structure length and light in weight \x0d\ decompression backflow prevention valve includes two independent check seals and automatic induction drainer, which is long and heavy. \x0d\ Low-resistance backflow preventer includes two-stage check seal+external automatic drainer, which is compact in appearance and light in weight \ \x0d\ Head loss of decompression backflow preventer: generally 0.07-0. 10MPa. For low-pressure partition, if the water loss is too low, the safety of partition can not be guaranteed; \x0d\ The head loss of the low-resistance backflow prevention valve is less than 0.03MPa, which is an air partition or a zero-pressure partition, with the highest safety level;