In the field of reverse osmosis water treatment, backpressure refers to the situation where the pressure on the product water side is greater than the pressure on the feedwater side. As mentioned earlier, the spiral membrane element is similar to a long envelope-shaped membrane pouch, with one end open and adhered to a product water center tube with perforations. Multiple membrane pouches are rolled onto the same product water center tube, allowing feedwater to flow over the membrane from the outside, and under the pressure of the feedwater, fresh water passes through the membrane into the membrane pouches and flows into the product water center tube. In order to facilitate the flow of product water within the membrane bag, a product water-guiding fabric support layer is inserted into the envelope-shaped membrane bag; to evenly distribute the feedwater over the membrane bag surface and provide turbulence to the feedwater flow, a mesh layer is inserted into the feedwater passage between the membrane bags. The three sides of the membrane pouch are bonded together with an adhesive, and if the pressure on the product water side is greater than the pressure on the feedwater side, the bonding lines will break, resulting in the loss or significant reduction of the membrane element's salt rejection, therefore, from a safety perspective, a reverse osmosis system cannot have backpressure. Since reverse osmosis membrane filtration is pressure-driven, backpressure will not exist under normal operation. However, if the system is shut down normally or due to a fault, valve settings or improper opening and closing of valves may cause backpressure, so proper measures must be taken to resolve the backpressure issue.
