Why do the elements of reverse osmosis safety filters get flattened?

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The filter element of the reverse osmosis safety filter was flattened; essentially, the pressure difference it endured exceeded its structural strength. During normal operation, as long as the pressure difference between the inside and outside is within the design range, it is safe for the filter element to be supported by the central frame. Once this balance is disrupted, “squashing” occurs. 1. Severely clogged filter element—squeezed flat: When the filter element is rapidly blocked by large amounts of suspended particles, colloids, microorganisms, or broken filter media and other impurities, the water flow resistance increases sharply. The water inlet pressure on the outside of the filter element remains almost constant (for example, 3 bar provided by the water pump), while the pressure on the inside drops significantly due to pumping by a high-pressure pump or poor flow of water; the resulting pressure difference can momentarily exceed the tolerance limit of the filter element (the typical limit for high-quality filter elements is around 2–2.5 bar). Deterioration in pretreatment performance—such as sand leakage from multimedia filters, leakage of activated carbon powder, turbidity of the water source due to disturbances, or excessive addition of PAC/PAM leading to floc formation—can cause the filter element to become clogged within a short period of time, ultimately resulting in it being “crushed” under external pressure. 2. The system creates a vacuum—suction-induced flattening. This is the most easily overlooked cause of “flattening”; it has nothing to do with whether the filter element is clogged, but rather stems from incorrect operating logic. When the raw water pump suddenly stops or the inlet valve closes, and the high-pressure pump fails to shut down in response, it will forcibly draw water from the safety filter. No water is flowing into the filter’s inlet pipeline at this time, and a closed space often forms due to the check valve being closed. The strong suction of the high-pressure pump quickly creates a negative pressure (vacuum) inside the filter. The inside of the filter element is evacuated to a vacuum, while the outer space, due to the lack of water addition and being sealed, has a pressure close to atmospheric pressure or even the low pressure resulting from cavitation. Under the effect of internal and external pressure differences, weak points in the filter element frame will become severely indented. This flattening often occurs very quickly and thoroughly. 3. Insufficient pressure resistance of the filter element itself: The central skeleton of polypropylene melt-blown or wound-filter elements is made of poor-quality material and has a thin wall thickness; thus, the designed maximum pressure difference is only 1–1.5 bar. Once the operating pressure difference is slightly on the high side, it becomes prone to deformation. Using ordinary filter elements designed for low-pressure conditions in situations where the inlet water pressure is high and backwashing is incomplete. Or in high-temperature water, the strength of PP materials decreases, significantly reducing their actual pressure resistance. Repetitive operation under high pressure differences causes the skeleton material to undergo creep and fatigue, eventually leading to sudden instability and flattening under a normal pressure difference. 4. Water hammer and improper operation: At the moment when the raw water pump or high-pressure pump starts or stops, the flow velocity of water in the pipeline changes abruptly, generating shock waves whose pressure is much higher than the normal operating pressure. This instantaneous high pressure difference energy is sufficient to cause a filter element in a critical state to instantly “burst” or be crushed. The rapid opening and closing of manual valves can also cause severe pressure fluctuations, leading to an imbalance in the pressure applied to one side of the filter element. 5. Insufficient design margin: The designed flow rate is far beyond the total processing capacity of the filter element, resulting in the pressure difference across a initially clean filter element already approaching the alarm value (e.g., 0.1 MPa); even slight contamination after operation can quickly cause it to exceed its pressure tolerance limit. Design flaws in the water distributor cause some filter elements to experience flow rates and dirt retention levels that are much higher than those of other elements, resulting in those specific elements being flattened first