The water source for preparing the standard test solution is reverse osmosis produced water, so it is almost free of impurities and there is no problem of membrane element contamination. In practical use, except for the secondary reverse osmosis system, which uses the water produced by the primary reverse osmosis system as raw water, almost all other reverse osmosis systems use raw water that has undergone ordinary pretreatment. Although the pre-treatment process removes some impurities, the incoming water quality is still poor compared to the water source used under standard testing conditions. So the designed water production of the membrane element should be less than the standard water production. If the standard water production is still used as the design water production, the reverse osmosis membrane element will soon be contaminated, causing damage to the membrane element. In order to avoid the above situation, membrane component manufacturers provide design guidelines to provide designers with a basis to follow. The design guidelines suggest selecting different design water production rates based on different inflow sources. Even if the reverse osmosis membrane element is used according to the design guidelines provided by the membrane element manufacturer in actual use, it will still gradually become contaminated. Of course, its performance can be partially restored through chemical cleaning after a period of time, but it is difficult to fully restore its performance. Therefore, experienced designers should consider this issue when designing. At this time, a water supply pump that can ensure the design water production rate after 3 years should be selected, that is, a higher pressure water supply pump needs to be designed. However, when the system is initially put into operation, it does not require a very high pressure to achieve the design water production rate. Therefore, the water supply pump pressure is abundant during initial operation, and as time goes by, the pressure surplus gradually decreases. Therefore, a manual regulating valve should be installed behind the high-pressure pump to adjust the water supply pressure. Sometimes a variable frequency control device can be installed on the water supply pump, and the variable frequency method can be used to regulate the water supply pressure. The manual regulating valve behind the high-pressure pump generally does not need to be adjusted frequently after setting, and is basically kept in a constant position for a period of time. This valve does not need to be opened or closed every time the system is started. But if there are no other valves behind the high-pressure pump, the high-pressure water source of the high-pressure pump will directly impact the membrane element every time the system is started, especially when there is air in the system, which will cause the phenomenon of "water hammer" and easily lead to the rupture of the membrane element. To prevent the occurrence of the above phenomenon, an electric slow door should be installed behind the high-pressure pump. After starting the high-pressure pump, the electric slow door should be slowly opened, that is, pressure should be slowly applied to the reverse osmosis membrane of the system. The electric slow door should be a fully open and fully closed valve, and its fully open and fully closed time can be adjusted, but it is generally set to 45-60 seconds. Therefore, from the perspective of safety of reverse osmosis membrane components, electric slow opening doors should be installed.
