How to troubleshoot a reverse osmosis (RO) pure water system that fails to start?

Reverse osmosis pure water equipment uses membrane separation technology to effectively remove inorganic substances, colloidal particles, bacteria, and organic matter from water. It is the best equipment for high-purity water preparation, brackish water desalination, and wastewater treatment processes. During operation, improper use and untimely cleaning and maintenance can cause the equipment to fail to start. First, check the process. If the reverse osmosis pure water equipment cannot be started, check the following steps: Check if the power plug is plugged in and if there is power. Check if the power switch connection is loose and reconnect the power cord. If the system displays no water and an alarm sounds, it indicates that the inlet water pressure is below the set value. Please check if the water source is open, if the system has inlet water, or if the tap water pressure is below 0.1 MPa. If so, please improve the inlet water pressure to an appropriate level. If the inlet water is normal, check if the pretreatment filter element is clogged. If it is clogged, please clean or replace the pretreatment filter element. If the inlet water condition is normal, check if the pretreatment filter element is clogged. If it is clogged, clean or replace the pretreatment filter element.

On-site testing revealed that the reverse osmosis pure water equipment failed to start because the water passage of the pressure protection switch on the inlet pipe and the pressure protection switch before the high-pressure pump were blocked by iron rust, preventing pressure sensing and signal output to the PLC control program, thus causing the equipment to fail to start. The turbidity of the water discharged from the sand filter tank was tested to be no higher than 1.0 NTU, meeting the requirements for entering the security filter, and there was no possibility of the security filter being blocked by solid impurities.

Sections of the same size were cut from the clogged security filter and placed in a dilute hydrochloric acid solution. After 5 minutes, the security filter sections in the hydrochloric acid solution turned white. After disassembling the pressure protection switch, it was found that the inlet pipe of the pressure protection switch was blocked by a yellowish-brown substance. After cleaning the pipe, the pressure protection switch could normally reflect the water pressure. Water quality analysis showed that the iron ion content in the water was as high as 0.5 ppm, and large yellowish-brown patches were visible in the removed reverse osmosis membrane, with yellowish-brown substances accumulating at both ends of the membrane.

By checking the inlet pipe of the reverse osmosis equipment, it was found that the increase in iron ions was caused by the use of the booster pump. The booster pump was introduced to ensure sufficient inlet water pressure for the sand filter and to ensure sufficient starting pressure for the high-pressure pump. However, the original water salinity was as high as 1.5 g/L. The improper selection of the booster pump caused rapid corrosion of the booster pump, leading to a large amount of iron ions entering the pipeline. The equipment, designed based on the original water, did not have a device for treating iron ions, resulting in the sudden introduction of iron ions affecting the safe operation of the equipment. After stopping the use of the booster pump and cleaning the water passage of the pressure protection switch, the equipment resumed normal operation.

Analysis of the fault phenomenon shows that the cause of the failure to start the reverse osmosis pure water equipment and the blockage of the security filter was the increase in iron ions in the original water. These iron ions were ferrous ions in the reduced state in the original water and could dissolve in water. This water was adsorbed or accumulated in the pipe of the pressure switch after passing through the security filter, and after the equipment was shut down, it was oxidized by oxygen in the air, turning into insoluble ferric iron, which is difficult to dissolve in water, causing blockage of the security filter and pipes, affecting the normal operation of the reverse osmosis pure water equipment.