Wastewater treatment. PAC, PAM. Problems with the back pressure valve and damper in the metering pump system

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Wastewater coagulation and sedimentation dosing system. Since the performance suddenly became very poor earlier, and because the pipes were damaged due to workers’ mistakes, it was decided to change the piping system. Because the company’s technicians use a \"rough\" installation method and never follow the instructions provided by Mettler. To avoid debugging issues, I decided to install it according to the diagram. Two types in the Mintonro GM series, with a maximum flow rate of 315 and a maximum pressure of 5. Flow rate 170, pressure 7. A float flow meter was installed because there was no experience in installing components such as backpressure valves, and there was concern that the conditions necessary for the metering pump to operate accurately could not be ensured; therefore, a flow meter was added to the PAC pipeline. Water is collected at the outlet using a cup, and the flow rate is roughly consistent with that of the flow meter. However, PAM will definitely have errors due to its high viscosity. So it needs to be more precise; otherwise, it’s like applying the pesticide blindly. The dampers are homemade, made using DN90 PVC pipes along with plugs. Description of the problem occurrence: 1. First attempt to run water, about 5 minutes. After startup, the calculated flow rate for the stroke is 230, while the actual flow rate is 240. After that, pressure was applied to the backpressure valve, from 0 to around 0.2 MPa, and the flow meter was able to stay at a value corresponding to the stroke – which is great. 2. After lunch, I tried it again; the back pressure valve did not move, and the flow rate increased gradually from low to high. Once the pressure in the pipeline reached a certain level, the back pressure valve opened, and the flow rate fluctuated around 230–240. After about 2 minutes, the flow meter suddenly reached its limit, the water pipe vibrated violently, and a whiplash-like sound was heard. Shut down. 3. Relax the back pressure valve spring. Power on again, apply pressure, and it gradually stabilizes; it remains the same as in situation 2 for a period of time. 4. Cut off the neck of the \"dampener\" and attach a living knot as close as possible to the pump head, in order to bring the \"dampener\" closer. The backpressure valve ranged from 0 to 0.2 Mpa, remaining stable at 230 with no fluctuations for about 6 minutes. The shutdown requires repeated testing. 5. When operation resumed, the back pressure valve remained unchanged, staying at around 0.2 Mpa. As the flow meter increased from 0 to 230, it suddenly reached its limit; the pipeline began to make popping noises and oscillate violently. 6. I called Minton Roy’s after-sales service; he said that the backpressure valve regulates the flow rate but causes pulsations, while the damper has nothing to do with the flow rate but helps to eliminate those pulsations. I understand that; in the end, you were unable to answer my question, so you had me reduce the back pressure valve. I adjusted the pressure to various levels within 0.1 Mpa several times, with durations ranging from 3 to 6 minutes, and severe pulsation would begin. The after-sales technician told me to buy a good damper, saying that a damper without a diaphragm and without 50% of the pipeline pressure is useless. Could you tell me why this is the case? Is the back pressure valve installed in the wrong location? Is the damper not working? Is the quality of the back pressure valve really that poor? I would like to ask my fellow students for some guidance; as a newcomer who has just graduated, I appreciate any advice you can offer.