Discussion on backflow when the circulation pump stops
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In the circulation system, the pump head is primarily consumed by the resistive elements in the pipelines (such as plate heat exchangers), as well as by local resistance along the flow path; in the absence of check valves, water backflow can occur after the pump stops running, leading to the pump running in reverse I think since all the head is consumed by the plate heat exchanger, there isn’t much water head at the rear end of the pipeline; therefore, when the pump stops, the water in the section of pipeline before the plate heat exchanger will flow back. At this time, if the pipeline is not long, it should be fine without a check valve as well. Moreover, without a check valve, the head required by the pump is reduced, as is the pressure resulting from backflow surges.
Circulating water systems are generally open systems; therefore, after the pump stops running, the water in the pipes flows in both directions along the divide line at the highest point. If there are no check valves, the pump will reverse direction. However, the middle part of the pipe will be under negative pressure for a while, causing the flow rate to decrease; once the water in the return pipe is exhausted, the water in the supply pipe will also run out. Unless the return valve is closed, some water will remain in the supply pipe (provided there are no leaks in the pipe), so it is still necessary to install a check valve
Failing to install a check valve will cause problems.