Gas in the pipeline can easily cause overpressure
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If a fire protection pipeline is not depressurized before the fire pump is started, it is said that this can cause overpressure in the pipeline. I’m not quite sure how this happens; even if there is gas in the pipeline, the maximum pressure should still be the maximum outlet pressure of the centrifugal pump. So why would overpressure occur? I asked some technicians, and they said that rapid flow of the liquid followed by sudden cessation due to resistance can lead to overpressure. I’m not entirely clear about this, and I hope fellow enthusiasts can discuss it
This pressure is the pressure at the pump outlet; when resistance is encountered and flow stops, it is referred to as outlet pressure buildup. As the outlet pressure rises, it is possible for the pressure to become too high, leading to damage to the pipelines or sealing surfaces, and it can also cause damage to the pump over time
This overpressure is determined by the elastic coefficient inherent in the gas itself; moreover, this doesn’t quite make sense, does it? If it’s needed urgently, I guess the pumps will be running with the valves open elsewhere to have water available:lol
In my understanding, as the pipeline operates and the water temperature rises, the gas inside expands and escapes, resulting in an increase in pressure.
This is just deception; it’s like a pressure test for pipes – if there is gas present, the pressure test results will be inaccurate, but the pressure won’t exceed that of the water supply pump
Once the fire hose system is installed, it also needs to be tested with water... The pipe should basically be filled with water. It would be strange if a newly installed system isn’t tested. In any case, it’s really unnecessary; when water is supplied temporarily, water should flow out, and gas should also be released
Well, upon reflection, the highest pressure is probably the pressure at the pump outlet. Some say that it is mainly due to the elastic coefficient of the gas, similar to the relationship between momentum and impulse. When liquid moves at high speed and suddenly encounters gas, the gas is compressed by the liquid, causing it to be compressed further until its pressure equals that of the liquid. Due to inertia, the gas continues to be compressed, resulting in overpressure that exceeds the pressure at the centrifugal pump outlet. Many technicians think this way, and it seems to make some sense, but no satisfactory explanation can be provided to refute it
Are you sure there is gas inside or a vacuum? If it’s a vacuum, then the situation your technician described will occur