Surge phenomenon and its prevention and control measures

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When the fan operates in the unstable operating region, there is a situation where fluid is output by the fan at times, and at other times fluid flows back from the piping system into the fan – a phenomenon known in professional terms as \"surge\". When the performance curve of the fan is hump-shaped, with a steeper slope on the left side of the peak and the operating point being far from the peak, surge is likely to occur. Methods to prevent and control surge include: 1) Try to avoid operating the equipment in the unstable region ； 2) Use the bypass or venting method. When the user requires a low flow rate and this causes the operating point of the equipment to move into the unstable zone, a bypass pipe installed at the equipment’s outlet (an exhaust valve can be used in air systems) can be utilized to allow the equipment to operate within its stable operating range at a higher flow rate, while the desired flow rate is directed to the working area. This method is the simplest, but also the least economical ； 3) Speed-throttling method. This method involves altering the performance curve of the fan by increasing its rotational speed and combining it with inlet throttling measures, so that the operating point of the fan enters the stable operating region to avoid surge.