The characteristic of the cross flow blower is that the fluid flows through the fan impeller twice, the fluid flows in radially first, and then flows out radially, and the inlet and exhaust directions are in the same plane. The exhaust gas is evenly distributed along the width of the fan. Due to its simple structure, small size and high dynamic pressure coefficient, cross flow blowers can reach long distances and are widely used in laser instruments, air conditioners, air curtain equipment, dryers, hair dryers, household appliances and grain combine harvesters.

　　If the area of the vent is small, the resistance of the resistance layer is large, the flow in the pipeline is small, the working requirements of the cross flow blower are low, the influence of the eccentric eddy current is small, and the flow is not obvious. However, when the rotating speed is high and the area of the vent is large, the eccentric eddy current control force is enhanced, the gas in the cross flow blower cannot be discharged or inhaled normally, the test system is abnormal, and the cross flow blower has a surge phenomenon and a surge period. Specifically:

　　(1) Noise increases.

　　When the cross flow blower is working normally, the noise is relatively small. However, when the surge phenomenon occurs, there will be a dull humming sound inside the cross flow blower, and a sharp roaring sound will be emitted from time to time, and the sound is relatively loud;

　　(2) Vibration intensifies.

　　When the cross flow blower is surging, the drive belt of the power trolley vibrates obviously, and the whole test device vibrates obviously;

　　(3) Difficulty in reading.

　　When the cross flow blower is surging, the values displayed by the micromanometer and the tachometer change rapidly, and the magnitude and magnitude of the change are large, which is a periodic change.