"Axial Fan" parallel operation when the operating point is A, the corresponding point of each fan are working at A1, the stable operation of the fan. If the fan is running in parallel ∞ unstable region, pipe and fan performance curve performance curve has two parallel intersection point B and point C. When running at point B, corresponding to each fan are working at B1 point, the fan remains stable operation. As a result of various factors can not be maintained at the point B is running, move to the next condition point C point, then the corresponding operating point of each fan in point C1 and C2 points respectively. This large flow of wind turbines in the C1 point stabilization work area, and a small flow of fan working in the C2 point unstable region due to a wind turbine works in the unstable region, and therefore the point C parallel condition is only temporary equilibrium state, may at any time be destroyed. This instability parallel conditions, not only have a greater flow rate deviates from a wind turbine or even a small flow back; unstable conditions in parallel with the model fan, but also lead to mutual objective switching the fan operating point, that is, two fans the size of the flow tautomers. Repeating the above process, the fan does not work in parallel operation, which is to analyze the fan "wind rush" phenomenon mechanism.