"Cooling Fan Manufacturer" is used in parallel operation of two or more fans. Two fans in parallel air flow volume of parallel operation of the fan and the fan alone generated graph, only under conditions of free space for a single fan air volume twice, and when the situation parallel "Cooling Fan Manufacturer" used in high system impedance , the system impedance is higher, the increase in parallel with the fan can lower the amount of wind. Therefore, the application is only recommended for use in the parallel case of low system impedance, namely "Cooling Fan Manufacturer" In the case of the operation is almost entirely free of air. Two series of static pressure generated by the fan, at zero up to twice the amount of wind conditions, in the case of free space, and can not increase the amount of wind. A series fans to pay more, at higher static pressure of the system, increase the amount of wind. Therefore, the operating system for high series impedance of the system can achieve the best results.