To achieve "220V Cooling Fan" air of purpose, the need for static and dynamic pressure. Full hydrostatic and hydrodynamic pressure is the algebraic sum of the total pressure is the difference between the total pressure of the fan given the increased amount of the total pressure, the fan between exports and imports. In practice, the nominal value of the maximum wind blowing amount is not obtained by the actual heat sink fan, air volume, does not mean that ventilation ability. Due to air flow, air flow in its path will encounter obstruct fan heat protracted sheet or element, the impedance will limit the free flow of air. That "220V Cooling Fan" when the wind increases, air pressure decreases. Therefore, there must be an intersection of optimal operating working point, namely wind cooling fan performance curve and drag the curve. In the operating point, the slope of the fan characteristic curve is minimized, and change the system characteristics curve was the lowest. Note that "220V Cooling Fan" static efficiency at this time (the amount of wind power ÷ × pressure) is the best. Of course, sometimes in order to reduce the system impedance, and even the selection of smaller size fan, you can also obtain the same amount of wind.