Theoretically, the centrifugal "Blower Fan" pressure - flow rate characteristic curve is a straight line, but the loss due to friction and other internal fan, the actual pressure and flow rate with the flow rate characteristic curve increases gradually falling, corresponding centrifugal fan power - flow curve with the flow rate increases and rising. When the "Blower Fan" is running at a constant speed when the conditions point along the pressure fan - flow characteristic curve shifts. The operating point of the fan is running, depends not only on their own performance, but also on the characteristics of the system, the resistance increases when the pipe network, pipeline performance curve will steepen. Fundamentals "Blower Fan" is adjusted by changing the external pipe network characteristic curve or the characteristic curve of the fan itself, to obtain the desired operating conditions.