"Waterproof Cooling Fan" speed is the number of revolutions per minute of the fan blades, the unit is rpm. Fan speed is determined by the motor inside the coil turns, voltage, number of fan blades, inclination, height, diameter and bearing systems. Speed and "Waterproof Cooling Fan" quality is not necessarily linked. Fan speed can be measured by the internal speed signal, can also be measured by an external, because as the ambient temperature changes, is sometimes necessary to meet the needs of different speed fan. Some manufacturers specially designed adjustable "Waterproof Cooling Fan" speed radiator, manual and automatic modes. Manual is designed to allow users to use a low speed in the winter low-noise, high speed to get good cooling effect during the summer.