The rotational speed n of centrifugal fan can be directly measured by tachometer, and its value is expressed by how many revolutions per minute (rpm / min). Small fan speed is generally higher, and often directly connected with the motor. The speed of the large fan is low, generally connected with the motor by belt drive, and the speed of the fan can be adjusted by changing the diameter of the pulley. The relationship is as follows:
In the form:
n1，n2-- The speed of a fan; the speed of a motor.
d1，d2-- Diameter of pulley of fan and motor.
To change the speed of the fan, simply change the diameter of any pulley in the centrifugal fan or motor.
When the speed of the fan is changed, the characteristic parameters of the fan and the characteristic curve of the fan are also changed, that is, the fan has its corresponding characteristic curve at each speed.
When the rotational speed is changed, the characteristic parameters Q, H, N of the fan can be calculated according to the following formula:
It can be seen that if the speed of centrifugal fan changes from n to n', the change of air volume of fan is proportional to the ratio of speed, the change of wind pressure is proportional to the quadratic power of speed ratio, and the change of power is proportional to the third power of speed ratio.
Therefore, when increasing fan speed, it is necessary to recalculate the required power and pay attention to whether the original motor will be overloaded.
Several performance parameters of ventilator are not fixed, they are all related to each other. When the ventilator works in the pipe network, these parameters are affected by the characteristics of the network, so it is necessary to know not only the performance of the fan, but also the characteristics of the network and the relationship between them, in order to choose a good fan and use a fan well.www.jnblower.com