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As per American Society of Mechanical Engineers (ASME) the specific ratio - the ratio of the discharge pressure over the suction pressure – is used for defining the fans, blowers and compressors (see. Table 5.1). Fan and blower selection depends on the volume flow rate, pressure, type of material handled, space limita-tions, and efficiency.
Fans and blowers provide air for ventilation and industrial process requirements. They are differentiated by the method used to move the air, and by the system pressure they must operate against.
BLOWER AND MOTOR CALCULATIONS By Norm Christopherson This section includes information on the sizing of motor pulleys, changing rpm and cfm of blowers, motor selection for blowers, belt length changes, and using fan laws for troubleshooting.
Rotary PD blowers provide flow ranges from 20 cfm to over 26,000 cfm with maximum compression ratios limited by the technology. Rotary lobe blowers, for example, are limited to a compression ratio of about 2:1. Compression ratio is
remembered that the power required by centrifugal blowers in-creases significantly with decreasing back pressure. This can lead to overloading of the motor. The "ebm-papst FanScout" selection software (see Page 13) presents the important factors, namely maximum efficiency and minimum noise, so you can always make the right choice.
Total efficiency of the fan is the ratio of actual air power to fan shaft power. Neglecting leakage loss and slip in the impeller, fan shaft power is the Euler power to drive the fan.
To adjust a direct drive fan’s speed (also motor speed) or to provide a means of meeting an exact performance requirement, a speed control can be furnished. Speed controls vary the voltage supplied to the fan and slow it down; a principle similar to the way dimmer light switches work.
