Fan Calculations

C.M.

I missed place my calc. to figure out more cfm on pulley size change.I thank you in advance for the help.

Eugene Silberstein 3

RPM and CFM

You will need the specifics on the blower you are using to determine the amount of air volume (in cfm) that the blower moves at a particular speed.

In the meantime, you can get a good starting point by using the following:



Drive Speed (Motor RPM) X Drive Pulley (Diameter) = Driven Speed (Blower RPM) X Driven Pulley ( Blower Pulley Diameter) 

For example, you can determine the speed of the blower if you know the speed of the motor and the diameter of the motor (drive) pulley and the diameter of the blower (driven) pulley.



Example: Let's say we have a motor that is turning at 1000 rpm with a 3 inch pulley connected to it and a blower that has a 4 inch puley attached to it.

The speed of the blower can be determined by:

Blower Speed = (motor RPM x drive pulley diameter) / driven pulley diameter

Blower Speed = (1,000 rpm x 3) / 4

Blower speed = 750 RPM

Now, if the blower pulley is changed to a 5 inch pulley, we get

Blower speed = (1,000 rpm x 3) / 5

Blower speed = 600 RPM

Remember: If you increase the diameter of the drive pulley  or decrease the diameter of the driven pulley, the blower will turn faster.If you decrease the diameter of the drive pulley  or increase the diameter of the driven pulley, the blower will turn slower. 

I hope this helps!