Expert: Paul Soderman - 4/11/2011

Question
Dear Mr. Soderman,

I have a fan/blower that I am going to use as fume extractor; therefore I am going to direct the intake opening towards my welding area and use the blower opening to the outside. The intake opening is 10 inches in diameter; if I reduce that to 5 inch diameter will I increase the suction power?

Thank you

Answer
Alfonso
By suction power I assume you mean the volume flow rate.  That is what you want to maximize.  But reducing the intake diameter will increase the system flow resistance and reduce the volume flow rate. So, it is important to keep the intake as clean and open as possible to allow the fan to move air as fast as possible.  To do that you want to avoid elbows and sharp corners and restrictions ahead of the intake.
Paul