Relationship between static pressure and CFM

[dmehling]

I am wanting to create a moderate amount of suction with a blower fan and I am trying to figure out the relationship between static pressure and airflow measured in CFM. Does higher CFM necessarily give you greater static pressure? I'm thinking I need between 150 to 200 CFM to get around 1 inch of static pressure, but that is a wild guess. When I search online for such a fan I find either a computer cooling fan which is not enough power or I get an industrial type blower fan that is way too powerful. I can't seem to find something in between.

 

[russ_watters]

Static pressure is pressure without motion (that's what the word "static" means). So there is no positive relationship between fan static pressure and flow rate, with two exceptions:

1. For a specific fan, each possible static pressure corresponds to a specific airflow. Ie, if you close a valve and increase the backpressure the fan has to overcome, the new cfm can be read from a fan curve by matching the new pressure to the curve.

2. In a situation where all of the static pressure is turned into velocity pressure - such as in a pressurized tank with an open valve, you can use Bernoulli's equation equating the two to find velocity from static pressure.

Without knowing the application, it is tough to help, but you can go online and find fan curves and see if they'll work for you. You'll notice on most that they show a static pressure for airflows all the way down to zero. Here's a catalog from a manufacturer I use a lot. Curves start on PDF page 20: http://www.lorencook.com/PDFs/Catalogs/AC.pdf