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

 

[ravenprp]

The relationship between static pressure and CFM can be a bit complex and can depend on several factors such as the design and size of the fan, the resistance of the system, and the fan speed. In general, as static pressure increases, CFM decreases and vice versa.

In your case, it seems like you are trying to find a balance between having enough airflow (CFM) to create a moderate amount of suction and enough static pressure to overcome any resistance in the system. It is important to note that higher CFM does not necessarily give you greater static pressure. In fact, if you have a fan with a high CFM but low static pressure, it may not be able to generate enough suction to overcome the resistance in your system.

To determine the specific CFM and static pressure needed for your project, it would be best to consult with a professional in the field or conduct some tests with different fan options. As you mentioned, a wild guess may not be accurate and could result in either a fan that is not powerful enough or one that is too powerful.

When searching for a fan, it is important to consider the specific requirements of your project and look for a fan that can meet those requirements. This may require some research and possibly consulting with a supplier or manufacturer to find a fan that falls within the desired range of CFM and static pressure.

In summary, the relationship between static pressure and CFM is not a straightforward one and can vary depending on different factors. It is important to carefully consider the requirements of your project and find a fan that can meet those specific needs in terms of both CFM and static pressure.