static pressure and airflow at reduced fan speeds

msparks

This is probably a stupid question but I've been going around in circles for a while now and have gotten myself completely confused.

I have a fan and a pump, with performance charts (static pressure vs. air flow) for both. I need to try and determine flow rates for each device when run at reduced speeds.

The fan/pump will be pulling a gas flow through a small tube, and exhausting to atmosphere. I know that's not the right way to use a fan, but that's what I'm stuck with right now. I can measure the pressure at the fan/pump inlet while running at different voltages.

Searching around the internet, I found that air flow is linearly proportional to fan speed and static pressure is proportional to fan speed squared.

So I'm guessing that if I'm at half the fan speed I should be at a quarter (.5²) of the static pressure. I can measure the pressure, multiply by 4 and look it up on the chart. Then take the corresponding air flow and knock it in half to get the actual flow rate.

That's a complete guess. If anyone can steer me in the right direction, I would appreciate it because I'm really stuck here. Thanks for your help.

Michael