Pond Boss Forums AERATION Systems questions CFM VS PSI

Look at the flow chart that has "Free Air Flow (CFM)" and Pressure (psig)". It's the top right grid with all the dots in it.

Our example system has 7 psi of back pressure. Find 7 psi on the graph and go straight up from there until you hit the solid line (this line is for 60hz applications which is the US standard), now shoot straight to the left and you hit the CFM line about at the 4 mark. This means your pump will put out about 4 cfm with a back pressure of 7 psi. That's an appropriate flow for a single vertex diffuser or even a double or triple. (edit: 4 CFM is likely too much for your average diffuser - 1 CFM per diffuser is a good rule of thumb)

You really need this chart to know exactly what's going on. A pump can say it's rated to 5 psi, but does that mean that it will pump air up to 5 psi back pressure (10 foot pond depth) AND then no more air comes out. OR, does it mean that an ample amount of air will still be coming out at 10 for depth...they (the advertisers) don't tell you that, but the chart does. When a pump is advertised at 5 CFM...that usually means that it will pump 5 CFM without any back pressure.