Journey,
This calculation of yours..."3.5psi x 0.196si = .686psi." is the force of the air in pounds not the pressure in pounds per square inch.
3.5 psi (Pounds/ Square Inch) TIMES 0.196 si (the cross sectional area of the line [Pi X radius^2] in Square Inches). The square inches cancel and you are left with pounds which is a unit of force. The pressure (psi) at any given depth is the same regardless of the line size. In other words...the pressure a pump will see while trying to pump air down to 7 feet deep will be 3.5 psi regardless of the line size (neglecting frictional losses). Pressure drop due to frictional loses are calculated using the size of line, length, and material surface.
At this point, I believe "This is the foundation of your math mistake".
This is the first time I have heard of any pressure loss for the Matala's. Is this something you derived from testing, or otherwise? I am not doubting the 0.144 psi number you state, just curious where it came from. I have heard and tested the Vertex ones to be around 1/2 psi. Knowing a good number for the Matala would be a good addition to pond aeration calcs.
I, too, believe that the diffusers work best around 1 CFM. Vertex's lift charts were developed at 1 CFM and I have read somewhere that the Matala's are rated for 1.5 CFM.
My approach for determining the actual CFM is to calculate the pressure caused by the depth of the deepest water (estimated at 0.5 psi per foot), let the above link calculate the back-pressure caused by the lengths & sizes of lines, throw in 0.5 to 1 psi for plumbing losses and add them together. This results in a theoretical pressure that a gage at the pump would indicate. Then go to the chart and back into the CFM's.
I am have difficulty understating how the Hiblow 120LL only pulls 90 watts under a loaded situation...that's incredible!
