Journeyman always chimes in with good posts (seriously). I do have the best of intentions and can be biased too. But, if my math is off, please correct me...I would hate to lead someone astray. And, the "half dozen comment" was overzealous...my bad.
Some more math...I will spell it out for good scutiny's sake...
Using the above calculator and the following estimates. I get 0.32 psi of added back-pressure for the 50 foot run...
- 3.5 CFM (an estimate of the air flow that I figured would represent the pump's ability from the chart and my experiences with compressed air flow in lines)
- 50 foot of 3/4" line (per journeyman's recommendation, bigger line does mean less back-pressure)
- & 4 psi which closely corresponds to the 3.5 CFM from the chart.
Doing the same for the added 100' lengths of 5/8" line, I get 0.44 psi with the following inputs...
1.75 CFM (half of the overall flow per line)
100 foot of 5/8" line ,
& 4 psi which corresponds to the overall 3.5 CFM from the chart.
That's 3.5 psi for the deepest diffuser depth plus, let's say for argument's sake , zero from the diffuser (which is highly unlikely), plus the combined back-pressures of 0.76 psi..equals 4.26 psi.
That puts the operating point of the pump outside the manufacturer's suggested pressure range . It will pump enough air for 2 Matalas at this pressure, but it won't be as efficient and will likely wear the pump faster.
I tend to error on the safer side with any estimations and those estimations, now, need to be adjusted due to the calculated back-pressures. It's kind of moving target if you know what I mean. But, I believe this exercise yields a close approximation of what will happen given the system parameters. This is shown by the closeness of my original guess of 4 psi and the resulting 4.26 psi. I would, ultimately, want to figure in some losses for valves and fittings which would make the pump even less appropriate. Note: using 1/2" line instead of 5/8" line would take the back-pressure to 5.18...that's off the chart.
If this system was all that I had to work with and was confident that it would turn the pond over...I would be inclined to move the diffusers up 2 feet in the water column to lesson the pressure associated with the depth of the deepest diffuser. This would put the pump in the suggested operating range. The next step would be to estimate the total gallons of pond water, the lift rates of the diffusers to see what kind of turnover cold be expected.
I also have done no calculations regarding pond size and would be concerned that 2 diffusers would not meet Purdue's expectations in the 1.4 acre pond, especially if the system would not be run 24/7. Hence my recommendation for a larger pump...meaning a few more diffusers too.
I would love to learn more than I think I know, so please...if anyone can find error in my thinking...I won't take offence, but rather appreciate the lesson.
