Here's a link to a good table that shows the pressure loss in a length of schedule 40 pipe. Since irrigation pipe is smooth plastic on the inside this chart should be good for that too. An example is that for a 3/4 inch pipe if you push 5 cfm through it you will lose 5 inches of H2O pressure. Multiply inches of water by 0.036 to get PSI. So in this case you lose 5 x 0.036 = 0.18 psi per 100 feet of pipe. So if you pumped this air 500 feet you would lose about 1 psi. So you have to add 1 psi to the pressure that your pump will be running at in order to get the CFM you want. This is in addition to the pressure caused by the depth of your aerator which is about 1/2 psi per foot then you need to add the back pressure of your aerator. So if you want to get 5 cfm out of an aerator that is 10 feet down you have to find a pump that will pump 5 cfm at 5 + 1 psi = 6 psi plus back pressure for your aerator. With this same example if you would use 1/2 inch pipe your pump would have to be capable of 5 cfm at 8.5 psi plus aerator back pressure. Bottom line is the pump needs to overcome the loss in the pipe plus the depth of the water plus the back pressure of whatever aerator you use. It would not be unereasonable to find that to pump air 500 feet a 1 inch pipe may let you get by with 1/4 to 1/3 hp pump while a 1/2 inch pipe may require a 1/3 to 1/2 hp pump. Moral of the story is even though you are only pumping air don't skimp on pipe size.

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Gotta get back to fishin!