I have a 1/2 Hp Duel rocking piston compressor would like input on air line size. I want it to be self weaighted was thinking 3/8 or 1/2 in. and the type of diffuser that will work well.
Thanks

For aerators, I like vertex membrane diffusers best, but a distant second would be 9" membrane diffusers out of Columbia, MO. To suggest an array, we'll need to know what size, depth and shaped pond? Any submerged structure? 5/8" ID self weighted will reduce the friction loss best.

IMHO it depends...line size will depend on how many diffuser lines you want to run. For example, if that pump is rated at 6 cfm and you are running one diffuser location you will need a big line to minimize back pressure on the pump. Now if you are planning on running 4 different diffuser locations off that 6 cfm pump the line size can be smaller as you will only be pushing 1.5 cfm thru each of the 4 lines.

With that said, IMO there is no downside (other than initial cost) of going with larger lines than you actually need. Anything you can do to reduce pump back pressure saves on electricity and is easier on the pump. There is a point however when increasing line size gains you nothing. By that I mean, for example, if the pressure drop across 100 feet of 3/8 tubing is near zero at your cfm flow rate, increasing line size buys you nothing.

Bill D This compressor is rated 5.2 cfm

Hey OZ,

I am not an aeration expert, just an old design engineer. IMHO since you have the compressor already, I would put together a plan on how many locations you want to place diffusers and then size things accordingly. Some ponds get by with one, I'm sure, while others with complex shore lines and lots of depth changes may require several locations. Since you already have the compressor, you may find one of the major manufacturers reluctant to offer design advice. If it was me, I would post as much info as you can on your pond (including a satelite image with depths indicated if possible), and maybe one of the forum experts will offer up an opinion or two. IMO, if in doubt, use bigger lines than you think you need.

Good luck!

Bill D.

OK, that's the CFM rating. That is only one part of the equation. Since every foot of water depth that the diffuser is placed needs 1/2 psi of pressure to overcome the water column pressure, at what psi is that 5.2 cfm rating at?

For instance, if your pond is 10' deep, your compressor should pump 1 cfm at 6 psi to get a good bubble plume from the diffuser disc. Yes, the disc says 1/2 cfm minimum to work, but that's just that - a minimum.

+1 My understanding, (and I am not an aeration pro!), my compressor is rated at 4.5 cfm @ 35 psig. To me, that means theoretically at 35 psig back pressure my compressor should deliver 4.5 cfm with a fixed displacement rocking piston pump. The flow will be higher at lower pressures as the leakage thru the pump will decrease with lower back pressure (pump efficiency will be higher at lower pressures). Theoretically, since my relief valve is set at 35 psig, I would drop from 4.5 cfm @ 35 psig back pressure to less than 4.5 cfm at 36 psig when the relief valve starts to pop. The actual airflow to the diffusers at 36 psig will be 4.5 cfm minus whatever is going out the relief valve. Just my thoughts!

pond and diffuser pictures

The first picture is the West end of my pond witch is 15 feet deep it goes east about 200 feet and the depth goes to ten feet then at the East end is five feet. The second picture is the East end. Third pic on the Dam Fourth pic North bank fifth pit. East end Picture six is the diffuser we made Sunday these are four 9inch disks got the idea off Pond Boss I had planed on placing this one diffuser closer to the west end rather then the center Well will I be able to use 3/8 air line when the pond is full will add another. Thanks what do you think I'm open