Esshup, just a quick question. I have been reading about diffusers and in fact just placed a double Matala 9" at about 9' a week ago as an initial experiment in evaluating if I want to go the full route of aeration of my entire pond. So I have been reading up on pump performance curves at various depths, line loss and size, etc. etc. But all my learning up until I actually put the diffuser in the pond and hooked it to an inexpensive compressor has been book learning where you no doubt have lots of practical experience (my temp setup seems to be working quite well and creating lots of water flow).

From my reading, it seems each foot of fresh water adds .43 pounds pressure. In other words an atmosphere of fresh water is about 34'. The Matala specks on my diffuser says it only adds about 6" water depth. In other words the pressure it takes to move the membrane is equivalent to .43/2 or .22 or about a quarter pound of air pressure. The line losses are kind of fuzzy to me. I know by hydraulics understanding that in hydraulic hoses hose size is very important because friction losses get high as velocity of fluid increases and the smaller the hose, the faster the velocity has to be to move a given volume of fluid (in fluid it takes four times the pressure to double the flow volume for a given diameter orifice). I am completely unfamiliar with friction losses in air but I know they exist. Don't know if they would be similar to fluid of not.

For those considering some of these issues I find illustrations helpful. Imagine putting a soda straw a foot long in your mouth and trying to breathe through it. You have to suck and blow much harder (takes more pressure for the single straw than the double) to breathe through a single straw than if you had two straws in your mouth. It would be easier yet with a foot long 5/8 garden hose and no problem at all breathing through a foot long piece of 2" PVC pipe. This is an illustration that I use in my own mind to help understand the importance of line size. If a person is at rest, breathing through a single soda straw is doable (low cfm requirements). If working hard it would take a 2" pipe to breath through to not restrict your breathing (high cfm requirements). This is all pretty easy to see.

Now the trick is transferring this understanding to using the correct line size for the pressure and flow in a aeration system. LOL Generally it seems the flow rates are pretty low in aeration systems, so is line size not too important? Does length of line come into play a lot?

I lied. It was not a simple or quick question question. Ok, finally to the main question. You use .5 for your pressure rather than .43. I am assuming that is just a ballpark figure that is shorthand for determining what the additive effects of the depth, line resistance and cracking pressure requirement of the diffuser? If this correct?
Sorry for the longwindedness.

snrub

John

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