Well, in our experience it's better just to dump off the usual manyfolds and 8 mm air lines. Switching to bigger size PVC pipe and air lines allows you to get more air delivered by the same air pump. I can't remember right now the exact pipe metrics we are using, maybe tomorrow I can tell exactly. Anyway I'm attaching a picture showing one of the first outlet arrangements I tried (still working) to replace an original manifold, so you can have an idea (not nice appeareance, I must admit
).
Some of the results of Frutos's experiments are clear and straightforward: i.e.,
you get more water flow pumping air whithout using airstones. Other results may be a little missleading, for example one might expect to easily build a gravity filter system that would run just on several airlifts fed by a 40 w air pump and still be able to easily get a magical 40,000 liter/h water flow. It's not so easy, don't forget that Frutos meassured the water flow delivered with almost zero water head (and no filter restriction).
However, it is feasible to run a pond and its filter system by airlifts moving an impressive amount of water with a fairly small wattage, if designed and built properly.
It would be too long to explain, maybe Frutos might take some pictures for you soon. Let me say he is currently using just a 100 w Resun airpump rated at a max. 150 liters/min. Yes, the whole pond filtered with a cheap airpump (114 euro in ebay germany)
. Maybe next summer, feding an estimated daily ration of 1 or 1 and 1/4 kg, he might need to add an extra airpump to increase water flow and filtration, but even 200 watts would be a nice figure. Let see.
Remember, he is using
big size air lines. He is also using
big diameter airlifts - 110 mm pipe, and
delivering water just under water surface level. That is the way you get the best airlift performance when everything else is equal, just
avoid lifting the water!
Another extremely important thing:
transfer ports must be huge to allow water entering the filter and then moving between filter sections and back to the pond easily, with as least flow restriction as possible. Frutos figured out a clever way to set up a sort of oscilating gate that will open when the airlifts are running, and close when they are stopped. And they do their job quite well.
Frutos started carrying out test whithout having heard or read a word about airlifts. I was quite skeptical, then I read a post by Alan Grey who used airlifts to drain debris out of the pond. I was very impressed by a video clip he uploaded in youtube, showing his 4 airlifts delivering a lot of water just running on a 40 w airpump.
Then I carried out a literature search and review on airlift design and performance and found several technical and scientific papers on airlift efficiency as well as demonstration of usage in low head recirculating aquaculture systems. I was surprised it is not a new issue, you can judge by this reference of a seminal paper published back in 1987:
N.C. Parker & M.A. Suttle 1987. Design of airlift pumps for water circulation and aeration in aquaculture. Aquacultural Engineering 6, 97-110
Even Ronald Malone (who developed bead filters for aquaculture) has conducted some research on this subject:
J.C. Loyless & R.F. Malone. 1998. Evaluation of air-lift pump capabilities for water delivery, aeration, and degasification for application to recirculating aquaculture systems. Aquacultural Engineering 18, 117-133.
there are some others, I just finally want to suggest that airlifts deserve to be taken into consideration.
