Backyard Aquaponics
A place to discuss aquaponics

dont axial fans have poorer performance when under any head?

Good input, keep it coming!

Currently my idea is to have low stock density to allow for the water loss during flood cycle. I think 4 gallons per fish is recommended, and during flood I will have over 3 gallons per fish, so I think that is acceptable. I do not want to add a sump. I want to keep it very simple.
So far, Im thinking a U shaped race 267 inches(678.18 centimeters) long and 120 inches (304.8 centimeters) wide and 36 inches (91 cm) deep. Perhaps I can use a trolling motor in a pipe at the top of the U to move water around the race. Fish seem to just love swimming against the water current in my tanks when the water is swirled and I think it does them good to get some exercise.

The grow beds are currently planed to be 12 inches(30.48 cm) deep, 12 feet (365.76 cm) wide, and 89 feet(2712 cm) long with stepping stones down the center to walk through the growing area so that I dont have to reach more then 3 feet(91cm) to plant and harvest; as I can reach from the center outwards and the outside edge in. The brow bed will be located up hill from the race and the bottom of the grow bed will be 6 inches to perhaps a foot above the top of the race. Do I need more drop?

yep, if its for water movement at zero head then i think its the superior choice

Also, what are your views on using pond liner instead of concrete? What would the grade need to be in clay soil?

EPDM is a robust liner, but may be costly, but needs a thinner grade for better protection against punctures. also provides better surface area (is rough) for microbes.

page 2 of the SRAC document:

the water is pumped into the race over the rim, but free flows out the back through a screen
so the race is not a closed "boat" that floats "on" the water, but just a containment system, a cage that floats "in" the water, with the water levels inside and out at the same height

Frank

I have no experience with propeller pumps, Steve, as the only ones you can buy are huge industrial ones
But, as they move the water forward rather than throwing it sideways as in a centrifugal pump,
they are considered as positive displacement pumps, especially adapted for high volume at low heads (1-3 m, exactly what we need)
and are considered capable of efficiencies between 60 and 80%

today I visited a trade fair on industrial pumps in search of small propeller pumps, but didn't find any

but I explained the problem of poor energy efficiency on the Grundfos pumps stand (one of the most renown centrifugal pumps manufacturers) and they are going to look at the matter

and on the stand of my main supplier (and personal friend) there were people from the factory (Speck Pumps)
They build a.o. huge propeller pumps
I had a long talk with them and have caught their attention
they are taking the request seriously and take it home to the factory for studying
but of course the development of a totally new range might take a year or two

I have used the data provided on the SRAC document (I hadn't noticed them at first) to make a calculation:
1 hp blower feeds 3 series of 9 airlifts which each together output 450 US Gal/min which totals 1350 US Gal/min at an average head of 1.5 inch, which equals 5073 l/min @ 0.038 m head for an input of 736 W
the energy efficiency of this system is a meager 4.37 %
nothing to write home about ...

Frank

6 inches should be ample to completely drain the growbeds, as the water level in the race will in all cases be lower than the rim

frank

Wow that sounds good. What do the large pumps look like? Do they have two, three,, four or more blades? A single prop?

I think I will fashion one to see how it works.