Backyard Aquaponics
A place to discuss aquaponics

You made this statement Frank....... This is simply not true...

I'm not asking for a debate, just correcting your statement so that others know that there CAN be a place for venturis in aquaponics ...

What has more friction going through a pipe, air, water, water and air?

Water and Air.

There is no question that it slows down flow - that's the whole reason it works. The thing is, a lot of us have some flow to spare and like the idea of achieving the flow we need and some aeration from one device (ie the water pump). Also built into my venturi device is an arm that I can adjust to direct the flow in the direction I want to encourage the whirlpool action in my fish tank.

please bear with me, Joel
and I ask you to please not correct my statements without at least saying why you think my reasoning is erroneous,
I want to learn too.

I don't make these statements out of the blue:
aeration is about exposing water surface to air surface
a Venturi connected to a pump consumes energy at the direct expense of water volume pumped
by definition the volume of air sucked in by the Venturi is less than the volume lost to pumping as no transformation of energy is 100% efficient.

so TMHO a Venturi is not a good aeration method and has a negative balance:
you suck in a little volume of air, but lose more water volume pumped than you gain in air volume aspirated
that extra water volume that is wasted by the Venturi can be exposed to air by simple, inexpensive, passive systems

so TMHO a Venturi for aeration is totally redundant in any AP system: it costs money, it complicates piping, it might need maintenance...
... all to no avail: the result will be worse than before unless the system is badly designed

so, more than energy inefficient, it is also not effective
leaving it out and paying attention to passive aeration methods will TMHO give a better, simpler result

so, TMHO, my statement is very true and motivated
still you may reject it, that choice is and stays yours.

Frank

Still think a Venturi on the return line into the FT would be more cost effective. The water has already been pumped so gravity is moving it. And a simple T on the end of the pipe would have to cheaper than a passive device that allows the water to get as much surface area. My new pump has more water than is needed so running the bleed off through a venturi is also an option on my system.

Frank
I had a look at the gutter system; have you factored in water loss and heat shift in the system?

Why do I think your statement is erroneous Frank?

Because your blanket statement said that there is no place in aquaponics for venturis. This is not a debate about whether you think they are efficient or not, it's not a debate about whether you want to use them. There are many factors you are not taking into account, factors that do NOT have anything to do with efficiency, factors that may be important in other peoples designs like noise for instance, venturis are extremely quiet with no splashing sound..

Simple fact is Frank that I use them in my systems, I love them, I have more pumping capacity than what I need and the venturi performs an extremely useful function for ME. It's simple, requires no maintenance, requires no extra fall, it's so small no one knows it's there, it's quiet, and it adds lots of oxygen.

I probably have a different set of parameters than you in whats important in this instance. If you take away efficiency from your argument above, which as I pointed out is not important to me in this instance. It costs only a few cents, I reduce the pipe diameter, so only need two reduction bushes, then drill a small hole in the smaller pipe (will post a pic later) . A reduction in pipe diameter is hardly complicating piping. There is NO maintenance required..

So therefore every point you raise against the use of venturis is not valid in MY case.. I'm not trying to say you should use them..

Now if you are going to respond please understand this one point, this is all I ask, you continually ignore the point no matter how many times it's made. in this case I DO NOT CARE ABOUT THE EFFICIENCY. With that one point in mind can you still put forward the statement "Venturi's are very interesting for special applications, AP is not one of them"?

Tried out the venturi last night, it works a treat. The great thing about it is you can get the O2 down to the bottom giving it time to be absorbed and the pressure is fantastic. I need an arm like Veggie to hold the thing in position on the bottom.

Lifting water to a higher level to use for 'passive' aeration is not free!

I wonder if anyone has actually done the numbers to compare this head loss with the loss in a venturi... But I really don't give a rats!

Purple frogs don't fart - prove me wrong!!!

A very simple venturi made by reducing the pipe diameter and drilling a small hole.

Firstly, can I suggest to the Mods that this thread be renamed to "Discussions relating to Venturis and other means of aeration"...

I had previously asked Frank to post a thread of his own regarding his designs and theories so that discussion would be contained within a single thread, rather than being repeated in every thread where "venturis" or "aeration" is mentioned.

Now to address some of the points...


It seems clear from the above that Frank believes that the volume of air sucked through a venturi is smaller than the volume of water it displaces by doing so....

And is therefore "inefficient".... presumably, from other arguement, because this results in an overall daily reduction in water flow/turnover....??

While this may in fact be the case.... there appears to be an underlying assumption made by Frank, that sufficient and more "efficient" aeration can be acheived by merely pumping the volume of water that the venturi has replaced....

Either, as sometimes suggested, by sheer flow rate and turnover, or more particularly by "inexpensive, passive systems"....

While I don't have any problem accepting that "passive" systems are capable of achieving aeration....

There appears to be no real comparative data presented to actually prove that the overall cost of pumping xxx volume of water over "passive" devices acheives more "aeration" than pumping the same volume of water through a venturi incorporated into the return line that is being pumped back to the tank anyway....

Or even that such passive devices might achieve greater "aeration" than that which might be acheived by merely allowing the returning water to "splash" back into the sump or tank....

In response to the passage I quoted Frank... I have to say... OK, so that's true and self evident ... the air displaces a certain volume of water....

But .... so what..... the system is constantly recirculating.... constantly being pumped...

If at the end of the day, sufficient aeration has been acheived... in a constantly, or fixed frequency/timed system of pumping.... then it is "effective" to say the least...

And has been acheived, and incorporated, by a singular design... utilising the same volume of water per day that would have been used anyway....

Aeration isn't achieved in "one hit".... if the water volume/turnover per day was so low as to mean that the amount of aeration is only just met, or falls short of that required because of the volume of water it displaces...

Then your system is badly designed, under-rated and potentially flawed anyway...IMO...

I have a FT that is mostly covered (with glass for winter heat gain), so use a venturi to suck in some fresh air as growbed empties into the FT/sump. Aerates well and, since the bottom of the GB is only a few inches above the FT level, I can't imagine a way to reduce power use further unless I am pumping far more water than is needed. Seems good so far.

I have doubts on how much water volume is lost in a venturi.
The moment I put the Venturi onto the outlet it acted like a jet engine. I would suspect that a similar volume of water is ejected and with the added volume of the O2 there is and increase in pressure and both are being pushed through the outlet but at greater speed. There is maybe some loss in water volume but I bet its minimal.
The venturi also has the added benefit of putting the O2 where you want it, at the bottom and the increased pressure from the outlet helps stir the water up.