Venturi aeration design

[Chelsea Brannan]

Hello Aquaponic Friends,

I was looking into adding a Venturi unit on my incoming water pipe that returns water from my DWC Trough to my Tote with the fish. I came across this great video from a trusted source that uses them in their fish hatcheries.

Does anyone have any experiences using these for added air? I am trying to avoid adding another electrical expense by running a large air pump. Any thoughts?

Here's the video:

https://www.youtube.com/watch?v=IZyrL5Ojqpo

[George]

If your power goes out for a week then you'll no longer wonder why people worry about backup power.  It hasn't happened here lately but it could, anytime during hurricane season.  

What about people who go out of town for a couple of days and the main pump fails - backup aeration might save their fish - stay gone too long with nobody to change out the pump and the biofilters will die.  That would be a big loss.

You buy insurance before you need it and I think of backup the same way.  Have it or don't have it but, if you can afford the extra cost, it may save some of your investment.  

Too, there is nothing wrong, in my view, with increasing your stocking along with increasing your aeration.  If your biofilter can handle it, that's an option.  My system is understocked but I plan to increase stocking by next spring.  Summer crops need more nutrients.

Regarding aeration, the species of fish you have might influence your decision.  Trout are at one extreme - bad idea to have trout with no backup aeration.  However, if you have fish that will readily breathe at the surface, that is more forgiving.  

[Chelsea Brannan]

ah yes, this is a good example, though I am glad you were able to fix it before it became a fish loss problem. I am trying to set up a system that uses as little power as possible, with minimal equipment needs. So I am experimenting  with water flow to create a good aeration mix. I do not want to add air stones or air pumps...if it can be helped.

Jim Troyer said:

That should work out well Chelsea

I'll give you a perfect example why you need the extra wiggle room.

This morning, (7/3/2013) I went out to feed the fish (40 various sized 4"-14") in my 700 gallon jacuzzi system.  It is hidden around the corner and the fish are very shy compared to the in-ground pond by the patio. I thought there were a couple of fish sucking air when I first got there but they turned and hid in the depths.  So I sat down in the chair to observe for a few minutes.  After they had all eaten a few fish would surface to suck air for a few seconds.   I also noticed the water was darker than normal as I can usually see the fish in the bottom, not today however.  The pump was not running but that is normal on a timed system so I didn't think anything about it.

The day before I had noticed one or two of the little guys were sipping the top but none of the bigger fish, so I chalked it up to being 118 degrees and reduced DO capability of the water.  On the way back inside I added an extra 15 minutes to each cycle so the pump would run 1/2 hour of every 2 hr cycle.

So this morning with more fish having trouble, I decided to turn on the pump manually and run it for a little while extra. I flipped the switch and walked around to where the system is and the water wasn't pouring out of the GB feed pipe.  I checked the pump and it was too hot to touch.  I unplugged the pump and after it cooled a few minutes, I took it out and went to the work bench to remove the pump cover so I could check the impeller.  There was a single piece of hydroton stuck between the impeller and the housing!  I fixed the pump, reinstalled it and everything works fine again.

3 days prior, I had a guy come over to buy fish and he brought along a 5 gal bucket of hydroton to soak in my system to get a quicker start cycling his system.  Not being a hydroton user I was unaware the clay balls would float.  I put his bucket in one of three interconnected 32 gallon trash cans I use for sump tanks and some hydroton floated but I figured if it floats there would be no problem.  Well it turns out, hydroton sinks after a while... A few clay balls ended up going through the pump and into the grow bed and several others had made it through 3 sump tanks but only one got stuck in the pump before the cycle of chaos began.

I don't use air stones or anything else in either my systems; I rely on the splash and circular water flows for DO and now I know my system has enough DO buffer so the pump can be off for 2 or 3 days without killing my fish or the plants. 

I'm very pleased that I have built into my system a large enough margin of safety that I could be so absent minded to not notice pump failure immediately and not kill everything in the process in a maximum hot spell of 118 degrees in the desert sun.   

I'm still wondering why everybody worries about additional aeration, air stones, back up power supplies, solar and what not in case the power goes out for a few hours...  Over crowding is a real issue, not DO, IMHO

[Chelsea Brannan]

We have a back up pump, but (i know i'll probably curse myself now for saying this) the power never falters more than  dimming or flickering during a severe storm. And that is rare at best. However, as a source for back up power, we have a deep cycle marine battery that is rechargeable (from another plug in source or solar panel) and it connects to an invertor that the pump can then be plugged into to. I had that set up as a left over from when I used to do temporary airbrush tattoos at parties.  that same power system is great for any small mobile power need. I've used it to power catering gear, camping gear, outdoor signage and lights, etc.

George said:

If your power goes out for a week then you'll no longer wonder why people worry about backup power.  It hasn't happened here lately but it could, anytime during hurricane season.  

What about people who go out of town for a couple of days and the main pump fails - backup aeration might save their fish - stay gone too long with nobody to change out the pump and the biofilters will die.  That would be a big loss.

You buy insurance before you need it and I think of backup the same way.  Have it or don't have it but, if you can afford the extra cost, it may save some of your investment.  

Too, there is nothing wrong, in my view, with increasing your stocking along with increasing your aeration.  If your biofilter can handle it, that's an option.  My system is understocked but I plan to increase stocking by next spring.  Summer crops need more nutrients.

Regarding aeration, the species of fish you have might influence your decision.  Trout are at one extreme - bad idea to have trout with no backup aeration.  However, if you have fish that will readily breathe at the surface, that is more forgiving.  

[Chelsea Brannan]

I really wish i had a DO meter to measure my current DO and then again after I add the Venturi.....Wish they weren't so pricey, ouch!

[Averan]

This will only work with water coming out of the pump. There isn't enough pressure in a line that is draining by gravity or simply overflowing to the next container.

[Chelsea Brannan]

The venturi is coming off the pump return. It would replace the spray bar that is in the picture i posted earlier.

Averan said:

This will only work with water coming out of the pump. There isn't enough pressure in a line that is draining by gravity or simply overflowing to the next container.

[Jim Troyer]

Hey Chelsea

Yes, venturi devices are expensive, mainly because they are difficult to manufacture in high production and the relativly low demand for them.  You can create your own venturi quite easily as they are actually very simple in principle.

If you click on the picture it won't be as blurry (sorry)

A venturi works just like a wing.  There is an area of high pressure where the fluid is compressed and an area of low pressure is created just behind the area of high pressure where the tube opens back up.  In this example we will be using the difference in the inside diameter of the fitting and pipe to our advantage.  Where the pipe opens up into the larger diameter of the fitting there will be an area of low pressure that will create a suction you can use to draw air into the water stream using the Bernoulli effect. This the same principle carburetors used to meter gasoline into your car engine.

I would place this apparatus at or near the exit of the pump outlet pipe into the fish tank.  You could use this inline before the spray bar you showed earlier in this discussion, but bear in mind enlarging the diameter of the pipe would be an advantage after any aeration device.

You will need a length of pipe; a PVC union the same size or bushing up to the next larger size fitting (better); a 3/16" or 1/4" tube like a fish bubbler uses; a drill bit about the same size as the outside of the air tube; sand paper; and some plumbers putty or JB weld. 

First off build a ridge of putty inside the PVC pipe to create the restriction in the pipe similar to the drawing above.  The larger you make the ridge, the greater the Bernoulli effect.  e.g.: You will want to build up about a 1/4" ridge in a 3/4" PVC pipe.  The bump should be made like a ramp that tapers at about a 30 degree angle and has a flat area about as long as the ramp.  You will want to roughen up the PVC with the sandpaper where ever you use the putty to give it "tooth" into the PVC.  After the "Bernoulli ring" has hardened, sand it lightly to reduce any rough spots.  Temporally fit the PVC union over the pipe to make sure it reaches the stop inside the union, if the pipe does not slip all the way in, sand it lightly until it does freely. 

In the PVC union fitting, drill your hole matching the air tube size just at the stop in the fitting so the upstream edge of the air tube (ideally) matches the downstream edge of the PVC pipe to get the greatest advantage. Insert the air tube so it protrudes slightly (1/16") into the inside diameter of the fitting.  Test fit everything again making sure it fits together well and the pipe contacts the air tube when fully inserted.  The pipe should ideally come to rest against the stop and air tube at the same time.  (You can fill a small gap with putty later if you missed when drilling the hole.) Trim the air tube with a 15-30 degree angle and use the high point on the upstream side for additional draft.  Glue the air tube into the fitting so it protrudes slightly (1/16") into the water stream with a large bump of plumbers putty on the outside of the fitting, making sure you seal the edges of the hole well and using enough putty so it will be solid enough to stay put for a long time without cracking.  Set aside to harden.  

Reassemble the PVC parts with PVC glue making sure there is proper alignment with the end of the pipe and the air tube.  After the glue has hardened, smear a small amount of putty at the margin between the PVC pipe and PVC fitting to make a smooth transition to reduce drag.  Be sure not too plug the air hole.  You can trim the air tube flush with the smallest inside diameter and lightly sand the margin to reduce a rough finish after the putty hardens.

After assembly into the system, you can test your handy work by placing your finger over the opening in the air supply hose you should be able to visibly see the difference in aeration when the air supply is cut off to prove your project was a success.

all the best,

Jim