An Off-the-Shelf Small Volume Venturi Aerator

Another entry that’s not so very profound. But I thought it might save someone else from putting effort into a similar attempt.

I changed over all my DWC tanks from air stones to venturi aerators to reduce noise in the greenhouse. But as I am using them, they are somewhat large for a 3.5-gallon or 5-gallon bucket, the common sort that is about twelve inches in diameter.

My goal was to see if I could make up a venturi aerator that would be a better fit in a bucket.

My current venturi consists of my usual pump, a Vivosun 800GPH, 24 watt pump, which I now find is no longer available on Amazon. The venturi section is a $6.20 1/2” plastic venturi from Amazon. It has been a good combination, because the venturi has a ½” NPT male thread that fits the pump’s NPT female discharge. The combination has been effective and has performed well in ten-gallon totes and 20-gallon barrels.

I first wanted to see just how small a pump was capable of producing a satisfactory stream of small air bubbles. I obtained an 80 GPH Aquaneat pump for $5.79 from Amazon. One-tenth the rate of the Vivosun, but the Vivosun was $23. And the Aquaneat was indeed physically much smaller and would be a substantial gain in space, if it worked.

 

I tried it with my standard venturi. But it simply did not have the power to produce any appreciable amount of air injection, as you can see here.

 

I then made up a mini-venturi for it by inserting a small tubing with a beveled cut end into a larger ½” tubing. I tried it as it was and with a smaller tubing telescoped inside the ½” tube before the air tap to increase velocity. Results were unsatisfactory. I tried that set-up again, but with a small barb irrigation tubing connector with a modified beveled end. It was similarly poor. The makeshift venturi produced some bubbles, but I believe it was insufficient to reliably aerate a 5-gallon vessel.

This wasn’t to surprising. The pump was weak, and while I believe a small pumps can produce some marginal aeration, it will require very careful design and construction can considerable cut and try to get it right.DIY venturis for pumps like my original are fairly easy to make without too much fiddling, but at $6 for an off the shelf venturi ready to thread into a pump discharge, I did not deem DIY worthwhile. And the off the shelf venturi has a spring loaded air valve protecting the air line from being pumped into, a necessity, should the venturi discharge become clogged, which would pump the whnole volume of nutrient out of the air line and possibly out of the reservoir. 

I then turned to a pump that, at 480 GPH, was less powerful than the 800 GPH Vivosun, but was somewhat physically smaller and several dollars cheaper. It is also a Vivosun, costing $18 on Amazon. Like the larger Vivosun, it has a ½” NPT female discharge.

 

A quick test with the venturi showed that it was as capable as its larger cousin of aerating the same volumes. But I had gained very little toward my goal to save space.

Now, I examined the shape of the venturi I was using. It is very much conventional, with a short run of decreasing diameter before the air tap, and a section expanding again after the tap. Normally the discharge end is intended to be connected to an irrigation hose that will receive the water and the fertilizer the venturi it injecting. I needed no such connection and reasoned that if all the expanding section was doing was expand, it made no difference how it expanded. So I cut away the last 2.5 inches of the venturi.

 

I tested it and could detect no reduction in aeration from cutting it off short.

 

But between the smaller pump and removing the excess venturi body, it brought the length of the combination down to just under six inches. It is shown above in the bottom of a clear vessel similar to the diameter of 3.5-gallon and 5-gallon common buckets. There is ample space to discharge the bubble stream.

The total cost, then, is about $24.20. There are no additional adapters required.

Previously, I was aerating six DWC containers with a 32 watt air pump for $45 and six air stones for about $10, or, with stop valves and tubing, about $60 for six tanks. So this is costing me a bit more than twice as much per reservoir, but the cost to my nerves of working around six very noisy air pumps is, for me, worth the difference as one-time costs. The venturis are virtually silent. And with the air pumps, I had to be vigilant to keep all the meandering air tubes from being pulled out of the manifolds.

Certainly not a complete exploration of the issues, but, if nothing else, it provides a way to install venturi aeration in a 3.5 o5 5-gallon bucket or similar without crowding. The original pump or similar would also fit comfortably with the cut down venturi.And if one wanted to fit it into an even smaller space, two 90-degree elbows could fold the venturi back alongside the pump. 

 FOLLOW-UP.: I tried another pump, smaller and rated less than the green 800GPH, but although it rated higher than the black one, it drew only a little air.