DIY Vortex Microstrainer

(See bottom of page for link to VERSION 2! Some important changes were made.)

This is my DIY version of Aquatic Eco-System's "Vortex Microstrainer, by Sweetwater." It's an inovative bit of work, a re-design of the basic rotating microscreen drum filter, as used in commercial aquaculture. Their variation has the drum floating vertically and spinning in the vortex, with the spray bar that cleans the screen, stationary. If you aren't the DIY type, by all means, buy one of these units from AES! It should prove out in the long run to be an excellent prefilter that will let your biofilter concentrate on it's *real* job, instead of wasting valuable surface area trying to be a mechanical filter too, with heterotrophic bacteria displacing ammonia-munching bugs. But if you are a DIY-type, then read on.

Due to working on a small scale, I had to re-do some things. My version is plumbed something like the one they had at the show. To see the AES VMS filter pics that I took at AKAPS 2002 in Orlando, click HERE, that page will open in a new window. The water outlet of the drum is actually a stand pipe, mounted in the bottom drain of my "mini-vortex." There simply wasn't room to plumb it in as per their design, shown below. If you click on that picture, a new window will open and take you to the AES web site.



This created a problem that was resolved by my filter plumbing, at least, it gives me one method of dumping the vortex.

I shut down the pump, valve off the bottom drain and skimmer feeds, and remove the stand pipe that serves as the water outlet of the drum. From the pump, the water goes through a 3-way valve. This was done to have a "medical by-pass," for pond treatments that must be routed around the biofilter. The by-pass return is a PVC pipe going horizontal over the edge of the pond, a male thread adaptor, to a 90 sweep that threads onto it. This means I can rotate the sweep towards the side of the pond and insert a length of pipe to take the water away from the pond.

The other method is to do the same shut-down procedure and simply drop a sump pump in the vortex. This is do-able, as the vortex is flat bottomed, made from a 55 gal. plastic barrel. I use sump pumps to clean out other ponds that have settlement tanks, because of my typical Florida "flat land" topography.

The other changes were things like going to a dual spray bar. The AES rep at the AFKAPS exhibit said they might go with that, also. I thought it would provide a better balance of forces. Besides, I wanted more cleaning power, as I went with a 105 micron screen, instead of their 250 or 500 micron version. If the increased flow can't do the job as the system matures, I can replace it with a larger screen size. In fact, I am about to change the screen to a 180-micron size, as a poorly modified PVC fitting in the vortex *sliced* the drum. A temporary patch was successfully made with a two-part adhesive, JB Weld.

Also, I did remove the vertical parts from the bucket that you see in these pics. These thin strips tended to bow, interfering with the spray nozzles, and thus, the rotation of the drum. I did leave the one that was used to seam the screen. In future versions, even that one will be eliminated. They are simply not needed. The flotation collar was way too thick and made the drum ride too high in the water. I cut that down to about half of what is shown.

The hardest part was making the stand pipe/water outlet for the drum. The slots that were cut away to allow water in must be properly placed. You have to allow for some variation in water depth, with the drum moving up and down with the water level. At the lowest water level, the drum will slide down the stand pipe. The top of the outlet pipe can't touch the top of the "axle" pipe, or the drum will hang up and not spin. This axle is fixed to the bottom of the drum and the stand pipe comes up inside it. Both of these pipes have a cap on the top end, to prevent a vortex action from sending air down to the pump.

At the maximum high water level in the vortex, the drum floats up the stand pipe. The lowest part of the cut-outs on the stand pipe needs to be high enough that they are still inside the drum, or you will be pumping dirty water from the vortex, instead of clean water from inside the drum.

You can determine just how to cut that stand pipe, or outlet if using AES's plumbing set-up, by making a scale drawing of the filter. I did it by trial and error. The important thing to remember is that the drum will rise and fall with water level inside the vortex. The part of the outlet pipe that is cut away to allow water in, *must* remain within the body of the screen drum. And the top of the outlet pipe must not touch the cap on the "axel" pipe that is fixed inside the drum, as the drum moves down to match a falling water level, as that will stop drum rotation.

Since everything so far has be constructed to allow modifications to be easily done, I did find that the drum tended to wobble in the vortex, causing the spray arms to come into contact with the screen from time to time. To correct this, I made a stabilizer out of some music wire. It is driven into a hole in the board that supports the spray arms over the vortex, and extends downwards with some bends that let it go past the spray arms and down through the cap on the axle pipe, and through the cap on the outlet pipe. To give it a smooth bearing surface where it passes through the axle pipe cap, I used a cut-off piece from an old, nylon hose barb.

Anyway, that's the basics of it. If you have any questions, let me know. The pond this system was installed on was rebuilt just 4 days before the filter drum was made. It is 1,450 gallons, a 40 six to eight inch fish load, with two 55 gallon TT's, each with 3 cubic feet of PVC ribbon. A quantity of media from a cycled TT was place in both filters, for a rapid cycle. The pond has a 2 inch (I KNOW!) bottom drain with an airstone mounted on the antivortex cap. I mounted a no-niche skimmer to help keep the pond clean and to reduce the draw down in the vortex. This didn't work well until I rebuilt the skimmer to use 3 inch plumbing, on Spike Cover's advice. This works very well.

One important thing I've noticed, if for any reason the drum stops rotating and the screen clogs up, the filter body will collapse somewhat and enough water will be able to flow out through the outlet pipe to keep the pump from becoming "water starved," allowing the filter system to continue it's function. This does dump a good deal of whatever was trapped in the vortex back into the pond, but this is far better than a burned-out pump and no water circulation. Sort of a "Fail-Soft" mode. (Motorola trademark term.)

About that screen size, the microscreen *will* develop a biofilm that will reduce the actual size of the holes in the screen. Over time, a 250 micron screen will close down to a point where is will be effectively screening down to 50 micron particles. Evolution Aqua's Answer prefilter occasionally needs to have the biofilm removed to keep running right. It looks like the AES VMS prefilter may avoid this for the most part, due to their starting with a much larger pore size, 250 to 500 microns, verses EA's 100 micron. I started with a 105 micron screen, but my spray system does deliver much more water that the AES design. Since I did manage to develop a rip in that screen, I'm replacing it with a 180 stainless steel screen. It is my thinking that the biofilm will reduce the effective screen size down to an acceptable size, while the spray system will keep it open enough to avoid having to remove it for cleaning too often. This *is* an experimental system after all, so it will continue to be "tweaked" from time to time. If any significant changes are made, this page will be updatated.

Enough of this! Here's the pictures of the beast:

Here you see the bottom of the converted bucket, and the hole for the outlet pipe.	This is how I molded the collar with expanding foam.
Top view, with collar, screen and base for the axel pipe.	Almost the working model. This is before I cut the thickness of the collar and replaced the "axle" pipe with a rigid plastic mesh net version.
Both versions of the spray arms, with a detail of the hose barb fittings, used as spray nozzles.	Detail of the slit-type spray arm, and the wire stabilizer that was added to control "drum wobble."

Here it is, in place and running. (Before the addition of the stabilizer wire.)

Go back to the DIY menu. Or, go on to Version 2, some changes have been made.