By Blane Perun
by luis mercado
Many different brands of skimmers are available these days as compare to a few years ago when only a few expensive brands were imported from Germany. Although the market has increased and prices dropped somewhat, not every hobbyists has the money available to buy some of the more advanced models available.
Some hobbyists prefer to build their own as that way they can control certain aspects of the installation such as space used, types of pumps needed and convenience of maintenance. In this short article I will describe how to build an effecient,low cost skimmer for just about any size tank you may have. The dimensions given are typical examples and the aquarists may choose to adapt the measurements for his or her own use.
Venturi skimmer use the Bernouli principle of air injection. A stream of highly pressurerized water is injected through a pipe which is restriced at one end. As it exits the restriction,an opening that is adjacent to the output of the restriction causes a pressure differential to occur. This has the effect of dragging air along with the stream of water producing many tiny bubbles. A venturi injector accomplished the aeration and mixing of water without any supplemental additions of air from an outside source.
this method of protein skimming is extremely effecient and less costly than constantly replacing airstones and also produces a more constant level of skimming without the constant adjustments inherent with air operated skimmers.
The basic construction is simple. A long tube of either acrylic or PVC pipe is used as the main reaction tube. I suggest a minimum of 4 inch diameter pipe for really effective skimming. I also suggest a minimum height of this reaction chamber to be 24 inches tall. Taller tubes can of coarse be used but shorter would reduce effective contact time and are in my opinion not very effective. A 4inch diameter is a good all around choice with 6 inch diameter about as big as I would go for aquariums up to 225 gallons or so.
In this design we will incorporate a second chamber inside the main reaction tube as in the diagram. This should be a two to three inch diameter tube which rises from the bottom of the main reaction tube to within about 2 inches of the top of said tube. This chamber will be the actual air saturation chamber and will also help to keep bubbles from exiting the skimmer into the aquarium or sump.
A 1/2 inch to 1 inch PVC pipe, depending on the Venturi valve used, will enter the top of the reaction tube, and will travel down the internal saturation tube to within about 1 inch off the bottomof the tube. From here the bubbles will travel upwards toward the collection cup and the skimmed water will travel back downward towards the output opening at the bottom of the skimmer. By having the water travel this path, saturation and contact time can be increased tremendously over other designs which just let the water swirl up towards the collection cup from the bottom of the reaction tube.
It is essential that the output opening be large enough to accomodate a rapid flow of water without too much restrictions. We will install a gate valve at this output to regulate the height of the water/air mixture inside the skimmer. I suggest using at least a 1 inch pipe and gate valve combination here.
As for the Venturi valve used, I suggest using the Mazzei Molded venturi valves Depending on the size of the aquarium and the pump you wish to use. there are two sizes commonly available. There is a 1/2 inch version and a 1 inch version of the valve. The 1/2 version will perform very well in almost all typical home aquarium. It has a either a threaded or slip opening which accepts 3/4 inch outside diameter flexible PVC hose. Make sure you use hose clamps at all the connections to insure that the hoses do not pop off due to the high water pressure.
The Venturi valve injects the water/air mixture at the top of the reaction tube and directs it downward into the saturation chamber.The collection cup at the top should be the same diameter as the main reaction tube. the neck leading up to the collection should be about 6-8 inches long with equal halves of the this tube inside and out of the collection tube.
Acrylic can be glued together using a solvent cement such as H-94, weldon-16 or straight Methylene Di-chloride. It is applied with a needle applicator for the thin watery mixture and with a larger hypodermic needle for the thicker cements such as the Weldon brands. Make sure the humidity is low and the temperature around 78-80 degrees where you intend to do the glueing. Please wear gloves and goggles to protect yourself as these glues can bond skin and eyes instantly. Some people are also sensitive to having htese substances touch their skin.
PVC tubing can be glued with the special PVC glues available in most hardware stores. You must first primpe every piece before glueing as this will increase strength and prevent leakage. PVC is extremely easy to glue but once glued it is permanent like acrylic. So make sure the pieces fit properly first before applying the glue.
A drain can be provided so that the collection cup emties into a seperate container by means of a hose and hose fitting. This is not essential but a good idea to have to avoid leaks due to overskimming. The collection cup should have a tight fitting cover with an air hole of about 1/4 inch diameter to allow the skimmer to operate properly.
By using a pressure pump such as a Little Giant or Lifeguard Quiet Pump to extract water from the sump through the venturi valve and exiting the skimmer back into the sump your skimmer should be ready to operate. Please test everything for water tightness. If small leaks occur at the glued joints, Silicone sealant can be applied to make them water proof. Use teflon tape at all threaded connections and you are all set.