Airlifts have been used as pumps in what we refer to as undergravel filters in aquariums for a great number of years. It is only in the recent past that airlifts have been applied to any great degree in aquaculture.

For a functional airlift the individual can make his own at a very low cost with very little maintenance necessary. It is easily constructed and installed. The flow rate can readily be regulated.The key to its success is proper sizing of the airlift (eduction) pipe, the depth of air injection, the air flow rate, and the method of air injection.

No matter what the size (length and diameter) of the airlifts, the greatest volumes of water are attained with the discharge elbow (head piece) 50% submerged in the water column. Water pumps, no matter what type, generally cannot compete in actual water movement when compared to airlifts being operated with an air blower. For an example, a 1 HP regenerative blower can pump 1400 gallons of water per minute with airlifts. This of course is extremely important when you consider destratification (mixing) and aeration of ponds/lakes.

For deep applications (lakes, reservoirs, etc.), the section of the airlift called the foot-piece can be extended downward where it far exceeds the point of air injection, ie. - air is injected at 36"; however, the total length of the airlift is 10 feet or more. Through this technique, high volume air blowers can be used.

AREA has conducted tests as shown in photo in order to develop a series of performance curves to insure optimum design and operating criteria of airlifts ranging from 1" to 8" in diameter. On the left side of the photo you will note a Rotron Regenerative Blower which provides air to both the pressure gauge and airflow meter. The air is then carried over to an airlift which is submerged in Tank #1. Water is supplied to Tank #1 through a pump from a nearby well, which maintains the water level at the top of the tank. The air flow was regulated and a series of tests were conducted with various submergence and lift heights. The water was pumped from Tank #1 to Tank #2 by the airlift and flume and the pumping rate was determined volumetrically over an average pumping time of five minutes.

The technique in determining the oxygen transfer efficiency of the airlift was not conducted under standard conditions. The holding tank was first filled with well-water and then the oxygen was stripped with nitrogen. During continuous pumping of the airlift, oxygen measurements were taken in the holding tank. Note in photo a tube leading down to a receiving retainer. Incoming water measured 0.5 milligrams per liter (ppm) at 25 degrees Centigrade. We realize that oxygen measurements at this point could be somewhat deceptive as opposed to the water flow going directly into the receiving tank. However, existing conditions in this flume would be alike to conditions in a pond, tank, raceway, or stream. We found that approximately 3 ppm (mg/1) of oxygen was added at this point. In later tests, the oxygen levels in the well had increased to approximately 6 ppm. This phenomenon is explained by the fact that oxygen will readily transfer when the water is significantly less the saturation.