Tech Talk 33
Airlifts are most efficient when moving water from one place to another within the water column. They become less efficient as the water is lifted higher above the surface. For our purpose here, we will split them into two categories: water-moving airlifts, and water-lifting airlifts, up to 4" in diameter.
Moving Water With Airlifts
Water is heavy when it is in the air, but weighs no more than the water around it when it is in the water. A water-moving airlift will translocate water using very little energy (compressed air). It just needs energy to accelerate and overcome friction. The more air that is injected and the deeper it goes, the more power available. An unconfined airlift doesn't even need a pipe. An air diffuser moves a lot of water within its mass of bubbles.
When trying to lift water to a high level, a water pump is simpler and more efficient than an airlift. However, raising water only slightly above the surface can be done easily and economically with compressed air and an airlift pipe.
How Does It Work?
- Do not use an air diffuser. Large bubbles work best, as they reduce water slippage. Air-injecting collars can improve performance slightly on short pipes but, typically, they are not worth the installation and maintenance difficulty.
- Smaller pipe diameters work best. If more water is needed, use multiples of small diameter pipes. Also, a sweep works better than an elbow.
- Water in the pipe is displaced with air, making the total weight within the pipe less than the weight outside the pipe.
- Since water seeks its own level by virtue of its weight (and its fluid nature), it will get pushed up an airlift pipe because the weight is less there (lower pressure).
- Ever hear the phrase, "Wind doesn't blow, it sucks?" It's true. The direction of flow is from high pressure to low.
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