Did you know you can use air to pump water? By bubbling air through an enclosed tube, it is actually possible to move a large amount of water with very little energy!
The GroPonix systems use airlift pump technology to pump and oxygenate the dirty water in an aquarium. The airlifts in these systems use the air from a 2.2W aquarium air pump. There are no moving parts in the airlift system, meaning the airlift can run for a very long time with little to no maintenance required. A very basic airlift pump is shown in the diagram below.
Notice how in this diagram the air is being pumped from a tube outside of the main airlift tube. Other systems pump air through a tube in the center of the airlift tube, making them less efficient.
Changing certain factors in the airlift design can either increase or decrease the amount of pumping power. Some different factors are shown in the diagram below.
Airlift 1: This is an idealized airlift pump, similar to that used in both of the GroPonix systems. The air outlet is near the bottom of the lift tube and the tube is submerged relatively low in the water. This makes the pump able to lift around 1/2 the height of the submerged tube (ie. air is released in the tube at 8 inches deep = 4 inches lifting capability).
Airlift 2: Same size lift tube as Airlift 1, but air outlet isn’t submerged very low in the water. This makes the water pump less powerful as the air does not expand as much with less water pressure (remember that pressure increases as you go deeper, in any kind of liquid).
Airlift 3: This time a thin tube is used as the airlift, which allows water to be pumped higher than the wider tubes. The way this works is that the air bubbles fill more of the tube and create a better seal between each slug of water. The downfall of this smaller tube is that the total volume of liquid pumped is less than that of the medium size tube.
Airlift 4: This time a wide tube is used as an airlift. As you can see in the diagram, the water does not get very high above the surface with this tube. This is because the bubbles do not form a solid seal in the inside of the tube because of a process known as ‘slippage’. Slippage causes the slugs of water to slip by the rising bubbles, meaning most of the water falls backwards towards the bottom of the tube instead of being pumped out the top.