An airlift pump is a gas lift pump which is powered by compressed air. Airlifts are used in cases where light suction is needed. Examples include dredging and collection of scientific specimens.
The only energy required is provided by compressed air. This air is usually compressed by a compressor or a blower. The air is injected in the lower part of a pipe that transports a liquid. It usually bubbles into another larger diameter pipe. By buoyancy the air, which has a lower density than the liquid, rises quickly. By fluid pressure, the liquid is taken in the ascendant air flow and moves in the same direction as the air. The calculation of the volume flow of the liquid is possible thanks to the physics of two-phase flow.
Airlift pump technology is superb due to its simple structure. However, it has the following weaknesses:
Airlift pumps are often used in deep dirty wells where sand would quickly abrade mechanical parts. (The compressor is on the surface and no mechanical parts are needed in the well). However airlift wells must be much deeper than the water table to allow for submergence. Air is generally pumped at least as deep under the water as the water is to be lifted. (If the water table is 50 ft below, the air should be pumped 100 feet deep).
It is also sometimes used in part of the process on a wastewater treatment plant if a small head is required (typically around 1 foot head).