An airlift pump is an apparatus that has no mechanical contact with the fluid that is being acted upon. These devices typically use a blower or compressor to pump bursts of air into a tube that is submerged in a fluid. The air rises back up through the pipe, which pushes some of the liquid upwards and creates a suction at the intake end. An airlift pump can be useful in any situation where the liquid is caustic or mixed with an abrasive that could damage a conventional pump. Some common uses for an airlift pump are in a sandy well or for dredging operations, both of which can involve water mixed with a potentially damaging abrasive material.
Two of the principles that allow airlift pumps to function are buoyancy and fluid pressure. When a pipe is submerged and air is pumped into it, buoyancy can cause the lighter air to force some of the liquid up the pipe. This creates fluid pressure, which can pull more liquid in through the intake. A typical airlift pump will inject air in short bursts, which allows fluid pressure to form but does not entirely fill the pipe with air. If the pipe in an airlift apparatus does not maintain alternating columns of air and liquid, the suction will typically fail and the device may need to be reset.
One common use for airlift pumps is in water wells. The water will be contained in a substrate of sand in some cases, which can make it difficult to extract using a traditional pump. Particles of sand suspended in water will tend to foul the moving parts inside a pump, which can lead to premature failure and costly repairs. Airlift pumps provide a solution to this since no moving parts ever come into contact with the water or the substrate material.
In a typical airlift water well, the pipe apparatus will extend quite a ways below the water table. Common designs involve extending the pipes twice as far below the surface as the water itself. This extra distance can allow sufficient fluid pressure to build up for the water to be force out of the ground.
Another use for an airlift pump is in dredging operations, either for clearing out silt or in nautical archaeological operations. Conventional pumps could be fouled by the silt in dredging operations or damage objects of archaeological interest. The main benefit of an airlift pump is that the pump itself can not be fouled by abrasives, though it can also be useful because there is no opportunity for a pump to abrade delicate materials that are being raised from a sea bed.