An air lift pump is a device that makes use of the principles of gravitation and inertia to pump water by injecting a flow of compressed air into a pipe filled with a column of water. This introduced air causes water to flow up and out of the pipe resulting in a constant flow of water out of the pump. Due to its simplicity, the air lift pump is well suited to uses where water contaminants would damage a mechanical pump or where the fluids or slurry being pumped require minimal mechanical agitation. Air lift pumps can be appropriate for waste water treatment, archeological research, and aquaculture where low discharge pressures are required.
An air lift pump installation typically consists of a vertical discharge or eductor pipe submerged in the body of water to be pumped. A separate air pipe is inserted into this eductor pipe a short distance from its bottom end. Air is then introduced into the column of water in the eductor pipe at a pressure exceeding that of the water pressure in the pipe. Gravitation then causes a body of air bubbles to rise in the eductor pipe due to the lower density of the air. This column of air bubbles carries the surrounding water with it by inertia as well as forcing the water above it to move upwards.
As the water moves upwards, it creates a void which draws water from the well into the eductor pipe to take its place. This creates a constant upwards movement of water in the pipe which represents the pumping mechanism of the air lift pump. The volume of the pumping process may be controlled by regulating the pressure of the introduced airflow which will also affect the "head" that the pump is capable of producing. The pump head refers to the vertical distance that the pump is capable of moving the water above the level of the well water.
Deep, sandy wells benefit from the use of an air lift pump as the sand suspended in the water rapidly abrades the moving parts of a mechanical pump. Air lift pumps have no moving parts; due to the relatively slow water flow, the interior of the eductor pipe also suffers minimal abrasion. The operation of an air lift pump is also beneficial in cases where slurry or fluids of a sensitive nature are being pumped. This is particularly true of applications such as archeological research sites where the contents of submerged slurry would be damaged by a mechanical pump.
Discharge capabilities of airlift pumps range from approximately 20 to 2,000 gallons (75 to 7,600 liters) per minute and may achieve heads of 750 feet (229 meters). The airlift pump is not suitable for applications that require high pressure discharge or high suction characteristics. The inlet end of the eductor pipe should ideally be covered by a sieve as ingress of large objects causes clogging of the pipe because of the low pressure characteristics of the system.