Air lift pump

Introduction:

An airlift pump is a gas lift pump which is powered by

compressed air. Airlift pumps are widely used by aquaculturalists. Common airlift applications are to pump, circulate and aerate water in closed, recirculating systems as well as in ponds. Centrifugal blowers are one of the most effective and inexpensive methods to produce or pump air because they produce relatively high volumes of air at low operating pressures.

A simple air lift pump

Principle:

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.

Working:

Water can be readily pumped from a well using an air-lift pump. There are no air-lift pumps in the Army supply system; however, in the field, you can improvise and make a pump using compressed air and the proper piping arrangement. The assembly consists of a vertical discharge (eductor) pipe and a smaller air pipe. Both pipes are submerged in the well below the pumping level for about two-thirds of the pump's length. The compressed air goes through the air pipe to within a few feet of the bottom of the eductor pipe and is then released inside the eductor pipe. A mixture of air bubbles and water forms inside the eductor pipe. This mixture flows up and out the top of the pipe. The pumping action that causes water to rise as long as compressed air is supplied is the difference in hydrostatic pressure inside and outside the pipe resulting from the lowered specific gravity of the mixed column of water and air bubbles. The energy operating the air lift is contained in the compressed air and released in the form of bubbles in the water.

You can use this arrangement for test pumping wells and for well development. You can use the well casing for the eductor pipe. However, to pump sand and mud from the bottom of a well during well development and completion, use a separate eductor pipe. This type of pump is also useful in wells that, because of faulty design, produce sand with the water. This condition will quickly create excessive wear on most pumps. By setting the educator pipe to the bottom of the screen, sand will be removed before it fills the screen.

Geyser Pump - The Way to Improve Airlift Pump Airlift Pump is a superb technology due to its simple structure. However, it has the following weaknesses:

� Weak suction � Unstable flow rate � Frequent clogging.

Airlift Pump has a series of bubbles in the vertical pipe as shown in the schematic above. There is a slippage of water and bubble in the pipe.

Even if, the amount of air is increased, the amount of slippage increases, therefore, the Geyser Pump is designed to eliminate this small bubbling, but to hold the supplied air for a while and instantly release a big bubble to the riser pipe.

Big bubble with a big buoyancy force ejects the water and sludge in the riser. The velocity of the liquid becomes more than 4

feet/sec. This high velocity clean the pipe by itself and that is why there is no clogging. The suction force is 12 times the one of airlift pump.

Geyser Pump and Geyser Hybrid Pump are used for relatively low-lift application. In the case of flow equalization and deep-well pumping, the submergence is limited and the lift is 20 feet to sometimes several hundreds feet. For this application, Geyser Ejection Pump is applicable. With the help of a check valve, much higher lift is realized. Utilization:

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).

They can also be used in ponds and aquaculture to aerate and mix the water.

Advantages and disadvantages

The following paragraph exposes the advantages and disadvantages of the airlift pump compared to other pumping techniques.

Advantages

• The pump is very reliable. The very simple principle is a clear advantage. Only air with a higher pressure than the liquid is required.

• The liquid is not in contact with any mechanical elements. Therefore, neither the pump can be abraded (which is important for sand water wells), neither the contents in the pipe can be abraded (which is important for archeological research in the sea)

Disadvantages

• cost: while in some specific case the operational cost can be interesting, most of the time, the quantity of air to compress is high compared to the liquid flow required

• Conventional airlift pumps have a flow rate that is very limited. The pump is either on or off. It is very difficult to get a wide range of proportional flow control by varying the volume of compressed air. This is a dramatic disadvantage in some parts of a small wastewater treatment plant, such as the aerator

• The suction is limited.

• This pumping system is suitable only if the head is relatively low. If you want to obtain a high head, you have to choose a conventional pumping system.

• Because of the principle, a lot of air remains in the liquid. In certain case, this can be problematic, as, for example, in a waste water treatment plant, before an anaerobic basin.

Reference: http://www.globalsecurity.org/military/library/policy/army/fm/5-484/Ch4.htm wikipedia.com