MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

953.4.2 Air-Lift MethodsCompressed air can be used in two different methods to lift water.The first method, using an eductor pipe, is the one commonly referredto by the general term air-lift pump.3.4.2.1 Eductor MethodIn this air-lift method, compressed air is forced down into awell through a pipe. At a point below the water level, the air is allowedto escape into an eductor pipe which extends from below the water levelup to the well surface or a discharge pipe. As shown in Figure 3.30, thesepipes can be arranged in one of three ways; (a) the air pipe can be a smallpipe inside the eductor, (b) a small air pipe can parallel the eductor onthe outside and then connect to it near the bottom, or (c) the air pipecan be larger than the eductor and fit around and below it. However, inall three schemes, the air will mix with the water, creating a lighterfluid in the eductor pipe than the water in the surrounding well. Theheavier fluid will thus force the air-water mixture up and out of the eductorpipe. Because the water pressure at the bottom of the eductor mustexceed the weight of air-water in it, the air and eductor pipes must besubmerged sufficiently to produce this pressure. A foot piece at the endof the air pipe is helpful in improving the efficiency by breaking up theairstream into small bubbles which mix more thoroughly with the water.Since air-lift pumps have no moving parts they require no other maintenancethan is required for the air compressor. They are very applicableto lifting abrasive or dirty water, thus one of their most common usages isin sewage works. The major cost of this type air lift installation (otherthan the well sinking) is the air compressor (see Chapter 5). The onlyother initial costs are for piping and the foot piece, all of which canbe improvisedfrom second-hand materials.