The discharge end of the air lift should be kept as close to the surface as possible to avoid reducing efficiency.
Although it can be used in shallow waters, it is better to use the underwater dredge, described in Section 2.6.3, in water depths less than 16 to 18 feet. The air lift can be from 10 to 70 feet long, but it is inefficient in lengths of less than 30 feet. the air pressure supplied is relatively unimportant, but it must be at least greater than the pressure at the depth of water in which the excavation is being performed. Experimentation is usually required to determine the volume of air necessary for maximum eiilciency. The seabed material starts to lift almost as soon as the low-density fluid in the discharge pipe rises. Pipe will buck at start up and if inlet is plugged, diver requires communication with surface.Īnd then submerging the intake end (foot piece) into the seabed material.
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