Abstract: When an underground pipe carrying a fluid, such as a buried water-pipe, develops a leak the leak must first be located before it can be repaired. One common location method makes use of the fact that the leaking fluid often creates a noise, typically a hissing sound, which is transmitted through the ground, and although rapidly attenuated can be heard with suitable highly sensitive ground microphones and is therefore useful to field crews as a means of locating leaks. Unfortunately, the sound levels can be grossly distorted by underground heterogenities, and can easily be confused or even swamped by other sound sources above ground, and in general ground microphones used like this do not seem to be effective.

Abstract: Flotation apparatus (1) for the purification of polluted water, comprising a flotation vessel (3) having an inlet means (23) for supplying polluted water to said vessel, an assembly (41) of spaced elements (43, 65) defining passages for the flow of water through said elements, and outlet means for surface sludge (15, 17) and outlet means (39, 45; 57, 61) for treated water, further comprising flow directing means for forcing the incoming polluted water to reach a level above said assembly (41) and to flow downwardly through said assembly and towards said treated water outlet means (39, 45; 57, 61); and a process for the purification of polluted water by flotation performed in such apparatus.