| 摘要 |
A method is described for propelling a pig (9) along an air-filled underwater pipeline (1) comprising the steps of opening a pipeline inlet (3) to permit entry of water to the pipeline means at a pressure corresponding generally to the ambient water pressure at a proximal end (8) of the pipeline, and coupling a pipeline outlet (5) at a distal end (6) of the pipeline to a fluid venting system (10, 11, 17) in which air is maintained at a pressure sufficiently below the ambient water pressure at the proximal end of the pipeline to create a pressure differential across the pig sufficiently large to cause the air in the pipeline to be vented from the distal end thereof, whereby the pig is propelled along the pipeline. A method is also described for propelling the pig along pipeline (1) when it is filled with water, in which the pipeline outlet (5) is connected to a fluid venting system in which fluid is maintained at a pressure sufficiently below the ambient water pressure at the distal end (6) of the pipeline to cause water in front of the pig to be vented from the outlet at the distal end of the pipeline into the fluid venting system.
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