| 摘要 |
A variable speed pig for a pipeline includes a housing having at least one and preferably several flow through passageways. The size of the flow through passageways is varied according to the desired speed of the pig. The pig includes an annular seal disposed about the housing for sealing engagement with the pipeline and the housing, and the flow through passageways are selectively blocked by a first plate disposed in the housing, the first plate having a plurality of first openings . A second plate is also disposed in the housing, and the second plate has a plurality of second openings that are aligned in fluid connection with the flow through passageways . The first plate is movable in relation to the second plate from a position in which at least some of the first and second openings are in fluid connection to a position in which substantially none of the first and second openings are in fluid connection. The plates may be adjusted by a step motor and controller which are in turn controlled by a comparator circuit that compares the actual speed of the pig with the desired speed. The collective effective cross-sectional areas (size) of the flow through passageways is decreased when the actual speed is lower than the desired speed by more than the pre-set amount and increased when the actual speed is higher than the desired speed by a pre-set amount.
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