| 摘要 |
An apparatus including a vertical main pipe having at least one twisted portion therein for forming an air column extending centrally through the vertical main pipe, a horizontal main pipe, and a bend connecting the lowermost end of the vertical main pipe to the horizontal main pipe; the improvement wherein said bend is formed with a twisted upper portion having an axis deviating helically from a normal axis extending between the axes of said main pipes and with a lower portion having a diameter which progressively increases toward the horizontal main pipe.
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