PURPOSE: To surely and easily perform the air extraction without generating leakage by forcing a resilient tonguelike valve through fastening of a sheet packing interposed between flanges at a discharge pipe and a transfer pipe, thereby opening and closing an air extraction hole.

CONSTITUTION: A swirl pump has a flange F1 connecting a transfer pipe 3 with respect to a flange F2 of a discharge pipe 2 lead out from a pump swirl chamber 1. In this case, at the flange F2, an air extraction hole 4 communicated with the pipe 2 is formed. At the seat of the flange F1, a portion not in contact with a peripheral part 4e of the hole 4 is added. The flanges F1, F2 are connected through a seat packing 5 disposed therebetween, and at the packing 5, a resilient tonguelike valve 6 in contact with the part 4e. The valve 6 is operated by the fastening of the packing 5.