PUMP

PURPOSE: To depressurize a shaft seal part so as to improve sealing effect, and discharge foreign matter and air simultaneously with water extraction so as to be prevented from being mixed into the shaft seal part by extracting water from a decompression chamber provided rather on the pump interior side than a shaft sealing device. CONSTITUTION: A decompression chamber 1 is provided rather on the pump interior side than a shaft seal part 3 in a no-water injection type shaft sealing device, and water is extracted from the decompression chamber 1 by a water extraction pipe 2, so that the interior of the decompression chamber 1 is decompressed to facilitate shaft seal. At this time, water extracting effect can be improved by forming the decompression chamber 1 in volute structure. In addition, a rotary ring 7 is provided on the rotor side, and centrifugal force by the rotor is used to facilitate water extraction and the discharge of foreign matter and air. Further effect can be obtained by forming the rotary ring 7 into a screw type, and the worsening of water permeability of packing caused by the intermixture of air can be prevented.