PURPOSE:To prevent invasion of water into a space between an impeller and a guide casing by a method wherein the pump is provided with a receiving pan, collecting lubricating water from a lower bearing, and a piping, retrieving the water at the outside of the pump, while high-pressure air is introduced into said space in the vertical type pump. CONSTITUTION:The lubricating water from the lower bearing 5 is discharged by the lubricating water receiving pan 17 and the lubricating water retrieving pipe 6 while high-pressure air is sent into a high-pressure air chamber between the impeller 9 and the guide casing 7 by an air pressure generating device 13 through the pipeline 15 to obtain the balance of pressure, thus, the invasion of water from sealing section 8 is prevented. On the other hand, leakage of air into the circulating water may also be prevented by this method. Leakage of the bearing lubricating water into the circulating water as well as the mixing of the circulating water into the bearing lubricating water may be prevented and the bearing lubricating water may be retrieved in 100% since the lower bearing is provided with the lubricating water receiving pan and a pressure in the high-pressure air chamber can be regulated.
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