PUMP AND ITS OPERATION METHOD

PURPOSE:To prevent an impeller from reverse running, scuffing and so on by extracting air from an air outlet opening which is positioned at the upstream side of the impeller by means of a vacuum pump, by sucking water into a pump until its level rises to the lower end of the impeller and by starting operation of the pump immediately thereafter. CONSTITUTION:In a horizontal shaft suction pump 10, an air outlet opening 11 is formed at the upstream side of an impeller 14 and connected to a suction pipe 4 and a vacuum pump 3, and a level detector 16 is disposed at an arbitrary position to detect water level at the lower end of the impeller 14 as well as at the upmost point via a communication pipe 15. The vacuum pump 3 extracts air in the pump 10 from the air discharge opening 11 and sucks water into the pump 10. When the water level reaches the lower end of the impeller 14, the pump 10 is started and thereafter when water is filled, the vacuum pump 3 is stopped and the pump 10 comes into main operation. This may be free from a chance of reverse revolution of the impeller 14, prevents scuffing between casings 12 and impeller 14, and eliminates the need of a flap valve.