Diagnose and Treatment of Charging Pump Cavitation in Nuclear Power Stations

The typical vibration characteristics, cause and solutions of the cavitation problem of the horizontal-12stages-single suction-bag type-centrifugal charging pump（RHM100-205.12） has been analyzed. There were abnormal vibration fluctuation and fluctuation value beyond the alarm limitation phenomenon when charging pump runs on in-charge condition. It was found that there was typical vibratory shock signal in time domain; broadband noise, blade passing frequency and harmonic component and so on in frequency domain especially by charging pump’s entrance side in vertical direction. It was diagnosed that cavitation corrosion fault happened near the first vane wheel,which was approved by strip inspection during overhaul. The lower cavitation safety margin k of charging pump RHM was the main cavitation cause, which should be increased in order to avoid the cavitation corrosion fault. It has proved that the charging pump’s cavitation can be influenced by changing the cap between first impeller and vane by experiment study infield. The cavitation has been improved effectively through expanding the cap by 1 mm. Also it has proved that the cavitation of the charging pump RHM can be diagnosed simply by monitoring its vibration characteristics near the pump entrance side in the vertical direction and the cavitation can be improved effectively through expanding the cap.