In this paper performed the analysis and comparison the measured values of pressure oscillations in the draft tube of Francis units obtained in tests from 1976 and 2009. HPP “Piva” has been operating since 1976. In July 1976, September 1976 and in October 1976, performed tests on Francis units HPP “Piva”, at different levels of head water elevations, reason for which measurements are repeated complexity of the observed problems, the excessive pressures oscillations in the unit’s draft tube. Also during 2009 performed measurements the pressure oscillations on the rim of the draft tube and at turbine head cover Francis units HPP “Piva”, as a supervising engineer I worked on these measurements.
During 1976, team from Litostroj-Ljubljana performed the measurements and recording of pressures oscillations in the middle of draft tube (in direction of the unit’s axis), at 0.25 Ds distance from the draft tube’s rim, and at the mere rim of the draft tube. The most unfavourable results were obtained, on the measuring point at 0.25 Ds from the rim the draft tube. In order improve the performances of Francis turbines installed in the HPP “Piva” units, it is very important thoroughly investigate and eliminate the causes of increased pressure oscillations in the draft tube HPP “Piva” units.