This report contains an investigation of fluid injection techniques used in the purpose of reducing deleterious flow effects occurring in the draft tube of Francis turbines when operating outside nominal load. There is a focus on implement ability at Jämtkrafts hydroelectric power plants and two power plants were investigated, located in series with each other named Lövhöjden and Ålviken. The only profitable scenario found with some degree of certainty was an increase in the operating range upwards to allow overload operation. Findings show that both air and water can be introduced in various locations to improve hydraulic efficiency around the turbine parts as well as reduce pressure pulsations in harmful operating regions. Investments in such systems have proven useful and profitable at several facilities with poorly adapted operating conditions. But due to losses in efficiency when operating injection systems, it turns out unprofitable in situations where it does not improve the operating range in a way that is resulting in increased annual or peak production.

Creation of vacuum is very slow, energetically and technologicaly demanding process. Closing of valve is very simple and fast process which produces pressure surges when moving cylinder of fluid is stopped. The goal of this thesis is to find out, if it is possible to combine these processes. To reach this goal, 1D model of compressible gas flow and pressure surges in direct pipeline was made. Then follows experimental measurement evaluation and assessment of potential that the technology offers.