In hydropower projects with Francis turbines or pump-turbines, the responsible author of the specification is often in a dilemma when it comes to specifying reasonable limit values for items like draft tube pressure pulsation (DTPP). They depend to a large extent from the main data of the turbine, and even more from the point of operation. Until today (2014) there is no help from international standards because quantitative regulations or recommendations are not yet at hand. Consider that the designer has limited possibilities to control the level of pulsations. If you specify unnecessarily high values then the vibration guarantee will be without effect, but if the limit values are unreasonably low, then the supplier will have to resort to ‘creative’ interpretation of the amplitude definition, and the guarantee will likewise be useless.
Hydro adviser will select physically sound, statistics-based guarantees with unambiguous, clear amplitude definitions; such guarantees will ensure an acceptable level of vibration and, at the same time, remain technically feasible for the supplier.