4. Efficiency and power measurement

4.1 On a scale model

To establish a performance hill, tests are generally carried out under constant head and without cavitation, i.e. the sigma displayed is significantly higher than the installation sigma. This is achieved by maintaining the downstream tank at atmospheric pressure. This makes it much easier to automate the measurement, otherwise you'd have to adjust the sigma manually, point by point, using the vacuum pump.

The influence of sigma is taken into account only at guaranteed yield points under guaranteed drops during cavitation tests.

Since mechanical losses are different between model and prototype, the hydraulic efficiency η _h is calculated from the mechanical power P...