Abstract: According to the present invention, the most challenging issues in this work have been to find systematic ways of enabling maintenance engineers to decide an adequate time for the replacement of vacuum pumps on the basis of their current performance assessment result. Further, the comparison of the currently evaluated diagnostics analysis results and the initial (or reference) data set is shown to enable maintenance engineers to decide the replacement of the considered vacuum pump according to the evaluated pump performance indicators. This quantitative diagnostic analysis result is expected not only to enable maintenance engineers to decide an adequate time for the replacement of vacuum pumps on the basis of their current performance assessment results but also to improve the reliability and confidence of the predictive maintenance of low vacuum pumps.