In mechanical engineering, like in other fields, the total cost of owning and operating a pump unit or installation is the focus of increased attention. When considering the purchase of a pump unit, customers consider not only the initial cost of investment, but also life cycle costs (i.e., operational costs like those related to energy, downtime, maintenance and spare parts). All of these items together are referred to as the total cost of ownership (TCO). Certain types of pumps and, therefore, specific pumping principles are most ideally suited to minimizing total cost of ownership for particular pumped liquids and pumping processes. Having the proper dimensions is also of critical importance. In each case the objective is to achieve a pumping process with the lowest possible TCO.