Although most drives in modern rotary machines are purely electrical, there are applications in which hydraulic drives are used to advantage. The most prominent example is the glass press. A conventional hydraulic system based on valve technology, however, wastes a large amount of energy in the phases of the pressing process in which the pressing cylinder does not need to perform any work although the motor must continue to run.
If, however, the asynchronous motor is replaced with a highly-dynamic servomotor, it is possible to supply only the amount of energy actually required in the associated phase of the pressing process. The power consumption so can be reduced by as much as 50%.