Abstract: A monitoring system for hydraulic pipelines and/or actuating devices including a volume flow sensor having a toothed rotor similar to that in a toothed rotor motor by which movements of the toothed rotor can be sensed by no-contact detectors which emit electrical pulses in respect of discrete quantities of oil displaced by and equal to the volume of a tooth of the toothed rotor. The system also includes a device by which the pulses are processed with respect to the direction of flow through the volume flow sensor and to the pulse frequency. The system also includes an indicator indicative of current operating conditions and a counter by which, after a limiting frequency has been exceeded, the pulses are counted and upon reaching a specified pre-assigned number of pulses that succeed one another during a period of uninterrupted counting a signal of leakiness is generated.