Device for maintaining a constant supply quantity, preferably for pressure-dependent installations

The invention relates to a device for maintaining a constant supply quantity, preferably for pressure-dependent installations, by means of which device freely selectable throughput quantities per time unit can be set and the pressure changes which occur can be kept constant in a flow installation which is operated with an impeller pump with a specific throughput quantity per time unit, independently of self-induced pressure behaviour. This is achieved in that, in the pipe between the installation and a pump operated by an inductive motor, a pressure-independent quantity meter is arranged, which is electrically connected via a transmitter and a controller to a rotary-current frequency inverter which adjusts the rotational speed of the induction motor by changing the frequency as a function of the quantity delivered by the pump.