Abstract: A flow rate controller for controlling the flow of a medium, includes an incoming channel, a measuring chamber, a running flow channel connecting the incoming channel and the measuring chamber, a control valve acting in the running flow channel, and an outflow channel for the controlled flow. A necessary flow channel leads from the incoming channel to the measuring chamber. There is a flow adjusting in the necessary flow channel. A service flow channel leads from the necessary flow channel to the outflow channel. In addition, the flow rate includes comprises control elements for leading the flow from the necessary flow channel selectively into the measuring chamber and service flow channel, respectively.