A device for processing of a liquid that includes a device-input for receiving the liquid to be processed at an input-pressure, a device-output for returning the processed liquid at an output-pressure, a process chamber having a chamber-inlet and a chamber-outlet with the chamber-inlet being connected to the device-input via a feed-line, and the chamber-outlet being connected to the device-output via a discharge-line. The feed-line includes a pump for increasing the pressure of the liquid from the input-pressure to a feed-pressure at the chamber-inlet, and the discharge-line includes a back-pressure mechanism adapted to maintain a discharge-pressure at the chamber-outlet upstream of the back-pressure mechanism at an excess-pressure above the output-pressure, and to reduce the pressure of the liquid from the discharge-pressure to the output-pressure downstream of the back-pressure mechanism. The pump in the feed-line is a first stage of a multiple-stage gear pump. The back-pressure mechanism in the discharge-line is a second stage of the multiple-stage gear pump. The second stage is mechanically coupled to the first stage.