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, and a process chamber having a chamber-inlet and a chamber-outlet, and a feed-line for connecting the chamber-inlet to the device-input. The feed-line includes a multi-stage pump for increasing the pressure of the liquid from the input-pressure to a feed-pressure at the chamber-inlet, a discharge-line for connecting the chamber-outlet to the device-output which discharge-line includes back-pressure means adapted to maintain a discharge-pressure at the chamber-outlet upstream of the back-pressure means 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 means. The pump in the feed-line is a first stage of a multiple-stage gear pump. The back-pressure means in the discharge-line is a second stage of the multiple-stage gear pump. The second stage is mechanically coupled to the first stage.