Method of clearing a pipe system from its contents, the pipe having a proximal end and a distal end, the method comprising: - providing an air supply to the pipe system at the proximal end by applying an air pressure decreasing from an initial pressure as the bulk of the pipe contents get discharged gradually at the distal end for obtaining a contents flow in the pipe system; the method further comprising: - determining a volume of air supplied to the pipe system by the air supply; - determining an estimated contents travel speed from the volume of the air supplied to the pipe; - controlling the air supply at the proximal end of the pipe for obtaining a predetermined pipe contents travel speed using the estimated contents travel speed, - wherein the air supply comprises a compressed air container having a container volume and wherein the determining a volume of air supplied to the pipe system comprises: - measuring a pressure in the compressed air container; and - measuring a pressure at the proximal end of the pipe system; - calculating the air volume supplied to the pipe system from a pressure difference in the air container between an initial pressure and a pressure in the air container after supplying air from the air container to the pipe system; - wherein the determining a volume of air supplied to the pipe system further comprises compensating the volume of air supplied to the pipe system for a supply line volume and an expansion of the air volume stored in the supply line prior to the supplying of the air to the pipe system. - providing an air supply to the pipe system at the proximal end by applying an air pressure decreasing from an initial pressure as the bulk of the pipe contents get discharged gradually at the distal end for obtaining a contents flow in the pipe system; - determining a volume of air supplied to the pipe system by the air supply; - determining an estimated contents travel speed from the volume of the air supplied to the pipe; - controlling the air supply at the proximal end of the pipe for obtaining a predetermined pipe contents travel speed using the estimated contents travel speed, - wherein the air supply comprises a compressed air container having a container volume and wherein the determining a volume of air supplied to the pipe system comprises: - measuring a pressure in the compressed air container; and - measuring a pressure at the proximal end of the pipe system; - calculating the air volume supplied to the pipe system from a pressure difference in the air container between an initial pressure and a pressure in the air container after supplying air from the air container to the pipe system; - wherein the determining a volume of air supplied to the pipe system further comprises compensating the volume of air supplied to the pipe system for a supply line volume and an expansion of the air volume stored in the supply line prior to the supplying of the air to the pipe system. - measuring a pressure in the compressed air container; and - measuring a pressure at the proximal end of the pipe system; - calculating the air volume supplied to the pipe system from a pressure difference in the air container between an initial pressure and a pressure in the air container after supplying air from the air container to the pipe system; - wherein the determining a volume of air supplied to the pipe system further comprises compensating the volume of air supplied to the pipe system for a supply line volume and an expansion of the air volume stored in the supply line prior to the supplying of the air to the pipe system.