ARCA Regler GmbH (Tönisvorst, Germany) delivered several compressor blow-off valves, DN 600/1200, with a low-noise trim design used for the largest axial compressor ever to be used in an air compression plant. The 160 tons heavy compressor manufactured by Siemens PGI, Duisburg, will be installed in the world’s largest air compression plant, that is run by SASOL (South African Coal, Oil, and Gas Co. Ltd.) in Secunda, South Africa. The turbo compressor provides a capacity of approximately 700,000 cubic metres per hour of air. Two valves in split range control the blow off operation. For security reasons and for start-up a third valve has been installed. The valves are required mainly during start-up and shut-down of the compressor. In critical operation or if the compressor must provide constant revolutions during fluctuation in consumption, excess gas is either diverted or blown off. The most important task of the surge limit control valve, however, is to serve as safety valve in case of adjustments in the surge protection control. The surge control prevents the so-called pumping as a result of flow interruption in case the flow drops below the minimum capacity. This may cause severe damage to bearings and rotor. For economical reasons the safety margin between blow-off line and surge limit is kept as small as possible. This is achieved by a sensitive control valve operation and the ability to quickly open without over-loading or stroking to the full open position in case of blow off. The South African Sasol uses the compressor for the production of oxygen which is used in coal gasification. Synthetic gas, which is produced in this process, is converted to sulphur-free fuel in further refining steps. Due to economical and environmental advantages the world demand of sulphur-free fuel will tremendously increase in the next years. ARCA Flow Group exhibited at the ACHEMA in Frankfurt, Germany from 19–24 March 2003.