This part of IEC 60534 establishes a theoretical method to predict the external soundpressure level generated in a control valve and within adjacent pipe expanders by the flow of compressible fluids. This method considers only single-phase dry gases and vapours and is based on the perfect gas laws. This standard addresses only the noise generated by aerodynamic processes in valves and in the connected piping. It does not consider any noise generated by reflections from external surfaces or internally by pipe fittings, mechanical vibrations, unstable flow patterns and other unpredictable behaviour. It is assumed that the downstream piping is straight for a length of at least 2 m from the point where the noise measurement is made. This method is valid only for steel and steel alloy pipes (see Equations (21) and (23) in 5.5). The method is applicable to the following single-stage valves: globe (straight pattern and angle pattern), butterfly, rotary plug (eccentric, spherical), ball, and valves with cage trims. Specifically excluded are the full bore ball valves where the product FpC exceeds 50 % of the rated flow coefficient. For limitations on special low noise trims not covered by this standard, see Clause 8. When the Mach number in the valve outlet exceeds 0,3 for standard trim or 0,2 for low noise trim, the procedure in Clause 7 is used