DIN EN 60534-8-4:2017-01

It is of great importance to be able to predict the noise emissions that are likely to be generated by control valves. Safety regulations, such as occupational health and safety guidelines, require that noise exposure to humans be limited. In addition, there are data showing that sound levels above certain levels can cause damage to piping or associated equipment (see also IEC 60534-8-3). Earlier standards for fluid-borne noise calculation for valves were heavily based on measurement data from manufacturers and did not meet the desire for generality or completeness. The method shown here can be applied to all conventional control valve types such as globe valves, butterfly valves, cage valves, eccentric plug valves and modified ball valves. A valve affects flow by converting pressure energy into turbulence energy, heat, and mechanical pressure waves in the valve housing and piping. A small portion of this mechanical vibration is converted to acoustic energy. The main portion of the noise is retained in the piping system, and a small portion is transmitted through the piping downstream of the valve. The way to calculate the resulting energy is actually clearly given. Difficulties arise in the first step in determining the acoustic efficiency as a measure of the conversion of mechanical energy into noise and in the second step from the determination of the noise emission reduction by the pipe wall. This part of the IEC 60534 series of standards considers only noise generated by normal turbulence and fluid cavitation. It does not cover noise due to mechanical vibration, flashing conditions, instabilities in the flow, or phenomena that cannot be predicted. In the typical installation, a very small amount of noise passes through the wall of the valve housing. The predicted noise corresponds to a measurement 1 m behind the valve and at a distance of 1 m from the outer pipe surface in an acoustic free field. Ideally, a straight pipe routing is assumed. Since an acoustic free field is rarely present in industrial installations, this prediction may differ from the actual results at the installation site. This prediction method has been validated using measured data for water and for a majority of control valve types in the nominal size range DN 15 to DN 300 for inlet pressures up to 15 bar. However, some low-noise valve types may not have been recorded. This method has an accuracy of +/- 5 dB(A) in most cases when xFz values determined by measurement according to IEC 60534-8-2 are used. The accuracy of this method for liquids other than water is currently uncertain. This part of IEC 60534 establishes a method to predict the noise generated in a control valve by liquid flow and the resulting noise level measured downstream of the valve and outside of the pipe. The noise may be generated both by normal turbulence and by liquid cavitation in the valve. Parts of the method are based on fundamental principles of acoustics, fluid mechanics, and mechanics. The method is validated by test data. Additional noise is generated when cavitation begins. Cavitation is the second stage of a two-stage process. Vapor bubbles form when the pressure at any point becomes less than the vapor pressure of the liquid. This condition occurs in the area of the vena contracta; that is, at a point with the maximum velocity and the minimum pressure in the valve. The second part of this process is the collapse of these vapor bubbles when the fluid pressure exceeds the vapor pressure and the vapor leaves the location of minimum pressure. The energy that the bubbles generated is released back to the flowing fluid in the form of a high intensity jet when the bubble collapses. This can result in noise and severe damage. The cavitation process, the energies converted in the process, the reasons why water is one of the most destructive fluids and why some other fluids are less destructive is part of current hydraulic research. The responsible body is DKE/K 963 "Stellgeräte für strömende Stoffe" ("Actuators with flowing substances") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.