Control valve noise is generated by high pressure drops across the valve and by the subsequent turbulence downstream. As a result, noise is radiated to the surrounding area by the downstream piping system. In situations where equipment damage or personal injury could be caused by a noise source, noise reduction is not only desired, it is mandatory.
A diffuser plate is a pressure reducing device that is installed downstream from a control valve. The total pressure drop needed for flow control of a flow control loop is divided between the valve and diffuser. This enables the valve to operate at a lower pressure ratio and greatly reduces the control valve noise level generated by steam, gas or vapour flow. A properly selected diffuser valve combination can result in a noise reduction of up to 40 dBA. The diffuser plate must be designed for each unique installation so that the noise levels generated by the valve and diffuser are equal.
Mitech’s locally manufactured diffuser plates are designed for use with its globe control valve on high pressure drop applications for gases and vapours. It significantly reduces the control valve noise level generated by the gas or vapour flow. The diffuser plates are installed downstream from the valve to create a back pressure. On high pressure drop gas applications, the valve size is selected to maintain the velocity at the outlet within the limit of Mach 0.33 (1/3rd of sonic). By creating a back pressure, the gas or vapour is compressed to a greater degree, and therefore a smaller valve can be selected while still keeping the velocity within acceptable limits.
Special trims are still often required inside the valve as the downstream plate is not effective at creating back pressure at low flow rates. In these conditions, the valve sees the full pressure drop. However, the velocity in the smaller valve is still acceptable due to the lower flow rate.
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