Installed downstream from the valve, the diffuser plates are designed to create a back pressure at the valve. 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 (one third of sonic) by creating a back pressure – the gas or vapour is more compressed and, therefore, a smaller valve can be selected and still keep the velocity within acceptable limits.
Special trims, such as Low Noise or ED Disk Stack, 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.
Usually the valve size can be reduced to less than half the size it would have to be without the plate, resulting in significant savings, particularly when the sizes involved are large. Several diffuser plates can be installed in series in an expanding pipework system, or they can be built into a single holder for ease of installation.
A typical application that can use this technology is a steam pressure-reducing station.