Why is control valve outlet velocity important, and what are the recommended limits?
The velocity of the control valve outlet is an important but frequently ignored part of designing the piping system and sizing the valve. When a liquid goes through a control valve, which slows down the flow, its speed goes up, especially at the outlet where the pressure drops. This speedup can cause two big problems: erosion can damage the pipes downstream, and noise levels that are too high can make the plant less safe and reliable. Think about putting your thumb over the end of a garden hose to make the flow speed go up. In the same way, high outlet speeds can wear out pipes, supports, and even insulation in a process plant. It also causes vibration and noise from the flow, which may need costly ways to reduce them. To avoid this kind of damage, Process Industry Practices (PIP) guideline PCECV001 suggests the following maximum velocity:
Liquids (Clean Service): ≤ 10 m/s
Clean Gases: ≤ 0.3 Mach
Steam: 0.3 - 0.5 Mach
Multiphase/Dirty Fluids: ≤ 3-5 m/s (be conservative)