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Hi, I’m the Industrial Control Assistant. Do you know what flash vaporization and cavitation are in control valves? Two phenomena, flash vaporization and cavitation, often occur with the liquid flowing inside control valves. Their occurrence not only affects the selection and calculation of the diameter, but also leads to severe noise, vibration, and material degradation. Under such circumstances, the service life of the control valve will **be shortened**; let’s analyze this in detail. As a liquid-phase medium, the fluid enters the control valve in liquid form; when it passes through the constriction in the control valve, the pressure of the fluid is lower than the vaporization pressure Pvapor, causing the liquid medium to turn into a gas phase. Its pressure then does not rise above the vaporization pressure again, and the medium remains in gas form as it exits the control valve. Flash evaporation is similar to a sandblasting effect; it acts on the valve body and the downstream sections of the pipelines, causing severe erosion of the inner surfaces of the control valves and pipes, and simultaneously reducing the flow capacity of those control valves. Cavitation occurs when the liquid medium flows into the control valve in a liquid state; as it passes through the constriction areas within the control valve, the pressure of the fluid drops below its vaporization pressure, causing the liquid medium to turn into a gaseous state. Subsequently, its pressure rises back above the vaporization pressure Pvapor, and finally, the medium becomes liquid again before exiting the control valve. The presence of cavitation can be initially determined based on certain phenomena: when cavitation starts, it produces a hissing sound; once cavitation reaches a fully stable state, a grating noise is heard in the control valve, similar to the sound produced by stones passing through it. Cavitation also causes significant damage to control valves and their internal components; it also reduces the flow efficiency of these valves, just like flashing does. We must take effective measures to prevent or minimize the occurrence of flashing or cavitation: ① Install the control valve as low as possible in the system, which can relatively increase the pressures at the inlet P1 and outlet P2 of the control valve ； ② A globe valve or throttle orifice plate can be installed upstream or downstream of the control valve in order to alter the original pressure drop characteristics of that control valve (this method is generally effective for low-flow situations) ； ③ The use of specialized anti-cavitation components can also effectively prevent flashing or cavitation; it allows for changes in the flow velocity of the fluid within the control valve, thereby increasing the internal pressure ； ④ Try to use control valves made of harder materials, as in the event of cavitation, such valves possess a certain degree of erosion resistance and wear resistance; they can tolerate the presence of cavitation under certain conditions without damaging their internal components. On the contrary, for control valves made of soft materials, their poor erosion resistance and wear resistance mean that when cavitation occurs, the internal components of the control valve are quickly worn out, preventing it from functioning properly in such conditions. In short, there are currently no engineering materials capable of withstanding cavitation under severe conditions; it is necessary to conduct a comprehensive analysis of the specific circumstances in order to select a relatively reasonable solution.