During valve operation, many people encounter such problems: sharp noise, severe vibration while the valve is running, and pitting, erosion or even perforation leakage found inside the valve after disassembly. This is valve cavitation. Many people mistake it for corrosion or wear, replace valves blindly but only treat the symptoms rather than the root cause, resulting in repeated failures, increased costs and unstable production. In fact, cavitation is not simple "damage", but a chain reaction caused by physical changes of fluid inside the valve. As long as the causes are identified, it can be eliminated or significantly suppressed to solve the problem fundamentally.
What Is Valve Cavitation?
In simple terms, when fluid flows through the throttling part of a valve, the flow rate increases sharply and the pressure drops rapidly. When the pressure is lower than the saturated vapor pressure of the fluid at the operating temperature, the liquid component vaporizes and generates a large number of bubbles. These bubbles flow with the fluid and collapse instantly when reaching a high-pressure area, producing extremely high local impact force (theoretically up to thousands of atmospheres), which continuously impacts the inner surface of the valve. Over time, pitting and erosion occur, accompanied by vibration and noise, and even lead to valve failure in severe cases.
Cavitation vs. Corrosion
Many people easily confuse cavitation with corrosion. Corrosion is a chemical reaction (e.g., reaction between medium and material), while cavitation is physical impact. They have different causes and completely different solutions. If cavitation is mistaken for corrosion, replacing corrosion-resistant materials will not solve the problem but only waste costs. It should be noted that in actual working conditions, cavitation damage may expose fresh metal surfaces and accelerate chemical corrosion, so the two may act synergistically and need comprehensive consideration.
Three characteristics to judge cavitation:
1.Sharp noise and vibration during operation
2.Pitting or honeycomb erosion inside the valve (rather than uniform rust)
3.Failures mostly occur at throttling parts (e.g., valve plug, valve seat)
Causes of Cavitation
Cavitation requires two conditions: excessive pressure difference across the valve and excessively high fluid velocity, which together cause local pressure lower than saturated vapor pressure.
Four common inducing factors:
1.Improper valve selection: valves with too small throttling clearance (e.g., ordinary globe valves) lead to sudden increase in flow velocity.
2.Unreasonable valve opening: long-term operation at small opening intensifies throttling effect and sharply increases pressure difference.
3.Mismatched working conditions: excessively high fluid temperature or large flow rate raises saturated vapor pressure, making vaporization easier.
4.Unreasonable internal structure: no flow guiding or pressure reduction design, resulting in eddy current and excessively low local pressure.
Solutions to Valve Cavitation
In most cases, no complex equipment modification is needed. Focus on reducing pressure difference, slowing down flow rate and optimizing structure to significantly suppress or reduce cavitation.
1. Optimize Valve Selection (Fundamental Solution)
Select valves with multi-stage pressure reduction or anti-cavitation design (e.g., multi-hole cage valves, labyrinth valves) for large pressure difference scenarios.
Avoid valves with small throttling clearance (e.g., globe valves) that easily cause severe throttling and cavitation.
Calculate the cavitation index during selection to ensure matching with actual pressure difference and flow rate.
2. Adjust Operating Conditions
Avoid long-term operation at small opening; keep opening within 30%–80% to reduce throttling effect.
Reduce fluid temperature and flow rate appropriately if conditions permit to lower saturated vapor pressure.
Install a pressure reducing valve upstream if pressure difference is too large to step down pressure gradually.
3. Optimize Valve Trim and Routine Maintenance
Replace with anti-cavitation trim (e.g., hard alloy valve plug and seat) to delay cavitation damage.
Inspect trim regularly, repair or replace pitting and worn parts in time.
Clean impurities regularly to avoid blockage at throttling parts and intensified flow and pressure fluctuation.
Conclusion
Valve cavitation is a solvable physical phenomenon. The key is to control pressure difference and flow rate to prevent fluid vaporization and bubble formation.