Cavitation is a phenomenon that occurs in control valves. It can cause severe damage to your valves, significantly shortening their lifespan. In this article, we’ll look at what cavitation is, what effect it has on your valves and other equipment, and how you can avoid it.
What is cavitation?
Cavitation occurs in control valves in liquid media applications. It happens when localized low pressure causes bubbles to form and then suddenly collapse.
- First, the liquid evaporates to vapor. In a control valve, if the liquid’s pressure falls below its fluid vapor pressure, vapor bubbles will form. These bubbles interrupt the continuity of the flow.
- Then, the vapor bubbles collapse. As the pressure recovers, the bubbles collapse suddenly. It’s this transformation, the collapsing of the bubbles, that causes damage to the valve.
Why does cavitation happen?
Cavitation happens in control valves when there’s variation in the flow velocity, in particular, when the fluid in the valve accelerates rapidly. It occurs when the pressure drop in the valve exceeds a critical point or when downstream pressure exceeds the fluid vapor pressure.
Valve characteristics can also contribute to cavitation. According to the Masoneilan Handbook of Control Valve sizing, “the more streamlined a valve is, the more pressure recovery is experienced. This increases the possibility of cavitation.”
How does cavitation affect your control valves?
Since cavitation is common, many control valves are built to withstand it for limited amounts of time. However, extended exposure to cavitation can seriously damage your control valves.
When the vapor bubbles collapse, they create an implosion that causes pitting in the metal of the valve. Over time this wear and tear results in severe erosion, which can cause the valve to fail.
Cavitation also creates high levels of noise and vibration, which can damage not only the valve, but also the piping, instruments, and other equipment.
How can you avoid cavitation?
There are several ways you can avoid excessive cavitation. Here are a few of them:
- Make sure you select the right valve for your application. If your valves are the wrong size or the wrong style, their likelihood of cavitation increases. In water and liquid systems with high pressure drop, use an anti-cavitation valve.
- Use multiple control valves or multistage control valves so that the pressure drop happens gradually rather than all at once. This is called pressure drop staging.
- Place the control valve at a lower elevation in the system or in an area where the fluid temperature is reduced.
Don’t let cavitation damage your valves and cause failures! Many of our Masoneilan control valves are specifically designed to resist cavitation in high pressure drop systems. Please contact us for help deciding which one is best for you.