Cavitation in machines and equipment is an essential concept to understand in asset management and maintenance. Why is it so important? It is a recurring threat in systems involving fluid flow. Addressing it is one of the significant ways to maintain system reliability. If not monitored and prevented, it can lead to unoptimized assets and costly downtime.
What is Cavitation?
Cavitation is a phenomenon that occurs when the pressure of a liquid drops below its vapor pressure, causing the formation of vapor bubbles in the liquid. These bubbles then rapidly collapse or implode when the pressure is restored, which can cause damage to nearby surfaces.
This can occur in various types of machinery, such as pumps, propellers, and turbines, and can lead to erosion, pitting, and other forms of damage. It is important to design machinery to minimize the risk of cavitation and to monitor and address any cavitation-related issues that do arise to prevent damage and maintain efficiency.
What Causes Cavitation?
Looking closely at the different types of cavitation below helps to understand further how it can occur.
Air Aspiration
This type of cavitation happens when air enters the fluid system through leaks. The air then gets dissolved into the fluid and forms vapor bubbles which later collapse and send damaging shock waves through the system.
Regular inspection of valves, joints, O-rings, and mechanical seals is the best way to prevent damage caused by air aspiration.
Internal Recirculation
Cavitation can also happen when the fluid flow inside a system is not within the standard recommended rate. This abnormal flow rate causes the fluid to recirculate, resulting in high heat and velocity, producing problematic vaporized bubbles.
To prevent this type of cavitation, technicians or operators need to ensure that proper fluid pressure is maintained at recommended rates and that discharge valves are properly installed and completely open while the system is running.
Turbulence
The turbulence created as fluid flows can cause changes in pressure across the system, thus producing cavitation bubbles. Turbulence results from improper use of the machine and substandard pipe sizes.
Prevent cavitation-causing turbulence by using units with standard sizes that fit your system and operating them within the recommended guidelines.
Vane Syndrome
Also called vane passing syndrome, this type of cavitation occurs when the space between the vanes of a system’s impeller, or the rotating part that makes fluid flow, is too small. This situation results in restricted flow, frictional heating, turbulence, and, finally, cavitation.
The use of the appropriate sizes of impeller and housing unit efficiently prevents cavitation by vane syndrome.
Vaporization
Also called ‘classic’ cavitation, vaporization or vaporous cavitation happens when the pump or system that moves the liquid dries up due to low water levels. This pump starvation can be due to clogged filters, narrow pipes, and restricting or partially closed valves.
Proper and close system monitoring should prevent vaporous cavitation or at least allow early detection. The use of suitable pipes and pump parts is also essential. Furthermore, it helps to ensure that the pump’s minimum energy requirement (or the NPSHr) is higher than the available energy in the system (the NPSHa).
Where Does Cavitation Occur?
Looking at the above conditions that promote the formation of cavitation bubbles, you will have an idea of the cavitation-prone areas of your machine or system. It will most likely occur in the following areas of a pump, propeller, turbine, and similar machines:
- Downstream of control valves
- Suction chambers
- Rapidly moving actuators
- Leakage paths such as across seats, valve seats, and spool lands
- Areas where there are sharp turns or rapid changes in cross-section lengths, like flaps, valves, and diaphragms
Support for Prevention and Detection
Cavitation can be prevented, or at least its damaging effects minimized, with regular and proper maintenance. And a digitized monitoring system like Redlist’s Lubrication Management software can help reach this goal quickly and efficiently.
The software can help you identify cavitation hotspots and plan the most efficient schedule to monitor and inspect these areas. User-friendly and intuitive, your technicians and operators will find it easy to record inspection results and repair details essential for future reference and analysis. Lubrication management is fast becoming an indispensable tool for competitive facilities in any booming industry.
