Prevention of pump cavitation using condition-based monitoring

So, how does cavitation occur and what makes it a concern for pump systems?

Cavitation happens when rapid pressure changes in a liquid medium cause vapor-filled bubbles to form. These bubbles can collapse under higher pressure, generating shockwaves that create micro-pits in the pump impeller. This leads to accelerated wear-out and erosion of the rotating blades. Additionally, the collapse of bubbles generates additional noise, knocking, and vibration, which further reduces pump efficiency by distorting the flow pattern.

The local implosions of cavitation bubbles can also alter the chemical properties of the liquid, producing free radicals, causing oxidation, and degrading chemical compounds. Although these effects occur in small amounts, they still result in changes to product quality—an important factor in the food and beverage or oil and gas industries.

It is important to note that cavitation can also impact other system components in contact with high-velocity moving fluids, including piping systems, pump components, engine housing, cylinder sleeves, HEX components, and hydro turbine components. So, early detection of cavitation in the pump along with fast remedial action can protect and extend lifespan of a whole system of components.

Detecting and avoiding cavitation is crucial for maintaining pump performance and preventing costly damage. Condition monitoring in the form of integrated CBM in the VFD offers an effective solution for achieving this. Cavitation detection can be achieved using current signature analysis in the VFD, enabling sensor-less detection. Cavitation produces turbulence, creating audible noise and a distinctive signature in the motor current. This turbulence is reflected in the motor current and become detected by the condition monitoring algorithm.

The algorithm compares the actual cavitation signature against user-defined threshold levels. If the values exceed the set thresholds for a predefined time, the event is flagged as cavitation.

The benefits of avoiding cavitation using condition monitoring are significant. With permanent monitoring using CBM integrated in the Danfoss VFD, both the detection and avoidance of cavitation become possible. This is a cost-effective solution that competes with traditional methods based on external sensors, such as sound, vibration, or pressure. By preventing pump wear-out and damage caused by cavitation, productivity is optimized, and component lifetimes can be extended. It becomes possible to perform predictive maintenance and this ultimately leads to a reduction in service and replacement costs.