Centrifugal pump cavitation is one of the most common—and costly—issues that engineers and maintenance teams face. It can cause severe damage to pump components, reduce efficiency, and lead to expensive downtime. Understanding what causes cavitation, how to detect it early, and how to prevent it can help keep your system running reliably and efficiently.
In this article, we’ll take a deep dive into cavitation in centrifugal pumps, exploring the key causes, detection methods, and practical prevention strategies that every plant engineer should know.
What Is Cavitation in a Centrifugal Pump?
Cavitation occurs when the pressure in a liquid drops below its vapor pressure, causing vapor bubbles to form in the pump. When these bubbles move into a higher-pressure area, they collapse violently, creating shock waves that can pit and erode metal surfaces inside the pump.
Over time, this leads to impeller damage, vibration, noise, reduced flow, and eventually pump failure. Even short-term cavitation can severely reduce pump efficiency and lifespan.
Common Causes of Cavitation
Several factors can lead to cavitation in centrifugal pumps. The most frequent include:
1. Low Net Positive Suction Head (NPSH)
When the available NPSH (NPSHa) is lower than the required NPSH (NPSHr) of the pump, the liquid entering the impeller eye can vaporize.
Causes of low NPSH include:
- High fluid temperature
- Excessive suction lift
- Inadequate suction line size or restrictions
- Air leaks in suction piping
2. Gas Entrainment
If gas or air is introduced into the liquid stream, it can lead to a mixture of vapor and liquid that disrupts normal pump operation. Gas entrainment can come from:
- Leaky seals or fittings
- Agitation or turbulence in the supply tank
- Improperly vented suction lines
3. Flow Discontinuities
Flow interruptions or turbulence at the impeller eye reduce the pressure locally, creating vapor bubbles. These discontinuities are often caused by:
- Poor suction piping design
- Sudden changes in direction or diameter
- Obstructions or debris in the suction line
4. Excessive Pump Speed
Operating the pump at too high a speed can reduce suction pressure below vapor pressure, triggering cavitation. This is especially common when a pump is run outside of its Best Efficiency Point (BEP).
How to Detect Cavitation
Cavitation can often be identified before major damage occurs. Look for these warning signs:
- Unusual noise: A “gravel” or “marbles” sound inside the pump
- Vibration: Excessive vibration due to uneven forces on the impeller
- Reduced flow or pressure: Cavitation decreases pump efficiency and head
- Pitting or erosion: Inspect impeller surfaces for damage
- Fluctuating amperage draw: Cavitation can cause erratic motor load behavior
If you notice any of these symptoms, it’s important to shut down the pump and inspect the suction system before more severe damage occurs.
How to Prevent Cavitation
Preventing cavitation starts with proper design, operation, and maintenance practices. Here are key strategies:
1. Ensure Adequate NPSH
- Verify that NPSHa exceeds NPSHr by a comfortable margin
- Minimize suction lift
- Keep suction piping short and free of sharp bends or restrictions
- Increase suction line diameter if needed
2. Eliminate Air and Gas Entrapment
- Check for air leaks in seals, flanges, or fittings
- Maintain proper submergence of suction inlets
- Install air separators or deaerators where applicable
3. Optimize Flow Conditions
- Maintain operation near the pump’s Best Efficiency Point (BEP)
- Avoid throttling suction valves
- Use proper suction piping design guidelines (straight runs, gradual transitions)
4. Control Pump Speed and Operating Range
- Avoid running the pump at speeds higher than designed
- Use variable frequency drives (VFDs) for precise control
5. Monitor and Maintain Regularly
Routine inspection and vibration analysis can catch early cavitation signs before they escalate.
The Cost of Ignoring Cavitation
Ignoring cavitation doesn’t just affect performance—it can lead to irreversible impeller damage, seal failure, bearing wear, and system downtime. These issues quickly escalate into costly repairs or replacement needs.
Preventative measures cost far less than a full pump rebuild or unplanned outage.
FAQs About Centrifugal Pump Cavitation
1. What does cavitation sound like?
Cavitation often sounds like rocks or gravel moving through the pump, caused by collapsing vapor bubbles striking the impeller surfaces.
2. Can cavitation damage be repaired?
Minor pitting can sometimes be repaired by resurfacing or replacing impeller blades, but severe erosion usually requires impeller replacement or a complete overhaul.
3. How can I calculate NPSH?
NPSHa is determined using system conditions (suction pressure, vapor pressure, and elevation), while NPSHr is provided by the pump manufacturer. Always ensure NPSHa > NPSHr by a safety margin of at least 3–5 feet (or more depending on system complexity).
4. Does temperature affect cavitation?
Yes. Higher fluid temperatures increase vapor pressure, making cavitation more likely, even at normal operating pressures.
5. What’s the best way to avoid cavitation long-term?
Proper pump selection, suction system design, and preventive maintenance are the best defenses. Always match the pump’s specifications to your system’s requirements and operating conditions.
Cavitation may start as a subtle vibration or noise, but its consequences can be devastating to a centrifugal pump system. By understanding what causes cavitation and how to prevent it, you can protect your equipment, maintain optimal efficiency, and extend the life of your pumps.
If you suspect your pump is cavitating or want help identifying and preventing future issues, contact Denver Pumps today. Our experts can help you diagnose, repair, and optimize your system for reliable long-term performance.
