How to Diagnose and Reduce Cavitation Damage in Split Case Pumps

Cavitation is one of the most common and destructive hydraulic problems affecting split case pumps. It occurs when local pressure in the fluid drops below its vapor pressure, causing vapor bubbles to form and collapse violently near the impeller or suction region. These micro-collapses generate high-energy shock waves that result in pitting, vibration, noise, erosion, and premature component failure.

For pumps already in service, early diagnosis and practical mitigation measures are essential to reduce damage and extend equipment life. This article summarizes effective cavitation diagnosis methods and field-proven solutions to reduce cavitation in operating split case pumps.

1. Cavitation Diagnosis Methods for In-Service Split Case Pumps

In field conditions, users often cannot perform factory cavitation tests (such as head-drop testing at constant flow). Therefore, practical diagnostic methods are widely used, often in combination.

Table 1: Comparison of Cavitation Diagnosis Methods

Method	Principle	Advantages	Limitations	Typical Application
Observation	Visual inspection of impeller and casing surfaces	Direct and intuitive	Post-damage only	Failure analysis
Noise	Detects crackling or bursting cavitation sounds	Simple, non-intrusive	Strongly affected by ambient noise	Severe cavitation
Vibration	Measures vibration frequency changes	Easy to deploy	Low sensitivity; masked by other faults	Supplementary use
Ultrasonic	Detects high-frequency signals from bubble collapse	High sensitivity, early detection, real-time monitoring	Requires sensors	Best for early-stage detection

Engineering Note: Ultrasonic detection is the most reliable method for early cavitation diagnosis and is well suited for integration into SCADA or condition monitoring systems.

2. Practical Methods to Reduce Cavitation During Operation

Once cavitation is identified, mitigation should focus on improving suction conditions, reducing inlet losses, and increasing NPSHa.

Table 2: Operational Measures to Reduce Cavitation in Split Case Pumps

Improvement Area	Practical Measure	Cavitation Reduction Mechanism	Implementation Difficulty
Inlet tank design	Install vortex breakers, increase submergence	Prevents air entrainment	Low
Suction piping	Shorten pipe, reduce bends, enlarge diameter	Reduces suction losses	Medium
Inlet pressure	Ejector system, booster pump, pressurized tank	Increases NPSHa	Medium–High
Pump selection	Double-suction split case pump	Improves inlet flow symmetry	Medium

3. Supplying Air into the Suction Line

Introducing a controlled amount of air into the suction line does not eliminate cavitation but can reduce erosion damage to flow passage walls. The air cushions the collapse of vapor bubbles, similar to methods used in hydraulic turbines.

Limitations:

This technique is rarely applied to split case pumps because air flow rate and injection location are difficult to control. Improper air supply can significantly reduce pump head, flow, and efficiency.

4. Use of Anti-Cavitation Materials

Material selection plays a key role when cavitation cannot be fully avoided.

Table 3: Cavitation Resistance of Common Pump Materials

Material Type	Cavitation Resistance	Typical Application
Cast iron	Low	Non-critical services
Bronze / copper alloys	Medium	Mild cavitation
Stainless steel	High	Cavitation-prone systems
Cr-Ni alloy steel	Very high	Severe cavitation environments

Best Practice: Replacing cast iron or copper components with stainless steel or Cr-Ni alloy steels can significantly improve durability in cavitating services.

5. Impeller Surface Protection Methods

Applying protective layers to impellers is a widely used and effective approach.

Table 4: Impeller Protection Technologies

Method	Advantages	Drawbacks	Durability
Epoxy / polymer coating	Low cost, easy application	Peeling over time	Low
Stainless steel surfacing	Good protection	Moderate cost	Medium
Alloy overlay welding	Strong adhesion	Skilled labor required	High
Alloy powder spray welding	Best cavitation resistance	Higher cost	Very high

6. Trimming the Impeller Head

Impeller trimming is a proven hydraulic modification technique. By reshaping and thinning the blade tip near the inlet, local pressure and velocity peaks are reduced. This lowers vapor bubble formation at the blade leading edge and decreases cavitation intensity.

Conclusion

Cavitation damage in split case pumps can be significantly reduced through a combination of diagnostic and mitigation measures rather than a single solution.

Key Guidelines:

Ensure installation height is within allowable suction limits

Keep suction piping short, straight, and free of air pockets

Avoid undersized suction pipes and unnecessary fittings

Monitor noise, vibration, pressure, and temperature during operation

Apply cavitation-resistant materials or surface treatments when needed

Through proper diagnosis, optimized hydraulic design, material upgrades, and proactive maintenance, users can effectively control cavitation, improve reliability, and extend the service life of split case pumps.