Cavitation In Pump

Cavitation is a common and highly destructive phenomenon in liquid flow systems. Understanding the causes and impacts of cavitation is of great significance for effectively preventing and controlling cavitation, protecting equipment, and improving system efficiency.

What is cavitation?

Definition

Reasons for Formation

1. Low-pressure zones: When the liquid flows through certain areas, such as the impeller inlet of a pump, the pressure drops below the vapor pressure of the liquid, causing the liquid to evaporate and form bubbles.
2. High velocity: Excessively high liquid flow rates can also cause a pressure drop, leading to bubble formation.
3. Increased temperature: Elevated temperatures lower the vapor pressure of the liquid, making it easier for bubbles to form.

Effects of Cavitation On Pumps

Physical Damage

• Impeller damage: Bubbles form and rapidly collapse on the impeller surface, generating strong localized impact forces that cause pitting, cracking, and even fracturing of the impeller.
• Pump casing damage: Cavitation can damage not only the impeller but also the pump casing, causing impact and abrasion that results in surface erosion, pitting, and other defects.
• Bearing damage: The vibrations caused by cavitation lead to abnormal wear on bearings, reducing their lifespan.

Performance Degradation

• Flow reduction: Cavitation reduces the pump’s flow rate because bubbles occupy part of the fluid passage, obstructing the normal flow of liquid.
• Efficiency loss: Cavitation causes unstable fluid flow, significantly lowering the pump’s energy conversion efficiency and increasing energy consumption.
• Pressure fluctuations: The formation and collapse of bubbles induce pressure fluctuations within the pump, affecting its stable operation.

Noise and Vibration

• Abnormal noise: Cavitation generates high-frequency noise, often described as a “gravel” or “knocking” sound, which is a typical characteristic of cavitation.
• Increased vibration: The shock waves caused by cavitation lead to pump body vibrations, which, over time, affect the operational stability of the pump and can damage its structure.

Reduced Pump Lifespan

• Accelerated wear: Physical damage and vibrations caused by cavitation accelerate the wear of internal pump components, shortening the pump’s operational lifespan.
• Frequent maintenance: Damage from cavitation necessitates more frequent repairs and component replacements, increasing maintenance costs and downtime.

The effects of cavitation on pumps are manifold, including physical damage, reduced performance, increased noise and vibration, and shortened pump life. By understanding the causes and effects of cavitation and taking effective preventive and control measures, we can significantly reduce the damage of cavitation on the pump, extend the pump’s service life, and improve the overall operating efficiency of the system.

Cavitation In Different Types Of Pumps

Pump Type	Common Cavitation Issues	Effects	Affect
Centrifugal Pump	Suction cavitation discharge cavitation	Impeller  damage, efficiency loss increased noise and vbration	Increase suction pressure, optimize impeller design, use anti-cavitation materials
Axial Flow Pump	Suction cavitation, turbulent cavitation	Control flow speed, use wear- resistant materials,regular maintenance	Control flow speed, use wear- resistant materials, regular maintenance
Mixed Flow Pump	Suction cavitation, discharge cavitation	Screw surface damage, increased noise, efficiency loss	Pump chamber damage, seal wear, flow fluctuations
Screw Pump	Suction cavitation, discharge cavitation	Performance  degradation, blade damage increased noise and vbration	Control flow speed, use wear- resistant materials, regular maintenance
Positive Displacement Pump	Suction cavitation, turbulent cavitation	Control pump inlet pressure, regular inspection and maintenance, optimize operational conditions	Control inlet pressure, use high-strength materials, and regularly replace seals.

Common Types Of Cavitation

1. Suction Cavitation

• Definition: Occurs at the pump’s suction inlet or impeller inlet area when the liquid pressure drops below the vapor pressure, causing the liquid to evaporate and form bubbles.
• Impact: Causes severe wear on the impeller surface, decreases efficiency, and generates noise and vibration.

2. Discharge Cavitation

• Definition: Occurs at the pump’s discharge outlet when the discharge pressure is too high, causing the bubbles in the liquid to collapse in high-pressure areas rapidly.
• Impact: Leads to damage to the discharge piping and impeller, reducing the pump’s performance and efficiency.

3. Turbulent Cavitation

• Definition: Occurs in turbulent areas of liquid flow where rapid changes in fluid velocity cause a localized pressure drop, leading to bubble formation.
• Impact: Causes pump vibrations, increased noise, and localized wear.

4. Blockage Cavitation

• Definition: Occurs when the fluid passes through narrow areas or encounters obstacles, causing an increase in local flow velocity and a pressure drop, leading to bubble formation.
• Impact: Results in decreased pump flow and efficiency, and localized damage to the impeller and pump casing.

5. Recirculation Cavitation

• Definition: Occurs at the impeller edges or within flow passages when fluid recirculation causes a localized pressure drop, leading to bubble formation.
• Impact: Causes severe wear at the impeller edges, increases noise and vibration, and reduces pump efficiency.

Prevention and Control of Cavitation

• Control flow rate: Ensure the pump operates within the design flow range and avoid low-flow operation. Install flow control valves to prevent excessively high or low flow rates.
• Maintain appropriate liquid temperature: Control the liquid temperature to prevent it from becoming too high and causing an increase in vapor pressure. Use cooling devices or heat exchangers to keep the liquid temperature within a safe range.
• Reduce suction line resistance: Optimize the design of the suction line to minimize the use of elbows and valves. Increase the diameter of the suction line and use pipes with smooth inner walls.

Maintenance Pump Cavitation

• Regularly Inspect Impeller and Pump Casing
• Vibration and Acoustic Monitoring
• Timely Replacement of Damaged Components

Effects of Cavitation On Fluid Equipment

Valves

• Impact: Cavitation causes wear and cracking of valve seats and discs, affecting sealing and control performance.
• Prevention: Use cavitation-resistant materials and designs, and control flow rate and pressure differential.

Pipes and Fittings

• Impact: Cavitation-induced vibration and shock lead to wear, cracks, and pipe rupture.
• Prevention: Use thick-walled or cavitation-resistant lined pipes, optimize layout, and install anti-cavitation devices.

Turbines

• Impact: Cavitation causes pitting and spalling on blade and casing surfaces, reducing efficiency.
• Prevention: Use cavitation-resistant materials, control water flow speed and pressure, and perform regular maintenance.

Ship Propellers

• Impact: Cavitation causes pitting and cracking on propeller blades, reducing efficiency and increasing vibration and noise.
• Prevention: Use high-strength materials, optimize blade design, and perform regular inspections and maintenance.

Heat Exchangers

• Impact: Cavitation causes erosion and cracking on tube bundles and casing surfaces, reducing heat exchange efficiency.
• Prevention: Use cavitation-resistant materials, control flow rate, and pressure, and perform regular inspections and cleaning.

Inlet and Outlet Devices

• Impact: Cavitation causes erosion and wear on surfaces, increasing flow resistance.
• Prevention: Design reasonable shapes, use cavitation-resistant materials, and perform regular inspections and maintenance.

Summary

Cavitation causes severe wear and damage to pump components, reducing efficiency and performance. It also generates noise and vibrations, requiring more frequent maintenance and shortening the overall lifespan of the pump. Therefore, maintaining and preventing pump cavitation is crucial.

The AOBL pump has high-quality, cavitation-resistant materials, offering excellent durability and longevity. It operates quietly with minimal vibrations, reducing maintenance needs and extending the overall lifespan of the pump. In addition, we also offer chemical pumps, sanitary diaphragm pumps, EODD diaphragm pumps. Feel free to contact us, our engineering team is here to assist you every step of the way.