Cavitation is a common issue in centrifugal pumps. If you hear unusual noises from a pump, cavitation is likely the cause. But what exactly is cavitation, and how can it be prevented? Read on to find out.
Cavitation (also known as vapor corrosion) refers to the phenomenon where, during high-speed relative motion between a liquid and a solid surface, local pressure drops below the liquid's vapor pressure, forming bubbles that collapse and cause surface damage to materials. When bubbles move with the fluid to high-pressure areas and collapse, they generate instantaneous impact forces of tens of thousands of psi and high temperatures, leading to fatigue spalling of the metal surface, formation of pockmarks, pits, or even sponge-like damage. This phenomenon commonly occurs in flow-through components such as water pumps, turbines, and propellers. It not only reduces equipment efficiency but also triggers vibrations, noise, and material failure, involving multiple factors such as mechanical impact and electrochemical corrosion.
This is the most frequently mentioned and easily understood cause. When the pressure at the pump's suction end is lower than the liquid's saturation vapor pressure, the liquid rapidly vaporizes to form bubbles. Many engineers only focus on the NPSH value under standard conditions while ignoring dynamic factors such as temperature fluctuations and liquid composition changes during actual operation. It is recommended to introduce a dynamic NPSH evaluation model during the selection phase, considering factors like flow velocity changes and pipeline resistance to improve prediction accuracy.
Even with good overall suction conditions, improper impeller design or operation deviating from the design point can create local low-pressure zones. Blade angles, the shape of the front cover, and even surface roughness can significantly affect the location and intensity of these low-pressure zones, thereby triggering cavitation.
When the pump operates at low flow rates or when the suction pipeline has poor sealing, it may lead to gas entrainment in the liquid or backflow, which increases the risk of cavitation.
When selecting a pump, it is essential to ensure that the system's available net positive suction head (NPSHa) is greater than the pump's required net positive suction head (NPSHr). This is the most fundamental and critical requirement for preventing cavitation.
Reduce the formation of local low-pressure zones through optimizing the internal flow path design of the pump, thereby minimizing the risk of cavitation.
For working environments prone to cavitation, choose high-cavitation-resistant materials for manufacturing key pump components, such as impellers.
In practice, it is often difficult to completely avoid pump operation under non-ideal conditions. Therefore, establishing an effective monitoring system to real-time monitor the pump's working status and adjust operating parameters promptly based on actual conditions is essential. This helps identify and correct operating conditions that may lead to cavitation in a timely manner.
Good installation practices, including proper pipeline layout, avoiding unnecessary bends and excessively long inlet pipes, are crucial for reducing cavitation. Meanwhile, regular maintenance can not only detect potential issues in a timely manner but also maintain the pump's optimal performance through cleaning, replacing worn components, etc.
High-Temperature Hot Water System
Issue: Frequent cavitation in a 105°C hot water pump.
Solution: Install a pre-pressurized pump to increase the system's NPSHa from 3 meters to 6 meters. This method effectively increases the liquid pressure entering the pump, reducing the risk of liquid vaporization and bubble formation at the pump inlet.
Volatile Liquid Transportation
Issue: The impeller of a liquefied petroleum gas (LPG) pump was damaged by cavitation within 3 months.
Retrofit Solution: Adopt an inducer design. By optimizing the pump's design, especially introducing an inducer to improve the pressure distribution before the liquid enters the impeller, the NPSHr was reduced from 4.2 meters to 2.8 meters. This approach reduces the likelihood of cavitation and extends equipment service life.
Large Water Conservancy Project
Issue: Severe cavitation noise (95dB) in a water intake pump station.
Optimization Measure: Change the drive motor from a 6-pole to an 8-pole motor, reducing the rotational speed from 980rpm to 735rpm. Lowering the speed can reduce the velocity gradient of the fluid inside the pump, thereby minimizing the formation of local low-pressure zones and alleviating cavitation. Additionally, lower speeds help reduce wear and tear between mechanical components and mitigate vibrations and noise caused by cavitation.
Regular Monitoring: Detect early signs of cavitation through vibration, noise, and performance testing.
Optimize Operation: Keep the pump running within the high-efficiency zone and avoid prolonged low-flow or high-load operation.
Material Upgrades: Use cavitation-resistant materials (such as stainless steel or duplex steel) and perform surface strengthening treatments when necessary.
Cleaning and Corrosion Prevention: Regularly clean the impeller and flow paths to prevent scaling and corrosion from reducing cavitation resistance.
System Improvement: Optimize the suction pipeline layout and install buffer tanks or flow stabilizers when necessary.
Preventing cavitation is crucial for ensuring the efficient and stable operation of pump equipment during maintenance. Effective cavitation damage prevention can be achieved through regular monitoring of vibrations and noise, optimization of operating conditions, selection of cavitation-resistant materials, maintenance of system cleanliness, and improvement of system design. As a leading pump solution provider in the industry, TEFFIKO is committed to delivering high-quality, high-performance products. Our products undergo rigorous testing to ensure excellent performance under various working conditions and have gained wide trust with competitive prices and superior services. Choose TEFFIKO, and you will receive support from a professional team and worry-free after-sales protection.
