Short Answer:

Cavitation is a harmful phenomenon that occurs when vapor bubbles form and collapse in a liquid due to a drop in pressure below the vapor pressure. The effects of cavitation are severe and can damage the hydraulic machines like pumps and turbines. It reduces efficiency, causes vibrations, noise, and leads to pitting or erosion of the metallic surfaces. Cavitation also decreases the overall performance and life of the equipment.

Cavitation effects are not only mechanical but also operational. The continuous formation and collapse of vapor bubbles generate shock waves that erode the turbine blades and impeller surfaces. Over time, this leads to increased maintenance costs, reduced power output, and unbalanced operation. Therefore, cavitation must be avoided through proper design and operation of hydraulic systems.

Detailed Explanation :

Effects of Cavitation

Cavitation has several negative effects on the performance, safety, and durability of hydraulic machines. When vapor bubbles collapse near metal surfaces, they release a large amount of energy in the form of micro-jets and shock waves. These high-pressure impacts strike the surface repeatedly, leading to physical damage, noise, and vibration. Below are the main effects of cavitation explained in detail:

Erosion of Metal Surfaces:
The most visible and harmful effect of cavitation is erosion or pitting. When vapor bubbles collapse, they generate localized high pressure and temperature. This causes tiny portions of the metal surface to break away. Over time, small pits merge to form rough and damaged surfaces, particularly on turbine blades, pump impellers, and draft tubes. This erosion reduces the smoothness of surfaces, which further disturbs fluid flow and worsens cavitation.
Loss of Efficiency:
Cavitation reduces the overall efficiency of turbines and pumps. When vapor bubbles are present, they occupy the space meant for liquid flow. This reduces the effective area of flow and the energy transfer between the fluid and the turbine blades or pump impeller. As a result, the output power decreases while input energy remains constant, leading to lower efficiency.
Vibration and Noise:
The rapid formation and violent collapse of vapor bubbles create high-frequency vibrations and loud noise. These vibrations can cause misalignment, loosen bolts, and damage bearings or other supporting components. The noise produced is often a distinct crackling or rattling sound, indicating severe cavitation conditions. In large turbines or pumps, this vibration can lead to fatigue failure of parts.
Structural Damage and Fatigue:
The repeated impact from collapsing bubbles leads to cyclic stress on the metal surface. This cyclic loading weakens the material over time, causing fatigue cracks and structural failure. In extreme cases, parts like blades, impellers, or casings may completely fail if cavitation is not controlled.
Reduced Flow and Pressure:
Cavitation reduces the flow rate and pressure head of pumps and turbines. The presence of vapor bubbles lowers the fluid density, which decreases the effective flow and increases flow resistance. This reduction in head and discharge directly affects the performance of hydraulic machines, making them operate below their designed capacity.
Corrosion and Material Degradation:
The combination of cavitation erosion and electrochemical reactions leads to faster corrosion. When the protective oxide layer on metal surfaces is damaged by bubble collapse, the exposed metal reacts with the surrounding fluid, resulting in rusting or oxidation. This accelerates wear and shortens the life of the equipment.
Unbalanced Operation:
Cavitation may occur unevenly on different parts of the turbine or pump. This causes unbalanced forces on the rotating elements, leading to unstable operation. The imbalance can further increase vibrations, mechanical stresses, and energy losses, making the machine unsafe for long-term operation.
Increased Maintenance and Operational Cost:
Continuous cavitation damage demands frequent maintenance and replacement of worn parts. This increases downtime and operational costs. The repair of components such as turbine runners, impellers, or casings is expensive and time-consuming, reducing the economic efficiency of the system.
Reduction in Life of the Equipment:
Due to erosion, fatigue, and corrosion, the working life of turbines and pumps is greatly reduced. Machines subjected to cavitation require early replacement compared to those operating under proper conditions. The overall lifespan of the equipment becomes shorter, affecting reliability and long-term productivity.

Conclusion:

Cavitation causes severe damage to hydraulic machines, reducing their efficiency, performance, and lifespan. Its main effects include metal erosion, vibration, noise, corrosion, and operational instability. Continuous cavitation can make machines unsafe to operate and increase maintenance costs. Therefore, it is essential to control cavitation by maintaining proper pressure levels, ensuring smooth flow passages, and designing components that minimize sudden pressure drops. Prevention of cavitation ensures better performance and long-term reliability of hydraulic systems.