Short Answer:

Cavitation damages hydraulic machines by forming small vapor bubbles inside the fluid when pressure drops below the vapor pressure. These bubbles suddenly collapse when they move into higher-pressure zones, creating strong shock waves that hit metal surfaces.

This repeated impact wears out parts like impellers, valves, and blades. Over time, cavitation causes surface pitting, vibrations, noise, and performance loss. If not controlled, it reduces machine life and leads to costly repairs in pumps, turbines, and other hydraulic systems used in civil engineering projects.

Detailed Explanation

Cavitation damage in hydraulic machines

Cavitation is a serious problem in hydraulic machines. It occurs when the pressure of a liquid drops below its vapor pressure, forming vapor bubbles in the fluid. These bubbles are not stable. As the fluid moves through the system and pressure rises again, the bubbles collapse violently. This collapsing action releases energy in the form of shock waves, which strike nearby surfaces inside the machine.

This phenomenon mainly occurs in fast-moving fluid areas, especially at the inlet of pump impellers, vanes of turbines, or valve openings. Although the bubbles are microscopic, the energy released when they collapse is very high. Repeated bubble formation and collapse can quickly damage the inner surface of metal parts.

How Cavitation Causes Damage

1. Surface Pitting:
   The collapsing bubbles create tiny high-pressure jets that erode the surface, leaving behind pits or craters. Over time, these pits increase in size and number, weakening the component.
2. Material Wear:
   The repeated forceful impacts loosen surface particles. This leads to gradual wear and thinning of metal parts, especially impeller blades and runner vanes.
3. Noise and Vibration:
   Cavitation causes abnormal noise (like hammering or rattling) and vibrations in the machine. This makes the machine unstable and may lead to loosening of joints or fasteners.
4. Loss of Efficiency:
   Due to roughened surfaces and material loss, the machine cannot move fluid smoothly. This increases power consumption and reduces flow performance.
5. Crack Formation and Failure:
   In extreme cases, the damaged parts may develop small cracks that grow into fractures. This can cause sudden breakdowns and shutdown of equipment.

Areas Commonly Affected by Cavitation:

• Pump impellers and casings
• Turbine blades
• Gate and control valves
• Hydraulic passages with sudden pressure drops

Causes of Cavitation in Hydraulic Machines:

• Low Inlet Pressure: Not enough pressure at the pump suction leads to vapor bubble formation.
• High Fluid Velocity: Fast flow increases the chance of pressure drop below vapor pressure.
• Poor Design: Sharp bends, small inlets, or improper blade angles encourage pressure drops.
• High Fluid Temperature: Higher temperatures reduce vapor pressure, increasing bubble formation.

Preventing Cavitation:

• Ensure adequate Net Positive Suction Head (NPSH) in pump design.
• Maintain correct fluid temperature and avoid overheating.
• Avoid sudden contractions in pipe sections or fittings.
• Use smooth, well-designed inlets and impellers.
• Regularly inspect and maintain hydraulic systems.

In civil engineering systems like water supply pumps, hydroelectric turbines, and irrigation machines, controlling cavitation is critical for long-term performance and safety. Ignoring cavitation can lead to equipment failure and expensive maintenance.

Conclusion:

Cavitation damages hydraulic machines by forming and collapsing vapor bubbles inside the fluid, which strike internal surfaces with great force. This causes surface pitting, noise, vibration, and mechanical wear. Over time, cavitation lowers efficiency and can destroy key components. Civil engineers must design and maintain systems carefully to avoid cavitation and ensure safe, smooth machine operation.