What is cavitation and why is it important?

Cavitation

We'll learn about cavitation. What is cavitation and why is it important?

Cavitation is a phenomenon that often causes damage to equipment such as water pumps, control valves, and other devices that handle fluids, pressure, and temperature.

The damage will appear as if a needle has punctured the bottom. This cavitation effect or air pockets can penetrate the metal or steel.

Cavitation Damage

What is cavitation ?

 There are 2 main types of cavitation:

1. When the temperature of the liquid increases

2. When the pressure decreases (pressure reduction, which is similar to the surface pressure of the flowing liquid, prevents it from vaporizing. There are several ways to reduce pressure, including using a vacuum pump).

Cavitation

Cavitation is the formation of air pockets in a liquid. It occurs when the pressure in a liquid at a constant temperature drops below the boiling point of steam, resulting in vaporization. The vaporized liquid then re-liquidates.

The damage is caused by a phenomenon known as a "single cavitation bubble." This is when a liquid droplet, approximately 3.3 mm in diameter, collapses, and then partially transforms into a gaseous liquid. Shear flow occurs, sucking gas into the surface, creating a microjet that penetrates and damages the workpiece, resulting in pitting.

Cavitation

In the case of a water pump, for example, if the suction pressure is insufficient to meet the pump's requirements, cavitation can also occur.

Pump Cavitation

If we observe the pump's inlet direction, we'll notice that the liquid pressure at the suction end of the pump will decrease. If the suction pressure is less than the vapor pressure, the liquid will change to a gas. As the liquid continues to flow into the pump, the pump will build up pressure, and the gas-based liquid will return to a liquid state. This creates a cavitation effect that destroys the internal components of the pump, creating pores.

Pump Cavitation

Therefore, to prevent cavitation in this case, the pump inlet pressure must be monitored to ensure it is at least within the required specifications. It's not just pumps that can suffer from cavitation effects.

A common problem is valves. When the valve is severely closed, the liquid passing through the valve increases in velocity. As the liquid passes at high speed, the pressure decreases, causing a change in state from liquid to vapor. As the velocity decreases, the pressure increases, and the liquid returns to liquid, causing cavitation effects and damage to the valve interior.

Cavitation Damage

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