What does vapor pressure refer to in the context of cavitation?

• A. The atmospheric pressure
• B. The pressure at which a liquid begins to vaporize at a given temperature
• C. The discharge pressure at a pump
• D. The pressure drop across a valve

Answer: (B)

Vapor pressure is the pressure exerted by a liquid’s vapor when the liquid and vapor are in equilibrium at a specific temperature. It represents how readily the liquid tends to vaporize: at that temperature, vapor molecules escape into the gas phase and push on the liquid surface.

In cavitation, the surrounding fluid experiences a drop in local pressure. When the local pressure falls to the liquid’s vapor pressure, vapor bubbles form. These bubbles can then travel to higher-pressure regions and collapse violently, producing shock waves that can damage surfaces and disrupt flow. This concept is distinct from atmospheric pressure, pump discharge pressure, or valve pressure drop; vapor pressure is a temperature-dependent property that governs when cavitation bubbles can form.