Which action reduces vapor pressure and helps prevent cavitation?

• A. Increase fluid temperature
• B. Increase flow rate
• C. Keep fluid temperature low
• D. Increase pipe diameter

Answer: (C)

Vapor pressure is the pressure at which a liquid begins to boil at a given temperature, and it rises as temperature increases. Cavitation happens when the local pressure in the system drops below this vapor pressure, causing bubbles to form and then collapse violently. Keeping the fluid temperature low lowers the vapor pressure, so the same system pressures are more likely to stay above the vapor pressure. This reduces the chance of vapor bubble formation and thus cavitation.

Raising the fluid temperature would raise vapor pressure, making cavitation more likely. Changing flow rate or pipe diameter can affect pressure drops and flow conditions, but they don’t directly reduce the liquid’s vapor pressure, so they’re not the primary way to prevent cavitation.