Opening a discharge on a pump drawing from a tank with the pump in gear demonstrates which pressure principle?

• A. Bernoulli's Principle
• B. Boyle's Law
• C. Pressure applied to a confined fluid from without is transmitted equally in all directions
• D. Archimedes' Principle

Answer: (C)

The main idea here is Pascal’s Law: pressure applied to a confined fluid is transmitted equally in all directions. When the pump draws from the tank and you open the discharge, the fluid is in a closed, continuous system. The pump’s action increases pressure in that fluid, and because the liquid and piping form a confined space, that pressure is transmitted uniformly through the entire system. That’s why opening the discharge allows the pressure generated by the pump to act throughout the line, including back toward the suction side.

The other principles don’t fit this scenario: Bernoulli’s relates pressure to changes in speed and elevation along a streamline, Boyle’s Law is about gas pressure and volume, and Archimedes’ Principle concerns buoyancy.