When priming, water enters the pump because which pressure pushes it into the pump?

• A. Astronomical pressure
• B. Atmospheric pressure
• C. Hydrostatic pressure
• D. Vacuum

Answer: (B)

Priming uses atmospheric pressure to push water into the pump. When you begin priming, the pump interior is at a lower pressure (a partial vacuum) as it tries to draw water. The surrounding air is at atmospheric pressure and presses on the water source, pushing water up into the pump until the pump casing is filled. Once full, normal pumping can start.

The other ideas don’t drive the initial fill: the inside vacuum is what allows atmospheric pressure to act, hydrostatic pressure depends on water depth rather than the priming push, and astronomical pressure isn’t a factor in firefighting priming.