How does vertical elevation affect discharge pressure requirements?

• A. Elevation has no effect on discharge pressure
• B. Elevation reduces pressure by 2 psi per foot
• C. Elevation adds approximately 0.433 psi per foot of rise
• D. Elevation adds about 10 psi per floor

Answer: (C)

Vertical elevation affects discharge pressure because water has weight, creating hydrostatic head as you lift the water to a higher point. For water, the hydrostatic pressure increase is about 0.433 psi for every one foot of rise. So to keep the same nozzle pressure at a higher elevation, you must add roughly 0.433 psi to the pump discharge pressure for each foot of elevation gained, in addition to accounting for friction losses in the hose.

For example, raising the outlet by 20 feet requires about 8.7 psi more pressure at the pump to maintain the same nozzle pressure (ignoring friction).

This is why the statement stating that elevation adds approximately 0.433 psi per foot is the correct understanding. The idea that elevation has no effect is incorrect, and suggesting 2 psi per foot overstates the head. Saying it’s per floor at 10 psi is also inaccurate, since a typical floor (about 10 feet) would be closer to 4.3 psi per floor.