Journeyman Plumber ExamWater Supply SystemsMedium
A plumber is troubleshooting a domestic hot water system in a multi-story building where residents on upper floors report insufficient hot water flow. The building has a 100-foot rise from the main water entry to the highest fixture. What is the approximate static pressure loss due to elevation in PSI at the topmost floor?
- A23 PSI
- B33 PSI
- C43 PSI
- D53 PSI
Show answer & explanationAnswer & explanation
Correct answer: C. 43 PSI
Water pressure decreases by approximately 0.433 PSI for every foot of elevation gain. For a 100-foot rise, the static pressure loss is 100 feet * 0.433 PSI/foot = 43.3 PSI. Therefore, 43 PSI is the closest approximation.
Why the other options are wrong
- A. 23 PSI would correspond to roughly 53 feet of elevation gain (23 / 0.433).
- B. 33 PSI would correspond to roughly 76 feet of elevation gain (33 / 0.433).
- D. 53 PSI would correspond to roughly 122 feet of elevation gain (53 / 0.433).
Static Head Pressure Loss (Elevation)
The reduction in water pressure due to the vertical rise (elevation) of the plumbing system, where pressure decreases approximately 0.433 PSI for every foot of elevation.
- Caused by the weight of the water column above a point.
- Does not depend on water flow, only elevation.
- Critical factor in sizing pipes and selecting pumps for multi-story buildings.
Memory trick: Higher you go, lower the PSI – 0.433 is the key.