CSLB C-36 Plumbing ContractorPlanning and EstimatingMedium
A plumbing contractor is planning the layout for a new residential water supply system. The plans call for a minimum water pressure of 40 psi at the highest fixture. The municipal water supply provides 60 psi at the property line. The contractor estimates a static head loss of 10 psi due to elevation and an additional 8 psi friction loss for the entire system. What is the expected water pressure at the highest fixture?
- A42 psi
- B48 psi
- C52 psi
- D58 psi
Show answer & explanationAnswer & explanation
Correct answer: A. 42 psi
To find the expected water pressure at the highest fixture, subtract all losses from the initial supply pressure: 60 psi (supply) - 10 psi (static head loss) - 8 psi (friction loss) = 42 psi.
Why the other options are wrong
- B. This might be a miscalculation or only subtracting one type of loss.
- C. This might be a miscalculation or only subtracting one type of loss.
- D. This only subtracts the static head loss (60 - 10 = 50), or other incorrect calculation.
Water Pressure Calculation
Water pressure at a fixture is calculated by subtracting all pressure losses (static head, friction) from the initial supply pressure.
- Static head loss occurs due to elevation changes (1 psi per 2.31 feet of elevation gain).
- Friction loss occurs as water flows through pipes, fittings, and valves.
- Total pressure at fixture = Supply pressure - Static head loss - Friction loss.
Memory trick: Starting pressure minus the 'downs' of elevation and pipe rub equals final pressure.