Journeyman Plumber ExamWater Supply SystemsMedium
A plumber is installing a water distribution system in a new commercial building. The design calls for a main cold water supply line to be sized based on a total fixture unit count of 450. Using the Hunter's Curve method for a system with 60 PSI available pressure at the meter and a desired minimum residual pressure of 20 PSI at the highest fixture, what is the approximate required meter and building supply pipe size?
- A1 1/2 inch
- B2 1/2 inch
- C2 inch
- D3 inch
Show answer & explanationAnswer & explanation
Correct answer: C. 2 inch
According to most plumbing codes and Hunter's Curve charts for commercial applications, 450 fixture units with 60 PSI available and a 20 PSI residual requirement typically corresponds to a 2-inch pipe size. This accounts for reasonable pressure loss over the system.
Why the other options are wrong
- A. 1 1/2 inch is generally too small for 450 fixture units, leading to excessive pressure drop.
- B. 2 1/2 inch would be oversized for 450 fixture units, increasing material costs unnecessarily.
- D. 3 inch is significantly oversized for 450 fixture units, leading to higher costs and potentially lower velocities.
Hunter's Curve Water Pipe Sizing
A standardized method used in plumbing to determine the appropriate size of water supply piping based on the total fixture units, available pressure, and desired residual pressure.
- Fixture units represent the probable flow rate for various plumbing fixtures.
- Charts or tables are used to correlate fixture units with pipe size for different pressure loss scenarios.
- Aims to ensure adequate flow and pressure at all fixtures.
Memory trick: Hunter hunts for the right pipe size, balancing flow and pressure.