In the Field · Part 4
Low pressure: the PRV, galvanized pipe, and the sequence that finds which one it is
"Low pressure" is the customer's word for three different problems: low static pressure from the street or a failed regulator, low flow from pipe that has closed up inside, and a fixture that is clogged at the aerator. Each has a different fix and a different price, and the gauge on the hose bibb tells them apart in the first five minutes. This lesson is the sequence: static, then flow, then isolate by fixture and by section, then the ladder, which runs from a $12 aerator to a whole-house repipe of galvanized pipe, with the pressure-reducing valve in the middle as both the most common cause and the most common cure.
What the full lesson covers
- Static pressure at the hose bibb with nothing running: under 40 psi is a supply or regulator problem; 40 to 80 is normal; over 80 requires a regulator by code (CPC 608.2). A regulator that reads low static has failed closed; one that reads high has failed open.
- Flow: open a second fixture while watching the gauge. A large drop under flow with normal static means restriction, which in a pre-1960s house means galvanized pipe closing up with rust and scale.
- Isolate: one fixture low is the fixture (aerator, cartridge, supply line, angle stop); one bathroom low is the branch; hot only is the heater's dip tube or nipples; everything low with good street pressure is the regulator or the main line.
- The ladder: clean or replace the fixture parts; replace the regulator (with the expansion tank the code requires); replace the failed branch; repipe the galvanized house, sized by fixture units.
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More lessons in The Field: Method, Code, and Cases
- 1The diagnostic method: verify, isolate, cheapest test first, cause not symptom, the options ladder, document
- 2Permits: when one is required, what is exempt, pulling it online, the inspection sequence, what inspectors look for, and handling corrections
- 3Daily-use code: drainage slope, venting, water sizing, cleanouts, trap arms, and fixture units, with the section for each
- 4Gas piping in practice: sizing, CSST bonding, the pressure test, appliance connectors and shutoffs, sediment traps, and seismic shutoff valves