What It Is
A pressure-reducing valve (PRV) is a spring-loaded device installed on the main water supply line that automatically reduces high municipal water pressure to a safe, steady level for residential use. Without one, pressure from the street - which can exceed 150 psi - would stress pipes, damage fixtures, and cause water hammer throughout the home. Most PRVs are factory-set between 50 and 75 psi and are adjustable within a range.
What It Does
The PRV acts as a pressure governor. Municipal water systems maintain high pressure to serve tall buildings, fire hydrants, and long distribution lines. That same pressure arriving at a residential fixture would shorten the life of faucets, washing machine hoses, and water heaters significantly. The PRV reduces it to a household-safe range and keeps it consistent regardless of fluctuations in street pressure.
A functioning PRV also reduces water hammer - the banging sound that occurs when water flow is suddenly stopped. High-pressure water stopped abruptly creates a larger hydraulic shockwave than lower-pressure water.
Where It Is Located
The PRV is installed on the main water supply line, usually near where the line enters the home through the foundation wall. It sits after the main shutoff valve and often before the water meter or expansion tank. It looks like a bell-shaped or bulge-shaped fitting with an adjustable hex nut or screw on top.
How It Works
Inside the PRV body is a spring-loaded diaphragm. Incoming high-pressure water pushes against the diaphragm; the spring provides opposing resistance. The balance point determines the outlet pressure. When street pressure rises, the diaphragm moves to close the valve slightly, maintaining consistent outlet pressure. Turning the adjustment screw compresses or releases the spring to raise or lower the set point.
PRVs have a typical service life of 10 to 15 years. The internal diaphragm and seat can wear out or debris can lodge in the valve seat, causing it to pass high pressure or fail to regulate consistently.
Common Problems or Signs of Failure
- Sudden increase in water pressure throughout the home - PRV no longer regulating
- Banging pipes (water hammer) that weren't present before
- T&P relief valve on water heater opening - excess pressure entering the system
- Chattering or humming sound from the valve under flow
- Low pressure throughout the home after years of normal operation - PRV spring has weakened
- Water dripping from the PRV body - internal seal failure
Can a Homeowner Check It?
- Attach a pressure gauge to a hose bib or washing machine connection to read your current household pressure
- Ideal range is 45-75 psi - readings above 80 psi indicate the PRV may not be functioning correctly
- Look at the PRV body for signs of moisture or corrosion around the connections
- Note when pressure-related symptoms started - sudden changes suggest a valve failure, gradual drift may be an adjustment issue
When to Call a Plumber
Call a plumber if your water pressure reads above 80 psi, if you have sudden pipe banging, or if the T&P valve on your water heater opens unexpectedly. A plumber can test the PRV, adjust it if it's still functional, or replace it if the diaphragm or seat has failed. PRV replacement is straightforward for a plumber and typically takes under an hour.
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