Calculation & Generation Results
About This Tool
Calculate municipal inlet water pressure drop, target downstream PSI (ASSE 1003 code limits 45-60 PSI), valve falloff, cavitation hazard, and required valve body size.
Frequently Asked Questions
Why does the Uniform Plumbing Code (UPC) require a PRV above 80 PSI?
Water pressures above 80 PSI void appliance manufacturer warranties (water heaters, dishwashers, washing machines), rupture toilet fill valves, accelerate pipe erosion, and trigger violent water hammer.
What causes PRV cavitation?
When high-pressure water drops drastically across a narrow valve seat (ratio greater than 3:1 or delta P > 80 PSI), localized pressure plunges below water vapor pressure. Vapor bubbles form and collapse violently, pitting and chewing through metal valve bodies.
What is 'falloff' in pressure regulators?
Falloff is the natural reduction in downstream pressure that occurs when water starts flowing through the valve compared to static pressure when all faucets are closed, typically 5 to 15 PSI.
Why does adding a PRV require a thermal expansion tank?
A PRV contains a check-valve mechanism that turns your home into a closed plumbing system. When the water heater warms up, thermal water expansion has nowhere to expand, spiking pressure to 150 PSI and discharging the safety relief valve.