A PRV is a Pressure Reducing Valve that is commonly placed on water distribution systems and within individual homes, multi-family homes and businesses.
Have you noticed any differences when using your plumbing items (faucets, shower/tub, hose bib, etc.)? This might be a symptom of your PRV. Is the water too harsh, is the pressure on it too high? Has a home inspector recommended replacing the valve?
Both a screaming noise and a knocking noise are signs of high water pressure. The typical inlet water pressure to a home is about 140 psi. Normally, it should not exceed 60 psi (IPC, 2015). The pressure regulator is usually preset to 55 psi. However, it can be adjusted anywhere from 25 to 75 psi. PRV's typically last 10 years but are usually warrantied for 1 year depending on the manufacturer. It is very common for these valves to fail. Symptoms can be present such as a water heater discharging at the temperature and pressure relief valve or water discharging from a pressure relief valve commonly referred as a thermal expansion valve.
***NOTE**IT IS IMPORTANT TO HAVE YOUR PRESSURE CHECKED AND VALVE SERVICED IN ORDER TO ASSURE THERE IS NOT TOO MUCH PRESSURE THAT CAN RESULT IN DAMGE TO YOUR PLUMBING SYSTEM AND APPLIANCES, INCLUDING PROPERTY DAMAGE OR EXCESS USE RESULTING IN HIGH WATER BILLS.