What is a PRV?
PRV stands for "Pressure Reducing Valve". It is a device that is used at your home to reduce the pressure coming from the water system into your house. Typically, a PRV is installed inside the home right at the point where the water enters the house from the yard or street. A typical PRV for home use looks similar to this:
A PRV works by using a spring and a plate to regulate the speed of the water that flows through the valve - as water speeds up, pressure levels drop. By making the opening through the valve smaller, the PRV reduces the pressure on the other side of the valve. PRVs usually come set from the factory at 50 pounds or so, but are adjustable to different levels, typically by turning the bolt at the top of the valve (the section with the yellow tag in the picture). For most PRVs, when the bolt is tightened, pressure inside the house is increased, and when it is loosened pressure is decreased. Typically, it takes very little turning to change the pressure dramatically, so a homeowner attempting to increase or decrease pressure in their house should probably limit turns to 1/4 turn or less and recheck the results before proceeding.
PRVs can also become clogged with debris. Usually to fix this situation the top of the valve must be removed to clean out the PRV. That means water must be shut off first before taking the valve apart. Often, by the time a valve needs to be disassembled for cleaning, the valve has worn to the point where it will not hold pressure properly anyway (the spring inside the valve begins to have fatigue and not expand properly), and it may be prudent to replace the valve at that time. Homeowners uncomfortable with working on basic plumbing within their homes should contact a licensed plumber to do repairs or adjustments, as poor installations or adjustments could cause serious damage to your home. It is the homeowner's responsibility to determine his or her level of expertise when it comes to installing or adjusting any plumbing devices within their home.