I’m retired from the company that invented the water pressure reducing valve (pressure regulator or PRV). Before I try to explain how it works, I have a few opinions to covey. Having an accurate measurement of the actual water pressure entering your rig is the most vital thing to adjusting a PRV. Guage accuracy is key here. IMO, cheap means likely inaccurate. A PRV cannot increase the pressure above what’s coming out of the supply line - it can only reduce it. Even the best PRVs are recommended by reputable manufacturers to be replaced ever five years (unless it’s tested to verify operation). Preset regulators are typically set at a conservatively lower pressure than most RVs can handle - 35psi is common. Your home typically has 55-65 psi, so don’t expect your RV to have similar flow. Most RVs can withstand 45-50 psi, maybe slightly more if you are a gambler. The more fittings between the PRV and your RV city water inlet, the more the pressure will be reduced below the set pressure. Worst are 90 degree elbows, filters and unusually long hose runs. Any PRV can control water pressure to a given set point, but in actual flow conditions the pressure will drop off because the typical RV setup lacks adequate flow to maintain the set pressure throughout the system. It’s the nature of the beast!
Your home’s pressure reducing valve is typically manufactured to water industry standards, so it’s highly reliable. RV valves may be made to a lower standard, if to a standard at all. Don’t expect accuracy or longevity. Valve quality is not indicated by the dome being metal or plastic, although metal will generally be more expensive.
The PRV uses a spring loaded diaphragm valve that tends to close under higher water pressure. This throttles the higher water pressure coming into the valve until the water pressure on the RV side and the spring pressure on the diaphragm valve are balanced. If the incoming water pressure goes up, the valve closes slightly, if it goes down it opens slightly - all the while keeping the pressure on the RV side at/near the set pressure.
These valves typically fail because the diaphragm has sprung a leak. Watch for water dripping from the dome.
I’m open to questions, or correct from a plumber, which I’m not.
