How often should PRVs be inspected and/or recalibrated to make sure they are functioning properly? Is there a good guide on how to recalibrate a PRV? I read somewhere that all PRVs made in the last decade or so had to also have vacuum relief ability. Is this true? It certainly would be nice to know that our safety valves can help protect against over and pressurization.

The Safety Exchange Says: PRVs and VRVs (vacuum relief valves) are important safety components on fermenters, bright beer tanks, and other brewery vessels. A VRV can keep a tank from collapsing like a beer can, while a PRV can prevent a cataclysmic rupture that could serious injure a passerby. Some devices relieve both pressure and vacuum, or you can install both devices.

PRVs tend to either have a spring that is rated to a particular pressure or have a frangible bar that fails above a certain pressure. Some designs are adjustable, but most are factory set. A common reason for tank failure is the buildup of fermentation residues in the PRV that prevent the mechanism from working correctly. You should determine the frequency of inspection and cleaning based on experience. Considering the possible consequences, more often than needed is way better than not often enough.