Illinois Plumbing Code Practice

The correct choice for what pressure tanks supplying water should be equipped with is a pressure relief valve. This device is crucial because it ensures safe operation by preventing excessive pressure build-up inside the tank. When the system generates pressure beyond the safe threshold, the pressure relief valve automatically opens to release excess pressure, protecting both the tank and the plumbing system from potential damage or failure.

The other options do not solely provide the necessary safety functions that a pressure relief valve offers. A check valve prevents backflow but does not address pressure issues within the tank itself. A pressure gauge is important for monitoring current pressure levels but does not serve to relieve pressure. A vacuum relief valve, while useful in specific systems, is not universally required for pressure tanks as it mainly deals with vacuum situations rather than excess pressure.