If a pressure relief valve for a boiler is accidentally installed on a water heater, it will leak like crazy from the start. These valves may look identical, but they're set to go off at 30 psi ...

Hidden behind the rear bumper or back panel of your vehicle are vents that get used every time you get in and out of your car ...

Normally, you don't see these air extractors (also called exhausters or pressure relief valves) because they're hidden under a plastic bumper cover on the outside, and under trunk trim on the inside.

Most interesting is the integration of the gear pump, 4-way selector valve, and relief valve into a single structure, which was printed with a resin printer (via the JLC3DP 3D print service).