Why is it needed for safety? The Blue Robotics watertight enclosures have come with a manual vent that has worked great for years. But, their next generation watertight enclosures have a locking cord that secures the flange to the tube and prevents the end cap from coming off.
In the rare situation that an excessive amount of pressure builds up in the tube it can create an unsafe situation and/or damage to the enclosure. Pressure build-up could be due to the buildup of gasses from a chemical reaction like something catching on fire, or from a slow leak into the enclosure while at depth followed by a quick return to the surface. The PRV automatically releases any excess pressure built up inside a watertight enclosure. It works automatically to relieve pressure, and it also works manually, like our original vent.