Is there such a thing as a “dual phase” pressure safety valve (PSV)? Not that I have ever encountered; yet that does not stop some from trying to “educate me” on their dual-phase PSVs. So why does this topic matter? Our PSV’s are our LAST LINE of defense in an overpressure event, and if they are NOT designed properly for the scenario, we can have a catastrophic failure of the pressure vessel. So let’s discuss “phase-matching” of our PSVs.