Cavity Relief

Cavity relief is a critical feature in Double Block and Bleed ball valves, designed to manage pressure build-up caused by trapped media inside the valve body. In process and pipeline systems operating across wide temperature ranges, liquids and gases can expand rapidly when heated, creating internal cavity pressure that must be relieved safely while maintaining isolation integrity. In this video, we explain why cavity relief matters, how trapped pressure develops inside DBB valves, and how different valve designs manage it. We look at floating ball valves, where pressure can be relieved from the body cavity back into the valve bore through ball movement and pressure differential, and trunnion-mounted ball valves, where spring-loaded seats move away from the ball once cavity pressure exceeds spring force. The video highlights how this automatic internal relief mechanism protects valve integrity without external venting or operator intervention, making it especially important in demanding services such as cryogenic and LNG applications. Oliver Valves DBB solutions are engineered to manage thermal expansion, control internal pressure, and provide safe, reliable isolation in critical operating environments.