A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially higher or lower than the ambient pressure. Examples include glassware, autoclaves, compressed gas cylinders, compressors (including refrigeration), vacuum chambers and custom designed laboratory vessels.  

Pressure vessels, autoclaves and steam sterilizers operating at pressures greater than 15 pounds per square inch gauge (psig) and larger than five cubic feet (ft3) volume fall within the Washington State Boiler and Pressure Vessel Code. As such, they have strict requirements for design, testing and approval.