In todays modern refineries, the need to achieve pressure control is available by the use of variable orifice valves in lieu of conventional orifice chambers. An orifice is a small opening or hole in a plate or pipe or body. The Vortex Quantum Orifice Gate is specifically engineered to handle dry bulk solids in gravity flow, dilute phase, or vacuum conveying systems with pressures up to psig (barg) depending on size. The first column is the API letter designation for the orifice, followed by the API and then the ASME orifice areas in the next two columns. the final, purchase relief valve can be greatly oversized.
An orifice valve is a flow control valve that is used to restrict or control the fluid flow.
Relief Valve Orifice Sizes - Control and Instrumentation
When the fluid passes through the orifice, the fluid flow gets restricted. Variable Orifice Valves - TapcoEnpro Variable Orifice Valve Improved Safety and Reliability of Flue Gas Systems with Variable Orifice Valves.