Valve & Pneumatics Glossary

Glossary

• Rotary actuator: A pneumatic drive that produces quarter-turn (90°) rotary output to open and close a ball or butterfly valve, typically via a rack-and-pinion mechanism.
• Linear actuator (air cylinder): A pneumatic drive that produces straight-line thrust, used for gate/slide valves, dampers and general push-pull automation.
• Double acting: An actuator that uses air pressure to move in both directions (open and close) and holds its last position if air supply is lost.
• Single acting (spring return): An actuator that uses air to move one direction and an internal spring to return it - providing a defined fail-safe position on loss of air supply.
• ISO 5211: The international standard defining the mounting flange dimensions and drive-square size between a part-turn actuator and the valve it operates.
• Namur interface: A standardised mounting pattern (per VDI/VDE 3845) for fitting solenoid valves and limit switch boxes directly onto a pneumatic actuator, without separate tubing.
• Solenoid valve: An electrically operated valve that switches compressed air to pilot a pneumatic actuator.
• Directional control valve (DCV): A valve that routes compressed air between different ports to control the direction of actuator movement - commonly described by port/position count, e.g. 5/2 or 3/2.
• 5/2 valve: A directional control valve with 5 ports and 2 switching positions - the standard configuration for piloting a double-acting actuator.
• 3/2 valve: A directional control valve with 3 ports and 2 switching positions - typically used for single-acting actuators or simple on/off air switching.
• Positioner: A device fitted to an actuator that drives the valve to a proportional (modulating) position in response to a control signal, rather than simple full-open/full-close.
• FRL unit: Filter-Regulator-Lubricator - a combined air-preparation unit that filters contaminants, regulates supply pressure and lubricates downstream pneumatics.
• Fail-safe: The defined behaviour of a valve/actuator on loss of air supply or power - e.g. "fail closed" or "fail open" - specified according to what is safest for the process.
• Class VI leakage: The tightest standard bubble-tight shut-off classification for a soft-seated valve (per ANSI/FCI 70-2) - effectively zero measurable leakage across the closed valve.
• IBR: Indian Boiler Regulations - governs the design, manufacture and certification of boiler and pressure-vessel fittings (safety valves, steam stop valves, etc.) in India.