Trim & Internals
Cage
The cage is a perforated or slotted cylindrical sleeve surrounding the plug in a globe valve. The plug rides inside it, and the cage windows — not the seat ring alone — meter the flow. Cages do three jobs at once:
- Guiding: they centre the plug over its full travel without bottom-stem guides, keeping the plug concentric with the seat.
- Characterizing: the shape and distribution of the cage windows set the inherent flow characteristic. Interchangeable cages let one body serve linear, equal-percentage or quick-opening duties.
- Balancing: with pressure fed through holes in the plug to the space above, the forces on top and bottom of the plug largely cancel — a balanced trim — allowing far smaller actuators.
In severe service, cage drilling patterns are engineered for cavitation resistance (multi-stage pressure division) and noise reduction (many small jets instead of one large one). Cage valves are today the default architecture for throttling globe service.
Related glossary terms
More like this: browse the full control valve glossary, or see how the terms fit together in How a Control Valve Works.
Editorial note. Definitions reflect common industry usage and the conventions of IEC 60534 and ISA-75. Engineering content is educational; always verify against the applicable standard and manufacturer data.