As the plug lifts, it uncovers windows or holes in the cage wall, and the shape of those openings sets the flow characteristic. Cage guiding keeps the plug stable against side loads, and multi-hole or stacked-disc cages split the pressure drop into many small jets to cut noise and cavitation damage. Swapping cages is a standard way to change characteristic or capacity.
Cage on the letdown valve is eroded around the bottom holes, that's why we can't get it to shut off.
Also heard as
- sleeve
Related terms
Trim
The replaceable internal parts of a valve that touch the process fluid, such as seat, disc or plug, stem and cage.
Control valve
A power-operated valve that modulates flow on a controller signal to hold pressure, level, flow or temperature at setpoint.
Cavitation
Vapor bubbles forming and then collapsing in a liquid passing through a valve, causing noise, vibration and pitting.
Flow characteristic
The relationship between how far a valve is open and how much flow it passes.