Valve Trim

The trim is a way of altering the behaviour of the valve to suit the fluid and the process.

A "linear" trim will vary the valve aperture linearly in response to the input signal. It may be that this response introduces instability in the control system, in which case other trims might be more suitable. "Equal percentage" is another style of trim, for example.

Trim behaviour is a function of the shapes of the valve seat and the valve plug, which must be matched. Seats and plugs are usually changeable.

Collectively, a valve's internal elements are known as it's "trim". Typically, valve trim includes four components: disk, seat, stem, and sleeves. The disk and seat interface, and the relation of the disk position to the seat, affect valve performance.