A control valve is a system consisting of valve and actuator with components to attach it to the valve or the actuation package. The basic type is known by how the valve is actuated, and the two types of actuation package in common use output linear or rotary motion to the valve stem. In general the motion of the internal components that serve to restrict flow, the valve trim, move in the same manner as the valve stem
A linear-motion control valve trim is composed of a fixed orifice restricted by a component that moves along or normal to the flow through the orifice. Axial-motion trim are found in globe-style (Z-pattern) and Y-pattern valves. The moveable component may consist of a shaped plug that varies the annular area between it and the orifice perimeter, or a sleeve that has a pattern of radial openings. A gate valve employs a component that moves in the plane of the orifice normal to fluid flow.
The moveable component in a rotary motion control valve trim includes the flow orifice. As it rotates, the flow area is restricted by the surrounding stationary components. Ball valves and plug valves are examples of this type of variable restriction.