A valve system comprising: a valve assembly configured to alter at least one flow characteristic of fluid flow through the valve system, the valve assembly comprising a valve stem movable within a support frame; a valve actuator configured to move the valve stem of the valve assembly between at least two positions along a first axis of movement within the support frame; and a positioner assembly being configured to sense at least one of the at least two positions of the valve stem of the valve assembly, a rotatable element of the positioner assembly configured to rotate about a second axis of movement that is laterally offset from the first axis of movement, the first axis of movement being substantially parallel to the second axis of movement, wherein the rotatable element comprises at least one track exhibiting a substantially helical shape extending about an outer portion of the rotatable element and the positioner assembly comprises at least one track follower that interacts with the at least one track in order to rotate the rotatable element in response to linear movement of the valve stem of the valve assembly; characterised in that the positioner assembly, including the rotatable element, is positioned directly adjacent and coupled to the support frame, in that the rotatable element is movably coupled to the support frame via a bracket assembly and one or more bearing assemblies, and in that the coupling between the valve stem and the track follower includes a first linkage, configured as a removable plate or arm, coupled to the track follower and a second linkage coupled to the valve stem and configured to guide the valve stem along a track defined along the support frame. a valve assembly configured to alter at least one flow characteristic of fluid flow through the valve system, the valve assembly comprising a valve stem movable within a support frame; a valve actuator configured to move the valve stem of the valve assembly between at least two positions along a first axis of movement within the support frame; and a positioner assembly being configured to sense at least one of the at least two positions of the valve stem of the valve assembly, a rotatable element of the positioner assembly configured to rotate about a second axis of movement that is laterally offset from the first axis of movement, the first axis of movement being substantially parallel to the second axis of movement, wherein the rotatable element comprises at least one track exhibiting a substantially helical shape extending about an outer portion of the rotatable element and the positioner assembly comprises at least one track follower that interacts with the at least one track in order to rotate the rotatable element in response to linear movement of the valve stem of the valve assembly; characterised in that the positioner assembly, including the rotatable element, is positioned directly adjacent and coupled to the support frame, in that the rotatable element is movably coupled to the support frame via a bracket assembly and one or more bearing assemblies, and in that the coupling between the valve stem and the track follower includes a first linkage, configured as a removable plate or arm, coupled to the track follower and a second linkage coupled to the valve stem and configured to guide the valve stem along a track defined along the support frame.