Valve positioner and method of making same

Abstract

A self-contained valve positioner having a single valve positioner housing including an actuator portion having a pneumatically operated actuator unit therein carrying a main valve member to position the main valve member relative to a main valve seat in a valve unit in relation to the magnitudes of first and second pneumatic signals directed to the valve positioner and one of which is being utilized as the fluid source therein for pneumatically operating the actuator unit, the single valve positioner housing including a pilot valve portion having a pilot valve relay disposed therein that initially receives the pneumatic signals and causes the one signal to operate the actuator unit in a manner to progressively open the valve member as the first signal being directed to the value positioner progressively increases from a first value to a second value and thereafter to progressively close the valve member as the first signal being directed to the valve positioner progressively increases from the second value to a third value. The pilot value relay sets the second and third values in relation to the magnitude of the second signal being directed to the value positioner.