Patent ID: 6382226
Filing Date: 2002-05-07
Classification: F16K,Y10T

Abstract:
In a microprocessor based valve positioner having a set point input and providing a drive signal for controlling a valve actuator with corresponding drive pressure for operating and positioning a valve stem and plug with respect to a valve seat of a fluid control valve in response to the valve stem position feedback to the valve positioner,a method for providing an indication of a possible failure in the valve stem or plug or seat, said method comprising: monitoring the drive signal; monitoring the drive pressure to the valve actuator for detecting a predetermined change from a steady drive pressure with no change in the set point; monitoring the valve stem position feedback to the valve positioner for detecting a predetermined change from a steady valve stem position feedback with no change in the set point; providing a stem/plug/seat event indication if at least one of the predetermined changes in steady drive pressure and valve stem position feedback is detected; responding to the stem/plug/seat event indication and initiating a monitoring of a process value for detecting any deviation in the process value, including monitoring the relationship of the process value for a set point value and detecting any changes in said relationship with no change in the set point; and providing an alarm in response to detecting a change in said relationship thereby indicating a possible valve stem breakage or a damaged valve plug or valve seat.