Control Valves are meant to control the process parameters namely Pressure, Flow, Level and Temperature.
Control Valve is the final control element in any closed-loop control. Based on their application type they are named as Pressure Control Valve, Level Control Valve, and Temperature Control Valve.
Calibration is the quantitative determination of errors of a measuring device and, where necessary, adjusting these errors to a minimum. The error is comparison with higher standard having traceability to National or International standard.
Control Valve Calibration
Following the receipt of the Work Request which is generated through SAP, the instrument engineer will submit Safety Document Request (Generated by SAP) one day in advance for the work planned. Some Industries will use manual work permit systems in the absence of SAP.
Confirm isolation before receiving the safety document.
Check the interlock in the relevant logic diagram for the valve to be stroked. Simulate or force the necessary signal like valve position etc to ensure safe operation of the process before starting the job.
Check the healthiness of I/P Converter, Position feedback transmitter, airlock relay, solenoid valve, and air supply pressure.
Check the manual operation of the valve using the hand wheel. Stroke the valve either from local or from DCS as applicable. Confirm the valve travel from local. Calibrate the Valve with the inbuilt option like “Auto Calibration” available in the valve positioner. Also, check the Limit switches function and adjust them as required.
For the SMART Control Valve, we can use a HART communicator to calibrate the control valve. Give the supply pressure according to the valve as per nameplate details. Connect the HART to the valve positioner. Then go to valve simulate command, enter 0% and observe the valve position. Next, enter 25% in HART and observe the valve travel position.
Similarly, enter 50%, 75% and 100% in the HART communicator then observe the valve stem travel position accordingly. You can find a manual scale (0% to 100%) with a needle on the valve to verify the valve travel position.
Confirm the signal status and remove all the simulation/forces, which were done before starting the job.
Clear and return the work Permit to the Plant Shift Manager. Update the Work Order in SAP.