SMP of a control valve

Standard maintenance procedure of control valve

  • Obtain a hot work or cold work permit as per requirement.

  • Carryout j.s.a/j.h.a/toolbox meeting as applicable

  • Isolate and barricade the area and use proper p.p.e and tools

  • Override if it is connected to any interlock

  • Ensure the control valve is isolated from the process. depressurise the entrapped process fluid by drain points

  • Clean the control valve with dry cotton and ensure the moving parts are free from dust and debris

  • Lubricate the moving part with appropriate grease or lubricant as prescribed by the valve manufacturer

  • If required tighten all the accessories of the valve like positioner, lockup relay, solenoid valve, feedback link, gland nuts etc. do leak checks in pneumatic tubes and actuator

  • Stroke the control valve from hmi/hart/control room in the steps of 25%,50%,75% and 100% both in increasing or decreasing steps

  • Observe the control valve movement in the field and ensure the travel indicator shows the correct opening/closing of the valve on the scale

  • If valve closing/opening/intermediate positions are matching w.r.t signal go to step “a” otherwise follow the steps below

  • Isolate and disconnect the signal cable of the positioner and connect the loop calibrator to the positioner

  • Apply the 4ma And adjust the zero adjustment in the positioner, ensure the valve is at 0%

  • Apply the 20ma And adjust the span adjustment in the positioner, ensure the valve is at 100%

  • Repeat the above two steps and ensure the valve travel once again

  • Disconnect the loop calibrator and restore the positioner signal cable

  • Stroke the control valve from hmi/hart/control room in the steps of 25%,50%,75% and 100% both in increasing or decreasing steps

  • Ensure the control valve feedback in hmi

  • Step “a”—inform the production department about the completion of the job and its taking in line

  • Normalize the override if applicable

  • Close the permit to work

    Servicing of control valve

    • Servicing of control valve is required if it is reported struck, passing or not responding with respect to signal

    • Obtain ptw from production, override if connected to any interlock

    • Major parts of control valve is to be memorized

    • Actuator


    • Body


    • Packing


      • Dismantling of control valve follows steps which can be explained briefly as below


      -mark the direction of actuator/bonnet/valve body with permanent marker

      -fix the control valve on a rigid support


      -loosen spanner-nut (yoke nut) and gland nut to remove the actuator connecting body


      -uncouple actuator upper stem from lower valve stem by removing stem connector (coupling nut)[split block with threads matching those on each stem]


    • 7
    • 8

      -separate valve actuator from the body by removing loosened spanner nut (yoke nut)

    • 9
    • -remove the lower stem and plug from the body for servicing by loosening four large studs and service gland packing. Inspect the internal trim parts such as plug, cage, seat ring etc. if found damaged replace with an o.e.m spare parts. Inspect the seat and plug if found scouring rectify by lapping. Replace all gaskets with new one


 -remove the (piston) diaphragm and (shaft) upper stem from the actuator by slowly loosening diaphragm hold down bolts (end cap screws)











-inspect and replace the worn/torn out parts with OEM parts and start reassembling in reverse order

-reassemble the (piston) diaphragm and (shaft) upper stem to the actuator and check the performance by lock up test.

-assemble lower stem and plug arrangement (trim) to the body and tighten the four bolts in bonnet to assemble the bonnet by placing the seat ring gasket first, then seat ring, cage(if applicable) and cage top gasket set (if applicable)

-now insert the lower stem through the yoke and place spanner-nut (yoke nut) in its place

-adjust for full closed condition by putting a wooden block in between the actuator stem and valve stem, and by pressing down the lower stem and actuator to ensure full close condition. Then tighten the spanner nut (yoke nut) & stem connector (coupling nut) and adjust the pointer scale for closed condition, now place the positioner along with feedback link and check for leaks. Lubricate all the moving parts

-perform the bench set confirmation checks of the actuator by applying specified range pressure directly to the actuator

  • restore all the accessories like positioner, feedback link, booster (if applicable),regulator, tubing etc

  • Calibrate the valve as described before.

  • ensure the proper stroke from the control room

  • inform the control room for the completion of the job and the valve taken in line

  • normalize the override if applicable

  • close the PTW

  • record the activities carried out and the spares consumed

  • prepare the check list/calibration sheet for the control valve

Finally I will explain once more dismantling of control valve…

Firstly uncouple actuator from body by removing stem connector (coupling nut)

Secondly remove yoke nut and separate actuator from body

Third remove studs to inspect lower stem, plug and gland packing

Fourth remove end cap screw (hold down bolt) to service the diaphragm, plate, upper stem and spring

Reassemble in the reverse order

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