I have a problem  with MOV motor operated valve paaing through. when I looked at the MOV data sheet, it was not speified that the valve as Tight Seal Closed but it is referred the seat leakage rate to API 598. So, i realized that the passing from the seat. Can any body help me to find a way to stop the passing?

As a non-english native I assume MOV stands for motor operated valve, and that the motor is an electrical actuator.

I fthis is correct I will support JLSeagull and add that a first class actuator will have both torque and limit switches for open and closed included.

In this case it is important that the closing (and opening) is stopped by the limit switches at a point where the valve is thight enough.

The torque switch for closing should be set/adjusted higher than the necessary closing torque, but not used to stop the valve in closed position, or stop the valve before properly closed. (The limit switch will give closed position, and should be accordingly adjusted, as mentioned above).

If valve is not thight enough after adjustment: seat or seat-sealing is damaged or you have a non-satisfactorily valve in general.

Typically the term leakage class applies to control valves per IEC/FCI.  I don't have a copy of the latest since FCI and IEC jointly published.  Motor operated valves are typically isolation valves that require API STD 598 compliance.  API STD 598 uses the terms "no bubbles" and "no drops" for resilient seated valves and metal seated valves NPS 2 and smaller for duration of the test.  This applies to the factory test.  Once the rusty hydrostatic testing fluid scratches the ball and seat then the factory testing is moot.  Still, sometimes you can move the ball a degree or two and find a fresh seating spot.

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