Probelm with MOV passing 3

[SZL]

Dear,

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?

Thanks

 

[JLSeagull]

Play with the actuator limit stops to assure that the valve is fully closed. This is easy with the valve out of the line but can be adjusted slightly with some trial and error inline.

Pump the lubricators with grease.

Remove and send the valve to a shop.

 

[gerhardl]

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.

 

[SZL]

I appreciate your support JLSeagull and gerhardl but in our case I think in the field the valve looks fully closed and at the same time the valve passes little quantity of gas. Also, we conducted chemical cleaning for the subject valve to eleminate this problem but the problem appread again. Please is there any another solution other than playing with actuater to resolve the problem?

 

[ione]

I would distinguish between a limit switch issue and a valve leakage class issue. What is the leakage class of your valve? If the valve is manufactured to allow a particular leakage, I don’t think you can get improvements only playing with limit switches.

 

[itascot]

You can start with what the differences are between valve position problem (valve does not reach desired position, hence does not seat/seal) and a seat leakage problem (seat damaged, poor surface finish, foreign bodies).
As suggested by ione, check your paperwork & verify the original seat leakage class requested, and remember that there is no such thing as a "zero-leakage" valve, even though you may see the term mentioned, it basically tells you how much a "zero-leakage" valve can pass; Eg. class V allowable leakage rates (critical service) 5 x 10-4 ml per minute of water per inch of orifice diameter per psi differential (5 x 10-12 m3 per second of water per mm of orifice diameter per bar differential).

Ciao,

 

[JLSeagull]

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.

 

[itascot]

Do you have the possibility to increase pressure to the valve & see if leakage increases OR decreases ? the results of this test can give a better idea of root problem.

Ciao,

 

[gerhardl]

Could you please give all details of fluid, pressure, valve, observed leakage and desired thightness.

You have either damage, unsuitable valve, or comability problems.

 

[NGiLuzzu]

And, most of all: how much a "little quantity of gas" is?
How do you notice and/or measure that?

The six Leakage Classes for Control Valves may be a good reference just to speak a common language... but please remember that the relevant standards"cannot be used as a basis for predicting leakage at conditions other than those specified" (see IEC 60534-4, NOTE to para. 4.2 and/or FCI-70-2, para. 2.2).


Regards, 'NGL

 

[bcd]

before we all get into a discussion and debate about leakage classes, let's get back to the issue at hand. A valve is leaking. Someone is surprised to find it leaking. So start at the begining.

1. What type of valve do you have?

2. Define the leaking gas (type, pressure, temperature)

3. Measure or estimate the amount of leakage. A few bubbles per minute or is it blowing through like the valve is partially open?

From this, we can direct the dialogue towards a conclusion for you.

 

[GTstartup]

Contrary to what Gerhardl said and although the manufacturer won't like it, it's not uncommon to tight seal a valve driven by a MOV by using the torque switch to stop on close not the limit.

 

[gerhardl]

GTStartup - I believe you!