Equalize Pressure for 18" Ball Valve

[kpnttn]

We have found one 18” Metaltite ball valve (full-bore, fail-close), from KTM, cannot be operated (cannot command to open), even though the equalize valve was already opened and the differential pressure across the valve was already 0 bard. Please be noted that there was no fault in actuator system.

Normally, this valve is always left open, while its operating condition (gas pressure) is around 70 barg. However, when we tried to reduce some gas pressure, we found that this valve can be opened.

After checking and comparing with other valve with the same size and type (also same actuator type), we found that some valves have tubing connection from the valve’s drain port to one side of differential pressure transmitter (low-pressure side).

Then, here come the questions:

- What is the function of this connection? Is it a balance line?
- Is this connection a must for this failed-to-open valve? If yes, why do we find some valves that can be operated without this connection? Do the operation conditions (pressure) concern?
- Are there any papers/articles/document regarding this application? If yes, please kindly advice.

 

[BigInch]

No, why is the dP there?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[JLSeagull]

It is common for pressure differential across a large valve. I could also envision some provision for a pressure connection to the internal port on a ball valve. As the first paragraph suggests, the differential pressure measurement could prevent opening the main valve until the pressure was equalized or greatly diminished.

I suspect that the main valve could be siezed do to non use. If this is a pneumatically acutated valve (it must be actuated to be fail closed), consider applying higher air pressure using an air cylinder. Be very careful regarding the maximum pressure rating for the actuator if you go this direction.

 

[dcasto]

There maybe a line break system similar to this.

http://www.emersonprocess.com/valve...oad_files/product_service_manuals/I-0057-.pdf

 

[JimCasey]

I tried looking up the directions for Tyco/KTM valve with Metaltite seats- no luck there. Nothing about a balancing port on their web page. If anything, pressure trapped inside the cavity should UNLOAD the seat(s). I'm thinking JLS has a pretty valid guess that the valve is just seized.

Max pressure in the actuator, some big-strong guys, >pushing< on a big cheater bar. ( Use appropriate care: Don't let anybody get in front of it 'cause once the valve starts to move it will likely go fast and it could cause an ouchie.)

 

[kpnttn]

Thank you very much for your kind suggestion.

For comments on increasing air pressure at the actuator, we have tried rising the pressure to 6 bar (25% increase from normally 4.8 bar), unfortunately, this could not help.

For comments on valve siezed, it might be possible. However, why the valve was siezed? Only from its non-operate? And why reducing some pressure in the line can make the valve re-operable?

Moreover, when thinking of the other valves (same size, same type), that have a connection from the valve's drain port to discharge side of differential pressure transmitter, I still wonder for the purpose of this connection. Also for equalization? Why using drain port? And why connect to one side of differential pressure transmitter instead of equalized valve?

Do anyone have any idea?

 

[BigInch]

Most valves require some movement from time to time. It seems all things in contact have a tendency to stick together and it appears to be true for anything mechanical.

Reducing pressure in the line will take some force off the contacting parts and thereby reduce any friction between the components.

I use valve drain connections for drains. If I need a dP, I make separate connections upstream and downstream of the valve.



BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[JimCasey]

I suspect the pressure connections are there to monitor block-and-bleed function. If the DP creeps up it shows the upstream seat is leaking.

 

[scalleke]

Whether the valve will lock up due to internal pressure depends on the balance of the seats. Something that the manufacturer will know.

Best Regards,

Scalleke