Plug valve not sealing for natural gas - ideas?

[USAeng]

We have tried 3 replacements for this 3" Dezurik plug valve and still it does not seal. Gas leaked by the plug on all 3. It does reduce the flow but doesn't really come close to shutting it off like intended (reduces flow about 90%). See attached submittal for the valve. Any ideas why this could be happening???

 

[LittleInch]

Note 3 on the drg on page 5 indicates that the SEAT indication on the valve should be on the other side from the high pressure - have you checked this and tried it the other way around?

Also the indication that the valve is closed appears to be movable. Has this somehow been moved during transit / installation? Have you operated the valve before installation to see whether it looks like it is completely closed / fully open when on the stops?

just some thoughts.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[USAeng]

yes installed as you say. I'm pretty much stumped.

 

[moltenmetal]

Is this intended to be a lubricated design? If so, you need to pump it full of grease...Many of the old plug valves were designed that way.

Other than replacing with a soft seated construction or a different type of valve, I have no suggestions.

 

[Compositepro]

Of course, the valve manufacturer should be asked this question.

 

[gerhardl]

Without going back to all the old discussions of all kinds of leaking valves: it is either wrong valvetype, wrong sealing (material surfaces), damaged surfaces or wrong lay-out or installation.

How was the replaced valves inspected, checked and tested? What was wrong?

Even if the valves where generally OK for the use, layout of pipeline and dirt, water or deposit and wrongly adjusted/mounted actuators and torque and limit switches could play a part.

 

[zdas04]

USAEng,
While I'm far from a fan of plug valves, did you consider the second part of LittleInch's first post? The travel stops are adjustable and you cannot tell by eye if they are properly adjusted. I've had a 1/8 turn of the shut-stop adjustment take a plug valve from copious leakage to mostly sealed. If that doesn't work and you've greased it then you'd need some hands-on diagnostics.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[Roberto1956]

I am according to zdas04 and would tell that the return of 1/8 turn may change according valve design and repair parts and you need to be patient on the bench working these combination.