Globe valve leak

[Shiras]

Hi All,

We have installed a 6'' #600 hand wheel operating globe valve in a reverse osmosis plant.
Valve shall be normally at closed condition. Inlet side shall remain closed (10 bar maximum) outlet side holding pressure 55-60 bar while running the system. We noticed back flow from out let to inlet & pressure is exceeding at inlet side. As per valve drawings inlet flow is through above the disc & outlet is holding the pressure below the disc. We have already replaced one valve due to this problem. Please clarify whether it is happening because of any design fault or valve defect.

In my view point, globe valve only can use to hold the pressure at inlet side. Is it true. Please help me to resolve this issue.

 

[LittleInch]

see double post answers here

http://www.eng-tips.com/viewthread.cfm?qid=383886

This one has the drawing though....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Danlap]

Hi Shiras,

Agree with you, conservatively this type of valve have undergo 4 pressure test. Body test (valve fully open) 15 minutes, Seat A and B (valve fully close) @ 5 minutes and Backseat test (valve approximately xx% open) @ 5 minutes. So in theory, all the components should hold your inlet side.
However the test period of 5 and 15 minutes are in favor for (mass) production test and not necessarily adequate for the Graphite packing to be 'self-settled' in certain case for long run

If the drawing is representing the actual Graphite packing configuration, that's quite a lot of graphite stack.
PS: Optimum rings which seals the 'pressure envelope' is the first 3-5 bottom rings
And the disadvantage of Graphite is shall used for low temperature (ambient), for optimum sealing it requires higher friction between the packing and stem. Normally interpreted as higher torque value for the Gland retainer bolts.

First, challenge back the manufacturer in regards with their packing design
I would suggest use PTFE / Teflon Ring in combination with Graphite for optimum sealing on ambient temperature.
Shall let say Graphite (only) packing is preferable with that enormous amount of packing set. Cycle the valve 20-50 times / pre-compressed the packing / let it run for xx hours, then ensure that the suggested torque value are still applied.
Graphite is porous thus the air void in between should be 'compressed' to provide maximum sealing.

Hopes that helps.
Regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[LittleInch]

I don't think the leakage is from the stem - it's from one side to the other....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Danlap]

Thanks Littelinch,
Silly me interpret it wrongly. Without further information provided,this is just another seating problem.
And yes, seeing similar discussion on other forum seems the originator of the topic not even following up.

Regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[Shiras]

Dear All,

Sorry i was not in the situation to access internet. Appologies for the repeated post.

Mr. Muktiadi, there is no leakage through stem, client noticed the pressure raising at inlet side and pressure drop at out let & they seperated the line and confirm the back flow from outlet side. Back seat pressure tested at 9.1 Mpa from manufacturer. hope that the back seat pressure test is pressurising the valve in opposite to the flow direction and the disc shall be closed condition. If so it should hold the 60 bar pressure. I just want to confirm that the failure is happened in valve or their design (plant design).shall we can install the valve in reverse direction? we are replaced the valve twice and still client arising the same problem, since the valve was working fine for the last 1 and half month.
Am a beginner to this field so expecting your valuable support.

 

[gerhardl]

It all depends on quality, wear and use.

I do not agree that a globe valve in principle is a poor choice of a closing valve. But, under circumstances, a pressure difference, combined with small impurities on the seat sealing, can create a leak, and increasing leaking over time because of pressure difference and cavitation over the small ,weak point'. Improper fitting and wear can also give leaks from different causes.

Please also remember the combined forces working upon the seat sealing: pressure force of windings and torque giving the clamping doown force, reinforced by pressure upside clack pr area unit times area units on the upper side, weakened by the pressure working on the underside.

One obvious test is to turn the valve around on the pipeline axis, letting the greatest pressure working to add to the clamping pressure on the clacks upper side.

The other option is to look at the valve seat construction and change the valve to get a highe quality seat, for instance combined with a seat construction with a 'skirt' protecting the sealing surface.

I presume of course that all valve choices are correct standard for pressure, fluid and application details.