Globe valve leak
Globe valve leak
(OP)
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.
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.





RE: Globe valve leak
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: Globe valve leak
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RE: Globe valve leak
RE: Globe valve leak
It looks a little odd - I've never seen what appears to be a two stage opening, but in this case the operation looks correct. When working as designed, the inlet big disc is held against the seat whilst the initial upward movement of the spindle lifts up the small disc and allows fine control over the initial flow. Then more turns leads to much larger flow as the big disc is lifted off its seat.
In your case it doesn't work well as the force required by the spindle down is high, the contact point with the big disc is small (the small disc) and any contaminants or particles will result in a passing valve.
Do you need this sort of valve? If not I would replace it with a more normal type or add an isolating valve.
I would love to see the valve characteristics...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Globe valve leak
RE: Globe valve leak
seats in the closed position only or valves which seal against the seats in the open and closed positions; unidirectional or bi-directional sealing.
The configuration of the flow path is normally only suitable for uni-directional flow and globe valves should be mounted in the line such that flow is in a direction from beneath the disk.
RE: Globe valve leak
RE: Globe valve leak
Sorry i was not in the situation to use internet. Thanks for your suggestions & support.
Little Inch & Latex man, hope that the ball valve is not suitable in this line. Because outlet holding a pressure (60 Bar) more than inlet (10bar max.). Am not sure about it. We are only traders and repeatedly the replaced valve also reported the same issue, so that i came to this forum for a solution. I just want to know if the valve installed in a reverse direction, is there wil be any flow? Your continuous support is requested.
RE: Globe valve leak
As said, this particular valve looks quite strange to me as it is a two part flat disc designed only to work with pressure on the inlet side higher than the outlet. A more normal globe valve with pressure normally coming from under the plate subject to reverse pressure differential would probably seal better, but you may find opening it under reverse differential pressure difficult or impossible.
If you swing this valve around it would seal better under reverse pressure differential, but if used in the "normal" direction of flow would be difficult to control. It looks to me to fundamentally the wrong type of valve.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Globe valve leak
Does it control the flow at some partially open position? Or, is it either wide open or all the way closed?
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: Globe valve leak
Me too confused, however we have decided to do seperate hydrotest for a better coclusion.
RE: Globe valve leak
RE: Globe valve leak
Why do you have the arrows on your drawing showing flow opposite of pressure?
RE: Globe valve leak
RE: Globe valve leak
Normally i would agree, but look closely at the valve. There are two discs. The smaller one relies on the larger disc being forced intro the seat by pressure. Only when you open up the valve by more than a couple of turns does it pull the big disc off the seat. All quite strange and nothing like your admirable section drawing.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Globe valve leak
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: Globe valve leak
It seems to be a misapplication of the valve since a double disc valve is not capable of the tight shut-off that the OP is requesting.
RE: Globe valve leak
a) Some kind of throttling operating where 60barg water is being letdown into the 10barg stream
b) Isolation between 60barg and 10barg when not in use.
Function (b) appears to have not been engineered properly - it is not possible use a single block valve of ANY type as positive isolation. Leakage is to be expected, but the bigger concern is misoperation.
If both these functions are still required, then the solution lies not in the type of valve, but in the excess pressure control and overpressure protection measures on the 10barg side.
RE: Globe valve leak
RE: Globe valve leak
A started many time s on this thread, this type of valve find it difficult to tight seal, but the wrong way around, virtually impossible.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Globe valve leak
and the inlet pressure is 10 bar. The flow direction is exactly as per the valve drawing. However the valves were at our premises, i can convey the details what i recieved from their end.
RE: Globe valve leak
The problem is that a double disk valve is not capable of tight shutoff.
RE: Globe valve leak
Am I correct in that there will be flow in two directions through this valve?
Flow under seat can be for throttling, flow over plug for on-off.
Piping Design Central
RE: Globe valve leak
"Double Disc Globe Valve : It features two discs bearing on separate seats spaced apart on a single shaft, which frees the operator from stresses set up by the conveyed fluid pressing into the valve. It is principally used on control valves and pressure regulators for steam and other gases. Tight shut-off is not possible."
"I wish you wouldn't double post - see http://www.eng-tips.com/viewthread.cfm?qid=383885 as this has a diagram of the valve."
RE: Globe valve leak
Piping Design Central
RE: Globe valve leak
Unfortunately, this type valve is not capable of tight shutoff. The OP needs to add a 2nd valve for isolation purposes.
RE: Globe valve leak
RE: Globe valve leak
Agreed the orientation of this globe valve would have some influence on the amount of leakage.
Once the 10barg side excess pressure bleed controls and overpressure protection measures are in place, it wouldnt matter what kind of globe valve is used here or even if there were to be a double block and bleed.