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]

Zhiras, your latest statement is the opposite of what you said earlier. If the purpose of this valve is as George states, then it is the wrong way around. It is designed to allow flow from top to bottom IMHO.

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.

 

[Shiras]

Littile Inch, 6o bar is holding beneath the disc (on Outlet) while it is closed position.
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.

 

[bimr]

Don't think it matters which way the flow is moving through the valve.

The problem is that a double disk valve is not capable of tight shutoff.

 

[Gator]

I don't recall seeing a "double disk globe valve" (as it is described in this case) are they common in certain industries? Note that the term "double disk valve" usually doesn't apply to the valve mentioned here.

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

 

[bimr]

Gator, reread the blog above. LittleInch had a sharp eye and noticed that it was a double disk valve. Unless you work with steam valves in power plants, you have never worked with a double disc globe valve.

"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."

 

[Gator]

Thanks bimr. A quick search for 'Double Disc Globe Valve' didn't turn up anything like the valve in the diagram posted in the other thread.

Piping Design Central

 

[bimr]

It appears that the OP wants to use the valve to throttle in one direction and when closed, use the valve as an isolation valve. However, when closed, the backpressure may be higher (coming from another source) and the valve will not hold.

Unfortunately, this type valve is not capable of tight shutoff. The OP needs to add a 2nd valve for isolation purposes.

 

[BigInch]

The circle is completed.

 

[georgeverghese]

From the original posting, it looks like the 10barg side does not even have the capacity to handle a minor leak from this valve, let alone misoperation with this valve wide open.

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.