Valves installed backwards

[dreidpc]

We have several flow-to-close, globe valves used to control the flowrate of boiler feed water to our steam generators. Many of these valves have developed leaks around the stem and packing. All of them are installed backwards as per the manufacturer's reccommendation for reducing pressure drop.

Is it common for valve suppliers to make such a reccommendation? It seems to me that the backward flow through the valve may be the cause of the leaking.

 

[zdas04]

I did an FEA on throttled globe valves in graduate school and if there was any difference in dP going "forwards" or "backwards" it was too subtle for my program to see.

When I was in the Navy in the last century we learned that "fowards" (i.e., the proper way to install a globe valve) was to have upstream pressure under the disk and downstream pressure against the packing. This was to give you every chance possible to avoid packing leaks on shut valves (the assumption is that when the valve is shut the pressure downstream will be lower than the upstream pressure, or at least not higher--an assumption that is as good as any and as wrong as any).

What I've found is that globe valves are pretty robust and durable and they are pretty forgiving of most installation problems (as long as you don't collect commissioning trash on the seat).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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[62hog]

The reason for installing the valve "backwards" is not for loss reductions, but for safety. If the globe and stem become damaged and seperated, or "fail", the valve will fail in the closed position, not the open position.

This is the way I have been taught by my boss who designed steam systems all over the world in the 60's and 70's.

I don't know much about statistics, but I do know that if something has a 50-50 chance of going wrong, 9 times out of 10 it will. Author unknown

 

[Ashereng]

62hog, this is true with a fail close application. For a fail open application, the flow would of course be the wrong way.

Another reason may be Cv. Flowing "backwards" gives smaller Cv - a cheap way to reduce Cv without buying a new valve.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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