5 replies to this topic

[daffe]

Hi,

I am working in an oil refinery. An accident has happened to me with a gate valve and I want to know how it is possible. Two gate valves on a pump suction and discharge were closed first. And the pump was drained out at the next stage. But after about one hour, I saw the suction valve (12") was full open and the pump was full of liquid!

Operating conditions were as follows:

Fluid = Naphtha
Temperature = 200 Deg.C
Suction Pressure = 10 Barg

How is it possible when nobody open the suction valve? Please lead me.

[Art Montemayor]

Daffe:

Firstly, you don't tell us the position of the subject gate valves. Are they in the normal, horizontal position? Are they in the vertical position? Or are they in the overhead (valve handle upside-down) position?

In my 48 years of installing and operating gate valves - in all sizes and colors - I have never seen or heard of one opening "spontaneously". In my opinion, this cannot happen. They may vibrate open (especially the upside-down installation mentioned above, but this would be a negligent installation and it would take a long time for the valve to vibrate into the full open position.

SOMEONE -another human - opened that valve and didn't stick around long enough to tell you (or did so in an ignorant manner and didn't want to admit it) - and left.

Or maybe I'm going daffy ........(pardon the pun).

[djack77494]

Having had the opportunity several times to manually open 12" gate valves, I wished it were possible for them to spontaneously open. Opening a large gate or globe valve with a handwheel operator is a very labor intensive operation that can take a considerable period of time and effort. I have to totally concur with Art's view that someone operated the valve and didn't stay around to admit to having done so.

[daffe]

Art and djack,

Thank you for the replies. But please rethink about the subject with this view that in one or two parts of the valve some damages may be taken place. For example the threads may be lost. By the way, the suction valve is in vertical position (so the stem is horizontal). In such situation can the fluid pressure open the valve (pushed out the stem with disk)?

[mishra.anand72@gmail.com]

You are answering your question. If it was drained completely, that means valve isolation was proper. Later, it was opened by somebody.

[djack77494]

In such situation can the fluid pressure open the valve (pushed out the stem with disk)?

I don't mean to be patronizing, but on further reflection my opinion has not changed. In regard to this new question, that is one of the nice things about using a gate valve for isolation - fluid pressure does NOT tend to open or close the valve. The fluid's pressure differential acts perpendicular to the main moving part, the disk. If you had been talking about a globe valve, I may have been more open to the concept of fluid pressure possibly affecting the valve's position (for a seriously damaged valve), but even there I don't see the handle spinning in response to the pressure.