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BFW System Bypass Valve Vibration

BFW System Bypass Valve Vibration

BFW System Bypass Valve Vibration

(OP)
Looking for advice in what we could be happening in our 650# BFW system, and how to correct it.

We recently ran a parallel line to our current 650# BFW supply to our 650# steam drum.  It is identical to the original line, which will be abandoned due to washed out CV and bypass globe valve. We liquid filled the line and pressure tested, then closed the upstream block valve on the CV line and the globe valve on the bypass. The pressure on the upsteam side was ~1120 psi and on the downstream ~650 psig.  As the globe valve was cracked open it began vibrating severely, backing the nut off of the handwheel, then developing a packing leak.  The packing bolts were tightened but the leak did not stop, and vibration would not allow the valve to be opened more.  The line was isolated from the system until we can solve the problem.

I assume we were flashing across the valve, accompanied with cavitation. I don't know the exact cause of the packing leak. Should the globe valve handle that pressure drop without developing the packing leak? Was the packing leak because of the vibration? How can I get the valve open enough to decrease the pressure drop and get the vibration down? I assume I can get the system stable enough to operate since the parallel line has operated without extreme vibration (but has chewed up the valves). I know I know, lots of questions with little data and no answers, but any observations will be appreciated.  Thanks!

RE: BFW System Bypass Valve Vibration

What size is this line/valve? It seems odd that the existing line that is parallel and of equal size does not experience this problem. Is it possible the globe valve was installed backwards? What is the temperature of the BFW line? Are you sure you are approaching saturation pressure as you open the valve?

I'm not a real engineer, but I play one on T.V.
 A.J. Gest, York Int./JCI

RE: BFW System Bypass Valve Vibration

One last thought was the block valve kept closed as you opened the globe valve, the reason I asked was, could you be expieriencing water hammer as the H.P. steam is entering the isolated globe valve containing BFW on the inlet side of the globe valve? Or possibly steam vapor that is collapsing as it hits the cooler BFW. Just some thoughts and maybe I'm way off base, forgive me if I'am

I'm not a real engineer, but I play one on T.V.
 A.J. Gest, York Int./JCI

RE: BFW System Bypass Valve Vibration

Sounds like cavitation is a routine occurance, which is why you lost the original valve.  This one probably vibrates, because the flow pattern entering and leaving the valve is dramatically different than the original.  I think there might be some radical piping in the modification.

IMO, based on the limited info you've provided, you must change the CV and straighten out and increase the straight runs of the flow path both to and from.  Alternate solution is somehow reduce the inlet pressure to the valve before opening it, if at all possible.

   Going the Big Inch! worm
http://virtualpipeline.spaces.msn.com

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