Control valve noise /vibration
Control valve noise /vibration
(OP)
We have developed a strange noise in the area of our control valves over the last month..would only come in for a minute or so up until the past few weeks.Along with the noise we see a very small change in our first stage psi..we have had the noise stop while stroking all 4 cv's but it stops at a different position depending on the valve.Any ideas would be welcomed.Thanks





RE: Control valve noise /vibration
Are the disk solid to the stem or loose?
are the disk balanced (or maybe samuelson design)?
seperate or shell mounted?
It is possible for flow around a disk to generate a lifting force that causes the disk to flutter. this can happen with wear, if the design has been proven.
any recent changes to valve design?
what type of controls?
do you have any actuator movement?
RE: Control valve noise /vibration
RE: Control valve noise /vibration
Can you change the admission mode, ie go from sequential CV opening to all 4 opening together, however if the design is marginal, all 4 may start to flutter. If you are operating at CV#4 crack point, going single admidssion will at least get it of its seat
RE: Control valve noise /vibration
RE: Control valve noise /vibration
RE: Control valve noise /vibration
RE: Control valve noise /vibration
85% of total CV would be the expected range where I would expect CV#4 to be opening (ie at crack point)for any sequential admission scheme. I do not think CVs have a backseat, the actuator usally has a top stop, I was saying operating just above crack point the disk could be hammering the seat. If a valve is fluttering above crack point, the disk is rattling on the end of the steam. A balanced valve can have considerable freedom between the disk and stem for its equalizer valve, which would then be hammered.
being on govenor usually means the CVs are constanly being adjusted to compensate for grid frequecny variations. this is usually very small movements (<1% total) ever couple seconds. But being on the govenor opens up the possibilty for noise in the control system to cause the valves to be cycled excessively. for example, I have seen CVs shaken 5% stroke at 10hertz due to a bad govenor.
being on load limit usually means that the opening potential of the govenor has been limited and thus the CVs no longer respond to the grid variations, unless the frequency increases significantly and then the CVs would close.
for whether or not you are in seqenced admission, if you have position meters for each of the CVs, you would notice at rated pressure, rated load, the CV 1, 2 & 3 would be near 100% but CV4 only 50%. Full load rated ususlly occurs at 95% total CV
when you slide pressure, you could adjust the govenor to allow all 4 CVs to go to 100% and stay there with load reduction with pressure drop. If you operate CVWO, does the noise go away
RE: Control valve noise /vibration
RE: Control valve noise /vibration
I'm not familair with Toshiba and I find CVs with back seat interesting. I guess it would reduce stem leak off when at CVWO and thus some effeciancy gain. IF the actuator does not have open end over travel and the actuator tops out just before the back seat, I would think that would cause a whistle
Is the unit in the US?
RE: Control valve noise /vibration
RE: Control valve noise /vibration
Any unusual trips or outages, etc?
rmw
RE: Control valve noise /vibration