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Flow Induced Vibration
2

Flow Induced Vibration

Flow Induced Vibration

(OP)
We have a 12" throttling butterfly valve that vibrates so badly that pieces fall off and controls are destroyed.  I can't locate anything useful on the Web.  Can someone please provide references for gas flow inside pipes producing vibration?  I'm working on a CAESAR analysis and need some background data.

We're flowing air at 100°F, 150 psig upstream, 40 psig downstream in about 20' of pipe.  Velocity upstream of the valve is about 330 ft/sec (Mach 0.3), downstream is about 850 ft/sec (Mach 0.7).  


Larry

RE: Flow Induced Vibration

Sohio,

Good grief!

Most butterfly valves require fluid velocities less than 100 ft/sec.

You need a characterized disk valve (possibly with noise trim) and a lo-db plate to drop the pressure downstream and keep the valve size reasonable. fisher / masoneilan /etc / etc all make good control valves and provide sizing selection software. You might be able to use the db-plate with your existing valve, but that is a big maybe.

One of the problems you face is that all noise treatment (in the valve) requires inlet and outlet velocities <0.3 mach. Use of the low-db plate will help by putting back pressure on the valve, but your inlet velocity is hurting the situation. Not surprized at the level of valve destruction. I am more surprized that you haven't thrown a disk.

the db plate is basically a thick plate R.O. with thousands of holes to take the pressure and breakup the jets to achieve a reducting in noise/vibration. A single hole plate might work but it will be extremely noisy.

In line silences are also available but you'll need more thean 20' and 12" pipe to install it.

Good luck,


Know the situation well.




RE: Flow Induced Vibration

Yow!

You have choked flow across a butterfly valve! It is definitely not suitable for that. Choked implies that somewhere in the flow profile there will be shock waves due to oblique shocks.  

A fluid speed of 100 m/s ( 326 fps) at the valve entrandce is the max if the fluid was at 1000 F (0.14 Mach) and your were using a globe style control valve.  I would suggest resizing the inlet and outlet pipes for not more than a o.15 mach number, and since your are at 100 F, that is about 66 m/s ( 215 fps) {16 " NPS}. And change out the valve for one suitable for choked flow- definitely not a single butterfly. For the pressure and temp rating s you discussed, an angle style globe valve would work fine. A venturi ball valve would work fine ( but noisey). But not a
single butterfly, or gate, valve.

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