Flow Induced Vibration 2

[TangoCleveland]

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

 

[hacksaw]

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&quot; pipe to install it.

Good luck,


Know the situation well.

 

[davefitz]

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 &quot; 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.