Vibrating Valve 1

[TangoCleveland]

We have high 150 psi air flow through a 12" valve, that is vibrating our piping at 2400Hz. Time waveform was counted to get the Hz number. Acceleration readings on adjacent pipe are 100 g's. We think we can anchor the valve to an adjacent concrete column 12" away. Calculated displacement is 0.005 inches. What's a good number to use for load on the anchor? If I use 100 g's and a 400 lb valve, I get 40,000 lb. This seems a little high. Does anyone have experience in this area? I'm also posting this in the Vibration forum.

Larry

 

[SPLIT]

In case of a control valve, it is important to check the flow capacity because if the valve is too small, it may cavitate igenerating autoinduced vibrations.I had solved this kind of problems by changing the valve or the internals with the manufacturers recomendations.
This kind of vibrations are dificult to control only with modificating or adding supports to the pipe, because the energy generated can be too high

 

[LSThill]

OldSohioEngr (Mechanical)

Before you start adding Pipe support you need to do your detail home work in Fluids Dynamics (CFD).

BOS Fluids, a fluid mechanics package that models steady state and transient flow in liquid or gas piping systems, including 2-D Computational Fluids Dynamics (CFD).

For years piping engineers have labored with simplifying hand methods, cumbersome analog computers, or user-unfriendly software products when needing basic steady state and transient fluid analysis capability. BOS Fluids was written specifically to address the need of the piping engineer for fluid reaction forces, and to provide a system whereby the fluid simulation results can be easily integrated back into the piping system design and analysis.

BOS Fluids is an interactive computer simulation package that models steady state and transient flow in liquid or gas carrying piping systems. The procedure is easy to use and interfaces with most pipe stress programs. The package contains the elements required to model most common unsteady flow conditions. The elements included in the simulation package are pipes, valves, pressure relief valves, vacuum breaker, air valves, pumps, equipment, surge vessels, inlets, outlets, and orifices. BOS Fluids makes fluid simulation simple and easily accessible and yet gives the analyst pressure transients and dynamic force results with an engineering accuracy.

Based on a number of realistic assumptions a simplified form of the time dependent conservation (Navier-Stokes) equations are solved for the internal channel flow. The assumptions made are:

1. Fluid behavior in pipes is one dimensional i.e. similarity of cross sectional distribution of properties does exist.
2. Fluid transport velocity is small compared to wave speed.
3. Wave fronts remain plane while propagating.
4. Gas simulations assume that flow velocities are below sonic, and that pressure drops through the system are less than 30%.

Based on these approximations friction effects are lumped. The present friction model used is Colebrook-White. The Darcy-Weisbach flow model is used for steady state pressure drop calculations and the basic theory applied in BOS Fluids can be found in Wylie & Streeter's "Fluid Transients" published by FEB Press. BOS Fluids is capable of simulating both the steady and transient behavior of liquid carrying closed conduit systems of pipes, valves, pumps and surge relief devices. The following special features are available:

1. Pipe stress models from either CAESAR or PipePak can be downloaded for fluid analysis.
2. The analyst can pick different fluids from a database or add their own fluids to the database
3. Two different models are available to simulate column separation: Concentrated Air Pocket (CAP) model and the Vapor Cavity Model (VCM).
4. Various pipe materials can be applied-both isotropic (Metals) and Orthotropic (FRP) materials are included.
5. Based on geometry typical pump properties are generated automatically.
6. Buried and above ground systems can be simulated.
7. Simultaneously the transient response of multiple sources: Pump starts, Pump Failures, Valve Operations can be simulated.
8. Harmonic option allows an analysis of the occurrence of standing waves.
9. Maximum and minimum pressures and velocities occurring during transient and/or harmonics are traced.
10. The force processor allows an analyst to survey the time history of the unbalanced forces on pipe sections and preprocesses the force time histories to be used in the dynamical module of the pipe stress program.
11. A spectrum breakdown of force time histories is available. The analyst can see the natural frequencies of the fluid response that tend to excite the piping system.
12. Both Metric (SI) and English Units can be selected.

Typical analyses using BOS Fluids include: water transmission and distribution systems, main cooling water systems for chemical plants, sewage water systems, combined power and drinking water cycle power stations, oil product transport lines, tanker loading and unloading systems and dynamical behavior of chemical liquid transport lines. Acoustic analyses for compressors and pumps.

Leonard@thill.biz

http://www.thill.biz

 

[btrueblood]

What kind of valve?
What is the pressure drop across the valve?
If you change the pressure drop, or valve position, does the noise reduce and/or the frequency change?

A freq. change with changing valve stem position would tend to indicate that you're getting vortex shedding. Changing internals of the valve would be the only way to fix this (adding "streamlining" to get rid of the vortex, generally caused by bluff downstream/trailing edges).

Noise intensity change with no freq. change would tend to point you towards finding a loose part somewhere, which is flapping around and generating noise. In this case, tightening or stiffening the offending component may fix the trouble.

As far as "g" levels go, did you have an anti-aliasing filter in line with the accelerometer (before the D-to-A converter), and were you sampling at a rate of more than 2x the rolloff freq. of the filter, and what is the rolloff of the filter (dB/octave). If the answers to any of the preceding are either "no" or "huh?", then don't believe the g levels you are getting, or even the freq. measurement. 2.4 kHz is a fairly high pitched "whine" or "squeal" -- is this what you are hearing (something pitched somewhere around the high keys on a piano)?

 

[TangoCleveland]

btrueblood,
The poor valve is a 12" butterfly, no special features. Pressure drop is about 90 psi. Our max noise is at 50% open, which is where the valve usually operates. At 13% open, noise is less, frequency is higher (2900Hz). Not sure about the vibration analyzer filter setup.

Also, the displacement I mentioned in the beginning is 0.0005", not 0.005". Slipped a decimal.

Ever work with constrained viscoelastic damping materials?

Thanks for the observations.

Larry