Calculo De Ruido En Valvulas De Control

Hydrodynamic Noise ∆SPLAr Corrections

The current hydrodynamic noise prediction method differentiates valve style only though variation of the pressure recovery coefficient, Km (FL2). Separate noise prediction corrections have now been established for standard valves, Cavitrol III – 1 Stage valves, and the rotary attenuator. These differences are reflected in the ∆SPLAr term of the generalsound pressure level prediction equation per the following equation: DSPL Ar + a * b Km ) 10 log 1 * 1 Ar Ar

where, ∆SPL Ar = Correction for effects of Ar and valve style Km = Pressure recovery coefficient Ar = Application ratio DP Actual P1 * P v coefficients given in following table:

+ a, b =

a Standard Valves Cavitrol III – 1 stage Rotary Attenuator 14.4 9.4 9.4

b 18.8 18.8 22.6Catalog 12
Printed in U.S.A. on recycled paper. Fisher Controls International, Inc., 1993, 1999; All Rights Reserved

April 1999 Page 3 1

Sound Characteristics Line and Point Sources

Line Source
Equal Noise levels are on an imaginary cylinder with the pipe centerline as the axis (figure 1). As an observer moves away from the pipeline, the sound pressure level (SPL) decreases inversely tothe changes in surface area of the imaginary cylinder. Use the following equation to find the sound pressure level when other than 1 meter from the pipeline surface. SPL + F ) 10Log 1 ) r R)r where, r = radius of pipe based on outside diameter (meters) R = distance from pipe surface (meters) F = noise level calculated at 1 meter Example What is the noise level 50 feet from a 12 inch pipeline (fromtable 1, radius is 6.38 inch or 0.16 m) when the Noise Prediction Technique calculates 95 dBA at 1 meter. SPL + (95) ) 10Log 1 ) 0.16 15.24 ) 0.16 SPL + 95 * 11.2 SPL + 83.8 dBA Note This procedure determines the noise level radiated only by the pipeline. Other noise sources could combine with the pipeline noise source to have a greater overall sound pressure level.
Figure 2. Typical PointSource

Figure 1. Typical Line Source

where, R = distance from source (meters) F = noise level calculated at 3 meters Example What is the noise level 50 feet (15 meters) from the point source when the Noise Prediction Technique calculates 100 dBA at 3 meters. SPL + 100 ) 20Log 3 15 SPL + 100 * 14 SPL + 86 dBA Note This procedure determines the noise level radiated only by the point source. Othernoise sources could combine with the point source noise to have a greater overall sound pressure level.

Point Source
Vent applications are typical examples of point source noise (figure 2). As an observer moves away from a point source, the sound level (SPL) decreases inversely to the changes in surface area of the imaginary sphere. Use the following equation to find the sound pressure levelwhen other than 3 meters from the point source and below a horizontal plane through the point source. SPL + F ) 20Log 3 R

Table 1. Radii of Nominal Pipe Sizes
RADIUS OF PIPE Inch Meter NOMINAL PIPE SIZES, INCHES 1/2 0.42 3/4 0.53 1 0.66 1-1/2 0.95 2 1.19 2-1/2 1.44 3 1.75 4 2.25 6 3.31 8 4.31 0.11 10 5.38 0.14 12 6.38 0.16 16 8.00 0.20 20 9.00 0.23 24 12.00 0.30 30 15.00 0.38 36 18.00 0.460.0107 0.0133 0.0168 0.0241 0.0302 0.0366 0.0445 0.0572 0.0841

Catalog 12
April 1999 Page 3 2
Printed in U.S.A. on recycled paper. Fisher Controls International, Inc., 1983, 1999; All Rights Reserved

Sound Characteristics Octave Band Sound Pressure Levels

Octave Band Sound Pressure Levels
Aerodynamic noise has an overall sound pressure level (measured one meter downstream of the valveand one meter away from the pipe-wall) which does not indicate the sound pressure level in each frequency band. Use the information in table 1 to determine octave band sound pressure levels and to construct a spectrum for a particular trim type and piping combination.

Example A 6-inch valve with Whisper TrimR III cage has an overall SPL of 85 dBA. The octave band SPLs are as follows: SPL at...