8/12/2019 General Info Nelson

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8/12/2019 General Info Nelson

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SizingInformationEngine Exhaust Silencers

Choosing the correct exhaust silencer for agiven engine is an important although notdifficult task. First of all, a degree ofsilencing is chosen that will satisfy thenoise requirements unique to each engineand location. Secondly, the silencer size isselected to accommodate the specifiedvolume of exhaust flow without imposingexcessive back pressure.

Selection of Silencer Type (Grade)Each silencer group described on pages7.37.6 has a number of a series withdifferent noise attenuation characteristics.

The series letter designation (e.g., EN2)indicates in relative terms the degree ofnoise attenuation; the higher the number,the greater the attenuation.

2 Industrial or Commercial grade

3 Residential grade

4 Critical grade

5 Hospital grade

The attenuation curves next to the tables oneach page indicate the attenuation in dB byoctave bands.

These curves are based upon typicalapplications. They will not necessarily definethe precise insertion loss for any specificapplication since the insertion loss achievedmay be influenced substantially by manyfactors, including engine size, type, speed,and unsilenced noise levels and frequency

distribution.

Selection of Silencer SizeThe open flow area within the silencershould be large enough to accommodatethe maximum possible exhaust flow withoutexceeding the engine manufacturersmaximum allowable back pressure.Improperly sized silencers may cause lossof power or damage to the engine.

Data required:

engine exhaust flow (CFM )exhaust temperature (F)maximum back pressure (inches of water)

The following formulas enable the correctsilencer size to be quickly determined.

1 Calculate gas velocity.

V = gas velocityP = back pressure, inches of waterc = silencer pressure drop coefficient

(Table 1)T = exhaust gas temperature, F

Note: Velocity should not exceed15,000 ft/min regardless of theallowable back pressure.

2 Calculate required flow area.

3 From Table 2, select the silencer sizewhich has a flow area equal to orgreater than that calculated, the actualback pressure can be calculated asfollows:

Universal Silencers engine exhaustsilencers are high quality, fully welded,reactive silencers designed to reduceexhaust noise on all types of internalcombustion engines. Each engine and eachoperating location requires a unique

combination of silencer properties. For thisreason many different silencer models arecataloged to cover most silencing problems.In cases where standard silencers will notmeet a particular spec, these customsilencers will satisfy the application need.

P

V 4005 c 530T 460

P = c V actual40052

530T 460

EN 2, 3, 4EN5 (1"10")EN5 (12" )ET2ET4ES2, 3

4.24.25.30.51.04.2

Silencer Model Pressure Drop Coeff. (C)

CFM

silencer flow areaV actual

CFM V

Flow Area Required (ft2)

Pressure Drop Coefficients1

0.00550.0120.0220.0340.0490.0670.0870.136

0.1960.3490.550.791.071.41.82.22.63.13.74.34.95.66.37.17.98.79.6

10.611.512.615.919.6

11223345

6810121416182022242628303234363840424446485460

Flow Area(ft2)

Diameter(in.)

Flow Area/Size2