1、Designation: E1265 04 (Reapproved 2013)Standard Test Method forMeasuring Insertion Loss of Pneumatic Exhaust Silencers1This standard is issued under the fixed designation E1265; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the laboratory measurement ofboth the acoustical and mechanical performance of pneumati
3、cexhaust silencers designed for quieting compressed gas (usu-ally air) exhausts from orifices connected to pipe sizes up to34in. NPT. This test method is not applicable for exhaustsperforming useful work, such as part conveying, ejection, orcleaning. This test method evaluates acoustical performance
4、using A-weighted sound level measurements.1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to addre
5、ss all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in Section 8
6、.2. Referenced Documents2.1 ASTM Standards:2C634 Terminology Relating to Building and EnvironmentalAcoustics2.2 ANSI Standards:3S1.4 Specification for Sound Level MetersS1.13 Method for the Measurement of Sound PressureLevelsS1.31 Precision Method for the Determination of SoundPower Levels of Broad-
7、Band Noise Sources in Reverbera-tion RoomsS1.33 Engineering Methods for the Determination of SoundPower Levels of Noise Sources in a Special ReverberationRoomB2.1 Taper Pipe Thread (NPT)Standard Designation forTapered Pipe Threads2.3 Federal Standard:Rules and RegulationsHand and Portable Power Tool
8、s andEquipment43. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, see Terminology C634. Particular terms of interestare: sound level and average sound pressure level.3.2 Definitions of Terms Specific to This Standard:3.2.1 flow ratiothe ratio of gas flow with the pneumati
9、cexhaust silencer installed relative to flow of the unrestrictedpipe.3.2.2 flow resistancethe reduction of fluid flow caused byvarious restrictions, surface roughness, devious paths,obstacles, etc. This term is sometimes referred to as “backpressure.”3.2.3 DiscussionFor this test method back pressur
10、e is aqualitative term, therefore, there is no need to measure.3.2.4 insertion loss of a pneumatic exhaust silencer (at aspecific supply pressure)the difference in averageA-weighted sound levels measured with and without thepneumatic exhaust silencer installed on an unrestricted or“open” pipe.3.2.5
11、Discussion Insertion loss, as defined in this testmethod, differs from the definition in Terminology C634.Asstated in 1.1, this test method uses A-weighting rather thandiscrete frequency bands. It compares a set of sound pressuredata measured in a reverberation room rather than determiningabsolute s
12、ound power levels. This test method is intended toassess the difference in sound regenerated at the pipe orificeand does not evaluate sound propagating along the pipeinterior.1This test method is under the jurisdiction ofASTM Committee E33 on Buildingand Environmental Acoustics and is the direct res
13、ponsibility of SubcommitteeE33.08 on Mechanical and Electrical System Noise.Current edition approved Feb. 1, 2013. Published February 2013. Originallyapproved in 1988. Last previous edition approved in 1995 as E1265 90 (1995)1,which was withdrawn July 2004 and reinstated August 2004. DOI: 10.1520/E1
14、265-04R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institu
15、te (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4This United States Occupational Safety and Health Administration Regulation,Federal Register, Vol 36, Number 105, Part II, p. 10653, May 1971, is availablefrom Superintendent of Documents, Government Printing Office, Washin
16、gton, DC204029371.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.6 pneumatic exhaust silencera device attached to apipe fitting or orifice. The silencer reduces the sound producedwhen the released pressurized exhaust gases (usual
17、ly air),merge with ambient (static) air in the region surrounding theorifice. Such silencers are not usually intended to performuseful work such as part conveying, ejection, or cleaning. Theport sizes of the pneumatic exhaust silencers addressed by thistest method are:18,14,38,12,58, and34 in. NPT (
18、based on theAmerican National Standard Taper Pipe Thread designation,(B.2.1), specified in fractions of an inch).4. Summary of Test Method4.1 A special air reservoir system terminates in a reverbera-tion room where acoustical measurements are made to assessthe sound produced by both an open pipe and
19、 the pipeterminated with a silencer. Both flow volume and A-weightedsound level measurements are made as the air supply valve isopened between the reservoir and the piping system. The testprocedure is repeated for three air reservoir pressures both withand without silencer. The flow ratios are calcu
20、lated from theflow volumes with an unrestricted pipe and with the silencer.The insertion loss is determined by the difference inA-weighted sound levels. This is done for each of the three airreservoir pressures. The overall pneumatic exhaust silencerperformance is then reported as insertion loss ver
21、sus flow ratio.5. Significance and Use5.1 This test method permits the evaluation of both theacoustical and mechanical performance of pneumatic exhaustsilencers designed for quieting compressed gas exhausts (usu-ally air). The data can be used by manufacturers to assess orimprove their products, or
22、by users to select or specify asilencer. The data acquired using this measurement methodallow for performance comparisons of competitive productsand aid in the selection of an appropriate device.5.2 Flow rate is an important parameter to consider whenthe application involves machinery or equipment t
23、hat requirescompressed air or other gases to be exhausted rapidly. Forexample, in an automatic pneumatic press, compressed airmust be exhausted rapidly to avoid a premature second cycle.For this reason, flow ratio is reported in addition to acousticalperformance.6. Assumptions6.1 Studies have shown
24、that the sound level (in decibels)produced by quieted pneumatic exhausts generally is linearwith supply pressure for the range of pressures covered in thistest method. It is assumed that the air supply pressures calledfor in this test method include those typical of most applica-tions. Sound levels
25、may be extrapolated for silencers operatingat pressures slightly beyond the test range.Alinear relationshipcan be assumed between discrete test supply pressures.6.2 Generally, the sound power produced by pneumaticexhausts is dominant in the frequency range from 500 to10 000 Hz. This frequency range
26、allows testing in a relativelysmall reveberation room. ANSI Standard S 1.33 (Appendix A),provides guidelines for the design of an appropriate test room.NOTE 1Reverberation rooms as small as 17 m3are sufficient formaking A-weighted measurements of noise generated by pneumaticexhaust silencers. The mi
27、nimum volume of 70 m3recommended in ANSIS1.33 can be ignored.6.3 The performance of pneumatic exhaust silencers tendsto deteriorate over time, due to clogging and other factors. Theprimary purpose of this test method is to evaluate the optimumperformance of pneumatic exhaust silencers, therefore onl
28、ynew or unused silencers should be tested. This test method mayalso be used to measure the performance of a silencer during itsactual or simulated service life.7. Apparatus7.1 Reverberation Room:7.1.1 The reverberation room shall conform to the require-ments in ANSI S1.33, except for the minimum vol
29、ume. (SeeNote 1.)7.1.2 The reverberation room shall be equipped with aduct-type muffler or silencer to control static air pressure whilesimultaneously reducing extraneous sound entering the testroom from adjacent areas.7.1.2.1 This duct-type muffler shall have an adequate“ free”cross-sectional area
30、to allow the air introduced by the testprocess to be vented rapidly, relieving the pressure within thetest room. The static pressure in the reverberation room shall bemeasured initially while testing the largest open pipe todetermine if the free cross-sectional area is adequate to allowair to escape
31、. If the gage pressure5rises to more than 4 kPa,then the cross-sectional area of the duct or the room volumemust be increased.7.1.2.2 The construction of the duct-type muffler and thereverberation room shall be adequate to ensure that thebackground sound level within the test room is at least 10dBbe
32、low the lowest sound level measured during the evaluation.The muffler shall also be so selected as to avoid “self-generated” sound.7.2 Piping System:7.2.1 The test apparatus shall consist of a system similar tothat shown in Fig. 1. The critical elements are the compressor-tank capacity, size of supp
33、ly pipes and method of assembly,lengths of certain pipe sections, and design of devices in the airstream (that is, valves, regulators, flow meters, temperature,and pressure sensors).7.2.1.1 Reservoir CapacityThe minimum air reservoirsize is determined by the maximum unrestricted pipe diameterplanned
34、 for the test. Use a reservoir whose size is adequate topermit obtaining three contiguous 1 s average sound levelswithin 2 dB of each other (see 9.3.3.2).NOTE 2Based on experience, the minimum storage tank capacity fortesting18 in. NPT devices is approximately 2.8 ft3(0.08 m3). Theminimum air reserv
35、oir size should be increased proportionally for largertest specimens.7.2.1.2 If a dedicated compressor and air reservoir arelocated near the test site and the piping meets the5The Magnehelic gage, available from F.W. Dwyer Co., P. O. Box 3029, 1123Mearns Rd., Ivyland, PA 18974, or equivalent, has be
36、en found satisfactory for thismeasurement.E1265 04 (2013)2specifications, the separate air reservoir of 7.2.1.1 may beeliminated. Once the required supply pressure has beenreached, the compressor motor must be shut down to ensurethat the compressor does not restrict as the air pressure isreleased fo
37、r the test.7.2.1.3 Water TrapThe system shall be equipped with awater trap (preferably at the tank outlet) to collect condensedwater and provide a means for draining moisture from thesystem.7.2.1.4 Supply PipesAll pipes in the system shall beSchedule 40 cast iron, steel, copper, or poly(vinyl chlori
38、de)(PCV). The final downstream segment of pipe shall be aminimum of 1 m-long steel or cast iron, appropriately sized forthe pneumatic exhaust silencer under test.NOTE 3Steel or cast iron is necessary to reduce transmission of soundthrough the pipe wall into the reverberation room.7.2.1.5 Method of A
39、ssemblyWhen assembling pipecomponents, avoid irregularities and obstructions that restrictflow or create unwanted turbulence. Burrs shall be removedand pipe threads properly mated to avoid exposed threads inthe gas stream. Changes in size and direction shall be accom-plished with the minimum number
40、of fittings. This is particu-larly important in the final pipe section and at the orifice wherethe pneumatic exhaust silencer is to be installed.7.2.1.6 Minimum Pipe SectionThe pipe section locatedbetween the pressure sensor and the pneumatic exhaustsilencer, shall be a straight section at least 1 m
41、 long to avoidturbulence prior to the silencer (see Fig. 1). Lengths of pipebetween the storage tank and pressure sensor shall be kept to aminimum to avoid flow-generated pressure losses.7.2.1.7 The final segment of pipe shall be positioned in thereverberation room so the pneumatic exhaust silencer
42、undertest is at least 1 m from any room surface. (See Fig. 2.)7.2.1.8 Valves, regulators, flow meters, temperature, andpressure sensors located in the test air stream shall be designedto minimize flow restriction and turbulence. A “ball” valve(straight-flow ball type, or equivalent) is recommended f
43、orflow control. This valve shall have an inside diameter equal tothe inside diameter of the upstream and downstream pipesegments connected to the valve. The temperature sensor shallbe located on the air reservoir rather than in the supply piping.The flow meter should preferably be a hot-wire anemome
44、ter oran electronic thermal mass flow sensor due to their minimaleffect on the airstream.NOTE 4Vortex-shedding flow meters that require a “blunt object” inthe airstream shall not be used. Similarly, differential-pressure transmitterflow meters, that require a flow restricting orifice plate, shall no
45、t be used.FIG. 1 Apparatus for Pneumatic Exhaust SilencersNOTE 1 Minimum dimensions in metres.FIG. 2 Microphone Location for Pneumatic Exhaust SilencersE1265 04 (2013)3It may be possible to use a differential-pressure transmitter flow meter inconjunction with a venturi, flow nozzle, or pitot tube to
46、 minimize flowrestriction.7.2.1.9 Precision Regulator, shall be provided prior to theair reservoir specified in 7.2.1.1. This regulator shall not allowpressure in the air reservoir to vary more than 2 % regardlessof supply pressure variation.7.2.1.10 “In-line” silencers (for treatment of sound withi
47、nthe airstream) are not recommended. These silencers maycreate undesirable flow restriction or turbulence. Sound propa-gating downstream from the compressor or other sources is notexpected to influence the test results.7.2.1.11 In instances where both a compressor and airreservoir are used, vibratio
48、n isolation must be provided for thepiping system to reduce potential structure-borne noise. Thiscan be accomplished by installing a section of reinforcedflexible hose between the compressor and the air reservoir.7.3 Acoustical Instrumentation:7.3.1 The sound level meter, microphone, and any associ-
49、ated instrumentation shall meet the requirements for a “Type 1Precision” sound level meter as specified in ANSI S1.4. Soundlevel measurements shall be made with A-weighted frequencycharacteristics. The instrumentation shall be capable of mea-suring sequential 1 s average sound pressure levels (as speci-fied in Terminology C634).8. Hazards8.1 Caution should be exercised when working with com-pressed gas (air) to avoid the risk of injury. The OccupationalSafety and HealthAdministration (OSHA) has established a 30psig blocked static air pressure limit fo
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