1、Designation: E 1265 04Standard Test Method forMeasuring Insertion Loss of Pneumatic Exhaust Silencers1This standard is issued under the fixed designation E 1265; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 pneumaticexhaust silenc
3、ers 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 performanceusing A-weighte
4、d sound level measurements.1.2 The values stated in inch-pound units are to be regardedas the standard. The values given in parentheses are providedfor information only.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility o
5、f 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 8.2. Referenced Documents22.1 ASTM Standards:C 634 Terminology Relating to Environmental
6、Acoustics2.2 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-Band Noise Sources in Reverbera-tion RoomsS1.33 Engineering Methods for the Determination of SoundP
7、ower 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 Tools andEquipment43. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, see T
8、erminology C 634. 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 pneumaticexhaust silencer installed relative to flow of the unrestrictedpipe.3.2.2 flow resistancethe redu
9、ction of fluid flow caused byvarious restrictions, surface roughness, devious paths, ob-stacles, etc. This term is sometimes referred to as “backpressure.”3.2.3 DiscussionFor this test method back pressure is aqualitative term, therefore, there is no need to measure.3.2.4 insertion loss of a pneumat
10、ic 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 DiscussionInsertion loss, as defined in this testmethod, differs from the definition in Terminol
11、ogy C 634. 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 sound power levels. This test method is intended toassess the difference in sound regenerated at
12、 the pipe orificeand does not evaluate sound propagating along the pipeinterior.3.2.6 pneumatic exhaust silencera device attached to apipe fitting or orifice. The silencer reduces the sound producedwhen the released pressurized exhaust gases (usually air),merge with ambient (static) air in the regio
13、n surrounding theorifice. Such silencers are not usually intended to perform1This test method is under the jurisdiction of ASTM Committee E33 onEnvironmental Acoustics and is the direct responsibility of Subcommittee E33.08 onMechanical and Electrical System Noise.Current edition approved August 1,
14、2004. Published August 2004. Originallyapproved in 1988. Last previous edition approved in 1995 as E 1265 90 (1995)e1,which was withdrawn July 2004 and reinstated August 2004.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For
15、 Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.4This United States Occupational Safety and Health Administration Regulation,Fe
16、deral Register, Vol 36, Number 105, Part II, p. 10653, May 1971, is available fromSuperintendent of Documents, Government Printing Office, Washington, DC204029371.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.useful work such as pa
17、rt conveying, ejection, or cleaning. Theport sizes of the pneumatic exhaust silencers addressed by thistest method are:18 ,14 ,38 ,12 ,58 , and34 in. NPT (based onthe American National Standard Taper Pipe Thread designa-tion, (B.2.1), specified in fractions of an inch).4. Summary of Test Method4.1 A
18、 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 the pipeterminated with a silencer. Both flow volume and A-weightedsound level measurements are made as the air supply valve isopened between
19、the reservoir and the piping system. The testprocedure is repeated for three air reservoir pressures both withand without silencer. The flow ratios are calculated from theflow volumes with an unrestricted pipe and with the silencer.The insertion loss is determined by the difference inA-weighted soun
20、d levels. This is done for each of the three airreservoir pressures. The overall pneumatic exhaust silencerperformance is then reported as insertion loss versus flow ratio.5. Significance and Use5.1 This test method permits the evaluation of both theacoustical and mechanical performance of pneumatic
21、 exhaustsilencers designed for quieting compressed gas exhausts (usu-ally air). The data can be used by manufacturers to assess orimprove their products, or by users to select or specify asilencer. The data acquired using this measurement methodallow for performance comparisons of competitive produc
22、tsand aid in the selection of an appropriate device.5.2 Flow rate is an important parameter to consider whenthe application involves machinery or equipment that requirescompressed air or other gases to be exhausted rapidly. Forexample, in an automatic pneumatic press, compressed airmust be exhausted
23、 rapidly to avoid a premature second cycle.For this reason, flow ratio is reported in addition to acousticalperformance.6. Assumptions6.1 Studies have shown that the sound level (in decibels)produced by quieted pneumatic exhausts generally is linearwith supply pressure for the range of pressures cov
24、ered 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 may be extrapolated for silencers operatingat pressures slightly beyond the test range. A linear relationshipcan be assumed between discrete te
25、st 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 allows testing in a relativelysmall reveberation room. ANSI Standard S 1.33 (Appendix A),provides guidelines for the design of an appropriate
26、 test room.NOTE 1Reverberation rooms as small as 17 m3are sufficient formaking A-weighted measurements of noise generated by pneumaticexhaust silencers. The minimum volume of 70 m3recommended in ANSIS1.33 can be ignored.6.3 The performance of pneumatic exhaust silencers tendsto deteriorate over time
27、, due to clogging and other factors. Theprimary purpose of this test method is to evaluate the optimumperformance of pneumatic exhaust silencers, therefore onlynew or unused silencers should be tested. This test method mayalso be used to measure the performance of a silencer during itsactual or simu
28、lated 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 volume. (SeeNote 1.)7.1.2 The reverberation room shall be equipped with aduct-type muffler or silencer to control static air pressure whilesimul
29、taneously 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 to allow the air introduced by the testprocess to be vented rapidly, relieving the pressure within thetest room. The static pressure in the r
30、everberation room shall bemeasured initially while testing the largest open pipe todetermine if the free cross-sectional area is adequate to allowair to escape. 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 con
31、struction of the duct-type muffler and thereverberation room shall be adequate to ensure that thebackground sound level within the test room is at least 10dBbelow the lowest sound level measured during the evaluation.The muffler shall also be so selected as to avoid “self-generated” sound.7.2 Piping
32、 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 supply pipes and method of assembly,lengths of certain pipe sections, and design of devices in the airstream (that is, valves, regulators, flow m
33、eters, temperature,and pressure sensors).7.2.1.1 Reservoir CapacityThe minimum air reservoirsize is determined by the maximum unrestricted pipe diameterplanned for the test. Use a reservoir whose size is adequate topermit obtaining three contiguous 1 s average sound levelswithin 2 dB of each other (
34、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 reservoir size should be increased proportionally for largertest specimens.7.2.1.2 If a dedicated compressor and air reservoir arelocated near the
35、test site and the piping meets the specifica-tions, the separate air reservoir of 7.2.1.1 may be eliminated.Once the required supply pressure has been reached, thecompressor motor must be shut down to ensure that thecompressor does not restrict as the air pressure is released forthe test.5The Magneh
36、elic gage, available from F.W. Dwyer Co., P. O. Box 3029, 1123Mearns Rd., Ivyland, PA 18974, or equivalent, has been found satisfactory for thismeasurement.E12650427.2.1.3 Water TrapThe system shall be equipped with awater trap (preferably at the tank outlet) to collect condensedwater and provide a
37、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 chloride)(PCV). The final downstream segment of pipe shall be aminimum of 1 m-long steel or cast iron, appropriately sized forthe pneumatic exhaust silen
38、cer 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 AssemblyWhen assembling pipe com-ponents, avoid irregularities and obstructions that restrict flowor create unwanted turbulence. Burrs shall be remo
39、ved andpipe threads properly mated to avoid exposed threads in the gasstream. Changes in size and direction shall be accomplishedwith the minimum number of fittings. This is particularlyimportant in the final pipe section and at the orifice where thepneumatic exhaust silencer is to be installed.7.2.
40、1.6 Minimum Pipe SectionThe pipe section locatedbetween the pressure sensor and the pneumatic exhaust si-lencer, shall be a straight section at least 1 m long to avoidturbulence prior to the silencer (see Fig. 1). Lengths of pipebetween the storage tank and pressure sensor shall be kept to aminimum
41、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 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
42、the test air stream shall be designedto minimize flow restriction and turbulence. A “ball” valve(straight-flow ball type, or equivalent) is recommended forflow control. This valve shall have an inside diameter equal tothe inside diameter of the upstream and downstream pipesegments connected to the v
43、alve. The temperature sensor shallbe located on the air reservoir rather than in the supply piping.The flow meter should preferably be a hot-wire anemometer oran electronic thermal mass flow sensor due to their minimaleffect on the airstream.NOTE 4Vortex-shedding flow meters that require a “blunt ob
44、ject” inthe airstream shall not be used. Similarly, differential-pressure transmitterflow meters, that require a flow restricting orifice plate, shall not be used.It may be possible to use a differential-pressure transmitter flow meter inconjunction with a venturi, flow nozzle, or pitot tube to mini
45、mize 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.FIG. 1 Apparatus for Pneumatic Exhaust SilencersNOTE 1 Minimum
46、dimensions in metres.FIG. 2 Microphone Location for Pneumatic Exhaust SilencersE12650437.2.1.10 “In-line” silencers (for treatment of sound withinthe airstream) are not recommended. These silencers maycreate undesirable flow restriction or turbulence. Sound propa-gating downstream from the compresso
47、r or other sources is notexpected to influence the test results.7.2.1.11 In instances where both a compressor and airreservoir are used, vibration isolation must be provided for thepiping system to reduce potential structure-borne noise. Thiscan be accomplished by installing a section of reinforcedf
48、lexible hose between the compressor and the air reservoir.7.3 Acoustical Instrumentation:7.3.1 The sound level meter, microphone, and any associ-ated instrumentation shall meet the requirements for a “Type 1Precision” sound level meter as specified in ANSI S1.4. Soundlevel measurements shall be made
49、 with A-weighted frequencycharacteristics. The instrumentation shall be capable of mea-suring sequential 1 s average sound pressure levels (as speci-fied in Terminology C 634).8. Hazards8.1 Caution should be exercised when working with com-pressed gas (air) to avoid the risk of injury. The OccupationalSafety and Health Administration (OSHA) has established a 30psig blocked static air pressure limit for hand-held air guns andnozzles (see 2.3). Since this test method uses air pressure inexcess of 30 psig, personnel conducting tests in accordancewith this tes
