ASTM_D_3796_-_09.pdf

Designation:D379609Standard Practice forCalibration of Type S Pitot Tubes1This standard is issued under the fixed designation D3796;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year 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 practice covers the determination of Type S pitottube coefficients in the gas velocity range from 305 to 1524m/min or 5.08 to 25.4 m/s(1000 to 5000 ft/min).The methodapplies both to the calibration of isolated Type S pitot tubes(see 5.1),and pitobe assemblies.1.2 This practice outlines procedures for obtaining Type Spitot tube coefficients by calibration at a single-velocity settingnear the midpoint of the normal working range.Type S pitotcoefficients obtained by this method will generally be valid towithin 63%over the normal working range.If a more precisecorrelation between Type S pitot tube coefficient and velocityis desired,multivelocity calibration technique(Annex A1)should be used.The calibration coefficients determined for theType S pitot tube by this practice do not apply in field use whenthe flow is nonaxial to the face of the tube.1.3 This practice may be used for the calibration of thermalanemometers for gas velocities in excess of 3 m/s(10 ft/s).1.4 The values stated in SI units are to be regarded asstandard.1.5 This standard does not purport to address 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.2.Referenced Document2.1 ASTM Standards:2D1356 Terminology Relating to Sampling and Analysis ofAtmospheres3.Terminology3.1 For definitions of terms used in this test method,refer toTerminology D1356.3.2 Definitions:3.2.1 isolated Type S pitot tubeany Type S pitot tube thatis calibrated or used alone(Fig.1).3.2.2 normal working velocity rangethe range of gasvelocities ordinarily encountered in industrial smokestacks andducts:approximately 305 to 1524 m/min or 5.08 to 25.4 m/s(1000 to 5000 ft/min).3.2.3 pitobe assemblyany Type S pitot tube that is cali-brated or used while attached to a conventional isokineticsource-sampling probe(designed in accordance with Martin(1)3or allowable modifications thereof;see also Fig.7).4.Summary of Practice4.1 The coefficients of a given Type S pitot tube aredetermined from alternate differential pressure measurements,made first with a standard pitot tube,and then with the Type Spitot tube,at a predetermined point in a confined,flowing gasstream.The Type S pitot coefficient is equal to the product ofthe standard pitot tube coefficient,Cp(std),and the square rootof the ratio of the differential pressures indicated by thestandard and Type S pitot tubes.5.Significance and Use5.1 The Type S pitot tube(Fig.1)is often used to measurethe velocity of flowing gas streams in industrial smokestacksand ducts.Before a Type S pitot tube is used for this purpose,its coefficients must be determined by calibration against astandard pitot tube(1).6.Apparatus6.1 Flow SystemCalibration shall be done in a flowsystem designed in accordance with the criteria illustrated inFig.2 and described in 6.1.1 through 6.1.5.6.1.1 The flowing gas stream shall be confined within adefinite cross-sectional area;the cross section shall be prefer-ably circular or rectangular(2).For circular cross sections,theminimum duct diameter shall be 305 mm(12 in.).Forrectangular cross sections,the width shall be at least 254 mm(10 in.).Other regular cross-section geometries(for example,1This practice is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.03on AmbientAtmospheres and Source Emissions.Current edition approved Oct.1,2009.Published October 2009.Originallyapproved in 1979.Last previous edition approved in 2004 as D3796-90(2004).DOI:10.1520/D3796-09.2For 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.3The boldface numbers in parentheses refer to the list of references at the end ofthis practice.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 hexagonal or octagonal)are permissible,provided that theyhave cross-sectional areas of at least 645 cm2(100 in.2).6.1.2 It is recommended that the cross-sectional area of theflow-system duct be constant over a distance of 10 or moreduct diameters.For rectangular cross sections,use an equiva-lent diameter,calculated as follows,to determine the numberof duct diameters:De5 2LW/L1W!(1)where:De=equivalent diameter,L=length of cross section,andW=width of cross s