1、Designation: E295 82 (Reapproved 2014)Standard Test Method forMeasured Speed of Oil Diffusion Pumps1This standard is issued under the fixed designation E295; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 determination of the mea-sured speed (volumetric flow rate) of oil diffusion pumps.1.2 The values state
3、d 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 address all of thesafety concerns, if any, associated with its use.
4、 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 Referenced Documents2.1 ASTM Standards:2E297 Test Method for Calibrating Ionization Vacuum GageTubes (Withdrawn 1983)
5、33. Terminology3.1 measured speedthe mass flow rate of gas admittedfrom a flowmeter divided by the resulting increase in equilib-rium static pressure near the inlet of the pump, using theequipment in Fig. 1.4. Summary of Test Method4.1 The pump under test is fitted with a test dome ofspecified desig
6、n (Fig. 1). Gas is admitted to the test dome in aspecified manner at a measured rate, and the resulting changein equilibrium pressure is measured in a specified way.5. Apparatus5.1 Test DomeThe test dome (Fig. 1) may be constructedby any material and by any method acceptable in high-vacuumpractice,
7、and will normally be connected to the pump by themethod provided for in the design of the pump. The insidediameter of the test dome shall be equal to that of the pumpinlet, and its mean height shall be 1.5 times this diameter (Note1). The gas shall be admitted through a tube projecting into thedome
8、and bent upward so that its exit is located on the axis,facing away from the pump inlet port, and at a distance fromthe pump inlet equal to the dome diameter. The opening to thevacuum gage shall be through a tube radially projecting intothe test dome. The tubulation center line shall be above theinl
9、et flange, 1 in. (25 mm) or14 D above the top of the flange,whichever is larger (see Fig. 1).NOTE 1A10 slope of the dome roof is required only if the dome isto be used for back-streaming measurements.5.2 Gage AttachmentThe gage connecting line shall beless than 6 in. (152 mm) long and at least34 in.
10、 (19 mm) ininside diameter; shall contain one right-angle bend upward tothe gage; and shall project18 in. (3.2 mm) into the test dome.If a McLeod gage is used, it shall be attached in a similarmanner, except that the connecting line, including a mercuryvapor trap, need not meet the dimensional restr
11、ictions above.The use of grease, wax, and rubber in assembling the gage linesshould be minimized.5.3 Flow-Measuring Devices:5.3.1 For flows greater than about 5 104torr L/s (that is,about 25 min/atmospheric cm3), and up to approximately 5 torrL/s (that is, about 15 s/100 atmospheric cm3), some type
12、ofconstant-pressure displacement tube with low-vapor pressurefluid shall be used. These tubes should be provided in a seriesof overlapping ranges so that very small through-puts may bemeasured in a reasonably short time and that very largethrough-puts may be measured in a time interval long enoughto
13、 allow precise measurement.5.3.2 Flow rates less than about 5 104torr L/s may bedetermined by a conductance method in which the test gascontained in a reservoir at known pressure is admitted to thetest dome through a known conductance.5.3.3 For flows greater than 5 torr L/s, special types ofconstant
14、-pressure fluid-displacement devices or a series ofvariable-area flowmeters (rotameters) of sufficient overlap toensure precise measurement should be used.5.3.4 The timing in all flow measurements shall be madewith a110-s stop watch or by some equally precise method.1This test method is under the ju
15、risdiction of the ASTM Committee E21 onSpace Simulation and Applications of Space Technology and is the direct respon-sibility of Subcommittee E21.04 on Space Simulation Test Methods.Current edition approved April 1, 2014. Published April 2014. Originallyapproved in 1967. Last previous edition appro
16、ved in 2006 as E295 82 (2006).DOI: 10.1520/E0295-82R14.2For 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 l
17、ast approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.4 Leak Control ValveThe leak control valve shouldprovide good control of flow and flow changes as reflecte
18、d inequilibrium pressures through the pressure range of interest.6. Test Gas6.1 Air shall normally be used in the measurement of pumpspeeds; and measured speed for air will be considered a basicperformance characteristic of a pump.6.2 The apparatus and method herein described may be usedfor measurin
19、g pumping speeds for gases other than air as maybe required.7. Calibration and Precision of Flow-Measuring Devices7.1 Constant-Pressure Displacement TubesTo cover con-veniently the input range suggested in 5.3, displacement tubesof at least three overlapping ranges should be provided. Thedisplacemen
20、t tubes should be precision burets of glass tubingselected for uniformity of bore and having accurately measuredinside diameters (accuracy 0.25 %, commercially available).The instruments should be designed, calibrated, and used insuch a way as to measure the actual quantity of gas transferredto the
21、test dome in some conveniently measurable time.Ambient temperature during the measurement shall be 23 63C. Meters of the constant-pressure displacement type maytake various forms. Two of these are shown in Fig. X1. anddiscussed in Appendix X2.7.2 Conductance MethodThis method of measuring inputrate
22、requires a conductance of accurately known dimensionsand a reservoir of test gas in which the pressure can be variedand accurately measured (see Fig. X2. and Fig. X3. andAppendix X3). It requires, in addition, that the dimensions ofthe conductance be so chosen as to permit the desired maxi-mum throu
23、gh-put (5 104torr L/s or more) at a reservoirpressure that does not exceed the condition for free molecularflow through any part (that is, the mean free path of gas in thereservoir must be equal to or greater than ten times the largestlinear dimension of the reservoir). Gas introduced into thereserv
24、oir must be directed away from the conductance en-trance.8. Calibration and Precision of Vacuum Gages8.1 To cover the full range of pressures at which pumpspeeds should be measured requires that at least two types ofvacuum gages be used:8.1.1 McLeod GageFor measuring pressures greater than103torr, a
25、 McLeod gage shall be used. The McLeod gage mayalso be used at lower pressures (down to about 105torr)provided the gage has an error less than 65 % at these lowerpressures. Only gages having individually determined gageconstants and individually calculated scales can be dependedupon for this precisi
26、on. Also, approved procedures must befollowed, particularly in the lower range of measurable pres-sures.8.1.2 Ionization GageFor measuring pressures less than105torr, an untrapped ionization gage of the Bayard-Alperttype shall be used.8.2 Calibration of vacuum gages used in this test methodshall be
27、based on Test Method E297.9. Procedure9.1 The following operating conditions should be noted forsubsequent incorporation in the report of speed measurements:type and speed of fore-pump system, type and quantity ofdiffusion pump fluid, power input to diffusion pump, andFIG. 1 Test Dome DimensionsE295
28、 82 (2014)2(optionally) cooling water flow rate, inlet temperature, anddischarge temperature.9.2 Speed measurements should not be made until thepressure poin the test dome has become 1 decade lower thanthe lowest test point, p.9.3 After the pressure pohas become constant, introduce gasto the test do
29、me at some constant measured mass flow rate, Q,for not less than 15 min and note the resulting equilibriumpressure, p.Ifp varies, use the arithmetic average value overthe time interval during which Q is measured. The pumpingspeed at this pressure is then derived from the followingequation:S 5 Q/p 2
30、po! (1)9.4 Adjust the rate of gas input to a series of values anddetermine the pumping speed at each resulting equilibriumpressure. Speed measurements should be made at pressuresdistributed over the whole operating pressure range of thepump.10. Results10.1 The measured speed of a pump shall be displ
31、ayed by agraph on which the speed is plotted on the ordinate as a linearfunction and the pressure plotted on the abscissa as a logfunction.10.2 Each speed curve shall be accompanied by a listing ofthe operating conditions specified in 9.1. Also, the pressure pobefore the time the measurements were m
32、ade shall be indi-cated.11. Precision11.1 All equipment and procedures used in making speedmeasurements shall be selected so that the probable error in thereproducibility of test results will be no more than 65 % unlessotherwise noted.APPENDIXES(Nonmandatory Information)X1. INTERPRETATION OF FLOWX1.
33、1 The lowest rate for intentionally admitted gas into thetest dome has been arbitrarily set to raise the pressure pto avalue at least ten times the pressurepoto ensure that themeasured rate of flow of gas, Q, represents essentially all thegas flowing through the pump under test conditions.X1.2 The t
34、otal quantity of gas passing through the pump,QT, may be explained more readily by the following expres-sion:QT5 QO1QL1Q (X1.1)where:QO= gas originating within this test dome as the result ofoutgassing,QL= gas leaking into the test dome unintentionally as theresult of the permeation through the mate
35、rials ofconstruction, leaks, and so forth, andQ = gas admitted intentionally through the controlled leak.X1.3 When speed measurements are made too near thepressure poof a pump, the resulting speed measurements maybe in error.Arbitrarily raising the pressure pto 10poavoids thisproblem.X1.4 The use of
36、 the term ppoalso eliminates the mis-leading concept that the speed of a diffusion pump drops tozero at some low pressure powhen no gas is intentionallyadmitted into the pump test dome.E295 82 (2014)3FIG. X1.1 Constant-Pressure Flow-Measuring DevicesX2. GAS FLOW MEASUREMENT BY CONSTANT-PRESSURE METH
37、ODX2.1 Constant-pressure displacement meters of many typeshave been used for measuring flow rates. Some simple typesare shown in Fig. X1.1. Referring to Fig. X1.1(a), a leak rateis determined by observing the time trequired for the displacedfluid to rise (or fall) through some arbitrary distancehin
38、thedisplacement tube. The leak rate,Q, can be determined inPVunits per second as follows:Q 5 BVo2 B 2 Ph!Vo2 v!#/t 5 Bv1PhVo2 v!#/t(X2.1)where:B = pressure of the gas filling the displacement meterat time zero,Vo= corresponding volume,Ph= pressure due to fluid head h,BPh= pressure of the gas remaini
39、ng at time t, andVov = corresponding volume.X2.1.1 Displacement devices may be designed so that thequantity Ph(Vo v) is negligibly small as compared with thequantity Bv. In such cases, Eq X2.1 reduces toQ 5 Bv/t (X2.2)X2.1.2 If it is not convenient to make Ph(Vo v) negligiblysmall, Eq X2.1 may be us
40、ed to construct a displacement scalethat reads quantity change directly.X2.2 For very small flow rates, a simple small bore tube orpipet, using a “slug” of fluid such as shown in Fig. X1.1(b), isideal.X2.3 For very large flow rates (5 to 50 torr L/s), a verticaldisplacement device with the fluid res
41、ervoir on top as shown inFig. X1.1(c) can be used conveniently and with a precision ofabout 61 % either as a primary measuring instrument or as astandard for calibrating variable-area-type meters (rotameters).E295 82 (2014)4FIG. X2.1 Speed Testing by Conductance-Tube MethodX3. GAS FLOW MEASUREMENT B
42、Y CONDUCTANCE-TUBE METHODX3.1 Two arrangements for controlling and determining theflow into the test dome by the conductance-tube method areillustrated. Figure X2.1 shows schematically an arrangementwhereby the conductance tube connects two large chambers inwhich the pressure measurements are made.
43、A gas supplychamber, pumped by an auxiliary (diffusion) pump, is con-nected to the test dome by a tube whose conductance, C, can bederived from its dimensions. The equilibrium pressure in thetest chamber can be varied by varying the leak rate into thechamber, or by adjusting the net speed of the aux
44、iliarypumping system connected to the gas supply chamber. Bayard-Alpert ionization gages shall be used for pressure-drop mea-surements. The flow rate, Q, into the test dome due to thepressure increase in the gas supply chamber is calculated asfollows:Q 5 CP12 P01! 2 P22 P02!# (X3.1)where:P01= ultima
45、te pressure in the gas supply chamber,P02= ultimate pressure in the test dome,P1= equilibrium pressure in the gas supply chamber whena leak is admitted, andP2= corresponding pressure in the test dome.X3.1.1 In practice, the tube conductance should be sochosen that the ratio (P1 P01)/(P2P02) is not l
46、ess than 100.In this case, Eq X3.1 may be simplified toQ 5 CP12 P01! (X3.2)and gage P2may be omitted.X3.1.2 The speed of the test pump, S, in litres per second, isdefined asS 5 Q/P 2 Po! (X3.3)where:P = equilibrium pressure at the test pump inlet andPo= ultimate pressure at the test pump inlet.X3.1.
47、3 From this it follows thatS 5 CP12 P01!/P 2 Po!# (X3.4)Since the conductance of a tube is constant and determinableonly for free molecular conditions, it is essential that theconductance-tube method not be used at supply-gas pressurestoo high to permit this type of flow.X3.2 Fig. X3. shows schemati
48、cally an arrangement wherebythe pressure drop in a straight tube is determined downstreamfrom the source of gas flow. This arrangement lends itself toboth theoretical conductance computation and comparativemeasurement (in some pressure ranges) with constant-pressuredisplacement devices such as are d
49、escribed in Appendix X2.E295 82 (2014)5FIG. X3.1 Schematic Diagram of Conductance-Tube Method for Measuring Pumping SpeedX3.3 If, as is generally the case, the speed of pumps changesonly slowly with pressure, absolute gage calibrations are notessential. However, in using the expression for Sabove, it isonly necessary that the relative sensitivities of the variousgages be known accurately. To obtain the relative sensitivities,it is then merely necessary to run the entire system at the samepressure.ASTM International takes no posit
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