1、Designation: E 295 82 (Reapproved 2006)Standard Test Method forMeasured Speed of Oil Diffusion Pumps1This standard is issued under the fixed designation E 295; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 determination of the mea-sured speed (volumetric flow rate) of oil diffusion pumps.1.2 The values st
3、ated in inch-pound units are to be regardedas the standard. The metric equivalents of inch-pound unitsmay be approximate.1.3 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-p
4、riate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 297 Method for Calibrating Ionization Vacuum GageTubes33. Terminology3.1 measured speedthe mass flow rate of gas admittedfrom a flowmeter divided by
5、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 design (Fig. 1). Gas is admitted to the test dome in aspecified manner at a measured rate, and the r
6、esulting 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, and will normally be connected to the pump by themethod provided for in the design of the pump.
7、 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 and bent upward so that its exit is located on the axis,facing away from the pump inlet port, a
8、nd 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 theinlet flange, 1 in. (25 mm) or14 D above the top of the flange,whichever is larger (see Fig. 1).NO
9、TE 1A 10 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. (19 mm) ininside diameter; shall contain one right-angle bend upward tothe gage; and shall pr
10、oject18 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 restrictions above.The use of grease, wax, and rubber in assembling the gage linesshould be minimiz
11、ed.5.3 Flow-Measuring Devices:5.3.1 For flows greater than about 5 3 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 ofconstant-pressure displacement tube with low-vapor pressurefluid shall be used. These tube
12、s 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 allow precise measurement.5.3.2 Flow rates less than about 5 3 104torr L/s may bedetermined
13、 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-pressure fluid-displacement devices or a series ofvariable-area flowmeters (rotameters) o
14、f 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 jurisdiction of the ASTM Committee E21 onSpace Simulation and Applications of Space Technolo
15、gy and is the direct respon-sibility of Subcommittee E21.04 on Space Simulation Test Methods.Current edition approved April 1, 2006. Published April 2006. Originallyapproved in 1967. Last previous edition approved in 2000 as E 295 82 (2000).2For referenced ASTM standards, visit the ASTM website, www
16、.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.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United S
17、tates.5.4 Leak Control ValveThe leak control valve shouldprovide good control of flow and flow changes as reflected 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
18、 a basicperformance characteristic of a pump.6.2 The apparatus and method herein described may be usedfor measuring 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
19、 range suggested in 5.3, displacement tubesof at least three overlapping ranges should be provided. Thedisplacement tubes should be precision burets of glass tubingselected for uniformity of bore and having accurately measuredinside diameters (accuracy 0.25 %, commercially available).The instruments
20、 should be designed, calibrated, and used insuch a way as to measure the actual quantity of gas transferredto the 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
21、 these are shown in Fig. X1.1 anddiscussed in Appendix X2.7.2 Conductance MethodThis method of measuring inputrate requires a conductance of accurately known dimensionsand a reservoir of test gas in which the pressure can be variedand accurately measured (see Figs. X2.1 and X3.1 and Appen-dix X3). I
22、t requires, in addition, that the dimensions of theconductance be so chosen as to permit the desired maximumthrough-put (5 3 104torr L/s or more) at a reservoir pressurethat does not exceed the condition for free molecular flowthrough any part (that is, the mean free path of gas in thereservoir must
23、 be equal to or greater than ten times the largestlinear dimension of the reservoir). Gas introduced into thereservoir 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 requ
24、ires that at least two types ofvacuum gages be used:8.1.1 McLeod GageFor measuring pressures greater than103torr, a 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 h
25、aving individually determined gageconstants and individually calculated scales can be dependedupon for this precision. 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 ioniz
26、ation gage of the Bayard-Alperttype shall be used.8.2 Calibration of vacuum gages used in this test methodshall be based on Test Method E 297.9. Procedure9.1 The following operating conditions should be noted forsubsequent incorporation in the report of speed measurements:type and speed of fore-pump
27、 system, type and quantity ofdiffusion pump fluid, power input to diffusion pump, and(optionally) cooling water flow rate, inlet temperature, anddischarge temperature.FIG. 1 Test Dome DimensionsE 295 82 (2006)29.2 Speed measurements should not be made until thepressure poin the test dome has become
28、1 decade lower thanthe lowest test point, p.9.3 After the pressure pohas become constant, introduce gasto the test dome 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 interva
29、l during which Q is measured. The pumpingspeed at this pressure is then derived from the followingequation:S 5 Q/p 2 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 pressuresdistr
30、ibuted over the whole operating pressure range of thepump.10. Results10.1 The measured speed of a pump shall be displayed 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 b
31、y a listing ofthe operating conditions specified in 9.1. Also, the pressure pobefore the time the measurements were made 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 resu
32、lts will be no more than 65 % unlessotherwise noted.APPENDIXES(Nonmandatory Information)X1. INTERPRETATION OF FLOWX1.1 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 pressure poto ensure that themeasur
33、ed rate of flow of gas, Q, represents essentially all thegas flowing through the pump under test conditions.X1.2 The total quantity of gas passing through the pump,QT, may be explained more readily by the following expres-sion:QT5 QO1 QL1 Q (X1.1)where:QO= gas originating within this test dome as th
34、e result ofoutgassing,QL= gas leaking into the test dome unintentionally as theresult of the permeation through the materials ofconstruction, leaks, and so forth, andQ = gas admitted intentionally through the controlledleak.X1.3 When speed measurements are made too near thepressure poof a pump, the
35、resulting speed measurements maybe in error.Arbitrarily raising the pressure p to 10 poavoids thisproblem.X1.4 The use of the term ppoalso eliminates themisleading concept that the speed of a diffusion pump drops tozero at some low pressure powhen no gas is intentionallyadmitted into the pump test d
36、ome.E 295 82 (2006)3FIG. X1.1 Constant-Pressure Flow-Measuring DevicesX2. GAS FLOW MEASUREMENT BY CONSTANT-PRESSURE METHODX2.1 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
37、 determined by observing the time trequired for the displacedfluid to rise (or fall) through some arbitrary distance hin thedisplacement tube. The leak rate, Q, can be determined in PVunits per second as follows:Q 5 BVo2 B 2 Ph!Vo2 v!#/t 5 Bv1 PhVo2 v!#/t(X2.1)where:B = pressure of the gas filling t
38、he displacement meterat time zero,Vo= corresponding volume,Ph= pressure due to fluid head h,BPh= pressure of the gas remaining 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 suc
39、h 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 used 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
40、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 reservoir 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 variab
41、le-area-type meters (rotameters).E 295 82 (2006)4FIG. X2.1 Speed Testing by Conductance-Tube MethodX3. GAS FLOW MEASUREMENT BY 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 sche
42、matically an arrangementwhereby the conductance tube connects two large chambers inwhich the pressure measurements are made. 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
43、 pressure in thetest chamber can be varied by varying the leak rate into thechamber, or by adjusting the net speed of the auxiliarypumping 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 du
44、e to thepressure increase in the gas supply chamber is calculated asfollows:Q 5 CP12 P01! 2 P22 P02!# (X3.1)where:P01= ultimate 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 p
45、ressure in the test dome.X3.1.1 In practice, the tube conductance should be sochosen that the ratio (P1 P01)/(P2P02) is not less than 100.In this case, Eq X3.1 may be simplified toQ 5 C P12 P01! (X3.2)and gage P2may be omitted.X3.1.2 The speed of the test pump, S, in litres per second, isdefined asS
46、 5 Q/P 2 Po! (X3.3)where:P = equilibrium pressure at the test pump inlet andPo= ultimate pressure at the test pump inlet.X3.1.3 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 t
47、heconductance-tube method not be used at supply-gas pressurestoo high to permit this type of flow.X3.2 Figure X3.1 shows schematically an arrangementwhereby the pressure drop in a straight tube is determineddownstream from the source of gas flow. This arrangementlends itself to both theoretical cond
48、uctance computation andcomparative measurement (in some pressure ranges) withconstant-pressure displacement devices such as are describedin Appendix X2.E 295 82 (2006)5FIG. X3.1 Schematic Diagram of Conductance-Tube Method for Measuring Pumping SpeedX3.3 If, as is generally the case, the speed of pu
49、mpschanges only slowly with pressure, absolute gage calibrationsare not essential. However, in using the expression for S above,it is only 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 position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination
