ISO 27895-2009 Vacuum technology - Valves - Leak test《真空技术 阀门 密封性试验》.pdf

1、 Reference number ISO 27895:2009(E) ISO 2009INTERNATIONAL STANDARD ISO 27895 First edition 2009-12-15 Vacuum technology Valves Leak test Technique du vide Vannes vide Essai dtanchit des vannes vide ISO 27895:2009(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adob

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4、 has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO 2009 All rights reserved. Unless otherwise specified, no

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6、e 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2009 All rights reservedISO 27895:2009(E) ISO 2009 All rights reserved iiiContents Page Foreword iv Introduction.v 1 Scope1 2 Normative references1 3 Terms and

7、definitions .1 4 Symbols4 5 Requirements.5 6 Test methods .5 6.1 Valve seat leak test5 6.2 Valve body leak test 7 6.3 Leak test on minimum and maximum pressures of compressed air for pneumatic valve operation (optional).9 6.4 Leak test on minimum and maximum torques of manual valve (optional) .9 6.5

8、 Leak test in operating temperature range (optional).9 6.6 Leak test after baking (optional)9 7 Test report9 Bibliography11 ISO 27895:2009(E) iv ISO 2009 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO m

9、ember bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governm

10、ental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Dir

11、ectives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bo

12、dies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 27895 was prepared by Technical Committee ISO/TC 112, Vacuum technology. ISO

13、 27895:2009(E) ISO 2009 All rights reserved vIntroduction Vacuum valves are the most common parts in vacuum systems. Valve manufacturers provide technical data for vacuum valves based on their own test methods and end users use these data to select valves. However, until the time of publication, the

14、re has been no International Standard specifying leak test methods for vacuum valves even though leak rate data are among the most fundamental. For example, the leak rate of the valve may vary in the time interval between gas filling and leak testing. There are three different types of leak: a) real

15、 leaks, i.e. macroscopic cracks or holes allowing gases to pass through; b) virtual leaks, caused by outgassing of volatile material inside a vacuum system or trapped volume; c) permeation leaks, i.e. microscopic holes of diameter comparable to that of an atom, which occur throughout the constructio

16、n material, e.g. in elastomers. Virtual leaks are not measurable by the leak test method specified in this International Standard. Valve design and the materials used should therefore be chosen to minimize the risk of virtual leaks occurring. INTERNATIONAL STANDARD ISO 27895:2009(E) ISO 2009 All rig

17、hts reserved 1Vacuum technology Valves Leak test 1 Scope This International Standard specifies methods for the leak testing of vacuum valves used for control of gas flow or vacuum pressure in a vacuum system. It is applicable to vacuum valves that can be closed to leak rates less than 1 10 5Pa m 3 /

18、s for trace gas. The methods employ a sealing arrangement for the valve body, which is also specified in this International Standard. The methods are suitable for the verification of valve specifications. A valve leak rate less than the nominal leak rate specified by the manufacturer during and afte

19、r the operation enables the specification of such valve operating conditions as operating pressure range, permissible pressure difference between ports, bake-out temperature or operating temperature, and life cycle. NOTE 1 The data for large valves and valves without a valve body can vary from those

20、 obtained during delivery inspection depending on the accuracy of the attachment surface of the vacuum device. NOTE 2 The data obtained from this procedure is based on the testing conducted on an individual unit of a vacuum valve and they can be different from those obtained during delivery inspecti

21、on if the test is performed with the valve incorporated into the equipment. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the refere

22、nced document (including any amendments) applies. ISO 3530, Vacuum technology Mass-spectrometer-type leak detector calibration 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 leak rate q vacuum valve technology throughput of a trace gas, whic

23、h passes through a crack, hole or gap in the wall, seat or sealing material of a valve under specific conditions NOTE 1 Adapted from ISO 3530:1979, 2.5.1. NOTE 2 The leak rate is expressed in pascal cubic metres per second. NOTE 3 The leak rate of the trace gas can be measured using a mass spectrome

24、ter-type leak detector. The leak rate depends on type of gas, pressure difference, and temperature. NOTE 4 The definitions standard air leak rate (3.2) and equivalent standard air leak rate (3.3) are more specific. ISO 27895:2009(E) 2 ISO 2009 All rights reserved3.2 standard air leak rate throughput

25、, through an opening such as a crack or hole, of atmospheric air having a dew point of less than 25 C under standard conditions: an inlet pressure of (100 5) kPa; an outlet pressure of less than 1 kPa; and a temperature of (23 7) C NOTE 1 Adapted from ISO 3530:1979, 2.5.2. NOTE 2 The standard condit

26、ions are taken from ISO 3530. 3.3 equivalent standard air leak rate short-path leaks of the molecular type having standard air leak rates of less than 10 7Pa m 3 /s EXAMPLE Helium (relative atomic mass 4) passes through such leaks more rapidly than air (average relative molecular mass 29,0), and a g

27、iven flow rate of helium corresponds to a smaller flow rate of air. NOTE 1 “Equivalent standard air leak rate” is taken as (4/29) 1/2= 0,37 times the helium leak rate under the standard conditions specified in ISO 3530. NOTE 2 Adapted from ISO 3530:1979, 2.5.3. 3.4 trace gas gas used to detect leaks

28、 NOTE Mass-spectrometer-type leak detectors are used as the leak measurement instrument. If a helium mixture is used, the leak rate is reported as a helium-equivalent value. 3.5 operating pressure p ovacuum valve technology pressure range for a valve in working condition NOTE If a pressure is within

29、 the operating pressure range, the valve can have a leak rate smaller than that specified by the manufacturer. 3.6 maximum operating pressure p o, max vacuum valve technology highest pressure at which the valve operates within its specifications 3.7 Pressure difference NOTE 1 Figures 1 and 2 show sc

30、hematic diagrams of angle valves and gate valves, respectively. NOTE 2 Manufacturers of bellow-sealed angle valves often specify a maximum pressure difference separated as differential pressures in the opening and closing directions. Usually, the critical case is the differential pressure in the ope

31、ning direction (p 1at “vacuum” and p 2at maximum pressure). 3.7.1 pressure difference p conventional angle and gate valves pressure difference between p 1and p 2 , where p 2is the pressure at the space toward the valve disc with elastomer on the valve seat and p 1is the pressure of the opposite side

32、 within the valve ISO 27895:2009(E) ISO 2009 All rights reserved 33.7.2 pressure difference p bellow-sealed angle valves pressure difference between p 1and p 2 , where in the opening direction p 1is the residual pressure at “vacuum” and p 2is the maximum pressure Key 1 port A 2 port B Figure 1 Angle

33、 valve Key 1 port A 2 port B Figure 2 Gate valve 3.8 maximum pressure difference p maxgreatest pressure difference at which the valve can operate normally NOTE If a pressure difference is lower than p max , the valve can have a leak rate smaller than that specified by the manufacturer. 3.9 pressure

34、range of compressed air for a pneumatic valve p ppressure range of the compressed air specified by the manufacturer for a pneumatic valve closed or opened by compressed air ISO 27895:2009(E) 4 ISO 2009 All rights reservedNOTE The compressed air pressure can be specified not only as an absolute press

35、ure but also as a pressure relative to atmospheric, i.e. the gauge pressure. 3.10 torque range for valves with an operating torque specified torque range specified by the manufacturer for a valve operated by torque wrench 3.11 operating temperature T o temperature at which the valve operates under n

36、ormal conditions NOTE An operating temperature range is specified by the manufacturer, within which a valve can be operated under normal working conditions with a leak rate smaller than that specified by the manufacturer. 3.12 baking temperature T b temperature at which the valve is baked NOTE Bakin

37、g reduces the outgassing from the inside wall of a valve during the pumping process. This is sometimes necessary for an accurate leak test. The appropriate baking temperature is specified by the manufacturer. 3.13 valve temperature T vtemperature of the body of the valve under test 4 Symbols Symbol

38、Designation Unit p natmospheric pressure Pa p ooperating pressure Pa p o, maxmaximum operating pressure Pa p outpressure of the hood Pa p ppressure range of the compressed air for pneumatic valve Pa p 1pressure at upper stream side (port A) Pa p 2pressure at down stream side (port B) Pa q leak rate

39、Pa m 3 /s T ooperating temperature C T bbaking temperature C T vvalve temperature C p pressure difference Pa p maxmaximum pressure difference Pa torque N m ISO 27895:2009(E) ISO 2009 All rights reserved 55 Requirements 5.1 All tests shall be made within the limitations of the operating conditions sp

40、ecified by the manufacturer. 5.2 During leak rate measurement, all sealing surfaces shall be clean and dry. 5.3 The mass-spectrometer-type leak detector shall be capable of measuring the leak rate of the test valve. The leak detector shall have a better detection limit than the nominal leak rate of

41、the test valve and sufficient leak rate measurement capabilities. 5.4 The mass-spectrometric leak detector needs sufficient warm-up time, which shall be specified by the leak detector manufacturer. The leak detector shall be tuned and calibrated with reference to a standard leak. The time interval s

42、hall be determined taking into account the performance of the leak detector. 5.5 Since temperature affects the leak rate, ambient temperature shall be (23 7) C. 5.6 For an accurate leak test, ISO 3530 is recommended. 6 Test methods 6.1 Valve seat leak test CAUTION Leakage of helium to the test envir

43、onment should be minimized to avoid the increase in background levels close to the leak detector. The configuration of the valve seat leak test is shown in Figure 3. Evacuate the test valve before the leak test is carried out. Key 1 valve under test 2 valve 3 vacuum pump (optional) 4 vacuum gauge 5

44、trace gas reservoir 6 leak detector system Figure 3 Schematic diagram for valve seat leak measurement The trace gas reservoir may have a regulator and a gauge to control the pressure of the gas. The vacuum pump can be useful for controlling partial pressures of the trace gas. ISO 27895:2009(E) 6 ISO

45、 2009 All rights reservedTable 1 specifies four different configurations for the valve seat leak test. Table 1 Methods for valve seat leak test Configuration No. p 1p 2Port A connected to Port B connected to 1 (basic) Vacuum (100 5) kPa trace gas Leak detector system Trace gas reservoir 2 (optional)

46、 Vacuum p o, maxLeak detector system Trace gas reservoir 3 (optional) (100 5) kPa trace gas Vacuum Trace gas reservoir Leak detector system 4 (optional) p o, maxVacuum Trace gas reservoir Leak detector system Configuration 1 in Table 1 is commonly used for the basic valve seat leak test. If needed o

47、r upon customer request, configurations 2, 3 or 4 may be used. Ports A and B are connected to the leak detector system and to the trace gas reservoir, respectively, for configurations 1 and 2. For configurations 3 and 4, ports A and B are connected to the trace gas reservoir and to the leak detector

48、 system, respectively. The trace gas supply line is evacuated before filling with trace gas. In each configuration, after a waiting period that is typically shorter than 30 s, start the leak rate measurement once the valve is filled with trace gas. The partial pressure of the trace gas and the sensi

49、tivity of the leak detector should be taken into account in the correction of the measured value. Normally, helium or a helium mixture is used as the trace gas. If a helium mixture is used, the volume fraction of helium during the test should be controlled to a constant value and should be higher than 10 %. A correction shall be made for trace gas volume fractions of less than 100 %. Perform rate measurements for real leaks before permeation leaks become apparent