Apparatus and method for automatic leak detection

Abstract

An apparatus for automatic leak detection includes a fixture having a primary seal and a secondary seal. The fixture is connected to a workpiece to enclose a test volume defined in the workpiece. The seals will interface with the workpiece to at least partially enclose a buffer volume. An enclosure will be connected to the fixture to enclose a test portion of the workpiece to form a test chamber. The secondary seal separates the buffer volume from the test chamber. There is a tracer gas pressure differential between the test volume and the test chamber. A port in fluid communication with the buffer volume removes fixture leaks from the buffer volume. A detector detects the tracer gas in the test volume or the test chamber, where the tracer gas pressure differential between the test volume and the test chamber causes workpiece leak accumulation of the tracer gas.

Description

Technical Field

[0001] This disclosure generally relates to an apparatus and method for automatic leak detection. Background Technology

[0002] During the manufacturing process of some devices, the devices undergo leak testing to identify defects. Leak testing can be performed at any stage of part manufacturing. If a leak or related defect can be identified early in the manufacturing process, the value-added process for parts destined to be rejected can be stopped. In some cases, a leak at a specific rate may be identified as a defect. Parts may need to be watertight, airtight, oiltight, or have a certain specification with a maximum permissible leak.

[0003] Existing methods exist for leak detection. For example, bubble testing can be used to detect leaks up to approximately 10... -3 Leakage at millibar l / s (mbar l / s). In practice, bubble testing can be used to identify and locate leaks in tires. An inflated tire is immersed in a bucket of water, and a series of bubbles will flow from the leak. The properties of helium atoms are applied to some existing testing methods to generate less than 10... -6 Detecting leaks in small defects with a leakage rate of mbar l / s.

[0004] In some existing leak detection systems using current methods, it may be difficult to distinguish between leaks that are classified as defects in the part sample and leaks caused by the test fixture or the junction between the test fixture and the part sample to be tested. Air bubbles can be generated through processes and mechanisms other than leakage. In tire immersion test examples, air bubbles may adhere to the tire surface and be confused with slow leaks.

[0005] It may be necessary to identify casting defects, such as cracks or porosity in cast iron parts (e.g., brake master cylinders). Some master cylinder sealing surfaces may be machined after casting to create a smooth sealing junction to prevent brake fluid leakage from the master cylinder and air leakage into it during use. Leak testing under as-cast conditions can present surfaces that are too rough for leak testing equipment to reliably and repeatably seal. When using certain existing testing methods and equipment, fastener leaks may be indistinguishable from defects in the sample. Therefore, the sensitivity of existing testing equipment can be adjusted to prevent such erroneous leaks from leading to the rejection of "good" parts. However, when using less sensitive tests, some defective parts may pass the leak test without being identified.

[0006] introduction

[0007] The first aspect disclosed herein is an apparatus for automatic leak detection, comprising: a fixture having a primary seal and a secondary seal disposed thereon, wherein the fixture is connected to a workpiece to enclose a test volume at least partially defined within the workpiece, wherein the primary seal and the secondary seal intersect with the workpiece to at least partially enclose a buffer volume; a housing connected to the fixture to enclose a test portion of the workpiece to form a test chamber, wherein the secondary seal separates the buffer volume from the test chamber; wherein the test volume and the test chamber have a tracer gas pressure difference established therebetween; a port in fluid communication with the buffer volume to remove at least a portion of a fixture leak from the buffer volume; and a detector that detects the amount of tracer gas in the test volume or the test chamber, wherein the tracer gas pressure difference between the test volume and the test chamber causes tracer gas to accumulate in the workpiece leak.

[0008] In an example of the first aspect, the buffer volume and the test chamber will have a sub-seal pressure difference established therebetween, wherein the sub-seal pressure difference causes the tracer gas to leak through the sub-seal, wherein the amount of tracer gas in the test chamber detected by a detector indicates the sub-seal leakage.

[0009] In an example of the first aspect, the primary seal includes a first lip of a double seal, and the secondary seal includes a second lip of a double seal, wherein a groove is defined between the first and second lips, and wherein the groove defines at least a portion of the buffer volume. In one example, the buffer volume is defined by the first lip, the second lip, and the workpiece boundary.

[0010] In an example of the first aspect, the buffer volume is defined by a primary seal, a secondary seal, a workpiece, and a retainer. In one example, the primary seal is attached to the secondary seal via at least a portion of the web.

[0011] In an example of the first aspect, the tracer gas pressure difference is established by making the tracer gas pressure in the test volume higher than the tracer gas pressure in the test chamber. In one example, the tracer gas pressure difference is established by delivering tracer gas into the test volume via opening a tracer-to-test-volume valve connected to a source of tracer gas.

[0012] In an example of the first aspect, the apparatus further includes a buffer volume inlet fluidly connected to the buffer volume for allowing purge gas to flow through the buffer volume and out through a port to remove at least a portion of the fastener leakage from the buffer volume by flushing at least a portion of the fastener leakage out of the buffer volume.

[0013] In an example of the first aspect, the device further includes a pump in fluid communication with the buffer volume for removing at least a portion of the fastener leakage from the buffer volume by at least partially evacuating the buffer volume via the pump.

[0014] In an example of the first aspect, the test chamber includes at least two fluid-separated sub-chambers, wherein a detector is in branch fluid communication with the at least two fluid-separated sub-chambers via a fluid communication branch, wherein at least one valve opens and closes the fluid communication branch to temporally separate the detector signal associated with each of the at least two fluid-separated sub-chambers.

[0015] In an example of the first aspect, the device further includes a differential pressure sensor that is in fluid communication with the buffer volume and the test chamber for determining the differential pressure between the buffer volume and the test chamber.

[0016] In an example of the first aspect, the tracer gas comprises helium. In an example of the first aspect, the tracer gas comprises hydrogen. In an example of the first aspect, the tracer gas comprises a constituent gas. In an example of the first aspect, the detector comprises a mass spectrometer. In an example of the first aspect, the detector comprises an electronic hydrogen detector.

[0017] In an example of the first aspect, the device further includes a housing seal disposed between the housing and the fixture to form a housing-fixture joint. In one example, the housing-fixture joint has a housing-fixture joint leakage rate less than the flow rate of the tracer gas into the test chamber. In one example, the housing seal comprises a brush seal.

[0018] It should be understood that any features of the device for automatic leak detection disclosed herein can be combined in any desired manner and / or configuration.

[0019] The second aspect disclosed herein is a method for automatic leak detection, comprising: attaching a workpiece to a fixture, thereby enclosing a test volume, wherein a primary seal and a secondary seal are each disposed between the fixture and the workpiece to enclose a buffer volume; attaching a housing to the fixture to enclose a test portion of the workpiece to form a test chamber, wherein the secondary seal separates the buffer volume from the test chamber; establishing a tracer gas pressure difference between the test volume and the test chamber; removing at least a portion of the fixture leakage from the buffer volume; and detecting the amount of tracer gas in the test volume or the test chamber, wherein the tracer gas pressure difference between the test volume and the test chamber causes the tracer gas to accumulate in the workpiece leakage.

[0020] In an example of the second aspect, the method further includes: using a tracer gas to establish a pressure difference between the buffer volume and the test chamber for the sub-seal; and detecting the amount of tracer gas in the test chamber to detect leakage at the sub-seal.

[0021] In an example of the second aspect, the primary seal includes a first lip of a double seal, and the secondary seal includes a second lip of a double seal, wherein a groove is defined between the first and second lips, and wherein the groove defines at least a portion of the buffer volume. In one example, the buffer volume is defined by the first lip, the second lip, and the workpiece boundary.

[0022] In the second aspect, the buffer volume is defined by the primary seal, the secondary seal, the workpiece, and the fixing element. In one example, the primary seal is attached to the secondary seal via at least a portion of the web.

[0023] In an example of the second aspect, establishing a tracer gas pressure difference involves making the tracer gas pressure in the test volume higher than the tracer gas pressure in the test chamber. In one example, establishing a tracer gas pressure difference involves delivering tracer gas into the test volume by opening a tracer-to-test-volume valve connected to a source of tracer gas.

[0024] In an example of the second aspect, removing at least a portion of the fastener leakage from the buffer volume comprises flowing purge gas through the buffer volume to flush at least a portion of the fastener leakage out of the buffer volume. In one example, removing at least a portion of the fastener leakage from the buffer volume comprises at least partially evacuating the buffer volume via a pump.

[0025] In an example of the second aspect, the tracer gas comprises helium. In an example of the second aspect, the tracer gas comprises hydrogen. In an example of the second aspect, the tracer gas comprises a constituent gas.

[0026] In an example of the second aspect, detecting the amount of tracer gas involves using a mass spectrometer. In another example of the second aspect, detecting the amount of tracer gas involves using an electronic hydrogen detector.

[0027] In an example of the second aspect, a housing seal is disposed between the housing and the fixture, thereby forming a housing-fixture joint. In one example, the housing-fixture joint has a housing-fixture joint leakage rate that is less than the flow rate of the tracer gas into the test chamber. In one example, the housing seal comprises a brush seal.

[0028] It should be understood that any feature of this method can be combined in any desired manner. Furthermore, it should be understood that any combination of the features of this method and / or the device used for automatic leak detection can be used together, and / or combined with any of the examples disclosed herein. Summary of the Invention

[0029] An apparatus for automatic leak detection includes a fixture having a primary seal and a secondary seal. The fixture is attached to a workpiece to enclose a test volume defined within the workpiece. The seals intersect with the workpiece to at least partially enclose a buffer volume. A housing is attached to the fixture to enclose a test portion of the workpiece to form a test chamber. The secondary seal separates the buffer volume from the test chamber. A tracer gas pressure difference exists between the test volume and the test chamber. A port in fluid communication with the buffer volume removes fixture leaks from the buffer volume. A detector detects tracer gas in the test volume or test chamber, wherein the tracer gas pressure difference between the test volume and the test chamber causes tracer gas to accumulate in the workpiece leak. Attached Figure Description

[0030] The features of the embodiments of this disclosure will become apparent from the following detailed description and figures, in which the same reference numerals correspond to the same or similar but possibly different components. For the sake of brevity, reference numerals or features having the functions previously described may or may not be described in conjunction with other figures in which they are presented.

[0031] Figure 1 This is a half-diagram of the workpiece on the leak test fixture;

[0032] Figure 2A This is a semi-illustrative diagram of an example of a leak testing apparatus according to this disclosure;

[0033] Figure 2B This is a semi-illustrative diagram of an example of a leak testing apparatus according to this disclosure;

[0034] Figure 2C This is a semi-illustrative diagram of an example of a leak testing apparatus according to this disclosure;

[0035] Figure 2D This is a semi-illustrative diagram of an example of a leak testing apparatus according to this disclosure;

[0036] Figure 3 This is a half-illustrative diagram of another example of a leak testing apparatus according to this disclosure;

[0037] Figure 4 This is a half-illustrative diagram of another example of a leak testing apparatus according to this disclosure;

[0038] Figure 5 This is a half-illustrative diagram of another example of a leak testing apparatus according to this disclosure;

[0039] Figure 6 This is a half-illustrative diagram of another example of a leak testing apparatus according to this disclosure;

[0040] Figure 7A This is a simplified diagram depicting an example of relative pressure in a leak testing device as disclosed in this article;

[0041] Figure 7B This is a simplified diagram depicting an example of relative pressure in a leak testing device as disclosed in this article;

[0042] Figure 8 This is a simplified diagram depicting an example of relative pressure in a leak testing device as disclosed in this article;

[0043] Figure 9 This is a simplified diagram depicting an example of relative pressure in a leak testing device as disclosed in this article;

[0044] Figure 10 This is a simplified diagram depicting an example of relative pressure in a leak testing device as disclosed in this article;

[0045] Figure 11 This is a flowchart depicting an example of a method for automatic leak detection according to the present disclosure. Detailed Implementation

[0046] Figure 1 This is a partial schematic diagram of the workpiece 30 on the leak test fixture 10. Tracer gas is injected into the test volume 32. If the leak path or mechanism ( Figure 1 If the tracer gas (not shown) is present in the workpiece 30, it will flow through the leakage path or mechanism into the test chamber 42. If the detector 50 determines that a certain amount of tracer gas is present in the test chamber 42, the detector 50 indicates that the workpiece 30 has a leakage path or mechanism. Figure 1 The leak test fixture 10 depicted includes a seal at the junction with the workpiece 30. Figure 1A fixture leak is depicted at the junction between the seal and the workpiece 30. The tracer gas flowing through the leak is labeled as fixture leak 14. Due to leakage pathways or mechanisms in the workpiece 30, the detector 50 may not be able to distinguish fixture leak 14 from the tracer gas. Therefore, when the tracer gas allowed into the test chamber 42 is actually fixture leak 14, the detector 50 of existing leak detection systems and methods may indicate the presence of a leakage pathway or mechanism in the workpiece 30, i.e., a false positive result. If the workpiece 30 has a leakage pathway or mechanism concurrent with fixture leak 14, the tracer gas may mix in the test chamber 42 and confuse the detector 50, potentially causing the detector 50 to indicate that a specific leak threshold has been detected. To compensate for such conditions, some existing leak detection systems may set the threshold used to indicate a leak high enough that fixture leak 14 does not cause false positive results. Such compensation schemes may reduce the sensitivity of existing leak detection systems and suppress the detection of small leaks. In the figures of this disclosure, the flow path 44 is depicted by a line. It should be understood that such flow path 44 may represent, for example, a conduit, sleeve, or channel defined within a part (e.g., a manifold). Connectors, gaskets, or seals may be used to prevent leakage at the connection of the flow path.

[0047] Figure 2A This is a semi-illustrative diagram of an example of an automatic leak detection device according to this disclosure. For example... Figure 2A As depicted in the embodiments of this disclosure, the device for automatic leak detection includes a fixture 10 having a primary seal 20 and a secondary seal 22 disposed thereon. The fixture 10 is connected to a workpiece 30 to enclose a test volume 32 at least partially defined within the workpiece 30. The primary seal 20 and the secondary seal 22 intersect with the workpiece 30 to at least partially enclose a buffer volume 34. In another embodiment, the device for automatic leak detection includes a housing 40 connected to the fixture 10 to enclose a test portion 36 of the workpiece 30 to form a test chamber 42. The secondary seal 22 separates the buffer volume 34 from the test chamber 42.

[0048] Test volume 32 and test chamber 42 will have a tracer gas pressure differential established therebetween. As disclosed herein, the tracer gas may contain any detectable gas or gas mixture. In some instances, the tracer gas is typically absent from air, or present in small amounts. In some instances, the tracer gas may contain helium (He). In some instances, the tracer gas may contain 10% He and 90% nitrogen (N2). In another instance, the tracer gas may contain 40% He and 60% N2. Helium is typically present in air at about 0.0005% by volume. It should be noted that the background level of the tracer gas may be locally higher in environments where the tracer gas is used for continuous testing. In another instance, the tracer gas may contain hydrogen. In yet another instance, the tracer gas may contain a constituent gas. As used herein, “constituent gas” means a mixture of hydrogen (H2) and nitrogen (N2). In some instances, the constituent gas may have a mixture of less than 5% H2 by volume in N2. In another example, the tracer gas may contain sulfur hexafluoride (SF6). In another example, the tracer gas may contain a detectable concentration of propane gas (C3H8). In another example, the tracer gas may contain a detectable concentration of methane gas (CH4).

[0049] In one example, detector 50 may include any electronic device for detecting the presence and / or quantity of a tracer gas or a component of a tracer gas. In one example, detector 50 includes a mass spectrometer 46. In another example, detector 50 includes an electronic hydrogen detector 51. An example of electronic hydrogen detector 51 is the SGAS701 trace hydrogen sensor purchased from Integrated Device Technology, Inc. The SGAS701 is a solid-state chemical impedance sensor designed to detect hydrogen in air. In one example, detector 50 may include a volatile organic compound (VOC) sensor. In one example, detector 50 may include a metal-oxide-semiconductor (MOS) based gas sensor. An example of a MOS-based gas sensor is the TGS821 hydrogen sensor purchased from Figaro. In one example, detector 50 may include a catalytic VOC sensor. An example of a catalytic sensor is the TGS6812-D00 hydrogen / methane / LPG sensor purchased from Figaro. In one example, detector 50 may include an electrochemical gas sensor. An example of an electrochemical gas sensor is the FECS50-100 hydrogen sulfide sensor purchased from Figaro. It should be understood that some detectors 50, such as some mass spectrometers 46, are compatible with operation in high vacuum. Other detectors 50 are better suited for operation at near atmospheric pressure. It should be understood that any combination of features of the methods and / or devices used for automated leak detection can be used together, and / or combined with any of the examples disclosed herein. Therefore, a detector 50 suitable for operating conditions encompassing a pressure range is selected.

[0050] Examples of devices for automatic leak detection disclosed herein may include a housing seal 27 disposed between the housing 40 and the retainer 10 to form a housing-retainer joint 29, such as... Figure 2A As depicted herein. In an example, the housing-fixture joint 29 may have a leakage rate less than the flow rate of the tracer gas into the test chamber 42. The housing seal 27 may use any suitable sealing technology. In an example, the housing seal 27 may comprise a brush seal. As used herein, a brush seal means a contact seal comprising an array or bundle of filaments spanning the gap between two surfaces. The filaments are arranged to inhibit or prevent the flow of fluid, dust, or particles through the gap. The filaments may be made of elastomers, plastics, hair, metals, or combinations thereof.

[0051] In such Figure 2A and Figure 7A In the example depicted, the tracer gas pressure difference is established by making the tracer gas pressure in test volume 32 higher than the tracer gas pressure in test chamber 42. For example, the tracer gas pressure may be above atmospheric pressure in test volume 32 and at atmospheric pressure in test chamber 42. In another example (see...), Figure 2C Test chamber 42 can be evacuated by vacuum pump 18, and tracer gas can be injected into test volume 32. In instances where the pressure in test volume 32 is higher than the pressure in test chamber 42, tracer gas will tend to flow from test volume 32 to test chamber 42 if a path is available. In one instance, the tracer gas pressure difference can be established by transferring tracer gas into test volume 32 via opening the tracer-to-test volume valve 48 connected to the tracer gas source 16. Figure 2A In this configuration, the tracer-to-test-volume valve 48 is connected to the source 16 of the tracer gas; and the tracer-to-test-volume valve 48 is opened to transfer the tracer gas from the source 16 to the test volume 32. The tracer gas can be removed or partially removed before being transferred to the test volume 32 to reduce dilution and increase the concentration of the tracer gas (e.g., by means of...). Figure 6 The vacuum pump 18 shown in the figure exists in the normal atmosphere in the test volume 32.

[0052] In an example, such as Figure 2A As depicted, the device for automatic leak detection may include a buffer volume inlet 38, fluidly connected to a buffer volume 34 for allowing purge gas to flow through the buffer volume 34 and out through port 12, to remove at least a portion of the fixture leak 14 from the buffer volume 34 by flushing at least a portion of the fixture leak 14 out of the buffer volume 34. The overall flow direction of the purge gas is determined by... Figure 2A-6 The flowing arrow 56 in the image represents this.

[0053] Without being bound by any theory, several transport modes of gas molecules are believed to be valid in this disclosure. Diffusion is the net movement of matter (e.g., atoms, ions, molecules) from a region of higher concentration to a region of lower concentration. Diffusion is driven by a concentration gradient. Diffusion depends on random particle motion and causes the tracer gas to mix in a volume without requiring directional overall motion. Diffusion is the gradual movement or dispersion of concentration within a bulk due to a concentration gradient, without a net movement of matter. “Overall flow” is the movement or flow of the entire bulk attributable to a pressure gradient. Water coming out of a tap is an example of overall flow. Percolation is the process by which gas escapes from a container through a hole with a diameter significantly smaller than the mean free path of a molecule. The escape of gas through the hole is attributable to the pressure difference between the container and the outside. Under these conditions, all molecules reaching the hole continue and pass through the hole because collisions between molecules in the region of the hole are negligible. In the figures of this disclosure, the size of the leakage is depicted as approximately the same as the size of the molecules for ease of drawing, not as a limitation. Therefore, although the tracer gas can move through defects in workpiece 30 via percolation, the defects can be much larger than the mean free path of the tracer gas, and the tracer gas can also move and mix via diffusion and overall flow. After the tracer gas enters buffer volume 34, eventually, in the absence of overall flow, the concentration of the tracer gas in the entire buffer volume 34 will be equal. In such a case, even in the absence of a pressure gradient, the tracer gas will tend to flow through the fixture leakage via diffusion. However, if there is sufficient purging overall flow, the concentration of the tracer gas in buffer volume 34 will be negligible, thus preventing the tracer gas from significantly flowing through the fixture leakage via any mechanism (i.e., overall flow, diffusion, or percolation).

[0054] Still referencing Figure 2A In one example, the device for automatic leak detection includes a port 12 in fluid communication with a buffer volume 34 to remove at least a portion of the fixture leak 14 from the buffer volume 34. The device for automatic leak detection includes a detector 50 to detect the amount of tracer gas in a test volume 32 or a test chamber 42, wherein a pressure difference in the tracer gas between the test volume 32 and the test chamber 42 causes the tracer gas to accumulate in the fixture leak 45. For example, if the pressure in the test volume 32 is higher than the pressure in the test chamber 42, the tracer gas in the fixture leak 45 will tend to accumulate in the test chamber 42. Conversely, if the pressure in the test chamber 42 is higher than the pressure in the test volume 32, the tracer gas in the fixture leak 45 will tend to accumulate in the test volume 32.

[0055] In such Figure 2BIn the example depicted, the test chamber includes at least two fluid-separated sub-chambers 33, 33'. Detector 50 forms branched fluid communication with the at least two fluid-separated sub-chambers 33, 33' via fluid communication branches 31, 31'. At least one valve 49 opens and closes the fluid communication branches 31, 31' to temporally separate the detector signal associated with each of the at least two fluid-separated sub-chambers 33, 33'. In this example, at least one valve 49 may be as follows: Figure 2B The 3-way valve shown in the document, however, covers any combination of valves that connect fluid communication branches with non-overlapping time intervals. Figure 2B The image shows at least two fluid-separated sub-chambers 33, 33' with a shared wall 52. In other instances, the individual sub-chambers may be completely separable and do not have a shared wall. In yet another instance, multiple detectors may operate in parallel. Therefore, the device can simultaneously determine the position of the signal from each detector.

[0056] In such Figure 2C and Figure 7B In the example depicted, the tracer gas pressure difference is established by making the tracer gas pressure in test volume 32 higher than the tracer gas pressure in test chamber 42. For example, test chamber 42 can be evacuated by vacuum pump 18, and tracer gas can be injected into test volume 32. In this example, vacuum pump 18 can generate any level of vacuum, even ultra-high vacuum. In this example, vacuum pump 18 can generate a high vacuum in test chamber 42. In this example, vacuum pump 18 can generate a rough vacuum in test chamber 42. In the example where the pressure in test volume 32 is higher than the pressure in test chamber 42, tracer gas will tend to flow from test volume 32 to test chamber 42 if a path is available. In this example, tracer gas can be delivered to test volume 32 by opening the tracer to test volume valve 48 connected to tracer gas source 16 and by evacuating test chamber 42 with vacuum pump 18. Figure 2C In this configuration, the tracer to test volume valve 48 is connected to the source 16 of the tracer gas; and the tracer to test volume valve 48 is opened to transfer the tracer gas from the source 16 to the test volume 32.

[0057] In such Figure 2D and Figure 7B In the example depicted, the tracer gas pressure difference is established by making the tracer gas pressure in test volume 32 higher than the tracer gas pressure in test chamber 42. For example, test chamber 42 can be evacuated by vacuum pump 18, and tracer gas can be injected into test volume 32. Figure 2D In the example depicted, vacuum pump 18 can generate a high vacuum in test chamber 42. As stated above, some detectors 50 are better suited for operation on samples where the high vacuum is closer to atmospheric pressure. Figure 2D In the example depicted, test chamber 42 is under high vacuum, and workpiece leakage 45 accumulates in test chamber 42. Cylinder 43 has a piston 37 that can translate within cylinder 43 to extract a sample from test chamber 42. Figure 2D In this configuration, actuator 39 is connected to piston 37 via piston rod 41 to actuate piston 37. It should be understood that any suitable actuator 39 for movable piston 37 is covered herein. For example, actuator 39 may be another piston, a rotary motor connected via crankshaft, a linear actuator, a screw drive, a hydraulic actuator, or a pneumatic actuator. Check valve 35 or other valves and conduits may be included to guide and contain fluid flow. For example, a valve (not shown) may allow clean air to flush the sample from detector 50 after testing. After piston 37 has drawn the sample into the cylinder, piston 37 may compress the sample, thereby concentrating workpiece leakage 45 and increasing the sample pressure to a pressure compatible with detector 50. It should be understood that valve repositioning can be used to reduce the pressure of samples drawn at higher pressures, for example, to be compatible with mass spectrometers operating samples under high vacuum.

[0058] Figure 3 This is a half-illustrative diagram of another example of a leak testing apparatus according to this disclosure. Figure 3 The instances described herein can be configured to interact with Figure 2A The examples depicted operate in the same mode; however, due to the additional valves and flow paths, Figure 3 The examples depicted can be configured to establish a tracer gas pressure difference between the test chamber and the test volume by opening the tracer to the test chamber valve 63 and injecting tracer gas into the test chamber 42. In some examples, the test chamber 42 may be pressurized; in others, it may not be pressurized. In examples where the test chamber 42 is not pressurized, the test chamber exhaust port 13 may be connected to the test chamber exhaust valve 68 to exhaust gas from the test chamber 42, and to make the pressure in the test chamber 42 equal to that of the ambient atmosphere 11 when the tracer gas is injected into the test chamber 42. Exhausting outside the test area reduces the possibility of exhaust gas interfering with the test results. Examples may include a housing seal 27 disposed between the housing 40 and the fastener 10 to form a housing-fastener joint 29, such as... Figure 3 As depicted in the illustration. In this example, the housing-fixture joint 29 may have a leakage rate less than the flow rate of the tracer gas into the test chamber 42. When the partial pressure of the tracer gas in the test chamber 42 is higher than the partial pressure of the tracer gas in the test volume 32, the tracer gas pressure difference between the test volume and the test chamber (e.g., the tracer gas partial pressure difference) causes tracer gas leakage to accumulate in the test volume 32. The flow of the tracer gas may be driven by a pressure gradient, a concentration gradient, or a combination of both.

[0059] Figure 3 The fastener leak 14 is flushed out of the buffer volume 34 by opening the intake valve 60 to allow air or nitrogen to flow through the buffer volume inlet 38. The fastener leak, along with the overall air flow, flows out of the buffer volume 34 through port 12 and is discharged via the open exhaust valve 67. In this example, the primary seal 20 can be attached to the secondary seal 22 via at least a portion of the web 28. Figure 3 In this configuration, a portion of the web 28 comprises multiple struts made of the same material constituting the primary seal 20 and the secondary seal 22. In one example, the portion of the web 28 may be co-molded with the primary seal 20 and the secondary seal 22. In another example, the portion of the web 28 may be overmolded over the primary seal 20 and the secondary seal 22. In yet another example, the web may be made of a material different from that of the primary seal 20 and the secondary seal 22. For example, a metal or plastic skeleton may be overmolded from an elastomer to form the primary seal 20 and the secondary seal 22, wherein metal spokes extend between the primary seal 20 and the secondary seal 22.

[0060] Figure 3 The gas flow from test volume 32 through second detector valve 65 to detector 50 is depicted. In other embodiments, detector 51 may be installed in test volume 32 and from which electronic, photonic, acoustic, or radio signals are transmitted. Similarly, gas flow may be transmitted from test chamber 42 through first detector valve 64 to detector 50. Gas flow may be transmitted from buffer volume 34 through third detector valve 66 to detector 50. In other embodiments, detector 51 may be installed in test chamber 42 and from which electronic, photonic, acoustic, or radio signals are transmitted.

[0061] Figure 4 This is a partial schematic diagram of another example of a leak testing apparatus according to this disclosure. In the example, as... Figure 4 As depicted, buffer volume 34 and test chamber 42 will have a pressure difference established therebetween at the sub-seal 22. In an example, establishing the sub-seal pressure difference may involve delivering tracer gas into buffer volume 34 by opening the tracer source 16 connected to the buffer volume valve 61. The sub-seal pressure difference causes the tracer gas to leak through the sub-seal 26. Figure 4 In the example depicted, the amount of tracer gas detected in test chamber 42 by detector 50 and / or detector 51 indicates a secondary seal leak 26. Figure 4 In the example depicted, differential pressure sensor 58 is connected to flow paths 44' and 44''. Therefore, differential pressure sensor 58 quantifies the pressure difference between buffer volume 34 and test chamber 42 (if a pressure difference exists). Differential pressure sensor 58 can output a differential pressure signal for use by an electronic control system in an apparatus for automatic leak detection according to this disclosure.

[0062] Figure 5 This is a partial schematic diagram of another example of a leak testing apparatus according to this disclosure. In the example, as... Figure 5 As depicted herein, the leak testing apparatus may include a vacuum pump 18, which is in fluid communication with a buffer volume 34 for removing at least a portion of the fastener leak 14 from the buffer volume 34 by at least partially evacuating the buffer volume 34 via the vacuum pump 18. As disclosed herein, the vacuum pump 18 may be any suitable pump 18. Figure 5 In the example depicted, vacuum pump 18 comprises a combination of roughing pump 19 and turbo pump 47.

[0063] As used herein, a roughing pump means a vacuum pump used as the first stage to achieve high or ultra-high vacuum. A roughing pump will achieve a rough vacuum. As used herein, the term "rough vacuum" means approximately 1 × 10⁻⁶. -3 The absolute pressure is 0.1 Pa. As used herein, the term "high vacuum" means approximately 1 × 10⁻⁶ Pa. -3 Up to 1×10 -9 Torr (0.1 Pa - 1 × 10) -7 The absolute pressure is Pa. As used herein, the term "hard vacuum" means the same as the term "high vacuum". As used herein, the term "ultra-high vacuum" means approximately 1 × 10⁻⁶ Pa. -9 Up to 1×10 -12 Tor (1×10 - 7 Pa-1×10 -10 The absolute pressure is approximately 760 Torr to 25 Torr (1 × 10⁻⁶ Pa). As used herein, the term "low vacuum" means approximately 760 Torr to 25 Torr (1 × 10⁻⁶ Pa). 5 Pa-3×10 3 Atmospheric pressure is an absolute pressure of approximately 760 Torr (1.013 × 10⁻⁶ Pa). As used herein, atmospheric pressure is approximately 760 Torr (1.013 × 10⁻⁶ Pa). 5 Pa). It should be understood that, without diminishing the leak detection capability of the equipment and methods of this disclosure, a typical leak may prevent the vacuum pump 18 from achieving a rough vacuum or a high vacuum. For example, such as Figure 5 As shown, the inlet valve 60 allows atmospheric or nitrogen gas to enter the buffer volume 34, so that any tracer gas can be flushed out of the buffer volume 34 by the action of the vacuum pump 18. This flushing allows the tracer gas to be removed from the buffer volume more quickly and completely compared to achieving a rough or high vacuum without flushing the buffer volume 34 using the vacuum pump 18. The inlet valve 60 regulates the flow of air or nitrogen gas into the buffer volume 34. Therefore, a vacuum can be achieved in the buffer volume 34 even when air or nitrogen gas flows into the buffer volume 34 via the inlet valve 60.

[0064] exist Figure 5 In this configuration, a coarse pump 19 is connected to a buffer volume 34, wherein a buffer volume coarse vacuum control valve 72 is configured to regulate the gas flow from the buffer volume 34 to the coarse pump 19. The coarse pump 19 is also connected to a test volume 32 via a test volume coarse vacuum control valve 71, which is configured to regulate the gas flow from the test volume 32 to the coarse pump 19. A turbo pump 47 is also connected to the test volume 32 via a test volume turbo vacuum control valve 74, which is configured to regulate the gas flow from the test volume 32 to the turbo pump 47. A mass spectrometer 46 can be used to analyze the gas pumped from the test volume 32 to determine the amount of tracer gas that may have entered the test volume 32. A supply valve 73 can be connected to the suction side of the test volume coarse vacuum control valve 71 and the test volume turbo vacuum control valve 74 to provide clean air or nitrogen, thereby flushing the tracer gas from the turbo pump and the mass spectrometer, for example, between test runs. Figure 5 and Figure 6 As shown, the supply valve 73 is connected to the test volume 32 to flush all vacuum systems connected to the test volume 32. The supply valve 73 can be used simultaneously with the inlet valve 60 to allow the same vacuum pump 18 to be used to evacuate both the buffer volume 34 and the test volume 32.

[0065] Figure 6 This is a partial schematic diagram of another example of a leak testing apparatus according to this disclosure. In the example, as... Figure 6 As depicted, the primary seal 20 includes a first lip 21 of a double seal 24, and the secondary seal 22 includes a second lip 23 of the double seal 24. A recess 25 is defined between the first lip 21 and the second lip 23, and the recess 25 defines at least a portion of the buffer volume 34. In an example, the buffer volume 34 may be defined by the first lip 21, the second lip 23, and the workpiece 30.

[0066] In this example, the buffer volume 34 can be limited by the main seal 20, the secondary seal 22, the workpiece 30, and the fixing member 10, such as... Figure 2A-2D , Figure 3 , Figure 4 and Figure 5 As depicted in the illustration. In this example, the primary seal 20 can be attached to the secondary seal 22 via at least a portion of the web 28, as shown in the illustration. Figure 3 and Figure 4 As depicted in the text.

[0067] Figure 7A This is a simplified diagram depicting an example of relative pressure in a leak testing apparatus as disclosed herein. Figure 7AIn this test chamber, test volume 32 is at a higher pressure than test chamber 42. Therefore, the flow direction 53 is from test volume 32 to test chamber 42. Purge gas flows into buffer volume 34; however, a counteracting amount of gas is discharged from buffer volume 34, keeping the gas pressure in the buffer volume at atmospheric pressure. If a main seal leak occurs, the pressure difference between test volume 32 and buffer volume 34 drives tracer gas to leak through the main seal (in the direction of flow arrow 54). Buffer volume 34 is at a pressure higher than that in test chamber 42, but not high enough to cause a significant amount of tracer gas to leak from buffer volume 34 into test chamber 42 through the fixture. Since the purge gas washes away almost all tracer gas from the buffer volume, and there is a low pressure difference between buffer volume 34 and test chamber 42, the amount of tracer gas passing through buffer volume 34 into test chamber 42 is negligible. Therefore, the number of false positive leak test results caused by fixture leakage is minimized.

[0068] Figure 7B This is a simplified diagram depicting an example of relative pressure in a leak testing apparatus as disclosed herein. Figure 7B In this test chamber, test volume 32 is subjected to a higher pressure than test chamber 42. Figure 7B In this test chamber 42, the test chamber is under high vacuum. Therefore, the flow direction 53 is from the test volume 32 to the test chamber 42. Purge gas flows into the buffer volume 34; however, an offsetting amount of gas is discharged from the buffer volume 34, keeping the gas pressure in the buffer volume at atmospheric pressure. If a leak is present in the main seal, the pressure difference between the test volume 32 and the buffer volume 34 drives the tracer gas to leak through the main seal (in the direction of flow arrow 54). Since the purge gas washes away almost all the tracer gas from the buffer volume, the amount of tracer gas passing through the buffer volume 34 into the test chamber 42 is negligible. Therefore, the number of false positive leak test results caused by fixture leakage is minimized.

[0069] Figure 8 This is a simplified diagram depicting an example of relative pressure in a leak testing apparatus as disclosed herein. Figure 8In this test chamber 42, the pressure is higher than that in the test volume 32. Therefore, the flow direction 53 is from the test chamber 42 to the test volume 32. Purge gas flows into the buffer volume 34; however, a counteracting amount of gas is discharged from the buffer volume 34, keeping the gas pressure in the buffer volume at atmospheric pressure. If a sub-seal leak is present, the pressure difference between the test chamber 42 and the buffer volume 34 drives the tracer gas through the sub-seal leak (in the direction of flow arrow 55). The buffer volume 34 is at a pressure higher than that in the test volume 32, but not high enough to cause a significant amount of tracer gas to be transferred from the buffer volume 34 to the test volume 32 through the seal leak. Since the purge gas washes away almost all the tracer gas from the buffer volume, and there is a low pressure difference between the buffer volume 34 and the test volume 32, the amount of tracer gas passing through the buffer volume 34 to the test volume 32 is negligible. Therefore, the number of false positive leak test results caused by the seal leak is minimized.

[0070] Figure 9 This is a simplified diagram depicting an example of relative pressure in a leak testing apparatus as disclosed herein. Figure 9 In this process, test chamber 42 is under a higher pressure than test volume 32. Therefore, the flow direction 53 is from test chamber 42 to test volume 32. Buffer volume 34 is also connected to a vacuum, such as... Figure 5 As shown in the diagram. Air or purge gas flows into buffer volume 34 at buffer volume inlet 38. The gas flow into buffer volume 34 is controlled to be less than or equal to the gas flow exiting port 12, thereby maintaining a vacuum in buffer volume 34. Buffer volume 34 is at a pressure higher than that in test volume 32, but not high enough to cause a significant amount of tracer gas to leak from buffer volume 34 into test volume 32 through the fixture. Since the purge gas washes away almost all tracer gas from buffer volume 34, and there is a low pressure difference between buffer volume 34 and test volume 32, the amount of tracer gas passing through buffer volume 34 into test volume 32 is negligible. Therefore, the number of false positive leak test results caused by fixture leakage is minimized.

[0071] Figure 10 This is a simplified diagram depicting an example of relative pressure in a leak testing apparatus as disclosed herein. Figure 10 In this test chamber 42, the pressure is higher than that of the test volume 32. Therefore, the flow direction 53 is from the test chamber 42 to the test volume 32. Figure 10 An example illustrating a leak in the main seal is depicted. The tracer gas flows from inlet 38 of the buffer volume into the buffer volume 34, as shown... Figure 4As shown in the diagram. If a primary seal leak is present, the pressure difference between the buffer volume 34 and the test volume 32 drives the tracer gas through the primary seal leak (in the direction of flow arrow 54). Therefore, the device can be used when such a primary seal leak becomes too large for the buffer volume and flushing process to overcome, and the severity of a fixture leak previously identified and characterized as being attributable to, for example, wear of the primary seal. If a secondary seal leak is present, the pressure difference between the buffer volume 34 and the test chamber 42 will cause the tracer gas to leak through the secondary seal (in the direction of flow arrow 55); however, unless the secondary seal leak is large, the pressure difference is not sufficient to cause significant flow through the secondary seal leak.

[0072] Figure 11 This is a flowchart depicting an example of a method 100 for automatic leak detection according to this disclosure. For example... Figure 11 As depicted, an example of the method 100 for automatic leak detection according to this disclosure includes connecting a workpiece 30 to a fixture 10, thereby enclosing a test volume 32, wherein a primary seal 20 and a secondary seal 22 are each disposed between the fixture 10 and the workpiece 30 to enclose a buffer volume 34, as depicted in box 102. As shown by reference numeral 104, method 100 includes connecting a housing 40 to the fixture 10 to enclose a test portion 36 of the workpiece 30 to form a test chamber 42, wherein the secondary seal 22 separates the buffer volume 34 from the test chamber 42. As shown by reference numeral 106, method 100 includes establishing a tracer gas pressure difference between the test volume 32 and the test chamber 42. As shown by reference numeral 108, method 100 includes removing at least a portion of the fixture leak 14 from the buffer volume 34. As shown at reference numeral 110 in the attached figure, method 100 includes detecting the amount of tracer gas in test volume 32 or test chamber 42, wherein the tracer gas pressure difference between test volume 32 and test chamber 42 causes the tracer gas to accumulate at workpiece leakage 45. In an example of method 100, the tracer gas may comprise helium, hydrogen, constituent gases, or any detectable gas or gas mixture.

[0073] In an example of this disclosure, the method 100 for automatic leak detection according to this disclosure may further include: using a tracer gas to establish a pressure difference between the buffer volume 34 and the test chamber 42 at the sub-seal 22; and detecting the amount of tracer gas in the test chamber 42 to detect a leak at the sub-seal 22. Detecting the amount of tracer gas may involve using a mass spectrometer 46. Detecting the amount of tracer gas may involve using an electronic hydrogen detector 51.

[0074] In an example of the method 100 for automatic leak detection, a housing seal 27 may be disposed between a housing 40 and a retainer 10, thereby forming a housing-retainer joint 29. The housing-retainer joint 29 may have a leakage rate less than the flow rate of the tracer gas into the test chamber 42. In an example, the housing seal 27 may comprise a brush seal.

[0075] In an example of method 100, the primary seal 20 may include a first lip 21 of the double seal 24, and the secondary seal 22 may include a second lip 23 of the double seal 24. A recess 25 defining at least a portion of the buffer volume 34 may be defined between the first lip 21 and the second lip 23. In an example of method 100, the buffer volume 34 may be defined by the first lip 21, the second lip 23, and the workpiece 30. The buffer volume 34 may be defined by the primary seal 20, the secondary seal 22, the workpiece 30, and the retainer 10. The primary seal 20 may be attached to the secondary seal 22 by at least a portion of the web 28. In an example, establishing a tracer gas pressure differential may involve making the tracer gas pressure in the test volume 32 higher than the tracer gas pressure in the test chamber 42. In an example, establishing a tracer gas pressure differential may involve delivering tracer gas into the test volume 32 by opening a tracer to test volume valve 48 connected to the tracer gas source 16. In one example, establishing a tracer gas pressure difference may involve making the tracer gas pressure in test chamber 42 higher than the tracer gas pressure in test volume 32. In another example, establishing a tracer gas pressure difference may involve delivering tracer gas into test chamber 42 by opening the tracer-to-test chamber valve 63 connected to the tracer gas source 16.

[0076] In an example of the method 100 for automatic leak detection according to this disclosure, removing at least a portion of the fastener leak 14 from the buffer volume 34 may include flowing purge gas through the buffer volume 34 to flush at least a portion of the fastener leak 14 out of the buffer volume 34. Removing at least a portion of the fastener leak 14 from the buffer volume 34 may also include at least partially evacuating the buffer volume 34 via a pump 18.

[0077] In an example of the method 100 for automatic leak detection according to this disclosure, a total leak test may be performed. In this example, the total leak test may be performed at any suitable time. In this example, a tracer gas pressure difference may be established between the test volume and the test chamber (106). Figure 11 A total leak test should be performed beforehand. The total leak test may include the use of a differential pressure sensor 58 ( Figure 4The pressure difference between buffer volume 34 and test chamber 42 is monitored. Differential pressure sensor 58 can alternatively be used to detect blockages in buffer volume 34. The total leak test may involve using vacuum pump 18 to evacuate air or another gas or gas mixture from test chamber 42, test volume 32, or buffer volume 34, wherein all shut-off valves are closed; and determining (e.g., via pressure gauge) whether the rate of pressure change in test chamber 42, test volume 32, or buffer volume 34 is within a predetermined range. In an example, the predetermined range may be suitable for determining the integrity of the test setup. For example, if vacuum pump 18 is unable to generate at least a low vacuum in test chamber 42 with a volume of 1 liter within 10 seconds, a total leak may exist. Remedial steps, such as resetting workpiece 30 or housing 40, or cleaning primary seal 20 or secondary seal 22, may be used to address the total leak before proceeding to method 100.

[0078] Throughout this specification, references to "one example," "another example," "example," etc., mean that a particular element (e.g., feature, structure, and / or characteristic) described in connection with the example is included in at least one example described herein and may or may not be present in other examples. Furthermore, it should be understood that, unless the context clearly indicates otherwise, the described elements for any example may be combined in various examples in any suitable manner. No language in this specification should be construed as indicating any non-required elements necessary for practical implementation.

[0079] As used in this article, the term "fluid" means gas, liquid, or a combination thereof.

[0080] In describing and claiming instances disclosed herein, the singular forms “a,” “an,” and “the” may include plural references unless the context clearly indicates otherwise.

[0081] The terms “connect / connected / connection”, “attach / attached / attachment”, etc., are broadly defined herein to encompass a variety of divergent connection arrangements and assembly techniques. These arrangements and techniques include, but are not limited to: (1) direct communication between one component and another component without intervening components; and (2) communication between one component and another component with one or more components present, provided that a component “connected to” or “attached to” the other component communicates with the other component in some way (despite the presence of one or more additional components). Additionally, two components may be permanently, semi-permanently, or releasably engaged with and / or connected to each other.

[0082] It should be further understood that "communication" should be interpreted as encompassing all forms of communication, including direct and indirect communication. Indirect communication can involve communication between two components with an additional component in between.

[0083] Although several examples have been described in detail, it should be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.

Claims

1. A device for automatic leak detection, comprising: A fastener having a primary seal and a secondary seal disposed thereon, wherein the fastener is connected to a workpiece to enclose at least partially a test volume defined in the workpiece, wherein the primary seal and the secondary seal intersect with the workpiece to at least partially enclose a buffer volume; A housing, which is connected to the fastener to enclose the test portion of the workpiece to form a test chamber, wherein the secondary seal will separate the buffer volume from the test chamber; The test volume and the test chamber will have a tracer gas pressure difference established therebetween; A port, which is in fluid communication with the buffer volume to remove at least a portion of the fastener leakage from the buffer volume; as well as A detector that detects the amount of tracer gas in the test volume or the test chamber, wherein the pressure difference of the tracer gas between the test volume and the test chamber causes the tracer gas to leak and accumulate in the workpiece.

2. The device of claim 1, wherein the buffer volume and the test chamber will have a sub-seal pressure difference established therebetween, wherein the sub-seal pressure difference causes the tracer gas to leak through the sub-seal, and wherein the amount of the tracer gas in the test chamber detected by the detector indicates the sub-seal leakage.

3. The device of claim 1, wherein the primary seal comprises a first lip of the dual seals and the secondary seal comprises a second lip of the dual seals, wherein a groove is defined between the first lip and the second lip, and wherein the groove defines at least a portion of the buffer volume.

4. The device according to claim 3, wherein the buffer volume is limited by the first lip, the second lip, and the workpiece boundary.

5. The device according to claim 1, wherein the buffer volume is defined by the main seal, the secondary seal, the workpiece, and the fixing member.

6. The device of claim 5, wherein the primary seal is attached to the secondary seal via at least a portion of the web.

7. The apparatus of claim 1, wherein the tracer gas pressure difference is established by making the tracer gas pressure in the test volume higher than the tracer gas pressure in the test chamber.

8. The apparatus of claim 7, wherein the tracer gas pressure differential is established by delivering the tracer gas into the test volume via opening a tracer to test volume valve connected to a source of the tracer gas.

9. The apparatus of claim 1, further comprising a buffer volume inlet fluidly connected to the buffer volume for allowing purge gas to flow through the buffer volume and out through the port to remove the at least portion of the fastener leakage from the buffer volume by flushing the at least portion of the fastener leakage out of the buffer volume.

10. The device of claim 1, further comprising a pump in fluid communication with the buffer volume for removing at least a portion of the fastener leakage from the buffer volume by at least partially evacuating the buffer volume via the pump.

11. The device of claim 1, wherein the test chamber comprises at least two fluid-separated sub-chambers, wherein the detector is in branch fluid communication with the at least two fluid-separated sub-chambers via a fluid communication branch, wherein at least one valve opens and closes the fluid communication branch to temporally separate detector signals associated with each of the at least two fluid-separated sub-chambers.

12. The device of claim 1, further comprising a differential pressure sensor in fluid communication with the buffer volume and the test chamber for determining the differential pressure between the buffer volume and the test chamber.

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