Method and assembly for testing the integrity of filter media

Abstract

To provide an integrity testing method for a porous filter medium incorporated in a housing.SOLUTION: A housing includes an interior separated by a porous filter medium into an upstream portion and a downstream portion, an inlet in fluid connection with the upstream portion, and an outlet in fluid connection with the downstream portion, and the outlet is connected to a filtrate conduit which has a closable end at a position remote from the outlet. The filter medium is tested in a state in which pores of the filter medium are wetted and filled with a liquid. The downstream portion of the interior and the filtrate conduit are filled with the liquid. The remote closable end of the filtrate conduit is closed. The upstream portion of the interior is drained and filled with a testing gas while retaining the liquid in the downstream portion. A gas-filled testing volume is fluidly connected to the downstream portion via the filtrate conduit. A pressure of the testing gas in the upstream portion corresponding to a predetermined testing differential pressure is generated and maintained at this pressure level.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for testing the integrity of a porous filter medium and an assembly for integrity testing.

Background Art

[0002] Generally, porous filter media are used in filtration devices to remove undesirable components from liquids. In the fields of pharmaceuticals, food processing and beverage processing, and biotechnology industries, filter media need to comply with certain performance criteria. The integrity test of the filter media provides a means to ensure that the filter media meet effective performance criteria.

[0003] The integrity test used in the prior art is a gas-liquid diffusion test that measures the flow rate of a gas through a wet porous filter medium. The porous filter medium is exposed on its upstream side to a pressurized gas having a pressure below the bubble point of the porous filter medium. When the porous filter medium meets effective performance criteria and has no defects, the gas flow rate is observed to be relatively small because it is limited to the gas diffusion effect. When there are defects in the porous filter medium, a considerably large gas flow rate generated by the bulk gas flow through the defective part of the porous filter medium is observed.

[0004] U.S. Patent No. 8,689,610 proposes a method for testing the integrity of a porous filter, in which a conduit is placed downstream of the filter under test and filled with a liquid. The conduit has a length-to-cross-sectional area ratio such that it substantially resists the diffusive flow of gas through the liquid downstream of the filter material. The wet porous filter is exposed upstream of it to a pressurized gas, typically air or nitrogen, at a pressure lower than the bubble point of the porous filter. The gas pressure is slowly increased at a predetermined rate, and the gas flow through the filter medium under test is measured by measuring the flow rate of the liquid downstream of the sample. The weight of the liquid thus moved is measured, and the gas flow rate is calculated based on the volume of liquid moved, thereby effectively eliminating the effect of diffusive gas flow. The obtained results are compared with data corresponding to a defect-free filter.

[0005] Another method for measuring the integrity of porous filters is disclosed in U.S. Patent No. 5,786,528. The proposed method involves applying a liquid considered non-wetting to the porous filter under test. The non-wetting liquid is applied to the upstream side of the filter under test. There is no liquid on the downstream side of the filter. To measure the integrity of the filter, the composite flow change is measured and evaluated using the initial system volume and the volume change related to the pressurization of the filter, thereby distinguishing various flow components and accurately determining the pore size or defects of the filter under test. The latter is based on a second flow component representing the ingress of liquid into and leakage of liquid from the pores of the filter.

[0006] U.S. Patent No. 6,324,898 proposes a method for testing the integrity of hollow fiber membranes. This method involves exposing a first surface of the membrane to air while leaving a second surface exposed to water. The membrane penetration pressure forces air through defects in the membrane. To roughly indicate whether a pair of membranes has significant defects, the air passing through the membrane is collected, its amount is measured, and compared to an acceptable amount of air.

[0007] Methods known in the art for testing the integrity of filter media often require special test environments and / or considerable time to prepare the test conditions, and therefore typically cannot be performed on industrial-scale filter assemblies without interrupting industrial filtration processes for excessive periods, and / or do not achieve the required level of accuracy and repeatability. [Overview of the project] [Problems that the invention aims to solve]

[0008] The objective of the present invention is to provide a reliable integrity testing method that can also be applied to filter assemblies used in industrial filtration processes. [Means for solving the problem]

[0009] According to one aspect of the present invention, a method for testing the integrity of a porous filter media is provided as described in claim 1. The testing method of the present invention is designed as a non-destructive integrity testing procedure. Therefore, the test can be performed within an assembly that forms part of a normal filtration system, and it is possible to resume filtration operation after the integrity test with minimal effort.

[0010] A porous filter medium having an upstream and a downstream side is incorporated into a housing, the housing having an interior separated by the porous filter medium into an upstream portion on or adjacent to the upstream side of the filter medium and a downstream portion on or adjacent to the downstream side of the filter medium, the housing further comprising an inlet fluid-connected to the upstream portion of the interior and an outlet fluid-connected to the downstream portion of the interior, the outlet being connected to a filtrate conduit having a closable end located away from the outlet, and the porous filter medium having a predetermined bubble point. The filter medium housed in the housing may be provided by a single filter element or a plurality of filter elements.

[0011] The properties of porous filter media can be defined in various ways, such as by average pore size, average flow rate, and pressure drop. However, the bubble point is a parameter that defines an important property of porous filter media when wetted with a liquid and can be easily measured. The bubble point can be measured according to the standard test method described in ASTM F316-03 (2019). The bubble point of a defect-free porous filter media is treated as a predetermined bubble point in this specification. In the context of the description of this invention, this term refers to an important parameter and important target setting of the porous filter media. The liquid selected to wet the filter media during the test has some influence on the resulting predetermined bubble point due to its surface tension, so the predetermined bubble point is associated with the type of test liquid.

[0012] The method according to the present invention involves the following steps, namely, The steps include: preparing a porous filter media in which the pores of the filter media are moistened and filled with liquid; The steps include preparing the downstream section and filtrate conduit inside the housing, which are filled with liquid to expel gas from the downstream section and filtrate conduit, The steps include closing the far, closable end of the filtrate conduit, The steps include: draining the liquid from the upstream section while retaining the liquid in the downstream section of the interior, and filling the upstream section with the test gas until at least the entire upstream side of the porous filter media is exposed to the test gas; The steps include: preparing a gas-filled test volume section, which is fluidly connected to the downstream part inside via the filtrate conduit filled with liquid; The steps include providing means for measuring the pressure in the internal downstream section, such as a pressure sensor, A step of generating a pressure in the internal upstream portion of a test gas corresponding to a predetermined test differential pressure and maintaining this pressure at such a pressure level, wherein the predetermined test differential pressure is lower than a predetermined bubble point in the porous filter media, The steps include: measuring the pressure of the gas in a test volume section, indicated by means for measuring pressure, after a predetermined period of time has passed since a predetermined test differential pressure was established; and Includes.

[0013] The measured pressure is compared to the pressure obtained when testing a defect-free filter media over the same period, for example, within 10 minutes. If the measured pressure is higher by a predetermined amount specified for the filter media in a particular filtration environment, the filter media being tested for integrity is considered defective.

[0014] When integrity testing is performed on a filter assembly incorporated into an industrial filtration system, the internal downstream section and filtrate conduit can often be completely filled with liquid (filtrate), and gases have already been expelled before filtration begins. According to one embodiment, the filtrate is not replaced with another liquid, and further steps of the integrity testing according to the present invention can be performed immediately. It is necessary to take into account the specific effect of the filtrate on a given bubble point due to its surface tension.

[0015] Once the closable end of the filtrate conduit is closed, the closable end remains in this state until the end of the integrity test.

[0016] The test volume section is selected according to the present invention such that a pressure rise of approximately 100 mbar or more is obtained within 10 minutes when a filter media having a bubble point corresponding to a predetermined bubble point is tested. This limitation on the size of the test volume section enables accurate and repeatable integrity testing, allowing for a clear distinction within a reasonable timeframe between filter media that meet the integrity criteria and those that may be considered defective.

[0017] The pressure of the gas within the test volume can be monitored by placing a means for measuring the pressure (hereinafter also referred to as a pressure sensor) in direct contact with the gas within the test volume. Alternatively, the pressure sensor may be placed upstream or downstream of the test volume, in contact with the liquid filling the downstream portion of the housing and the filtrate conduit connected to the outlet of the housing. Due to the incompressibility of the liquid under the relevant pressure conditions, the relevant pressure value indicated by the pressure sensor always reflects the pressure changes within the test volume with sufficient accuracy.

[0018] The gas supplied to the test volume section and the test gas supplied to the upstream section may be the same or different. Therefore, typically, the gas in the test volume section is selected from gases such as nitrogen and air, which are chemically neutral and are considered not to react with or dissolve in the fluid in measurable amounts.

[0019] While the change in gas pressure within the test volume can be continuously monitored over time, according to the present invention, it is typically sufficient to measure the gas pressure within the test volume only once, for example, a few minutes after the predetermined period has elapsed and the pressure difference has been established.

[0020] According to another aspect of the present invention, a filter assembly for testing the integrity of a porous filter medium is provided, the assembly comprising one or more housings, each housing having an interior separated by the porous filter medium into an upstream portion on or adjacent to the upstream portion of the filter medium and a downstream portion on or adjacent to the downstream portion of the filter medium, the housing further comprising an inlet fluidly connected to the upstream portion of the interior and an outlet fluidly connected to the downstream portion of the interior, the porous filter medium comprising one or more housings having predetermined bubble points, A gas-filled test volume section, to which fluid can be connected, is located in the downstream part of the housing. A means for measuring the gas pressure in the test volume section, A filtrate conduit that provides a flow path extending from an outlet inside a housing to a test volume section, the filtrate conduit having a closable end at a position remote from the outlet, A pressure source that generates a pressure of a test gas corresponding to a predetermined test differential pressure in an upstream portion of the housing and is suitable for maintaining this pressure at such a pressure level, wherein the test differential pressure is lower than a predetermined bubble point of a porous filter medium and comprising.

[0021] The assembly of the present invention can be provided as a separate test unit, but can form part of a wide variety of filter assemblies not only on a laboratory scale but also on an industrial scale.

[0022] Furthermore, the method according to the present invention can be carried out using a wide variety of liquids to wet the filter medium and fill the downstream portion of the housing. Therefore, there is no need to drain the liquid filtered in the normal filtration process in an industrial filter assembly and replace this liquid with a special test liquid. In contrast, the filtered liquid (filtrate) can be retained within the wet filter medium, within the downstream portion of the housing, and within the filtrate conduit connected to the outlet of the housing.

[0023] According to the present invention, the test volume section is limited to a relatively small volume, as pointed out above, and can be provided by connecting a special test gas chamber to the downstream portion of the assembly, or alternatively, can be provided in a part of the filtrate conduit downstream of the outlet of the housing. The small-volume test volume section enables a more accurate integrity test. Furthermore, significant test results can be obtained, for example, in a short period of about 5 minutes.

[0024] If there are multiple housings within the assembly being tested, a common test volume section can be used, but the criteria for determining the size of the test gas volume section are still determined as generally described above.

[0025] The test gas can be selected from a wide variety of test gases. The only prerequisite is that the solubility of the test gas in the liquid is relatively low, for example, to avoid substantial obstacles to the test procedure. Typically, nitrogen or air are preferred test gases, especially for water or aqueous liquids used to wet hydrophilic porous filter media. If the wetting properties of the filter media are poor, an alcohol / water mixture may be used. Here again, nitrogen or air are preferred test gases. Since the bubble point of the filter media depends on the liquid used to wet the filter media, a given bubble point needs to be appropriately adjusted depending on the liquid used to wet the filter media being tested. Detailed description of the invention

[0026] Preferably, the test volume is limited to a volume such that when a filter media having a bubble point corresponding to a predetermined bubble point is tested, a gas pressure increase in the test volume is obtained within 10 minutes of approximately 0.1 to approximately 0.8 times, preferably approximately 0.2 to approximately 0.6 times, a predetermined test differential pressure.

[0027] For example, if the test differential pressure is at a level of 1240 mbar, a desirable pressure increase of approximately 120 mbar or more, preferably in the range of approximately 200 mbar to 500 mbar, can be obtained after a predetermined period of 10 minutes.

[0028] These limits in the test volume section can be easily measured and, furthermore, provide test conditions that allow for easy measurement of the integrity of the filter media being tested over a reasonable period of time. Therefore, the predetermined period may be set to a few minutes, for example, 5 or 10 minutes. Thus, when the integrity test is performed in an industrial filtration system, especially under conditions where a suitable bubble point is obtained from the combination of liquid and filter media, it is not necessary to replace the filtrate downstream of the filter media with a different liquid, and the normal filtration process only needs to be interrupted for a short period. Nevertheless, the pressure rise within the test volume section allows for a clear and accurate distinction between defective and non-defective filter media.

[0029] As already mentioned above, the method according to the present invention can be carried out in a wide variety of environments, and therefore, in particular in environments in which the housing forms part of an industrial filtration system for filtering liquids in the fields of food and beverages, chemistry, biotechnology, and pharmaceuticals.

[0030] In particular, in such cases, the liquid filling the downstream portion inside the housing and the filtrate conduit may be the filtrate of the fluid normally filtered within the filter assembly. This also saves time when resuming normal filtration operation.

[0031] Furthermore, the filter media may be a membrane filter media, particularly a hollow fiber membrane filter media or a pleated membrane filter media. According to a further aspect of the present invention, the porous filter media may be provided in the form of a filter candle.

[0032] According to a preferred embodiment of the present invention, the test gas is selected from inert gases, particularly nitrogen, and air.

[0033] The small amount of carbon dioxide present in normal air may react to some extent with the liquids in the assembly, but this does not negatively affect reproducibility and therefore does not cause problems. Furthermore, the differences in solubility of the various test gases identified above do not significantly affect the test results and are therefore acceptable.

[0034] According to the method of the present invention, the filter assembly may comprise one or more additional housings, each housing having an interior incorporating porous filter media, and each interior being separated by its respective porous filter media into an upstream portion on or adjacent to the upstream side of the filter media and a downstream portion on or adjacent to the downstream side of the filter media. Each housing has an outlet in the downstream portion of its interior, which is typically connected to a common tubing system, a portion of which forms a filtrate conduit. Preferably, a valve can be connected to each outlet to allow individual testing of the filter media in each housing.

[0035] As noted above, this assembly can preferably form part of a filtration system, particularly an industrial-scale filtration system for filtering liquids in fields such as food and beverages, chemicals, pharmaceuticals, and biotechnology.

[0036] Therefore, it is not necessary to remove and isolate the porous filter media from its typical environment for testing.

[0037] In many cases, this assembly comprises two or more housings incorporating porous filter media, each housing having a valve connected to the outlet of the downstream portion. Thus, one or more porous filter media incorporated into the housings can be configured to test each housing and one or more filter media separately contained in each housing.

[0038] In a further embodiment, the porous filter media is provided in the form of a membrane filter media, particularly a hollow fiber membrane filter media or a pleated membrane filter media.

[0039] The housing / assembly typically includes an inlet valve for fluid connection between the upstream portion inside the housing and the pressurized test gas source.

[0040] The assembly according to the present invention may be equipped with valves for fluid connection and disconnection of the test volume section to the downstream portion of the housing. Thus, the test volume section can be provided as an integral part of the industrial filter assembly and can be selectively fluid-connected to the downstream portion inside the housing when performing integrity tests according to the present invention.

[0041] Preferably, the test volume section is provided with an outlet for fluid connection between the test volume section and the environment. Thus, the test volume section can be flushed and / or drained, and the pressure within the test volume section can be adjusted to predetermined test conditions.

[0042] As previously noted, the volume of the test volume section is preferably limited to a relatively small volume compared to the volume of the downstream assembly of one or more filter media. Even when designed for testing large industrial filtration systems, the test volume section can typically be limited to about 10 L or less, more preferably about 5 L or less, and most preferably about 2 L or less.

[0043] Alternatively, the test volume section may be provided by a portion of the filtrate conduit downstream of the housing, which can be defined by an upstream valve and a downstream valve that form the test volume section in between. Such a portion of the filtrate conduit preferably has an outlet for flushing and / or draining the portion of the conduit, filling the portion with gas, etc.

[0044] Preferably, each housing comprises a separate inlet in its upstream portion inside and, optionally, a valve for supplying a test gas to the upstream portion during the implementation of the method of the present invention.

[0045] These and further aspects and advantages of the present invention will become apparent from the drawings, the following detailed description of the drawings, and the examples. [Brief explanation of the drawing]

[0046] [Figure 1] Figures 1A to 1E schematically show a series of test steps in a prior art integrity test. [Figure 2] Figures 2A to 2D schematically illustrate a series of test steps in the integrity test according to the present invention. [Figure 3] Figures 3A to 3C schematically show examples of changes to the test steps in Figures 2A to 2D of Figure 2. [Figure 4A] The filter assembly used in the following example is shown. [Figure 4B] Another filter assembly used in the following example is shown. [Figure 4C] The filter elements of the filter assembly shown in Figures 4A and 4B are shown in detail. [Figure 4D] The filter elements of the filter assembly shown in Figures 4A and 4B are shown in detail. [Figure 4E] The filter elements of the filter assembly shown in Figures 4A and 4B are shown in detail. [Figure 4F] The filter elements of the filter assembly shown in Figures 4A and 4B are shown in detail. [Figure 5A] The pressure / time graph showing the results obtained in the example is shown. [Figure 5B] The pressure / time graph showing the results obtained in the example is shown. [Figure 6] This shows another specific type of filter element used and tested in accordance with the present invention. [Figure 7A]A three-dimensional diagram shows a complex industrial filtration system configured as an assembly according to the present invention. [Figure 7B] A partial cross-sectional view shows a complex industrial filtration system configured as an assembly according to the present invention. [Modes for carrying out the invention]

[0047] FIG.1A in Figure 1 schematically shows an assembly 10 for testing the integrity of a filter media 12 according to a method known in the prior art. Assembly 10 can also form part of a filtration system (not shown here) that enables non-filtrate filtration on an industrial scale.

[0048] Assembly 10 comprises a housing 14 having an interior 16 that houses a filter element 18 incorporating a filter medium 12 whose integrity is to be tested. The filter medium 12 separates the interior 16 of the housing 14 into an upstream portion 20 and a downstream portion 22.

[0049] The housing 14 is provided with an inlet 24 in the upstream portion 20 of the interior 16, where a valve 26 is provided to connect or disconnect the upstream portion 20 of the interior 16 to / from a supply line 28 that supplies unfiltrate.

[0050] The housing 14 is provided with an outlet 30 in the downstream section 22, which allows the filtrate to be drained from the downstream section 22 into a filtrate conduit 32. The filtrate conduit 32 is typically provided with a valve 34 which allows the assembly 10 to be separated from further downstream equipment (not shown here).

[0051] The upstream portion 20 of the interior 16 further comprises a test gas inlet 36, which can be opened and closed by a valve 38, the purpose of which will be described below.

[0052] During normal filtration, the housing 14, which has an upstream section 20 and a downstream section 22, and the filtrate conduit 32 are completely filled with liquid. During normal filtration operation, the pressure levels of both the upstream section 20 and the downstream section 22 are typically in the range of about 1 bar to about 9 bar, which is above the ambient pressure.

[0053] When preparing for integrity testing, assembly 10 can be subjected to a washing and flushing step to ultimately regenerate the filter media and remove any detergent residue from assembly 10. In a further step, assembly 10 is filled with water. This state is shown in FIG. 1A of Figure 1.

[0054] Subsequently, the assembly 10 is substantially completely drained by the opened valves 26 and 34, as indicated by the arrows in FIG. 1B of Figure 1. This step can be facilitated by an additional vent valve (not shown). However, care must be taken to keep the filter media 12 moist. The upstream section 20 and the downstream section 22 are drained by valve 26 and the supply line 28, while the volume section of the filtrate conduit 32 is drained from the assembly 10 by valve 34.

[0055] Figure 1, FIG. 1C shows the assembly 10 in a basically completely drained state immediately before the start of the integrity test. As shown in Figure 1, FIG. 1C, the bottom of the filter element 18 can tolerate a small amount of liquid 40, for example, about 100 mL or less, which is about 10% or less of the downstream volume of a 30-inch filtration cartridge commonly used in such applications.

[0056] Subsequently, valves 26 and 34 are closed, and at this point, assembly 10 is ready for integrity testing. The filter media 12 of the filter element 18 remains moist.

[0057] As shown in FIG. 1D of Figure 1, valves 34 and 38 are open when the test gas is supplied to the upstream portion 20 of the interior 16 through the inlet 36. The exemplary test pressure is about 1.2 bar, above the ambient pressure, but still below the bubble point of the filter media 12 being tested (about 1.6 bar in this example). The integrity test is initiated by closing valve 34 after the test pressure has been generated in the upstream portion 20.

[0058] Therefore, the downstream section 22 of the interior 16 is initially still below ambient pressure. Next, the test gas enters the downstream section 22 of the interior through the filter media 12, which has been moistened by the gas diffusion process, because the pressure difference across the filter media 12 falls below its predetermined bubble point. The pressure of the gas in the downstream section 22 and conduit 32 slowly rises as the gas passes through the filter media, as shown in FIG. 1E of Figure 1, with the valve 34 remaining closed. The pressure in the downstream section is detected by the pressure sensor 50. The pressure rise observed in the downstream section 22 and filtrate conduit 32 after 10 minutes is substantially less than 100 mbar, depending on the available volume in the downstream section 22 and conduit 32.

[0059] If there is a defect in the filter media 12, this pressure increase will be somewhat more pronounced. Therefore, it is possible to roughly evaluate the condition of the tested filter media.

[0060] Figures 2A to 2D in Figure 2 illustrate the steps of the method for integrity testing according to the present invention, which yields test results in a significantly shorter time and with higher accuracy than conventional methods.

[0061] Figure 2A shows a filter assembly 100 for testing the integrity of the filter media 112. This assembly 100 also forms part of a filtration system (not shown here) that enables filtration of unfiltrated liquid on an industrial scale.

[0062] Assembly 100 comprises a housing 114 having an interior 116 that houses a filter element 118 incorporating a filter medium 112 to be tested for integrity. The filter medium 112 separates the interior 116 of the housing 114 into an upstream portion 120 and a downstream portion 122.

[0063] The housing 114 has an inlet 124 in the upstream portion 120 of the interior 116, where a valve 126 is provided to connect or disconnect the upstream portion 120 of 116 to / from a supply line 128 that supplies unfiltrate.

[0064] The housing 114 has an outlet 130 in its downstream section 122 that allows the filtrate to be drained from the downstream section 122 into a filtrate conduit 132. The filtrate conduit 132 is equipped with a valve 134 located away from the outlet 130, which allows the assembly 100 to be separated from further downstream equipment (not shown here).

[0065] The upstream portion 120 of the interior 116 further comprises a test gas inlet 136, which can be opened and closed by a valve 138, the purpose of which will be described below.

[0066] During normal filtration, the housing 114, having its upstream section 120 and downstream section 122, and the conduit 132 are completely filled with liquid, as shown in FIG. 2A of Figure 2. The pressure level during normal filtration operation can, here again, be typically about 1 bar to about 9 bar, above the ambient pressure. So far, assembly 100 corresponds to the assembly described with reference to FIG. 1A of Figure 1.

[0067] Furthermore, in contrast to assembly 10, the conduit 132 of assembly 100 comprises a gas-filled chamber 140, which provides a limited test volume section that can be connected to and disconnected from the conduit 132 by opening and closing valve 142. Typically, the chamber 140 comprises a drain 144 and a valve 146 for connecting / disconnecting the drain 144 to and from the chamber 140. In addition, the chamber 140 comprises a valve 148 for ventilating the chamber 140 to the environment. The chamber 140 shown in FIG. 2A of Figure 2 has already been flushed and drained. During normal filtration operation, typically the pressure inside the chamber 140 is at ambient pressure with valve 142 closed and valves 146 and / or 148 open.

[0068] When preparing for integrity testing, assembly 100 can be subjected to a washing and flushing step to ultimately regenerate the filter media 112 and remove any detergent residue from assembly 100. In a further step, assembly 100 is then typically filled with water to wet the filter media 112 and to ensure that the downstream portion 122 of the interior 116 and the filtrate conduit 132 up to the valve 134 are essentially free of gas. This condition is shown in FIG. 2A of Figure 2.

[0069] Next, the upstream portion 120 of the interior 116 of the housing 114 of assembly 100 is completely drained by the opened valve 126, as indicated by the arrow in FIG. 2B of Figure 2. Drainage can be facilitated by opening valve 138. However, care must be taken to keep the filter media 112 moist, which is facilitated by retaining water in the downstream portion 122 and the filtrate conduit 132. Thus, valve 134 remains closed, and the chamber 140 is still disconnected from the filtrate conduit 132 (valve 142 remains closed). Since only the upstream portion 120 needs to be drained, the time required to prepare assembly 100 for integrity testing is already short. A small amount of liquid 152 may remain in the upstream portion 120 of the interior 116.

[0070] FIG.2C in Figure 2 shows the upstream portion 120 of the interior 116 of the housing 114 of assembly 100 in a fully drained state at the start of the integrity test. Valve 126 is closed, and the test gas is supplied to the upstream portion 120 of the housing 114 through the open valve 138. In the upstream portion 120, a test pressure difference is generated to a level below a predetermined bubble point in the filter media 112, for example, to a level reaching about 80% of the predetermined bubble point above ambient pressure. The pressure level of the test gas in the upstream portion is maintained at such a level. Chamber 140 provides a test volume filled with gas at ambient pressure. With valves 146 and 148 kept closed, valve 142 is then opened.

[0071] The integrity test is initiated by opening valve 142, which allows the gas to diffuse through the filter media 112 into the downstream portion 122 of the interior 116, resulting in an increase in the downstream pressure level, which can be measured by a pressure sensor 150 that may be provided to fluidize the chamber 140, or by a pressure sensor 150 that may also be provided in any other part of the downstream assembly 100 of the filter media 112, such as the conduit 132.

[0072] The test volume is significantly limited compared to the test volume used in the prior art. In this example, the test volume is limited to such an extent that a pressure increase of approximately 400 mbar or more of the test gas can be obtained within 10 minutes of the start of the test, compared to the prior art method. Therefore, significantly more accurate test results can be obtained in a shorter time.

[0073] If the filter media 112 is defective, the pressure rise will increase significantly over time.

[0074] Once the integrity test is complete, the filtration process can be quickly restarted. This is done simply by closing valve 142 to disconnect the fluid from assembly 100 in the test chamber 140. At this time, independently of the operation of assembly 100, the chamber 140 providing the test volume may be flushed and drained as needed.

[0075] Figures 3A and 3B illustrate the steps of the integrity test method according to the present invention, which is provided in a manner different when the test volume is compared with the assembly 100 of Figures 2A to 2D.

[0076] FIG.3A in Figure 3 shows a filter assembly 200 for testing the integrity of the filter media 212. This assembly 200 can also form part of a filtration system (not shown here) that enables filtration of unfiltrated liquid on an industrial scale.

[0077] The assembly 200 comprises a housing 214 having an interior 216 that houses a filter element 218 incorporating a filter media 212 to be tested for integrity. The filter media 212 separates the interior 216 of the housing 214 into an upstream portion 220 and a downstream portion 222.

[0078] The housing 214 has an inlet 224 in the upstream portion 220 of the interior 216, where a valve 226 is provided to connect or disconnect the upstream portion 220 of 216 to / from a supply line 228 that provides unfiltrate.

[0079] The housing 214 has an outlet 230 in its downstream section 222 that allows the filtrate to be drained from the downstream section 222 into a filtrate conduit 232. Typically, the filtrate conduit 232 has a valve 234 at its closable end located away from the outlet 230, and the valve 234 allows the assembly 200 to be isolated from further downstream equipment (not shown here).

[0080] The upstream portion 220 of the interior 216 further comprises a test gas inlet 236 which can be opened and closed by a valve 238, as already described in relation to FIG. 2A / FIG. 2C of Figure 2 and the operation of valve 138.

[0081] During normal filtration, the housing 214, having its upstream section 220 and downstream section 222, and the conduit 232 are completely filled with liquid. The pressure level during normal filtration operation can also be, here, typically about 1 bar to about 9 bar, above the ambient pressure. So far, assembly 200 corresponds to the assemblies in FIG. 1A of Figure 1 and FIG. 2A of Figure 2, respectively.

[0082] However, assembly 200 further comprises a valve 252 located in the filtrate conduit 232 downstream of valve 234. The space 254 in the conduit 232 between the two valves 234 and 252 functions as a chamber for providing a limited test volume section according to the present invention. During the normal filtration operation of assembly 200, valves 234 and 252 remain open.

[0083] As previously shown and explained in relation to FIG. 2A in Figure 2, once the upstream section 220 is drained, valve 234 remains closed, allowing liquid to drain from the space in the conduit section 254. Valve 252 then opens to fill this space with gas, typically at ambient pressure. Valve 252 is then closed again, at which point a predetermined test volume of gas is held within the assembly 200. This state is shown in FIG. 3B in Figure 3.

[0084] During integrity testing, valve 234 is opened to fluidly connect the test volume section of conduit section 254 to the downstream section 222. Depending on the orientation of the assembly and its filtrate conduit 232, the gas in the test volume section may remain in conduit section 254, or it may move upward, for example, to section 256 of the filtrate conduit 232, as shown in FIG. 3C of Figure 3.

[0085] Here again, the test volume is significantly limited compared to the test volume used according to the prior art. In this example, the test volume is limited to such an extent that a pressure increase of approximately 400 mbar or more of the test gas can be obtained within 10 minutes of the start of the test, compared to the prior art method. Therefore, more accurate test results can be obtained in a shorter time. [Examples]

[0086] An exemplary test assembly 300 was configured as shown in Figure 4A, comprising a housing 302 with six filter candles 304, which provide the filter media to be tested, incorporated inside 306. The internal volume of the housing is approximately 30 L.

[0087] In these specific examples, the filter candle 304 is of type AB3BB7W32 (available from Pall Corp. (New York, USA) as Pall BB Final Beer filter cartridges). Each filter candle 304 comprises three axially aligned 10-inch (254 mm) long filter elements 305, which provide a filter medium in the form of a pleated polyethersulfone membrane. The filter elements 305 are 0.6 m 2 It is characterized by its nominal filtration area and forward flow limit of 8 mL / min at a differential pressure of 1240 mbar. The bubble point of the filter media of the filter candle 304 is approximately 1600 mbar when tested in an aqueous medium (DI water). The overall forward flow limit of a set of six filter candles 304 (each containing three 10-inch filter elements resulting in a candle length of 30 inches) is 144 mL / min at a test differential pressure of 1240 mbar. The nominal filtration area is 10.8 m². 2 It will become.

[0088] The upstream portion 312 of the interior 306 has an opening 316 or inlet at the lower end of the housing for the fluid to be filtered. The downstream portion of the interior has an outlet 318 designed for draining the filtrate from the housing 302.

[0089] The inlet 316 is connected to a piping system 320 that provides a supply passage for unfiltrate during normal filtration operation. The piping system 320 includes a valve 322 that can be closed to shut off the further supply of unfiltrate.

[0090] The piping system 320 further includes a branch section 324 which includes a further valve 326 that allows fluid to be drained from the upstream portion 312 of the interior 306 of the housing 302. To drain the upstream portion 312 of the interior 306 of the housing 302, valve 322 is closed and valve 326 is opened.

[0091] The upstream portion 312 of the interior 306 of the housing 302 is provided with an additional inlet 328 connected to a pressure source 330 in the upper portion of the housing 302. The pressure source 330 can be used to supply gas, for example, a test gas, to the upstream portion 312 of the interior 306, in order to provide a test gas and pressure difference, and further to accelerate and complete the draining of unfiltrate from the upstream portion 312 of the interior 306 of the housing 302 in preparation for the integrity test according to the present invention.

[0092] The outlet 318 of the downstream portion 314 of the interior 306 of the housing 302 is connected to a conduit 336 designed to receive filtrate from the housing 302. The filtrate conduit 336 further includes a branch 338 to which a chamber 340 supplying gas within the test volume section can be attached. During normal filtration operation, the chamber 340 is isolated from the branch 338 by closing a valve 341. Furthermore, a pressure sensor 342 is connected to the chamber 340. The portion of the filtrate conduit 336 downstream of the branch 338 can be isolated by closing a valve 344.

[0093] During the initial installation of assembly 300, the assembly can be flushed with deionized water supplied to the assembly via valve 326 and branch 324 with valve 322 closed. Care is taken to ensure that the filter media of the filter candle 304 is completely wetted and that air is discharged from the assembly via the filtrate conduit 336 and, at its closable end, via valve 344. At this time, chamber 340 is isolated from branch 338 by closing valve 341.

[0094] In preparation for integrity testing of the filter media provided by the filter candle 304, valve 322 is closed to drain deionized water from the internal upstream portion, and then valve 326 is opened. Valve 344 is typically kept closed during such process steps, thereby maintaining the filter media of the filter candle 304 in a moist state.

[0095] At this point, the downstream portion 314 of the interior 306 and the conduit 336 are at ambient pressure. The chamber 340 providing the test volume is typically maintained at ambient pressure by opening the valve 346.

[0096] Once drainage from the upstream section 312 of the internal 306 is complete, the valve 326 is closed. A test gas, air in this example, is introduced into the upstream section 312 until the pressure difference reaches 1240 mbar, which is approximately 80% of the predetermined bubble point (1600 mbar) of the filter media in the filter candle 304. This (absolute) pressure level is maintained throughout the following test procedure.

[0097] Valve 346 is closed, valve 341 connecting chamber 340 and downstream conduit 336 is opened, and the increase in gas pressure in the test volume section within chamber 340 is measured by pressure sensor 342.

[0098] Figure 4B shows assembly 380, which has a basic structure that is substantially the same as assembly 300. Therefore, the same reference numerals are used, and in relation to this, the above description of Figure 4A can be referred to.

[0099] However, assembly 380 differs from assembly 300 in that the test volume section is provided by a section 384 of the conduit 338, which is defined at its upstream end by valve 341 and at its downstream end by valve 382. Furthermore, the conduit 338 is equipped with a pressure sensor 386.

[0100] In preparation for the integrity test according to the present invention, compartment 384 of conduit 338 is drained and filled with gas at ambient pressure. The volume of compartment 384 is also limited to produce a significant pressure increase within a 10-minute time limit.

[0101] More detailed diagrams of the structure of the filter candle 304 and the filter element 305 that basically constitutes the filter candle are provided in Figures 4C, 4D, and 4F, which are described in more detail below.

[0102] The filter candle 304 comprises a polyethersulfone membrane as a pleated porous filter medium 350 and has a single open end. The open end 308 of the filter candle 304 is sealed and mounted in an opening in a wall 310 that traverses the interior 306 of the housing 302, and the filter candle 304 hangs vertically from the wall during normal filtration operation with its open end 308 facing upward. The interior 306 of the housing is separated into an upstream section 312 and a downstream section 314 by the filter medium of the filter element 305 of the filter candle 304.

[0103] A detailed structure of the filter element 305 is provided in Figure 4C. The filter element has a length of 254 mm (10 inches) and 0.6 m 2 A pleated filter media 350 having a nominal filtration area is provided. As noted above, the forward flow limit is 8 mL / min at a differential pressure of 1240 mbar. The predetermined bubble point of this filter media is approximately 1600 mbar.

[0104] The pleated filter media 350 is housed within a hollow cylindrical structure, with individual pleats 352 arranged radially around an inner hollow grid-like support structure 354. A hollow grid-like support structure 356 is provided on the outer circumference of the pleated filter media 350. The upper end 358 of the filter element 305 is open, while the lower end is closed by an end cap 360.

[0105] Figure 4D schematically shows the filter element 305 in two cross-sectional views (a cross-sectional view parallel to the longitudinal axis and a cross-sectional view perpendicular to it), and the flow of fluid entering and leaving the filter element 305 is indicated by arrows.

[0106] As shown in Figures 4E and 4F, two or more filter elements 305 can be axially aligned, sealed, and connected to form filter candles 304', 304. In such a configuration, only the lowest filter element 305 retains its end cap 360.

[0107] A filter candle may comprise one or more filter elements 305 arranged axially. The filter candle shown in Figure 4D consists of only one filter element 305. The filter candle 304' shown in Figure 4E comprises two axially aligned filter elements 305, while the filter candle 304 used in the assemblies of Figures 4A and 4B comprises three axially aligned filter elements 305, schematically shown in Figure 4F.

[0108] For illustrative purposes, the pressure levels measured over time by pressure sensors 342 and 386 of filter assemblies 300 and 380, respectively, are shown in Figures 5A and 5B. The values ​​shown in Figure 5A are based on a setting where the test volume (chamber 340) is set to 6850 mL, while the values ​​shown in Figure 5B correspond to values ​​measured using a test volume (conduit section 384) of only 1000 mL.

[0109] Figures 5A and 5B show the pressure rise in the downstream section 314 over time, corresponding to the pressure rise in the conduit 338 and the chamber 340 and conduit section 384, respectively, for different settings.

[0110] The bottom curve shows the pressure rise actually measured for assemblies 300, 380 when the filter media of all 18 filter elements 305 are defect-free. The curve immediately above shows the pressure rise resulting when the filter media of all filter elements is just within the upper limit of the effective forward fluid flow rate specified in the filter element specifications.

[0111] If there is a small defect in one of the filter media of the filter element 305 (indicated here by a single pinch hole resulting in a forward gas flow rate of 70 mL / min), the pressure level will rise over time, as shown by the third curve from the bottom. The top curve illustrates the situation when two defects of this magnitude are present.

[0112] The comparison of the curves in Figures 5A and 5B clearly demonstrates that the appropriate limitation of the test volume according to the present invention provides the advantage of obtaining significant and reliable integrity test results in a short period of time.

[0113] Larger test volumes require measurement times of 10 minutes or more (see Figure 5A), but if the test volume is significantly reduced, a clear distinction between perfect and defective filter media may be possible after just 5 minutes (see Figure 5B).

[0114] Figure 6 shows a filter element 400 that can be used in any one of the assemblies 100, 200, 300, and 380 with several modifications. The filter element 400 is designed for tangential flow filtration.

[0115] The filter element 400 comprises a filter medium provided by a plurality of hollow fiber membranes 402 arranged parallel to each other to form a hollow fiber membrane bundle 412. The hollow fiber membrane bundle 412 is housed in a hollow cylindrical housing 414 having a supply inlet 422 at a first end 420 and a residual liquid outlet 446 at a second end 444 on the opposite side.

[0116] The housing further comprises two permeate outlets 450, 452 adjacent to the first end 420 and the second end 444. Upon entering the housing 414, the unfiltered liquid is guided into the individual hollow fibers 402 from the end of each hollow fiber 402 adjacent to the supply inlet 422. While this liquid flows through the hollow fibers 402 toward the residue outlet 446, some of this liquid and / or its components cross the hollow fiber membrane 402 and accumulate in the housing 414, where it is drained as permeate through the permeate outlets 450, 452.

[0117] The remaining portion of this liquid is drained through the residual liquid outlet 446.

[0118] The filter element 400 and its filter medium, i.e., the hollow fiber membrane 402, can be tested for integrity in the same way as the filter element 305 described above. The only additional procedure taken is to close the residual liquid outlet 446 to create a pressure difference during testing only across the membrane of the hollow fiber 402.

[0119] Otherwise, in order to implement the present invention with respect to this type of filter media, only the procedures for integrity testing described above should be observed.

[0120] Figures 7A and 7B show, for example, an industrial-scale filtration system 500 for beer filtration.

[0121] System 500 is configured on a rack 502 and includes eight filter assemblies 510 mounted on the rack 502 in two parallel rows. The filter assemblies 510 are configured similarly to those described in the context of Figure 4A, but differ in that they provide approximately 50% more filtration area per housing by having seven filter candles, each having four filter elements that are 10 inches (254 mm) long.

[0122] Figure 7B shows a cross-sectional view of the system 500, with the interior 520 of the front row assemblies 510 visible. Each assembly 510 comprises a housing 512 having an interior 520. The upper portion of the interior 520 is positioned a separation wall 522 that provides seven openings 524 designed to receive seven filter candles 526. Each filter candle 526 consists of four axially aligned filter elements 528, as shown and described in relation to Figure 4F.

[0123] All assemblies 510 are connected at their lower ends to a common supply line structure 540 that supplies unfiltrated liquid to the assemblies 510.

[0124] All assemblies 510 are connected at their upper ends to a common filtrate conduit structure 550 that receives the filtrate from the filter assemblies 510. Typically, the system 500 includes a vent conduit 552 connected to the filtrate conduit structure 550, which allows for ventilation of the assemblies 510 and the filtrate conduit structure 550, and thus the entire downstream portion of the system 500.

[0125] The system 500 may include a chamber 560, for example, as shown in Figures 7A and 7B, which forms part of the vent conduit 552, providing a test volume section when it is necessary to perform integrity testing of the system. Such a chamber 560 forms a permanent part of the system 500. The section of the vent conduit 552 incorporating the chamber 560 typically includes valves 562 and 564, which allow the chamber 560 to be easily ventilated, flushed, and drained.

[0126] According to further alternative designs of system 500, the test volume section may be provided separately from the ventilation conduit 552 of the conduit structure 550 (not shown).

[0127] The system 500 in Figures 7A and 7B is configured based on the filter element used in the embodiments of Figures 4A and 4B, with a capacity of 130m.2 This can provide a nominal filtration area. The system 500 as a whole is capable of filtering beer at a rate of approximately 150 hL / h to approximately 250 hL / h. If all assemblies 510 are tested simultaneously, the maximum diffusion forward gas flow rate will be somewhat greater than 1.8 L / min. Typically, such a setting is avoided, and each assembly 510 is tested separately at a maximum diffusion forward gas flow rate of 224 mL / min. During integrity testing, each assembly 510 can be tested separately using a common test volume section 560.

[0128] In the context describing the present invention (in particular, in the context of the following claims), the terms “a,” “an,” “the,” and “at least one,” and similar references, should be interpreted as encompassing both singular and plural, unless otherwise stated herein or unless there is a clear contextual contradiction. The use of the term “at least one” following a list of one or more items (e.g., “at least one of A and B”) should be interpreted as meaning one item (A or B) selected from the listed items or any combination of two or more items (A and B), unless otherwise stated herein or unless there is a clear contextual contradiction. The terms “comprising,” “having,” “including,” and “containing” should be interpreted as unrestrictive terms (i.e., “including, but not limited to”), unless otherwise noted. The descriptions of value ranges herein are merely intended to serve as a concise way of referring individually to each of the individual values ​​within the range, unless otherwise stated herein, and each individual value is incorporated herein as if it were individually stated herein. All methods described herein may be performed in any suitable order unless otherwise stated herein or unless there is a clear contextual contradiction. The use of any examples or illustrative words provided herein (e.g., "etc.") is merely intended to make the invention more clear and, unless otherwise claimed, does not limit the scope of the invention. Nothing herein should be construed as indicating that any non-claimed element is essential to the practice of the invention.

[0129] Preferred embodiments of the Invention, including best modes for carrying out the Invention known to the inventors, are described herein. Modifications of these preferred embodiments may become apparent to those skilled in the art by deciphering the foregoing description. The inventors anticipate that those skilled in the art will appropriately adopt such modifications, and the inventors intend that the Invention may be carried out in ways different from those specifically described herein. [Explanation of symbols]

[0130] 10, 100, 200, 300, 380, 510…Assemblies, 12, 112, 212, 350…Filter media, 14, 114, 214, 302, 414…Housings, 16, 116, 216, 306, 520…Internal, 18, 118, 218, 305, 400, 528…Filter elements, 20, 120, 220, 312…Upstream section, 22, 122, 222, 314…Downstream section Minutes, 24, 124, 224, 316, 328… Inlet, 26, 34, 38, 126, 134, 138, 142, 146, 148, 226, 234, 238, 252, 322, 326, 341, 344, 346, 382, ​​562, 564… Valve, 28, 128, 228… Supply line, 30, 130, 230, 318… Outlet, 32, 132, 232, 336… Filtrate conduit, 36, 136, 236… Test gas inlet, 40, 152…Liquid, 50, 150, 250, 342, 386…Pressure sensor, 140, 340, 560…Chamber, 144…Drain, 254…Conduit section, 256…Filtrate conduit section, 304, 304', 526…Filter candle, 308…Open end, 310…Wall section, 320…Piping system, 324, 338…Branch section, 330…Pressure source, 352…Pleats, 354, 3 56…Hollow lattice support structure, 358…Upper end, 360…End cap, 384…Compartment, 402…Hollow fiber membrane, 412…Hollow fiber membrane bundle, 420…First end, 422…Supply inlet, 444…Second end, 446…Residual liquid outlet, 450, 452…Permeate outlet, 500…System, 502…Rack, 522…Separation wall, 524…Opening, 540…Supply line structure, 550…Filtrate conduit structure, 552…Ventilation conduit

Claims

1. A method for testing the integrity of a porous filter media having an upstream side and a downstream side, The porous filter media is incorporated into a housing, the housing having an interior separated by the porous filter media into an upstream portion of the filter media and a downstream portion of the filter media, the housing further comprising an inlet fluid-connected to the upstream portion of the interior and an outlet fluid-connected to the downstream portion of the interior, the outlet being connected to a filtrate conduit having a closable end located away from the outlet, and the porous filter media having a predetermined bubble point. The aforementioned method, To provide the porous filter media in which the pores of the filter media are moistened and filled with liquid, To provide the downstream portion of the interior of the housing and the filtrate conduit, which are filled with liquid to expel gas from the downstream portion of the interior and the filtrate conduit, Closing the closable end of the filtrate conduit, With the liquid in the downstream portion of the interior retained, the upstream portion of the interior is drained, and the upstream portion of the interior is filled with the test gas to the extent that at least the entire upstream side of the porous filter media is exposed to the test gas. To provide a gas-filled test volume section that is fluidly connected to the downstream portion inside via the filtrate conduit filled with the aforementioned liquid, To provide means for measuring the pressure in the downstream portion of the interior, The method involves generating a pressure in the upstream portion of the interior of the test gas having a pressure level corresponding to a predetermined test differential pressure, and maintaining the pressure of the test gas at that pressure level, wherein the predetermined test differential pressure is lower than the predetermined bubble point of the porous filter media. The pressure of the gas in the test volume section is determined by the means for measuring the pressure after a predetermined time has elapsed since the predetermined test differential pressure was established. Includes, The method is such that the test volume section is selected such that a pressure increase of 100 mbar or more of the gas in the test volume section is obtained within 10 minutes when a filter media having a bubble point corresponding to a predetermined bubble point is tested.

2. The method according to claim 1, wherein the test volume section is limited to a volume such that when a filter media having a predetermined bubble point is tested, a pressure increase of the gas in the test volume section of 0.1 to 0.8 or 0.2 to 0.6 times the predetermined test differential pressure is obtained within 10 minutes.

3. The method according to claim 1 or claim 2, wherein the test gas is an inert gas, nitrogen, or air.

4. The method according to any one of claims 1 to 3, wherein the porous filter media is provided in the form of one or more filter elements, or in the form of one or more filter elements that are in the form of a porous membrane filter media, and the porous membrane filter media is a pleated membrane filter media or a hollow fiber membrane filter media.

5. The method according to any one of claims 1 to 4, wherein the filtration system comprises one or more additional housings, each of which has an interior and incorporates a porous filter medium, each interior being separated by the respective porous filter medium into an upstream portion on the upstream side of the filter medium and a downstream portion on the downstream side of the filter medium, and each housing has an outlet in its downstream portion, or has an outlet in its downstream portion and has a valve connected to the outlet in the downstream portion.

6. The method according to any one of claims 1 to 5, wherein the housing forms part of an industrial filtration system or forms part of an industrial filtration system for filtering liquids in the fields of food and beverages, or chemicals, or pharmaceuticals and biotechnology.

7. An assembly for testing the integrity of a porous filter media, wherein the assembly is One or more housings, each of which has an interior separated into an upstream portion and a downstream portion, and each of the one or more housings further comprises an inlet that is fluidly connected to the upstream portion of the interior, and an outlet that is fluidly connected to the downstream portion of the interior, A porous filter medium, wherein the porous filter medium separates the interior of a housing into an upstream portion on the upstream side of the porous filter medium and a downstream portion on the downstream side of the porous filter medium, the filter medium is provided in the form of one or more filter elements, and the porous filter medium has predetermined bubble points, A gas-filled test volume section, which can be fluidly connected to the downstream portion of one or more housings, Means for measuring the pressure of the gas in the test volume section, A filtrate conduit providing a flow path extending from the outlet inside one or more housings to the test volume section, wherein the filtrate conduit has a closable end located away from the outlet, A pressure source suitable for raising the pressure of a test gas in the upstream portion of one or more housings to a pressure level corresponding to a predetermined test differential pressure, and for maintaining the pressure of the test gas at the said pressure level, wherein the predetermined test differential pressure is lower than the predetermined bubble point of the porous filter media, and An assembly comprising:

8. The assembly according to claim 7, wherein the assembly forms part of an industrial filtration system, or forms part of an industrial filtration system for filtering liquids in the fields of food and beverages, or chemicals, or pharmaceuticals and biotechnology.

9. The assembly according to claim 7 or 8, comprising two or more housings incorporating a porous filter medium, each housing having a valve connected to the outlet of the downstream portion.

10. The assembly according to any one of claims 7 to 9, wherein the filter element is in the form of a filter candle, and / or the porous filter media is a pleated filter media, and / or a membrane filter media, or a hollow fiber membrane filter media.

11. The assembly according to any one of claims 7 to 10, wherein the housing or the assembly comprises an inlet valve for fluid connection between the upstream portion of the housing and a pressurized test gas source.

12. The assembly according to any one of claims 7 to 11, further comprising a valve for fluid connection and fluid disconnection between the test volume section and the downstream portion of the housing.

13. The assembly according to any one of claims 7 to 12, wherein the test volume section is provided with an outlet for fluid connection between the test volume section and the environment.

14. The assembly according to any one of claims 7 to 13, wherein each housing comprises a separate inlet and valve for supplying a test gas to the upstream portion inside the housing.

15. The assembly according to any one of claims 7 to 14, wherein the test volume section is provided in the portion of the filtrate conduit, the portion of the filtrate conduit is separated by an upstream valve and a downstream valve that define the test volume section between them, and is provided with an outlet.

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