Test probe for a filter

A test probe for filter leakage detection. The test probe (1) has an elongated housing (5) with a longitudinal inlet portion for admitting gas into a first chamber of the housing through an inlet of the inlet portion, and an outlet portion for letting gas out of a second chamber of the housing through an outlet of the outlet portion. Further, the test probe has an intermediate element comprising a throttling portion. The intermediate element is arranged between the inlet portion and the outlet portion, wherein the first and second chambers are fluidly interconnected via the throttling portion, wherein the throttling portion is elongated and extends longitudinally of the housing, wherein the throttling portion is arranged to cause a smaller vacuum upstream of the throttling portion than downstream of the throttling portion when gas is sucked through the test probe.

FIELD OF THE INVENTION

The present invention relates to test probe for detecting leakage of a filter.

BACKGROUND OF THE INVENTION

In some environments where undesired substances are removed from a gas, such as air, by filtering the gas, it is important to continuously check that the filter is working and detect any leakage of the filter. One way of checking the filter is to use a test probe, by means of which gas is collected downstream of the filter and analyzed with respect to the undesired substance. Since it is desirable that the test probe does not noticeable interfere with the gas flow it cannot cover the whole area. Different concepts of test probes which are moved to scan the filter area have been developed. One kind thereof is an elongated test probe, which extends along the length or width of the filter and is moved back and forth perpendicularly of its longitudinal extension to scan the area in the vicinity of the filter surface. A typical elongated test probe is made of a tube with several inlet holes through the tube wall distributed along the length of the test probe, and a central outlet. However, this kind of test probe is subjected to problems with a nonlinear intake of air through the inlet holes, wherein the gas flow velocity through an inlet hole depends on the distance from inlet hole to the outlet, and thus differs along the length of the test probe. This in turn causes a lower sensitivity to leakage at the edges of the filter compared to a more centrally positioned leakage.

U.S. Pat. No. 7,658,787 discloses a test probe having several inlet openings, called sample ports, each being funnel shaped towards a respective outlet tube. The sample ports are arranged side by side along the probe. This probe design partly solves the problem, but at the prize of a large number of tubes. An alternative solution would therefore be desirable.

SUMMARY OF THE INVENTION

It would be advantageous to provide a solution which requires a less number of and/or has an even more linear air intake.

To better address this concern, in a first aspect of the invention there is presented a test probe for filter leakage detection in gas filtration, the test probe comprising:an elongated housing having a longitudinal inlet portion for admitting gas into a first chamber of the housing through an inlet of the inlet portion, and an outlet portion for letting gas out of a second chamber of the housing through an outlet of the outlet portion; andan intermediate element comprising a throttling portion.
The intermediate element is arranged between the inlet portion and the outlet portion. The first and second chambers are fluidly interconnected via the throttling portion, which is elongated and extends longitudinally of the housing. In an operative state where gas is sucked out of the outlet, the throttling portion is arranged to cause a lower vacuum upstream of the throttling portion than downstream of the throttling portion. Thereby the test probe has a more equal gas flow velocity through different parts of the inlet portion than a test probe lacking the throttling portion.

In accordance with an embodiment of the test probe, in the operative state, a mean gas flow velocity through the throttling portion is higher than a mean gas flow velocity through the inlet portion. Thereby a larger pressure drop is generated past the throttling portion than past the inlet portion, which forces the airflow distribution to even out along the throttling portion. In accordance with an embodiment of the test probe, a total open area of the throttling portion is smaller than a total open area of the inlet portion. This embodiment has the same advantage as the just mentioned embodiment. In accordance with an embodiment of the test probe, the total open area of the throttling portion is 1-80% of the total area of inlet portion.

In accordance with an embodiment of the test probe, the total open area of the throttling portion is provided by several holes distributed along the length of the throttling portion. The holes provide for fine tuning of the throttling effect along the length of the throttling portion.

In accordance with an embodiment of the test probe, the housing comprises an elongated front element and an elongated rear element, extending longitudinally of the housing and defining an interior space of the housing, which interior space is divided into the first and second chambers by the throttling portion, which extends between the front and rear elements through the interior space. This embodiment provides for a simple yet functional construction of the test probe.

In accordance with an embodiment of the test probe, the inlet portion comprises a front element first edge portion of the front element and a rear element first edge portion of the rear element, arranged adjacent and parallel to each other and in engagement with longitudinally spaced distance portions arranged between the front element first edge portion and the rear element first edge portion, wherein the spaces between the distance portions constitute openings into the first chamber.

In accordance with an embodiment of the test probe, the distance portions comprise protrusions of a comb shaped intermediate element first edge portion of the intermediate element.

In accordance with an embodiment of the test probe, the distance portions comprise at least one of dimples or washers.

In accordance with an embodiment of the test probe, the inlet comprises a longitudinal array of openings. This is advantageous in that the positions and shapes of the openings can be optimized to provide the desired performance of the test probe.

In accordance with an embodiment of the test probe, the front element comprises a front element second edge portion, wherein the rear element comprises a rear element second edge portion, wherein the intermediate element comprises a intermediate element second edge portion, wherein the front element second edge portion, rear element second edge portion and intermediate element second edge portion are engaged with each other, with the intermediate element second edge portion positioned between the other ones, wherein the front element further comprises a front wall extending between the front element first and second edge portions, wherein the rear element comprises a rear wall extending between the rear element first and second edge portions, wherein the intermediate element comprises an intermediate wall extending between the intermediate element first and second edge portions, which intermediate wall comprises a middle wall portion extending between the front wall and the rear wall and comprising the throttling portion.

In accordance with an embodiment of the test probe, the front wall and the rear wall are bent to form a rhombic transversal cross-section of the housing.

In accordance with an embodiment of the test probe, the intermediate wall is bent to have a stepped shape.

In accordance with an embodiment of the test probe, the throttling portion comprises a mesh.

In accordance with an embodiment of the test probe, the throttling portion comprises a porous material.

In accordance with an embodiment of the test probe, the throttling portion comprises a longitudinal array of holes. This is advantageous in that the positions and shapes of the holes can be optimized to provide the desired performance of the test probe.

In accordance with an embodiment of the test probe, comprising partitioning walls arranged transversally of the housing through the chambers dividing them into sub-chambers, wherein the outlet portion comprises an outlet at each sub-chamber.

In accordance with an embodiment of the test probe, comprising a third chamber between the first and second chambers, and an additional throttling portion extending in parallel with the throttling portion of the intermediate element and between the inlet portion and the intermediate portion, and which, in the operative state, is arranged to cause a smaller vacuum in upstream of the additional throttling portion than downstream of the additional throttling portion.

DESCRIPTION OF EMBODIMENTS

An exemplifying use of a test probe1according to the present invention is for testing a filter2mounted in a duct3, through which a gas flows. At the downstream side of the filter2, it has a surface with a significant extension in two dimensions. The test probe1is elongated, and is attached at its ends to guides4mounted at opposite ends of the filter2. The test probe1is mounted in the vicinity of the surface of the filter2, and is arranged to be driven back and forth along the guides4in order to scan the filter2to check for leakages. Gas is sucked into the housing5of the test probe1, and further through a tube6to an analyzer, such as a photometer or a particle counter, etc. depending on what undesired substance the filter is meant to remove, or what measurement technology is preferred by the user of the test probe.

More particularly, according to a first embodiment of the test probe the elongated housing5comprises a longitudinal inlet portion7for admitting gas into the housing5, and an outlet portion8for letting gas out of the housing5. Further, the housing5comprises a first chamber9, a second chamber10, and an intermediate element11comprising a throttling portion12. Gas enters the first chamber9, and thus the housing5, through an inlet13of the inlet portion7, and exits the second chamber10, and thus the housing5, through an outlet14of the outlet portion8.

The intermediate element11is arranged between the inlet portion7and the outlet portion8, and the first and second chambers9,10are fluidly interconnected via the throttling portion12, i.e. gas is able to flow from the first chamber9to the second chamber10via the throttling portion12. In this embodiment of the test probe1, the throttling portion12constitutes a partition wall which divides the housing5into the first and second chambers9,10.

The throttling portion12is elongated and extends longitudinally of the housing5, and more particularly along the full length of the housing5. The throttling portion12comprises several holes15distributed along the length of the throttling portion12, and more particularly the holes15are consecutively arranged.

The housing5comprises an elongated front element16and an elongated rear element17, extending longitudinally of the housing5and defining an interior space of the housing5, which interior space is divided into the first and second chambers9,10by the throttling portion12, which extends between the front and rear elements16,17through the interior space. At the inlet portion7the front and rear elements16,17are positioned close to each other separated only by distance portions18, which define the inlet13as several elongated openings19consecutively arranged along the length of the inlet portion7. The longitudinal extension of the distance portions18is small relative to the longitudinal extension of the openings19such that the total extension of the inlet13constitutes a substantial part of the length of the inlet portion7. Preferably, but not necessarily, there is a hole15opposite to each distance portion18, and at least one hole15opposite to each opening19.

More particularly, the inlet portion7is defined by a front element first edge portion20of the front element16and a rear element first edge portion21of the rear element17, arranged adjacent and parallel to each other and in engagement with the longitudinally spaced distance portions18arranged between the front element first edge portion20and the rear element first edge portion21. The spaces between the distance portions18constitute the openings19into the first chamber9. Typically, the first edge portions20,21are straight and parallel with each other, forming slit shaped openings19. Thus, the inlet13can be regarded as linear, as opposed to the prior art test probe having a set of circular holes, allowing for placing the test probe1closer to the filter surface, which, in turn, increases the sensitivity of the test probe1by reducing the dilution of the gas and possible content of particles exiting a leakage of the filter before being captured by the test probe1.

In this first embodiment, the intermediate element11has a comb shaped intermediate element first edge portion22comprising several protrusions, i.e. comb teeth,23, which protrude in between the front element first edge portion20and the rear element first edge portion21and define the distance portions18. In alternative embodiments the distance portions are for example dimples or washers, as will be elaborated below.

Furthermore, the front element16comprises a front element second edge portion24, wherein the rear element17comprises a rear element second edge portion25, wherein the intermediate element11comprises a intermediate element second edge portion26, wherein the front element second edge portion24, rear element second edge portion25and intermediate element second edge portion26are engaged with each other, with the intermediate element second edge portion26positioned between the other ones. The front element16further comprises a front wall27extending between the front element first and second edge portions20,24, the rear element17comprises a rear wall28extending between the rear element first and second edge portions21,25, and the intermediate element11comprises an intermediate wall29extending between the intermediate element first and second edge portions22,26, which intermediate wall29comprises a middle wall portion30extending between the front wall27and the rear wall28and comprising the throttling portion12.

The front wall27and the rear wall28are bent to form a rhombic transversal cross-section of the housing5, which is an advantageous shape. The intermediate wall29is bent to have a stepped shape, wherein the intermediate wall29has a first intermediate wall portion31extending adjacent to a part of the rear wall28, and extending perpendicular to the middle wall portion30between the middle wall portion30and the intermediate element first edge portion22, and a second intermediate wall portion32extending adjacent to a part of the front wall27and in parallel with the first intermediate wall portion31, and extending perpendicular to the middle wall portion30between the middle wall portion30and the intermediate element second edge portion26.

In an operative state, i.e. when the test probe1is arranged at a filter and used for checking the filter for leakages, gas is remotely actively sucked through a tube33connected with the outlet14. Consequently the gas, which has passed through the filter2, is sucked in through the inlet13, through the holes15of the throttling portion12, and out of the outlet14. Thus vacuum, i.e. an under pressure, is caused within the housing5. The throttling portion12is arranged to, in this operative state, cause a smaller vacuum upstream of the throttling portion, i.e. in the first chamber9, than downstream of the throttling portion12, i.e. in the second chamber10. Due to this pressure relation, the gas that enters the first chamber through the openings19passes the openings19at a relatively similar gas flow velocity for all openings along the whole length of the housing5. Thereby a leakage is equally detectable independently of where in the filter it occurs.

The mechanisms causing this are as follows. If the derivative δΔp/δv is large, the forces on a small air package towards an area with lower speed is large. This means that a large δΔp/δv will force more air to choose the path that otherwise would have low velocity. Since the pressure drop in a high Reynolds number Re flow, where inertial effects are dominant, past an obstacle is proportional to v2, δΔp/δv is proportional to v. Consequently, by reducing the open area at the throttling portion12, and thereby increasing v locally, that derivative is increased. At the same time, the forces required to change the direction of the air, which are also inertial, can affect the air flow in the lower speed region upstream of the throttling portion12.

Preferably, the total open area of the throttling portion, i.e. the total area of the holes15is smaller than the total open area of the inlet portion7, i.e. the total area of the openings19. An advantageous relation between the total open areas is that the total open area of the throttling portion is 1-80% of the total area of the inlet portion7. A more preferred relation is 10-60%, and a most preferred relation is 20-40%. It should be noted that if the percentage is too low the required suction effort becomes too high, while if the percentage is too high the desired effect of evening out the airflow distribution along the throttling portion12becomes too low.

According to a second embodiment of the test probe, the throttling portion41of the intermediate element40comprises a mesh42as a substitute for the holes15of the first embodiment, as illustrated inFIG. 5.

According to a third embodiment of the test probe, the throttling portion46of the intermediate element45comprises a porous material, such as a filter medium47, as illustrated inFIG. 6. The filter medium47is chosen such that it lets any particles to be detected pass, but still limits the gas flow.

According to a fourth embodiment of the test probe, the holes52,53of the throttling portion51of the intermediate portion50have different dimensions, such that a hole52arranged opposite to a distance portion54is larger than a hole53arranged opposite to an opening at the inlet, i.e. between the distance portions54, as illustrated inFIG. 7. This is to compensate for the slight hindrance that the distance portions54cause.

According to a fifth embodiment of the test probe59, it comprises partitioning walls60,61arranged transversally of the housing62through the first and second chambers dividing them into sub-chambers63,64, wherein the outlet portion comprises an outlet at each sub-chamber63,64, as shown inFIG. 8. A respective tube65,66is connected with each outlet port. These partitioning walls60,61and sub-chambers63,64can be provided either as individual partitioning walls60,61inserted into the same housing62or as several individual housings, which are attached to each other side by side. In this embodiment, each partitioning wall60,61extends transversally of the test probe59between the front and rear elements67,68, and the intermediate element69is divided into sections70,71. Thus, each section70extends between two adjacent partitioning walls60,61.

According to a sixth embodiment of the test probe75it comprises a third chamber76between the first and second chambers77,78, and an additional throttling portion79extending in parallel with the throttling portion80of the intermediate element81and between the inlet portion82and the throttling portion80of the intermediate element81, as illustrated inFIG. 9. In the operative state, i.e. when the test probe75is in use, the additional throttling portion79is arranged to cause a smaller vacuum upstream of the additional throttling portion79than downstream of the additional throttling portion79. As is understood by the person skilled in the art, alternatively, the additional throttling portion79can be provided between the throttling portion of the intermediate element81and the outlet portion83. This double throttling portion embodiment can be provided to have a lower total pressure drop over the whole test probe than the embodiments having a single throttling portion while achieving the same equalization of the gas flow velocity.

According to a seventh embodiment of the test probe85, as illustrated inFIG. 10, the protrusions86of the intermediate element87separating the front element88from the rear element89at the inlet portion90can be regarded as washers. Each protrusion86is provided with a boring close to its free end, and the front and rear elements88,89are provided with borings aligned with the boring of the protrusion. A fastening element, such as a rivet,91extends through the borings and clamp the elements87,88,89together.

According to an eighth embodiment of the test probe95, a short segment of which is shown in the exploded view ofFIG. 11, dimples96are instead arranged as distance elements for providing the opening of the inlet portion. In this eighth embodiment the intermediate element97is attached to the rear element98below the inlet portion100, and thus it does not reach in between the front element99and the rear element98at the inlet portion100. The dimples are formed in the rear element98at the inlet portion100, but they can be formed in the front element99instead of or in addition to the dimples of the rear element98. The front and rear elements99,98are interconnected by means of rivets101or some other suitable fastening element.

The seventh and eighth embodiments can be provided with any one of the different kinds of throttling portions described above. Furthermore, it would be understood by the person skilled in the art what features of the different embodiments can be combined although not explicitly written above.