Deformed valve for use in flow paths

Abstract

The present invention relates to a modified umbrella valve and a system for controlling flow in a flow path that includes the modified umbrella valve. The modified umbrella valve has a solid shaft, a first end, and a second end. A flexible umbrella is located at the first end of the shaft. A stop element having an enlarged diameter relative to the diameter of the shaft is located at the second end of the shaft.

Description

[Technical Field]

[0001] The present invention relates to a valve for a breath-controlled inhaler for pulmonary inhalation. [Background technology]

[0002] Inhalers that allow patients to inhale aerosols are needed for numerous medical applications, such as inhalation therapy for asthma, cystic fibrosis (CF), and various other respiratory diseases. Aerosols are dispersions of small solid particles or liquid droplets in a continuous gas phase. Medical inhalation therapy typically requires an aerosol of fine droplets of a liquid formulation of a bioactive ingredient or drug that ideally reaches even the smallest branches of the peripheral lung, such as the bronchioles and alveoli.

[0003] To achieve the desired homogeneous distribution of droplets in the gas phase, the liquid formulation is atomized in the inhaler by a nebulizer, for example an ultrasonic nebulizer, a nozzle nebulizer, or a membrane nebulizer.

[0004] Components of currently available nebulizers include, for example, a reservoir for liquid or solid particles, an aerosol generator, a mixing chamber, a mouthpiece, and an air passage between the air inlet and the mouthpiece. Depending on the design of the inhaler, additional components may be present, for example to control the air flow.

[0005] Various inhalers are known from the prior art: International Publication No. 2006 / 083014, U.S. Patent No. 11,534,559, U.S. Patent No. 11,458,264, U.S. Patent Application Publication No. 2021 / 0252236, U.S. Patent Application Publication No. 2022 / 0126036, and International Publication No. 2013 / 132056.

[0006] In these breath-controlled inhalers, the patient generates an airflow within the inhaler when inhaling through the mouthpiece. The airflow mixes with the aerosol generated by the aerosol generator, and the air-aerosol mixture is transported to the mouthpiece through an air channel. In some inhalers, the patient removes the inhaler's mouthpiece when exhaling and then reapplies the mouthpiece for inhalation. However, patients frequently exhale into the mouthpiece and thus into the air passages within the inhaler. As a result, breathing air can reach the interior of the inhaler, potentially causing damage through moisture over the long term or, in the case of powder inhalers, wetting and swirling the powder.

[0007] Therefore, many known inhalers have an exhalation valve that prevents exhaled air from reaching the interior of the inhaler, particularly the liquid or powder reservoir as well as the control electronics, through the mouthpiece and allows the user to exhale into the mouthpiece. Exhalation valves used are, for example, duckbill or flapper valves, as described in U.S. Patent Application Publication Nos. 2022 / 0126036, 2021 / 0252236, and U.S. Patent No. 11,458,264. During inhalation, these valves open when airflow is generated from the air inlet to the mouthpiece, and during exhalation, the exhalation valve closes when airflow is generated from the mouthpiece toward the interior of the inhaler. Exhalation valves can also be used to divert gas flow to the surroundings (environment) during exhalation.

[0008] US Pat. No. 11,534,559 discloses an umbrella valve as a breath-controlled air inlet valve that opens in the event of negative pressure in the air inlet chamber of the inhaler.

[0009] The valve present in the air passage is an obstruction in the air channel, and therefore affects the airflow during inhalation. Therefore, the valve should be designed to affect the airflow as little as possible during inhalation and optimally block the air passage during exhalation.

[0010] The modified umbrella valve according to the present invention particularly meets this requirement. Furthermore, the present invention resides in a system for controlling flow in a flow path comprising a modified umbrella valve. By way of example, a breath-controlled inhaler comprising a modified umbrella valve and the use of the modified umbrella valve in the air channel of the inhaler are described herein. It is understood that the modified umbrella valve and the system for controlling flow in a flow path are not necessarily associated with air and for use in an air channel, but may very well be used with other gases and in gas flow channels in general. Therefore, the terms "air channel" or "air passage" or "air flow" should also be understood in the broader sense of "gas channel" or "gas passage" or "gas flow," as the case may be, unless specifically used in connection with a breath-controlled inhaler, as explained below.

[0011] The modified umbrella valve is a check valve. The modified umbrella valve includes a solid shaft having a first end and a second end. A flexible umbrella is located at the first end of the shaft. A stop element having an enlarged diameter relative to the diameter of the shaft is located at the second end of the shaft.

[0012] During use, the modified umbrella valve is attached to the central hole of the perforated plate, which is positioned in the air channel. The perforated plate can have different thicknesses, porosities, and diameters. The diameter of the flexible umbrella substantially corresponds to the diameter of the air channel or is slightly larger to provide radial sealing. The diameter of the stop element must be larger than the diameter of the central hole of the perforated plate into which it is inserted. The stop element can be angled to facilitate insertion. This is the only way the stop element can hold the second end of the shaft upstream of the perforated plate. At the same time, the stop element should not be so large that it affects the air flow through the air channel; for example, it should cover as few of the perforations in the perforated plate as possible.

[0013] When airflow in the air channel strikes the outside of the umbrella valve (positive pressure), the umbrella is pressed against the perforated plate, closing the perforations in the perforated plate in the axial direction. Additionally, the slightly larger outer diameter of the umbrella valve compared to the inner diameter of the air channel creates an additional seal. In contrast, when negative pressure is generated outside the umbrella, the umbrella is lifted from the perforated plate and folded in the opposite direction to the perforated plate. At the same time, the effective diameter of the umbrella decreases, freeing up part of the diameter of the air channel for airflow through the perforated plate. The first end of the shaft moves away from the perforated plate, depending on the shaft length, until further movement is stopped by a stop element.

[0014] The shaft length should be selected so that the folded umbrella is as far away from the perforated plate as possible to minimize airflow through the perforated plate. The shaft and stop mechanism hold the umbrella portion of the valve in place relative to the perforated plate. On the other hand, if the folded umbrella is too far from the perforated plate, the umbrella may tilt when the negative pressure is reduced and not return correctly to its seat on the perforated plate. Therefore, the shaft length should preferably be in the range of 20% to 50% of the umbrella diameter, with 30% to 40% being particularly preferred. This allows for linear movement of the umbrella valve and improves airflow during inhalation. With larger diameters, this ratio of shaft to umbrella diameter can be further increased or decreased based on the application and the inhalation and exhalation forces the umbrella valve is subjected to.

[0015] In one embodiment in which the umbrella diameter is in the range of 9.5 mm to 10.5 mm, the shaft is at least 2 mm, preferably at least 2.5 mm, particularly preferably at least 3 mm long. In said embodiment, the shaft is at most 5 mm, preferably at most 4 mm long. Particularly preferred, the shaft in said embodiment is in the range of 3 mm to 4 mm long.

[0016] The umbrella of the umbrella valve is preferably made of silicone or a similar flexible material with sealing properties, such as thermoplastic elastomer (TPE) or thermoplastic urethane (TPU). The shaft can be made of the same material, or a rigid plastic such as PEEK (polyether ether ketone) or PC (polycarbonate), or metal. The stop element can be integrally formed with the shaft, made of the same material as the umbrella, or attached to the second end of the shaft and made of a different material. The stop element prevents the second end of the shaft from sliding through the hole in the perforated plate. The umbrella can also be integrally formed with the shaft, for example, by multi-component injection molding with a form-fit connection or inter-material bonding, or as a separate component that is attached to the shaft after the shaft is fitted into the guide in the perforated plate. The number of individual components that make up the modified umbrella valve depends on how the modified umbrella valve is fitted.

[0017] A system for controlling flow in a flow channel according to the present invention comprises: an air channel; a perforated plate located in the air channel and having a central hole; a modified umbrella valve as described above mounted in the central hole of a perforated plate; Equipped with.

[0018] In one embodiment, the diameter of the flexible umbrella of the modified umbrella valve corresponds to the diameter of the air channel.

[0019] In one embodiment, the diameter of the stop element is larger than the diameter of the central hole of the perforated plate into which it is inserted.

[0020] In one embodiment, the length of the shaft is 1.2 to 5 times the thickness of the perforated plate, preferably 2 to 4 times the thickness of the perforated plate, and most preferably 2 to 3 times the thickness of the perforated plate.

[0021] Exemplary breath-controlled inhalers include: An air inlet; a mouthpiece having a mouthpiece opening; an air channel between the air inlet and the mouthpiece opening, the air channel comprising a mixing chamber; a reservoir for liquid or solid particles; an aerosol generator connected to the reservoir for converting liquid or solid particles from the reservoir into an aerosol and introducing the aerosol into the mixing chamber; A modified umbrella valve between the air inlet and the mixing chamber; Equipped with.

[0022] In one embodiment, the modified umbrella valve is mounted in the central hole of a perforated plate. The perforated plate is located in the air channel between the air inlet and the mixing chamber. The perforated plate can also function as an air filter to retain particles or moisture and can be equipped with an appropriate mesh. The plate typically has a thickness of 0.3 mm to 3 mm.

[0023] The breath-controlled inhaler preferably includes an air inlet valve between the modified umbrella valve and the air inlet, the air inlet valve being controlled via a pressure sensor that opens the air inlet when a certain negative pressure is present in the mouthpiece.

[0024] The aerosol generator is preferably an electromechanical aerosol generator with a vibrating membrane that seals the reservoir towards the mixing chamber. As a result of the vibration, an aerosol is generated (membrane nebulizer), which mixes with the air flow in the air channel.

[0025] In one embodiment, a breath-controlled inhaler according to the present invention comprises a head, a base, and a mouthpiece. The head comprises a reservoir and an aerosol generator, and the base comprises an air inlet and a first section of an air channel. The base may further comprise an air inlet valve, electronics for operation of the aerosol generator, and a pressure sensor. The mouthpiece comprises a mouthpiece opening, a second section of the air channel having a mixing chamber, and a modified umbrella valve at the beginning of the second section of the air channel.

[0026] The location of the modified umbrella valve at the entrance to the second section of the air channel prevents the possible intrusion of exhaled air from the mouthpiece, which opens directly into the first section of the air channel in the base, and prevents moisture damage to the electronics present there. This can occur when a user accidentally exhales into the device. Even with the presence of a gasket, leaks can occur due to the complexity of the sealing interfaces between components and tolerance differences between them. This prevents proper alignment and application of force to the elastomeric gasket necessary to ensure a leak-tight seal. Moisture can also originate from the environment, for example, if the inhaler is used in a warm room with high air humidity after being shipped at a low temperature. Damage to the electronics in the base is particularly important because the base is intended to be reusable and, while the mouthpiece and head are replaced periodically, the base is intended to remain suitable for relatively long periods of use. Additionally, the location of the modified umbrella valve between the air inlet and the mixing chamber prevents the aerosol-laden airflow en route to the mouthpiece opening from being affected.

[0027] In the mouthpiece, the patient generates an airflow into which the aerosol generated by the vibrating membrane flows. Through the mouthpiece opening, the patient inhales a mixture of aerosol and air. The required air is drawn through the air inlet opening into the air channel in the base, from where it reaches the air channel in the mouthpiece.

[0028] Exemplary embodiments of the invention are illustrated in the figures and are described in more detail below. [Brief explanation of the drawings]

[0029] [Figure 1a] FIG. 1 shows an umbrella valve from the prior art in a closed position. [Figure 1b] FIG. 1 shows an umbrella valve from the prior art in an open position. [Figure 2] 1A and 1B show an umbrella valve with a short shaft and with a long shaft. [Figure 3a] FIG. 1 shows a modified umbrella valve in an idle state in a first variant of the air channel of the inhaler. [Figure 3b] FIG. 10 shows a modified umbrella valve during inhalation in a first variant of the air channel of the inhaler. [Figure 3c] FIG. 10 shows a modified umbrella valve during exhalation in a first variant of the air channel of the inhaler. [Figure 4a] FIG. 10 shows a modified umbrella valve in an idle state in a second variant of the air channel of the inhaler. [Figure 4b] FIG. 10 shows a modified umbrella valve during inhalation in a second variant of the air channel of the inhaler. [Figure 4c] FIG. 10 shows a modified umbrella valve during exhalation in a second variant of the air channel of the inhaler. [Figure 5] 1 is an exploded view of an inhaler from the prior art; FIG. [Figure 6] 1 is a longitudinal section of an inhaler from the prior art; FIG. [Figure 7] FIG. 1 shows the measurement results for moisture in an inhaler from the prior art that does not have an exhalation valve. [Figure 8] FIG. 1 shows the results of measurements on moisture in an inhaler from the prior art with a modified umbrella valve. [Explanation of symbols]

[0030] 10 Umbrella valve from the prior art 12 Shaft end from the prior art, umbrella valve 14 Shaft, umbrella valve from the prior art 15 Hooks and umbrella valves from the prior art 16 Umbrellas and umbrella valves from the prior art 18 Perforated plate 19 Perforation 20 Transformed Umbrella Valve 23 Stopping Elements 24 shaft 26 Umbrella 28 Central hole 29 Perforated or filter plate 100 base units 101 air inlet opening 102 air outlet opening 103 Groove 104 Key Lock Elements 110 Air Channel 118 Air inlet valve 119 Pressure Sensor 200 mouthpieces 200a First segment of mouthpiece 200b Second segment of mouthpiece 201 Air intake opening 202 Horizontal opening 203 Mouthpiece opening 206 Steps 207 Air Channel 208 Mixing Chamber 300 Aerosol Head 301 Aerosol Generator 302 Reservoir 303 Key Lock Element 304 Lid 309 mesh DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1a shows a prior art umbrella valve 10 in the closed position. The shaft 14 is located in the central hole of a perforated plate 18, where it is secured to one side of the perforated plate 18 by an umbrella 16 and to the other side by a hook 15. The hook 15 is an extension of the shaft 14. The shaft end 12 is spaced from the umbrella 16, allowing the shaft 14 of the umbrella valve 10 to be pulled through the central hole of the perforated plate 18 when engaged. In the closed position, the umbrella 16 of the umbrella valve 10 closes the perforations 19 in the perforated plate 18. The umbrella valve 10 is in the closed position when a medium (gas or liquid) exerts pressure on the outside of the umbrella 16 (arrow A). At a certain pressure of the medium, the umbrella 16 folds in the opposite direction (arrow B) through the perforations 19 in the perforated plate 18 and toward the bottom side of the umbrella 16. The outer region of the umbrella 16 lifts away from the perforations 19 so that the medium (air or liquid) can flow through the perforations 19 (FIG. 1b, arrow C).

[0032] Figure 2 shows umbrella valves with both long and short shafts. When mated, they are not pulled through the central hole in the perforated plate, but are pushed to one side until the hook engages. The shaft functions as a mating aid and as a support due to the undercut. The shaft has little axial mobility purely for mating purposes. In the prior art, the shaft does not perform the function of axial sliding under negative / positive pressure in the air channel due to better clearance of the flow cross section.

[0033] Figures 3a and 4a show a modified umbrella valve 20 in an idle state as part of a system for controlling flow in a flow path that may be present in, for example, an inhaler 400 (Figures 5 and 6). The two variations of the air channel 207 in Figures 3a-3c and 4a-4c differ in that the air channel 207 in Figures 3a-3c has a constant diameter, while the air channel in Figures 4a-4c has a step, causing the air channel to widen between the perforated or filter plate 29 and the mixing chamber 208.

[0034] The modified umbrella valve 20 comprises a shaft 24 and an umbrella 26 at its first end. The modified umbrella valve 20 differs from the known umbrella valve 10 in that the stop element 23 is located at the second end of the shaft 24. Furthermore, there is no hook 15, as in the prior art umbrella valve 10, that secures the shaft 24 in a fixed position to the perforated or filter plate 29. In the idle state, the umbrella 26, as a result of its natural tension, is arched toward the shaft 24 and is located in an undefined position within the air channel 207 at a maximum distance from the perforated or filter plate 29 limited by the stop element 23. In Figures 3a and 4a, the umbrella of the modified umbrella valve in the idle state is located directly above the perforated or filter plate 29. The shaft 24 is attached to the central hole 28 of the perforated or filter plate.

[0035] 3b and 4b show the situation when an airflow is generated through the perforated or filter plate 29 in the direction of arrow D. The air flows through the perforated or filter plate 29 and, in doing so, lifts the umbrella 26 of the umbrella valve 20. The airflow causes the umbrella 26 to detach from the perforated or filter plate 29 as far as permitted by the stop element at the second end of the shaft 24. The umbrella 26 of the umbrella valve 20 is then folded away from the shaft 24 in the direction of the airflow D. Now, the air flows relatively unimpeded further down the flow path, for example, into the mixing chamber 208, where the airflow mixes with the aerosol from the lateral opening 202 connected to the aerosol generator 301. The air-aerosol mixture then flows further in the direction of the inhaler mouthpiece opening 203 (arrow E).

[0036] When an air flow is generated in the opposite direction (Figures 3c / 4c, arrow F), the umbrella 26 is pressed against the perforated or filter plate 29. At the same time, the umbrella 26 closes the perforations in the perforated or filter plate 29 in the axial direction and the air flow stops. An additional sealing effect can be generated in the radial direction by the umbrella valve being slightly oversized relative to the inner diameter of the air channel.

[0037] Figure 5 shows an exploded view of an inhaler 400 from the prior art (EP 2724741) which has been improved by fitting a modified umbrella valve 20 in place, and Figure 6 shows a longitudinal cross section of the inhaler 400. The inhaler 400 comprises a base unit 100, a mouthpiece 200 and an aerosol head 300.

[0038] The base unit 100 comprises one or more air inlet openings 101, an air outlet opening 102, a groove 103 for accommodating the mouthpiece 200, and one or more key locking elements 104. The air inlet openings 101 and the air outlet openings 102 are connected inside the base unit 100 to form an air channel 110. Under operating conditions, during a user's inhalation phase, air flows from the upstream end to the downstream end of the air channel 110, i.e., from the air inlet openings 101 to the air outlet openings 102.

[0039] The pressure sensor 119 measures the negative pressure of inhalation and activates the aerosol generator 301 from a certain minimum pressure, opening and closing the air inlet valve 118 to control the airflow. The pressure sensor 119 is in contact with the air passageway as an orthogonal bypass to the main gas flow of the airflow in the air channel 110.

[0040] The mouthpiece 200 comprises a first segment 200a comprising an air intake opening 201 attachable to the air outlet opening 102 of the base unit 100 and a lateral opening 202 for connection to an aerosol generator 301. The air intake opening 201 is followed by an air channel 207 which widens in the region of the lateral opening to a mixing chamber 208. In the mixing chamber 208, during use, air mixes with the aerosol mixture from the aerosol head 300. The first segment 200a is insertable into the groove 103 of the base unit 100. The second segment 200b is located downstream of the first segment 200a and comprises a continuation of the air channel 207 from the first segment 200a and a mouthpiece opening 203.

[0041] The aerosol head 300 comprises an aerosol generator 301, a reservoir 302 for liquid, and one or more male or female key lock elements 303 that are complementary to the key lock elements 104 on the base unit 100. The base unit 100, mouthpiece 200, and aerosol head 300 are interconnectable.

[0042] Assembly of the base unit 100 with the mouthpiece 200 and aerosol head 300 is accomplished by inserting the first segment 200a of the mouthpiece 200 into the groove 103 of the base unit 100, then placing the aerosol head 300 on the first segment 200a of the mouthpiece 200, and applying gentle pressure to both the aerosol head and the base unit to engage the key lock element(s) 303 of the aerosol head 300 with the complementary element(s) 104 of the base unit 100. These several assembly steps are intended to create an airtight connection between the air outlet opening 102 of the base unit 100 and the air intake opening 201 of the first segment 200a of the mouthpiece, and between the aerosol generator 301 and the lateral opening 202 in the first segment 200a of the mouthpiece 200. Further, the aerosol generator 301 is positioned in the aerosol head 300 such that when the (one or more) key lock elements and the (one or more) complementary elements are engaged, the aerosol generator 301 is at least partially inserted into the lateral opening 202 of the first segment 200a of the mouthpiece 200.

[0043] Through the outlet opening 102 of the base unit 100, air flows via the air intake opening 201 of the first segment 200a of the mouthpiece 200 into the air channel 207 of the mouthpiece 200. The air outlet opening 102 is circular and may be positioned, for example, in a central region of the base unit (e.g., as shown in FIG. 5). The air outlet opening 102 may be provided with a sealing element, for example in the form of a gasket, a sealing lip, or a bellows, which serves to establish an airtight connection with the air intake opening 201 of the mouthpiece 200.

[0044] The air intake opening comprises a perforated or filter plate 29 with a central hole 28, which accommodates the shaft 24 of the modified umbrella valve 20. At the same time, the umbrella 26 is located in the air channel 207 of the mouthpiece 200, and the stop element 23 is located in the region of the air outlet opening 102 of the base unit 100 (see also Figures 3a-3c / 4a-4c). The modified umbrella valve 20 prevents air flows, particularly those formed when exhaling into the mouthpiece opening, from passing through the possibly incomplete seal and across the air intake opening 201 and the air outlet opening 102 into the base unit 100.

[0045] When assembled, the base unit 100 can include one or more electrical connectors for electrically connecting with complementary connectors on the aerosol head 300. This is particularly important when the aerosol head 300 includes an ultrasonic or piezoelectric aerosol generator 301, such as an aerosol generator 301 that includes a vibrating membrane 309 (membrane nebulizer).

[0046] The power supplied to the aerosol generator can be provided, for example, by an internal or rechargeable battery housed in the base unit 100, or by an external energy source connected to the base unit 100 via a cable.

[0047] FIG. 7 shows moisture measurements in a prior art inhaler without a modified umbrella valve 20. A moisture sensor was located in the base 100 near the pressure sensor 119. The user inhaled through the mouthpiece 200 and immediately exhaled. From the graph in FIG. 6, it can be seen that the moisture sensor measured an increase in relative air humidity during the exhalation phase (time units 320 to 610 on the x-axis). From 35% relative air humidity at 23°C, the relative air humidity increased to a peak of 57%. On average, the increase in relative air humidity at the sensor during the exhalation period was approximately 10%.

[0048] FIG. 8 shows moisture measurement results for a prior art inhaler with a modified umbrella valve 20. Just as in the test without the modified umbrella valve, the user inhaled through the mouthpiece and then immediately exhaled. From the graph in FIG. 7, it can be seen that the moisture sensor measured a slight increase in relative air humidity during the exhalation phase (time units 169 to 553 on the x-axis). The increase in relative air humidity was clearly lower than without the modified umbrella valve 20. From 45% relative air humidity at 25°C, the relative air humidity increased to a peak of 54%. On average, the increase in relative air humidity at the sensor was approximately 1.4%.

Claims

1. A modified umbrella valve (20) comprising a solid shaft (24) having a first end and a second end, characterized in that a flexible umbrella (26) is located at the first end of the shaft (24) and a stop element (23) having an enlarged diameter compared to the diameter of the shaft (24) is located at the second end of the shaft (24).

2. The modified umbrella valve (20) according to claim 1, characterized in that the length of the shaft (24) is in the range of 20% to 50% of the diameter of the umbrella (26), particularly preferably in the range of 30% to 40%.

3. 2. The modified umbrella valve (20) according to claim 1, characterized in that the diameter of the umbrella (26) is in the range of 9.5 mm to 10.5 mm, and the shaft has a length of at least 2 mm, preferably at least 2.5 mm, particularly preferably at least 3 mm.

4. 2. The modified umbrella valve (20) of claim 1, wherein the diameter of the umbrella (26) is in the range of 9.5 mm to 10.5 mm, and the shaft is in the range of at least 3 mm to 4 mm in length.

5. The modified umbrella valve (20) according to any one of claims 1 to 4, characterized in that the umbrella (26) is made of a flexible material such as silicone, a thermoplastic elastomer (TPE) or a thermoplastic urethane (TPU).

6. The modified umbrella valve (20) according to any one of claims 1 to 5, characterized in that the shaft (24) is made of metal or hard plastic, preferably PEEK (Polyetheretherketone) or PC (Polycarbonate).

7. The modified umbrella valve (20) according to any one of claims 1 to 6, characterized in that the umbrella (26) is integrally formed with the shaft.

8. 1. A system for controlling flow in a flow path, comprising: a gas channel (207); a perforated plate (29) located in the gas channel (207) and having a central hole (28); a modified umbrella valve (20) mounted in the central hole (28) of the perforated plate (29); Equipped with The modified umbrella valve (20) comprises a solid shaft (24) having a first end and a second end, a flexible umbrella (26) located at the first end of the shaft (24), and a stop element (23) located at the second end of the shaft (24) having an enlarged diameter compared to the diameter of the shaft (24). system.

9. The system of claim 8, wherein the diameter of the flexible umbrella (26) corresponds to the diameter of the gas channel (207).

10. 9. The system according to claim 8, wherein the diameter of the stop element (23) is greater than the diameter of the central hole (28) of the perforated plate (29) into which it is inserted.

11. 9. The system of claim 8, wherein the length of the shaft (24) is 1.2 to 5 times the thickness of the perforated plate (29), preferably 2 to 4 times the thickness of the perforated plate (29), and most preferably 2 to 3 times the thickness of the perforated plate (29).

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