FI113407B - impactor - Google Patents

Description

1, 113407

Impaktor

The present invention relates to a device for the segregated measurement of aerosol particles according to the preamble of claim 1.

5

As environmental regulations become stricter, the need to measure different particle emissions is increasing dramatically. The need for measurement occurs, for example, in research and development of various combustion processes, such as internal combustion engines, and flue gas and exhaust gas cleaning methods. In addition, particle emissions are measured to control emissions from existing installations, etc. Further, particle emission measurements are performed e.g. vehicle type-approval, etc.

Aerosol particles as used herein refer to particles whose properties, essentially the small size and light weight of the particles, allow the particles to be transported with the flow of air or gas. The typical size of aerosol particles varies from 10 nm to 10 μηι, but depending on the conditions and process, larger or smaller particles behaving like aerosol particles may occur. Speaking of so-called. particulate matter, most often refers specifically to aerosol particles.

It is known that the health hazards of, for example, dust and exhaust gas emissions from traffic depend on the size distribution of the aerosol particles contained in said emissions. The smallest particles, when inhaled, are more easily transported deep into the lungs, sticking to the tissues, and thus more likely to remain permanently in the body than the larger particles. During the particle formation process, different particles may end up in different particle sizes, whereby different size particles can have different composition and thus different health effects due to their different toxicity.

35 It is also known that, for example, the development and research of combustion processes. in black work measuring the properties of the aerosol particles contained in the process flue gases at different points in the process provides important information about the operation and status of the process. In this respect, it is interesting to be able to measure not only the total number / mass of particles but also to determine the particle size distribution, for example, and to be able to determine, for example, the composition of particles of different sizes. This information helps to optimize the combustion process and its operating parameters 5 for better efficiency and to reduce the emissions generated by the process.

Measurements of aerosol particles capable of size separation in connection with flue gas filtration and / or purification processes provide 10 important information e.g. co. process filtration or purification capability. Particle measurements can, for example, identify error situations in which the filtration or purification capacity of the process is reduced. The particle size data obtained by the measurements can be used to select the most suitable filtration and purification method for a particular object and process.

The need for aerosol particle measurement also exists in processes other than those mentioned above, which produce mainly harmful particle emissions. For example, the pharmaceutical industry needs measurement methods for aerosol particles in its production and quality control, as does the material engineering industry producing dust or powdered materials.

As can be seen from the few examples above, there is a clear need to be able to measure aerosol particles so that, in addition to the total number or mass of particles, it is possible to obtain information on the size distribution of aerosol particles; . lyses, such as to determine the chemical composition of the particles.

Thus, to accomplish this, a device is needed which firstly separates aerosol particles from the air or gas stream on the basis of their size, and secondly collects particles of different size classes for subsequent analysis of the particle 35s.

The state of the art for this purpose is commonly known as the so-called.

a measuring device called an impactor. The impactor collects 3 112407 particles from the gas stream, classifying the particles in their so-called. aerodynamic size for different size classes. A prior art impactor is disclosed, for example, in U.S. Patent No. 4,327,594. The operation of the impactor will now be briefly described with reference to Figure 1.

5

In Figure 1, an air or gas flow 11 containing aerosol particles to be examined and measured is introduced into the front chamber 12 of the impactor 10 through the openings in the nozzle portion 4a through the openings in the nozzle portion 4a to the next chamber 4, rearwardly of the gas portion 4a. The flow direction of the gas flow 11 from the openings of the nozzle part 4a changes sharply as it meets the collecting platform 4b. Particles of sufficiently large aerodynamic particle size transported by flow 11 are unable to follow the sudden change in direction 15 of flow 11, but collide with the catch pad 4b while being caught there. Those aerosol particles having an aerodynamic particle size such that they are capable of following flow 11 circulate with said flow collecting tray 4b and pass through openings of the next nozzle part 3a to the next chamber 3.

20

The impactor shown in Figure 1 is a so-called. a cascade impactor containing a plurality of successive chambers, so-called. degrees. At each stage: 4; 3; 2; 1 has a nozzle portion 4a; 3a; 2a; 1a, and behind said nozzle portion: ·] a collecting tray 4b; 3b; 2b; 1b. This cascade impactor structure, based on successive steps of 4; 3; 2; 1 to 25, allows the collection of aerosol particles in a size-selective manner. By known means, by selecting the number of openings in each nozzle part 4a; 3a; 2a; 1a and: the size, the distance of the surface of the collecting tray 4b; 3b; 2b; 1b from the same degree nozzle part 4a; 3a; 2a, 1a and the gas volume flow through , each stage of the impactor can be 4; 3; 2; 1: · dimensioned so that each stage only accumulates aerosol particles larger than a certain particle size on the collecting medium 4b; 3b; 2b; 1b. Ts. . '. the local gas velocity when the flow 11 encounters the collection tray 4b; 3b; 2b; 1b is increased as the flow proceeds from one step * ·; · '35 4; 3; 2; 1 to another, and / or in the flow 11 is caused by: T: 4; 2; 1 steeper change in direction of flow. In this case *: ·>; until the final stage, only aerosol particles with the smallest aerodynamic size can reach. Before the gas flow 11 4 113407 leaves the impactor 10, after the final stage 1, if necessary, the gas flow can be further directed through a filter 5, into which the remaining particles contained in the gas flow are collected in the filter 5. By appropriately dimensioning the successive stages 4, 3, 2; 1 of the impactor relative to one another in a known manner, only particles of the desired size classes can be deposited at each stage.

The so-called impactor stage. the cut diameter is defined as the value of the particle diameter of the particle 10 having the diameter in question. the degree gains 50%. Particles larger than this are collected. degrees with a particle size very rapidly with increasing probability, and correspondingly smaller particles get to the next degree with the flow.

The operation of the impactor, the dimensioning of successive steps of the cascade impactor, and the more precise determination of the aerodynamic size of aerosol particles are well known to those skilled in the art and are therefore not discussed further herein.

20

The present invention relates to the design of an impactor, in particular to solutions for mounting a collecting tray 4b; 3b; 2b; 1b, which in the prior art impactors make the use of the impactors unnecessarily complicated, thereby increasing the error of operation and also reducing the accuracy and reliability of measurement results.

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Typically, a separate thin collector film 30 is provided on the impactors 4b; 3b; 2b; 1b on top of a backing plate for mechanical support or the like. Depending on the application, the collection film may be, for example, an aluminum foil or polycarbonate film. Due to the small size of aerosol particles, and especially when measuring relatively pure gases; -: The total amount and mass of aerosol particles deposited on the collection film is very small. Typically, the change in mass of the capture film due to the aerosol particles accumulating on the film 35 during the measurement is one, '··. to a few milligrams. In this case, it is important that the mass of the membrane serving as the collecting medium is minimized so that the mass of the particles collected can be determined as precisely as possible by gravimetric analysis. The accuracy of the scales used in gravimetric analysis typically allows for the detection of differences in weight of at least about 10 micrograms. 5 The use of a separate collection membrane as a collection tray 4b; 3b; 2b; 1b allows the impactor to be graded to different stages 4; 3; 2; Typically, this is done cautiously using tweezers or the like, whereby the collection membrane is not contaminated or damaged during treatment, and thus the amount of particles collected on the film during the release process is not changed. Transparencies intended for analysis and subsequent transfer and storage are adequately protected. By replacing the used collection diaphragms in the impactor with new clean diaphragms, the impactor can be quickly re-used, if necessary.

15

In order to obtain a reliable measurement result, a collecting foil serving as a collecting tray 4b; 3b; 2b; 1b, for example 0.4 mm thick and having a diameter of 50-100 mm, must be secured sufficiently firmly to flow downstream of said membrane and gas stream 3; The distance between 1a remains exactly constant. The attachment must also be sufficiently strong to prevent vibration or movement of the film caused by gas flow and / or movement of the impactor on the membrane. . release of adhered aerosol particles from the collection film. In the prior art / 25 Impactors, the attachment of the collection membranes: to the backing plates, etc., which serve as the mechanical support for the membranes, is typically done as follows.

In a commonly used manner, the collector film is pressed at its edges: 30 into a backing plate supporting it by means of a separate spacer ring. Said spacer ring may itself be supported upstream of the nozzle member, ···. wherein the distance between the collector diaphragm and said nozzle member is also determined by the height of the spacer ring. The main problem with this attachment method is that the attachment: 35 has its own separate component: the intermediate ring. Impactors are typically used for measurements in field and / or industrial conditions. The impactor is then opened by the collection membranes. for exchange in conditions that are not optimal for the job 6 113407. While lifting the aforementioned spacer ring off the collecting diaphragm, it has been found in practice that often the user accidentally drops the spacer ring onto the collecting diaphragm, and / or punctures the collecting diaphragm with the spacer itself, or the tool used to lift it. In many commercial cascade impactors with spacer rings, it is also possible to assemble the impactor incorrectly so that the spacers 4, 3, 2, 1 of the various stages rotate with each other, resulting in incorrect spacing between the collecting diaphragms and the corresponding nozzle parts. In this case, the impactor does not operate as intended, and the error can only be detected the next time the impactor is opened.

It is also known to attach a collector film to a recess 15 which is formed on a backing plate serving as a mechanical support for the collector membrane, to which, for example, a collector film made of aluminum foil is fixed by pressing a collector film with a slightly larger diameter. In this case, the collecting diaphragm remains in place in the recess due to the tight fit between the diameters mentioned above. The problem with this method of attachment is that a separate tool is needed to press the collector film 20 into place. Removing the collection film from the recess with tweezers or the like is also difficult due to tight fitting and easily leads to damage to the thin collection film and / or sample. Collector film too loosely attached. . may also spontaneously detach from the well during measurement.

25 v: The collector film can be further secured to a recess in the back plate or the like by means of a locking ring or the like, which presses the edges of the collector film.

"·: Separate fastening means for attaching to the back plate by means of threads, etc., by means of which the collector film is pressed along its edges; **; 30 to its back plate are also known. These fastening methods also require separate components and / or tools with their components. and / or I ·: "The sample collected on the collection membrane may be damaged.

v: 35 Adhesive, tacky, and / or greasy substances are typically not suitable for attaching collection membranes to a backing board or similar substrate because these substances interfere with gravimetric analysis of the collection membrane.

. Ts. when removing the collection film from its substrate, the amount of 7 113407 adhesive or other material adhered to the collection film varies randomly, whereby determining the mass of particles collected on the film by comparing the mass of the film used for measurement with a predetermined mass of the same pure film.

The main object of the present invention is to provide an impactor whose construction, and in particular the solution used to adhere the collector membrane serving as an aerosol particle collecting substrate, avoids the above problems of prior art impactors. It is therefore an object of the invention to provide a simple and easy-to-use impactor whose good operating characteristics also allow for improved reliability and accuracy of measurement results.

To accomplish this purpose, the impactor of the invention is essentially characterized in what is disclosed in the characterizing part of independent claim 1.

Other dependent claims disclose some preferred embodiments of the invention.

The invention is based on the idea that holding a separate collection film in place supports a so-called "collector film". a collection diaphragm and a collection tray are provided on top of the collection tray by means of one or more projecting press members formed in the preceding nozzle section in the flow direction of the gas flow. Ts. when assembling this stage of the impactor, it is not necessary to: · *: attach the collection diaphragm separately to its collection tray, but rather lift the corresponding nozzle part into place and collect the collection diaphragm; ···. 30, the presser members at the bottom of the nozzle member press the collecting diaphragm tightly against the collecting tray, thereby holding it tight. in place during measurement. This prevents the use of separate attachment components for the collection film attachment ::: and the work required to handle them. Correspondingly, the impactor in question. degree when opening 35 by lifting the corresponding. nozzle part removed, the collecting diaphragm is ready: to be removed from its base without further intervention. This significantly reduces the damage to the collection film and the sample collected on the film. risk compared to prior art solutions.

8 113407

In a preferred embodiment of the invention, the nozzle member is provided with press members which are spaced at intervals relative to one another on a circle having a diameter substantially equal to the diameter of a circular collection diaphragm. In this arrangement, the press members interfere as little as possible with the flow from the nozzle member towards the surface of the collection diaphragm.

In another preferred embodiment of the invention, a nozzle-10 portion is provided with a press member which is arranged to press a collection film in the middle thereof. Hereby, for example, curvature of the collection film and / or vibration caused by the flow of the collection film on the film can be effectively prevented. This is particularly important in situations where a wide area collecting membrane is used and / or the material of the collecting membrane causes a tendency for the above phenomena to occur. Said centered pressing member may be used in combination with the said outer peripheral pressing members or also as a single pressing member. The centered wrestling member is also advantageous because it does not obscure any area of the collection diaphragm from the current door 20 from the nozzle part.

In a preferred embodiment of the invention, when the impactor is a cascade impactor having successive degrees, the parts contained in the various stages are further shaped so that the impactor cannot be "assembled incorrectly". That is, the mechanical v: contact surfaces of each step are shaped to fit only v with the right component of the previous and next impactor.

Thus, the impactor of the invention contains a total of fewer parts, and particularly small parts that are difficult to handle, than the corresponding prior art impactor, thus being more advantageous to manufacture. When using an impactor, i.e. assembling and disassembling, a smaller number of parts naturally facilitates and accelerates the use of the impactor. A lower quotient also facilitates cleaning of the impactor v: 35, and the risk of unwanted contamination with parts. These aforementioned advantages of the impactor of the invention are significant, especially in applications and applications where measurements are repeatedly made. Since it is not possible to assemble the impactor 9 113407 according to the invention improperly, this method is avoided. total measurement failures due to human error.

In the impactor of the invention, the assembly film 5 is fastened / detached in a very simple manner, and the movable parts are still of such a size and shape that they can be easily grasped without the use of tools or other aids. Thus, especially when working in field conditions, the likelihood of damage or contamination of the collecting membrane itself, or of the aerosol particle sample contained therein, is significantly reduced compared to prior art impactors.

The following more detailed description of the invention further illustrates to the person skilled in the art the preferred embodiments of the invention as well as the advantages of the invention with respect to the prior art.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 illustrates a cross-sectional view of a known operating principle of the impactor, Figure 2 illustrates a cross-sectional view of a preferred embodiment of the impactor Fig. 3b shows a nozzle portion of Fig. 3a as an end view, Fig. 4a illustrates a cross-sectional view of an alternative embodiment of the nozzle part of Fig. 2, 0 ': 35 Fig. 4b illustrates a nozzle portion of Fig. 4a, end view, Fig. Figure 2 illustrates the structure of the impact tray of Figure 2, and Figure 5b shows the end of Figure 5a.

5

Figure 2 illustrates a preferred embodiment of the four-step impactor 20 of the invention. In Figure 2, the gas flow 21 is shown entering the impactor 20 from above and exiting the impactor 20 from below.

10

Impactor 20 cosmically selects aerosol particles based on their aerodynamic size using the same known basic physical principle as described above in connection with FIG. Thus, in the following, it is no longer necessary to re-present the basic principle 15, but the advantages of the structure of the impactor 20 according to the invention will be revealed by mainly explaining the disassembly and assembly of the impactor 20. The numbering of the 20 degrees of the impactor corresponds to the numbering of the 10 degrees of the impactor shown in Figure 1, i.e., in the flow direction, the numbers are 4,3,2 and 1.

20

The lower part 25 and the upper part 26 of the housing 20 of the impactor 20 are fixed to each other by means of a band or similar fastening means which presses the lower part 25 and the upper part 26 gas tight against each other. Removable mentioned. . the mounting member, the upper part 26 of the housing can be lifted out of its lower part; 25 25 off. Along with the upper part 26 is a fourth-order nozzle part 24a, V ·: which is fastened with screws or the like to the upper part 26.

Removing the top portion 26 reveals a fourth-order collecting tray 24b, f ": and a collecting tray 24c over it. With the top portion 26 in place r": 30, the collecting diaphragm 24c is held by the protruding press members 24d and / or press member 24e. Thus, in order to remove the collection film 24c, it is only necessary to lift the top part 26 and the nozzle part 24a with it, after which the collection film 24c can simply be removed with tweezers v: 35 or the like. The lifting of the upper part 26 is easy to carry out by hand because, due to its size and shape, said upper part has an I; easy to grasp firmly.

11 113407

To expose the next-order collecting tray 23c, the nozzle portion 23a is lifted out of position, so that the previous-order collecting tray 24b is also raised. Due to the size of the nozzle part 23a, it can also be gripped firmly by hand, making it unlikely to fall onto the other components of the impactor 5. Removing the nozzle portion 23a exposes the collection membrane 23c.

Similarly, the disassembly of the impactor 20 continues by removing the nozzle portion 22a, and with it the collecting tray 23b, and further the nozzle portion 10 21a, and with it the collecting tray 22b. The last, the so-called. the first-stage collecting tray 21b is lifted off with the retaining member 23, which retains the filter 24 in place.

The assembly of the impactor 20 takes place in reverse order. 15 To prevent improper assembly of the impactor, it is first possible to fit only the retaining member 23 with the retaining member 23 facing right, into the empty bottom part 25 of the housing. The design of the mechanical contact surface of the holding member 23 then fits into the corresponding contact surface of the lower part 24.

20

Further, only the nozzle part 21a, mounted in the correct direction, fits over the nozzle part 21a, only the nozzle part 22a in the correct direction, and so on, until all degrees of the impactor 20 are ·! stacked in place. The collection trays 24b; 23b; 22b; 21b are preferably:. 25 all similar so they can be installed anywhere. to any degree of impactor. If recesses 24b; 23b; 22b; 21b are used in the collecting bases 24b; 23c; 22c; 21c, they should be mounted in the respective nozzle parts 24a; 23a; 22a; 21a facing in the direction of flow, or otherwise, an installation error is detected at the latest when attempting to close the housing of the impactor 20, whereby the lower portion 25 and the upper portion 26 of the impactor housing cannot be pressed tightly together: because the overall height of the remaining portions is too high.

Figures 3a and 3b illustrate the structure of the first-order nozzle portion 21a of the impactor of Figure 2. Fig. 3a ·: · *: A cross-sectional view corresponds to section A-A in Fig. 3b.

12 112407

The nozzle portion 21a comprises a sealing member 33, such as an O-ring seal groove, and a corresponding seal for sealing downstream the nozzle portion 21a to the upstream nozzle portion 22a. The nozzle portion 21a is similarly flushed downstream to the 5 components below, in this case to the retaining member 23. The mechanical contact surfaces of the nozzle portion 21a with which said nozzle portion engages in a downstream direction with the upstream and downstream component of the impactor 20 are shaped such that the component of the impactor 20 can be superimposed on one another only in the correct order. In the example of Figure 3a, with the nozzle portion 21a being a circular plate-like body, the aforementioned mechanical contact surfaces are formed on the outer periphery of the nozzle portion 21a, on the upper and lower surfaces of the plate-like nozzle portion.

The protruding press members 21d formed on the underside of the nozzle part 21a press the collecting diaphragm 21c on the collecting tray 21b tightly against the said collecting tray 21b. The collecting tray 21b is arranged to rest on the support member 23 in a point-supported manner on the resilient support members 31, for example rubber pads or the like. The mounting means 32 for the said support members 32 are provided in the holder-20 member 23, said mounting holes shown in Figures 3a and 3b being shown in the structure of the nozzle part 21a, and in which the supporting members 31 are similarly designed for supporting the previous stage. These flexible support members 31 '; ] · 25 is intended to allow the collection films 24c; 23c; 22c; 21c to vary in thickness within certain limits without affecting the operation v of the impactor 20. Ts. the supporting members 31 ensure that the collecting diaphragm 21c is always in contact with the pressing members 21d, and thus the distance 30 between the nozzle part 21a and the collecting diaphragm 21c, as determined by the dimensioning of the pressing members 21d, is as intended.

Figure 3b shows the positioning of the three-I press members 21d formed on the underside of the nozzle part 21a at a 120 degree circumference having a circumference substantially equal to that of the collecting diaphragm 21c.

: 35 When the nozzle portion 21a is pressed onto the collecting tray 21b, the pressing members 21d press the collecting film 21c onto the collecting tray 21b. Because, the capture film 21c is not exposed to any of the above attachments. rotating or lateral movements, but only a force exerted directly from above, the collecting diaphragm 21c is thus not at risk of wrinkling or otherwise being damaged during attachment.

Figures 4a and 4b illustrate an alternative embodiment of the first-order nozzle part 21a of the impactor 5 of Figure 2. Fig. 4a is a cross-sectional view corresponding to section A-A in Fig. 4b. In addition to the press members 21d, the nozzle part 21a shown in Figures 4a and 4b is formed with a press member 21e arranged to press the collection film 21c in the middle. Hereby, for example, curvature of the collection film 21c and / or vibration caused by the flow of the collection film on the film can be effectively prevented. This is particularly important in situations where a wide area collection film is used and / or the material of the collection film causes a tendency for the above phenomena to occur. The centrally located press member 21e 15 is also advantageous in that it does not obscure any area of the collecting diaphragm 21c from the flow from the nozzle member 21a.

In the embodiments of the nozzle part 21a shown in Figures 4a and 4b, the collection diaphragm 21c is further pressed by four press members 21d spaced 90 degrees on a circumference having a circumference substantially equal to the diameter of the collection diaphragm 21c.

Figures 5a and 5b further illustrate: *. the structure of the impactor collecting tray 24b; 23b; 22b; 21b. A recess 52 is provided on the upper surface facing the flow direction 24b; 23b; 22b; 21b of the collecting tray 25 for collecting foils 24c; 23c; 22c; 21c, such as aluminum foil. The diameter of said recess 52 is selected such that the protruding pressing members 24d; 23d; 22d; 21d formed on the underside of the preceding nozzle member are located in the region of said recess 30 near its edge. Thus, the press members 24d; 23d; 22d; 21d press the collection film 24c; 23c; 22c; 21c tightly against the bottom of the aforementioned recess 52. Apertures 51 are provided in the collecting tray 24b; 23b; 22b; 21b to direct the flow to the next stage of the impactor. Preferably ··· * the impactor when assembling the bottom of the nozzle portion, the collecting diaphragm: * 35 24c; 23c; 22c; 21c near the peripheral press members 24d; 23d; 22d; 21d v: positioned at the pins 53 remaining between the openings 51, ; 21d minimize gas interference. As the number of the pressing members 24d; 23d; 22d; 21d 14 varies, the number of openings 51 may also vary accordingly to allow the aforementioned placement.

In the examples and figures, the above-mentioned impactor may be, for example, 5 four-step cascade impactors with 50% cut-off diameters of 2.5 μηη, 1.0 μιτι, 0.5 μιτι and 0.2 μιτι. It will, of course, be understood that the use of the invention is not limited to cascade impactors of this type, nor generally to 4-step impactors, but that embodiments of the invention may vary within the scope of the inventive features set forth in the claims below.

The shape of the cross-section of the impactor transverse to the flow direction may be any suitable shape, including a circular shape other than that shown in Example 15. The impactor may have the required number of consecutive degrees, or just one degree, for each application. The collecting foil serving as the collecting tray may be any suitable material. The collector film may be circular, or, for example, annular, the annular shape being formed when a circular / oval region is removed from the circular / oval collector film. The shape of the collection film may also be any other shape suitable for the purpose, including angular.

/ 25 If necessary, different membranes of the same impactor may be used to collect collection membranes made of::: material. The collection trays may v: use the exemplary collection diaphragm recess, "" * · but also the collection trays without the recess in question. The flexible support of the collection tray may be arranged as in the examples: 30 by means of support members 31, or also by e.g. is a single, flexible O-ring ···., or equivalent, arranged to support and rotate the collection tray • »along its edges.

»· * T * v: 35 It will still be apparent to one skilled in the art that protruding pressing members formed downstream of the nozzle member and retaining the collection diaphragm may be non-exemplary. the number, which number can also vary with different degrees of is 113407 nozzle parts. When the collection film is sufficiently rigid, it is also possible to use only one pressing member 24e; 23e; 22e; 21e disposed in the center of the collection film to press the said collar. collection foil to its collection tray.

5

It will be further understood by one skilled in the art that the invention can be used both in vacuum impellers in which the flow is directed to the impactor by a downstream suction pump or the like, and in impactors in which the flow 10 directed into the impactor is discharged through the impactor.

Claims (7)

16 112407 An impactor (20) comprising one or more successive stages (4; 3; 2; 1), each stage (4; 3; 2; 1) comprising at least a nozzle portion 5 (24a; 23a; 22a; 21a), a collecting tray (24c; 21c; 21c; 21c; 21c; 21c; 21c; 23c; 21c; 21c; 21c; 21c; 21c; 21c; 21c; 21c; 21c; 21c; 21c; 21c; aerosol particles contained in a gas stream (21) passing through the impactor (20) are collected on a substantially uniform collection film (24c; 23c; 22c; 21c), characterized in that the nozzle (24a; 23a; 22a; 21a) the surface 15 facing the collection tray (24b; 23b; 22b; 21b) comprises one or more small protruding press members (24d; 23d; 22d; 21d, 24e) relative to the collection area of said collection film. ; 23e; 22e; 21e) for holding the collecting diaphragm (24c; 23c; 22c; 21c) in place on the collecting tray (24b; 23b; 22b; 21b) which are shaped, positioned and dimensioned to substantially interfere with the flow of the surface of said collecting diaphragm. Impactor (20) according to Claim 1, characterized in that: T: the pressing elements (24d; 23d; 22d; 21d) are arranged on the rear surface of the nozzle part, T: 25 (24a; 23a; 22a; 21a), which substantially .:; the diameter of the collection film (24c; 23c; 22c; 21c). Impactor (20) according to Claim 2, characterized in that the press members (24d; 23d; 22d; 21d) are three and are arranged on said circumference at 120 degrees relative to each other. Impactor (20) according to one of the preceding claims, characterized in that the nozzle part (24a; 23a; 22a; 21a) comprises only, or in addition to other press members (24d; 23d; 22d; 21d), a press member (24); 24e; 23e; 22e; 21e). Impactor (20) according to one of the preceding claims, characterized in that the nozzle part (s) 171 13407 (24a; 23a; 22a; 21a) contained in the impactor (20) are arranged to match only the immediate impact of the impactor (20). with the corresponding component of the previous and / or next stage (4; 3; 2; 1) such that the nozzle part (s) (24a; 23a; 22a; 21a) can be mounted in position 5 between said previous and / or next component only in certain directions. Impactor (20) according to one of the preceding claims, characterized in that the impactor (20) comprises a resilient support member (31) for supporting the collecting tray (24b; 23b; 22b; 21b) against the said collecting tray (24b; 23b) downstream. ; 22b; 21b) a preceding nozzle portion (24a; 23a; 22a; 21a). Impactor (20) according to one of the preceding claims, characterized in that said impactor (20) is a four-step cascade impactor with 50% cut-off diameters of 2.5 μιτι, 1.0 μιτι, 0.5 μιτι and 0.2 μηι. 112407