non-return valve

Abstract

Check valve (1, 1a) with - a base body (2) with at least one through-opening (4, 5), - an electrically conductive membrane (3) which has, successively along an X-direction, a first section (3.1) attached to the base body with a first electrical contact (7), and a second, movable section (3.2), wherein the base body (2) has at least one electrode extending in the X-direction which is connected to a second electrical contact (8), and wherein in a closed position the membrane (3) covers the at least one through-opening (4, 5) and the second section (3.2) is arranged adjacent to the at least one electrode, wherein at least one resistive element (6, 6a) extending in the X-direction is arranged on the base body (2) as the electrode, wherein in the closed position the second section (3.2) rests against the resistive element (6, 6a).

Description

[0001] The invention relates to a check valve.

[0002] EP 1 417 988 A1 discloses a breathing device. The breathing device has an inhalation opening and an exhalation opening, each of which is associated with a valve. The exhalation valve and its seat are electrically conductive. When the exhalation valve is closed, an electrical signal is generated, allowing a motor of the exhalation valve to be operated. This drives a ventilator, which generates ventilation in the inhalation valve.

[0003] FR 2 898 656 A1 deals with a pressure relief valve for a crankcase. A warning system is activated when two conductors make contact, which occurs when the pressure in the crankcase becomes so great due to freezing water components in blow-by gases that one of the conductors bends and contacts the other conductor.

[0004] Various methods are known in the art for measuring the flow of a fluid, i.e., a gas or liquid, through a pipe or similar device. In this context, flow can be defined as the volumetric flow (volume per unit time) or the mass flow (mass per unit time). Measuring devices used for this purpose are sometimes referred to as flow sensors or flowmeters. Apart from mechanical solutions, such as oval gear meters or turbine meters, various other measuring methods (optical, electromagnetic, ultrasonic, and others) enable the detection of the current flow of a fluid. The majority of available methods deliver high-quality results but are typically very costly to implement. This represents a particularly relevant limitation for the automotive industry, where costs play a major role.

[0005] Solutions have also been proposed in which a flow sensor is integrated into a check valve. Such a check valve, which prevents the flow of a fluid in one direction and allows it in the other, can be used in a wide variety of applications. If flow measurement is desired, integrating a corresponding sensor into the check valve is advantageous, as this generally saves space. However, a structurally simple and cost-effective solution is also desirable in this case.

[0006] In the field of automotive engineering, such a check valve with a flow sensor could be used, for example, within a brake booster system, which would make it possible not only to control the direction of the air flow from a brake booster to a vacuum source (e.g. a vacuum pump), but also to measure the flow.

[0007] GB 954 048 A discloses a check valve with a valve body and an annular diaphragm inserted therein, which, in a closed position, rests against a central insert element of the valve body. The diaphragm closes an opening formed circumferentially around the insert element between the insert element and the outer wall of the valve body. In an open position, the diaphragm is lifted from the insert element, thus releasing the opening. The diaphragm interacts with a rod guided slidably through the outer wall, which in turn can act on an external potentiometer, via whose resistance the flow rate through the check valve can be determined.

[0008] US 3,587,326 A discloses a device for measuring acceleration. A test mass is connected to an elastic membrane that seals a fluid-filled chamber. The chamber is connected via a check valve to a tube containing a drop of liquid metal. On the opposite side of the drop, the tube transitions into a closed chamber and is filled with a pressurized gas. Opposite transducer sections of the tube are coated with a conductive element and a resistive element, respectively, each extending in the axial direction. These elements, together with the metal drop, form part of an electrical circuit. The resistance of the conductive element can be used to determine the position of the metal drop, which in turn depends on the position of the test mass under the influence of acceleration.

[0009] US 8 800 473 B1 describes a flow sensor with a base part, which can be inserted, for example, into a pipe system, and a pivotably mounted, spring-loaded dam element which, in a rest position, can at least partially fill a pipe cross-section. An arcuate display section is arranged on the dam element, which moves into a display chamber of the base part when the dam element is deflected from the rest position. The display chamber can, for example, be transparent so that the position of the dam element, which corresponds to a flow rate, can be read visually. Alternatively or additionally, the position can be recorded electrically, for example, via a Hall sensor on the display chamber and a magnetic element on the display section.

[0010] US 3,914,994 A discloses a flow sensor with a tubular body and a pivoting valve flap arranged therein. The valve flap contacts a switch in a fully closed position and contacts a resistance wire in different positions in a partially or fully open position. The resistance wire acts like a potentiometer, allowing the opening state and thus the flow rate to be determined via the resistance.

[0011] US Pat. No. 4,926,903 A shows an arrangement with a butterfly valve that can be pivoted about an axis driven by an actuator. The axis is coupled to a potentiometer via a reduction gear, which measures the pivot angle. Furthermore, the torque in the axis is measured. Using a relationship, for example, empirically determined, the flow rate along the butterfly valve can be determined from the measured values ​​for the pivot angle and torque.

[0012] US 4 213 021 A discloses a check valve with a valve body in which a spring-loaded closing element is arranged, with which the valve body can be closed. The closing element has a magnet and a reed switch arranged in the wall of the valve body, which is closed or opened by the magnet depending on the position of the closing element. This allows the flow rate within the valve to be determined from the state of the reed switch. To prevent hysteresis effects from leading to opening or closing at significantly different flow rates, the closing element has a special geometric design with a nose section. This ensures that the flow rate remains approximately constant over a certain displacement path of the closing element.

[0013] US 2008 / 0 053 537 A1 discloses a check valve with a valve body having an opening, and a flap pivotably mounted on the valve body, which can open or close the opening. First and second conductor elements are arranged on the valve body and are spaced apart from one another. A third conductor element is arranged on the flap and dimensioned such that it can close the gap between the first and second conductor elements. Depending on the arrangement, it is thus possible to determine the open or closed state of the flap by closing an electrical circuit.

[0014] In view of the state of the art shown, there is still room for improvement in the provision of a check valve that is simple and cost-effective to manufacture and allows the most precise flow measurement possible.

[0015] The invention is based on the object of providing a check valve with an integrated flow sensor that can be manufactured simply and cost-effectively.

[0016] According to the invention, the object is achieved by a check valve having the features of claim 1, wherein the subclaims relate to advantageous embodiments of the invention.

[0017] It should be noted that the features and measures listed individually in the following description can be combined with one another in any technically reasonable manner and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0018] The invention provides a check valve. A check valve is considered to be any type of valve that, depending on a pressure difference on both sides of the valve, allows the passage of a fluid, i.e., a gas or liquid, in one direction and prevents it in the opposite direction. In particular, the check valve according to the invention can be used to regulate the flow of a gas, e.g., air. The check valve has a base body with at least one through-opening. The base body can also be referred to as the valve body and corresponds to the stationary part of the check valve, which is installed, for example, on or in a fluid line. For this purpose, it can have connecting means such as threads or holes for receiving screws. In the operating state, the at least one through-opening serves to allow the fluid to pass through the check valve.There are no restrictions within the scope of the invention regarding the geometry of the at least one through-opening. For example, the through-opening can be elongated or short in the intended direction of fluid flow.

[0019] Furthermore, the check valve has an electrically conductive membrane which, along an X-direction, has a first section fastened to the base body and having a first electrical contact, and a second, movable section. The term "membrane" implies that it is a flexible body that is flat in at least some sections. The term "X-direction" in this context serves only as a reference and does not imply any orientation in relation to the installation position within a fluid line, the direction of flow of the fluid, or the like. Along this X-direction, two sections can be distinguished: the first is fastened to the base body, while the second is movable relative to the base body (and the first section). This mobility is naturally accompanied by a deformation of the flexible membrane.The second section can be lifted off the base body, meaning it can move perpendicular to its surface. The first section can be attached to the base body, for example, by adhesive bonding or ultrasonic welding, but can also be attached force-fitting and / or form-fitting, for example, by clamping.

[0020] The membrane is electrically conductive, which includes the possibility that it is made entirely of an electrically conductive material (e.g. a polymer matrix in which electrically conductive particles are embedded) or that it is only partially electrically conductive, e.g. having a conductive coating. A first electrical contact is arranged on the first section, which enables, for example, connection to a current or voltage source. The electrical contact can be very simple, e.g. as a metallic pin to which a cable can be soldered, or as a plug-in connector. It is also possible for an electrical line permanently connected to the check valve to be directly connected to the electrical contact. Such a line can, for example, also be designed as a conductor track on a circuit board that forms at least part of the base body.Additional conductor tracks can be applied to such a circuit board, whereby a layered arrangement of several insulated conductor tracks is also possible. It goes without saying that the first electrical contact is conductively connected to the membrane or its electrically conductive part.

[0021] Furthermore, the base body has at least one electrode extending in the X-direction, which is connected to a second electrical contact. The at least one electrode extends in the X-direction, which means that it has a non-negligible extension in the X-direction. It is also possible for several electrodes to be provided consecutively in the X-direction. Likewise, several electrodes can be provided which are spaced from one another transversely to the X-direction. At least one electrode can be formed flat on or below the surface of the base body. The electrode or each electrode is connected to the second electrical contact, which includes the possibility that the second electrical contact is formed directly on an electrode. The at least one electrode can - apart from the connection to the second electrical contact - be electrically insulated from the outside (e.g.by a dielectric) or it can be at least partially electrically contactable. The at least one electrode is inherently electrically conductive, so that charges can be displaced or currents can flow at least within it. The above statements regarding the design of the first contact also apply to the second contact. The second electrical contact is, of course, electrically connected to the at least one electrode and allows connection to a current or voltage source. It can, in particular, be arranged on the base body.

[0022] In a closed position, the membrane covers the at least one through-opening and the second section is arranged adjacent to the at least one electrode. This is of course the closed position of the check valve, in which it prevents a fluid from passing against the intended direction. Here, the membrane acts as a closing element that covers the at least one through-opening. One can also say that the membrane completely closes the through-opening or closes it by completely covering it. In order to act as a movable closing element, the membrane covers the through-opening at least partially with the second, i.e. movable, section. The through-opening is preferably predominantly, ideally completely, covered by the second section.Furthermore, in the closed position, the second section is arranged adjacent to the at least one electrode, which includes the possibility that the second section contacts the at least one electrode. Due to the proximity of the electrically conductive membrane to the at least one electrode, the closed position can be determined by measuring at least one electrical quantity. For example, the at least one electrode can be insulated by a dielectric, with the electrically conductive membrane acting as a counter electrode. The capacitance of the arrangement changes depending on the position of the second section relative to the at least one electrode, with a specific, often characteristic, capacitance being able to be assigned to the closed position. In this case, the first and second electrical contacts would be connected to the poles of a voltage source, which leads to a capacitance-dependent charging of the arrangement.

[0023] In a through-opening position, however, the second section is at least partially lifted off the base body, which means, on the one hand, that at least one through-opening is at least partially exposed, but on the other hand also that the second section moves away from at least one electrode. This always leads to a change in the electrical properties, e.g. to a change in capacitance, whereby a relationship exists between a changing electrical measured variable and the exposed area of ​​the through-opening. With the check valve according to the invention, it is therefore possible to determine the opening state of the valve or the flow through it by measuring an electrical variable. Depending on the geometric and material design of the various elements, the relationship between the measured variable and the flow can be complicated (in particular non-linear), but it can, for example,determined in experiments by calibration.

[0024] The invention thus provides a check valve that can also be used as a flow sensor. The check valve can be constructed relatively simply and thus inexpensively. A very space-saving design is also possible. It should also be noted that normally the second section of the diaphragm is the only moving part of the valve, resulting in virtually no wear and virtually no risk of the valve becoming blocked. Normally, the only movement is the lifting of the second section from the base body, meaning there is no friction between moving parts.

[0025] During the transition from the closed position to the open position, preferably the part of the second section furthest from the first section detaches from the base body first. As the pressure difference increases, further parts of the second section successively detach, gradually releasing the at least one passage opening. This, in turn, causes the second section to gradually move away from the at least one electrode, which is accompanied by a gradual change in the measured variable.

[0026] According to the invention, at least one resistance element extending in the X-direction is arranged on the base body as an electrode, with the second section resting against the resistance element in the closed position. The term "resistance element" naturally implies an electrical resistance, but is not to be interpreted in a restrictive manner with regard to the total resistance or the specific resistance. Thus, the resistance or the specific resistance of the resistance element can, under certain circumstances, be lower than that of the electrically conductive membrane. The resistance element can, for example, be formed in a layered form as a carbon, metal, or metal oxide film resistor.

[0027] In the closed position, the second section rests against the resistance element. This creates an electrical connection, which is why the membrane must be electrically conductive at least on the side facing the resistance element. In the closed position, an overall electrical connection is established from the first electrical contact via the electrically conductive membrane and the resistance element to the second electrical contact. This allows an electrical current to flow, and the ratio of voltage to current allows the total resistance to be determined, which is characteristic of the closed position.

[0028] In the open position, the second section is at least partially lifted off the base body, which means on the one hand that the at least one through-opening is at least partially exposed, but on the other hand also that the second section may only partially or no longer be in contact with the resistance element. This changes the total resistance measurable between the first and second electrical contacts, with a relationship existing between the measured resistance and the exposed area of ​​the through-opening. With this configuration, it is therefore possible to determine the opening state of the valve or the flow rate through it by measuring the resistance. The relationship between the resistance and the flow rate can be complicated (in particular non-linear), but it can be determined, for example, in tests through calibration.

[0029] During the transition from the closed position to the open position, preferably the part of the second section furthest from the first section detaches from the base body first. As the pressure difference increases, further parts of the second section successively detach, gradually releasing the at least one passage opening. This, in turn, causes the second section to gradually detach from the resistance element, which is accompanied by a gradual change in the overall resistance. In this respect, the check valve functions similarly to a potentiometer, with the diaphragm or its second section acting as the control element.

[0030] Preferably, the resistance element is arranged next to a through-hole in a Y direction running perpendicular to the X direction. During the above-described process of successive detachment from the base body, which occurs along the X direction, the release of parts of the through-hole occurs, so to speak, parallel to the detachment from the resistance element. This means that the increase in flow rate and the change in the overall resistance also occur in parallel, which makes it easier to determine a relationship.

[0031] Likewise, the resistance element is preferably arranged adjacent to a through-opening. This means that either the resistance element is directly adjacent to the through-opening, or there is a gap that is, however, significantly smaller than the expansion of the resistance element or the through-opening in the corresponding direction, for example, at most 20% or 30%. This creates a closer connection between the release of the resistance element and the release of the through-opening, and also allows the membrane to be optimized in terms of its surface area, since it must at least cover the through-opening and touch the resistance element. In this context, it is advantageous if there is no large gap between the through-opening and the resistance element.

[0032] Advantageously, an end of the resistance element facing away from the first section extends in the X direction at least as far as the at least one through-opening. In other words, the end of the resistance element furthest away from the first section in the X direction is at least as far away as the furthest end of each through-opening. The advantage of this arrangement is that even if only the furthest end of the through-opening is exposed by lifting off the second section of the membrane, this always leads to the second section becoming detached from part of the resistance element. This in turn brings about a change in the overall resistance, so that even a minimal exposure of part of a through-opening can be electrically detected.

[0033] It is also advantageous if an end of the resistance element facing the first section of the membrane extends in the X direction at least to the first section. This means that the resistance element extends in this direction at least to the end of the second section. This means that even when the second section is almost completely detached from the base body, slight changes in the position of the second section can still be electrically detected.

[0034] In principle, the invention can be implemented with exactly one through-opening and exactly one resistance element. In a preferred embodiment of the invention, the base body has at least two through-openings, between which the resistance element is arranged. It is preferred that the resistance element be arranged along the Y-direction between the two through-openings. With such an arrangement, the membrane can, for example, be subjected to symmetrical flow, which typically also leads to a symmetrical or uniform lift-off from the through-openings. The two through-openings and the resistance element can extend adjacent to one another in the X-direction, in a strip-like manner.

[0035] With exactly one through-hole, it may be advantageous to provide two resistance elements between which the through-hole is located. Otherwise, with only one resistance element, a slight, asymmetrical lifting of the membrane, for example, could result in undetectable detection because it occurs on the side of the membrane opposite the resistance element.

[0036] In principle, it is sufficient for the check valve to function if the diaphragm is flexible, whereby it can, if necessary, simply be guided into the closed position by the flowing fluid or the pressure difference or can be held in this position. To enable reliable closure of the through-opening, however, it is preferred that the second section can be elastically deflected from the closed position. This means that, due to a pressure difference through a fluid, the second section can be deflected in such a way that it opens the through-opening. However, this deflection is elastic, which means that a restoring force occurs which returns the second section to the closed position as soon as there is no longer any external pressure difference or external force acting. The closed position can correspond to a relaxed position of the second section, or the second section can be pre-tensioned against the base body in the closed position.To achieve elastic deflection, the membrane itself can be designed to be elastic. Alternatively, an additional return element could be provided that acts on the membrane.

[0037] Advantageously, the second electrical contact is arranged at an end of the resistance element opposite the first electrical contact. One could therefore say that the second electrical contact is arranged at the outermost end of the resistance element. This maximizes the spatial distance between the two electrical contacts. Normally, parts of the resistance element that are farther away from the first electrical contact than the second electrical contact carry no current, or only carry a small amount of current, and have little influence on the overall resistance. Thus, the design described here corresponds to optimal utilization of the entire resistance element.

[0038] As already indicated above, the check valve can act as a type of potentiometer, via whose resistance the flow can be measured. In terms of sensitivity, it is advantageous if the smallest possible change in flow leads to the largest possible change in resistance. On the one hand, this can be influenced by choosing the specific resistances of the resistance element and the conductive membrane. On the other hand, the geometry of the at least one through-opening can also play a role. For example, it is advantageous if at least one through-opening has a greater extent in the X direction than in the Y direction. In particular, the corresponding extent can be, for example, at least twice or at least five times. One could also say that the cross-section of the through-opening is elongated in the X direction and narrow in the Y direction.Another advantage here is that, in the event that the second section detaches asymmetrically (i.e., detaches further on one side of the through-hole than on the other), the associated measurement error is reduced. It is also often the case that such asymmetric detachment occurs less frequently or is less pronounced with a larger number of through-holes.

[0039] Considering a possible asymmetrical detachment of the second section, it may also be advantageous if at least one resistance element has a greater extension in the X direction than in the Y direction. Here, too, the corresponding extension can be, for example, at least twice or at least five times greater.

[0040] As already mentioned above, there are basically no special restrictions regarding the specific resistances of the membrane and the resistance element. However, it is advantageous for the membrane to have a lower specific resistance than the resistance element. In particular, the specific resistance can be significantly lower, for example, ten or one hundred times lower. With such a design, the total resistance is predominantly determined by the portion of the resistance element to which the second section of the membrane is not in contact. The remaining parts of the resistance element are, in a sense, bridged by the membrane.

[0041] The way in which the total resistance changes when the second section is detached can be influenced by the geometry of the resistance element. For example, a cuboid-shaped resistance element whose specific resistance is significantly greater than that of the membrane would result in an essentially linear relationship. According to an alternative embodiment, at least one resistance element has an extension in the Y direction and / or in the Z direction that changes along the X direction. If the extension in the X direction is viewed as the length of the resistance element, its width (in the Y direction) and / or its thickness (in the Z direction) can change. The corresponding extension can change, for example, linearly or non-linearly depending on the X coordinate.

[0042] The check valve according to the invention can be integrated into a wide variety of systems in which the actual valve function is to be combined with flow measurement in a space-saving and cost-effective manner. For example, in a brake booster system, the check valve can be used in a connecting line between a brake booster and a vacuum source (a mechanically or electrically operated vacuum pump or the engine intake manifold). This makes it possible to easily determine the flow. This opens up various possibilities, e.g., detecting leaks in the system without directly measuring the pressure within the brake booster. This allows the expected pressure in the brake booster to be determined or estimated indirectly. An expected flow can be derived from the expected pressure in the brake booster and the pressure in the vacuum source.If this expected flow rate does not match the measured flow rate, the presence of a leak can be determined. This is advantageous over prior art systems that rely on direct pressure measurement in the brake booster for such fault diagnosis, which is complex and costly due to the pressure sensor that must be integrated there. In contrast, the check valve according to the invention is cost-effective and easy to integrate.

[0043] Further advantageous details and effects of the invention are explained in more detail below with reference to exemplary embodiments illustrated in the figures. They show: Fig. 1 a schematic representation of a first embodiment of a check valve according to the invention in a closed position; Fig. 2 a schematic representation of a part of the check valve from Fig. 1; Fig. 3 a schematic representation of the check valve from Fig. 1 in a first passage position; Fig. 4 a schematic representation of the check valve from Fig. 1 in a second passage position; and Fig. 5 is a schematic representation of part of a second embodiment of a check valve according to the invention;

[0044] In the different figures, identical parts are always provided with the same reference symbols, which is why they are usually only described once.

[0045] Fig. 1 shows a schematic perspective view of a first embodiment of a check valve 1 according to the invention. The check valve 1 has a base body 2, to which an electrically conductive membrane 3 is attached. More precisely, a first section 3.1 of the membrane is attached to the base body 2, for example by adhesive bonding, while a second section 3.2, which in the present example is significantly larger in area, is movable relative to the base body 2. The second section 3.2 can be bent and thus lifted off a surface 2.1 of the base body. The two sections 3.1, 3.2 are arranged one after the other in an X-direction. The first section 3.1 has a first electrical contact 7, which is connected to an electrical circuit 9.

[0046] The base body 2 is shown here with a rectangular cross-section, although this is purely schematic. It can also have a round cross-section, for example, and be provided with threaded elements or holes for screws, by means of which it can be secured within a fluid line.

[0047] The further structure of the check valve 1 is described with reference to the partial view in Fig. 2, in which the membrane 3 has been omitted. The base body 2 has two through-openings 4, 5, each with a rectangular cross-section, which are elongated in the X-direction, which in this case means that their extension in the X-direction is approximately five times the extension in the Y-direction running transversely thereto. The two through-openings 4, 5 serve to allow a fluid, e.g. air, to pass through the base body 2. The intended flow direction of the fluid corresponds to a Z-direction perpendicular to the X-direction and the Y-direction. However, if the fluid has a higher pressure on the side of the membrane 3, the through-openings 4, 5 are closed by the membrane 3, i.e. the check valve 1 is located in a Fig. 1 shown closed position.

[0048] A web is formed between the through-openings 4, 5, on which a resistance element 6 is arranged. The resistance element 6 has the form of a rectangular, comparatively thin layer (e.g., a metal oxide layer) applied to the surface of the web. The specific resistance of the resistance element 6 can, for example, be at least 10 times greater than the specific resistance of the membrane 3. The resistance element 6 extends in the X direction over the entire length of the through-openings 4, 5. An end 6.2 of the resistance element 6 facing away from the first section 3.1 extends just as far in the X direction as the through-openings 4, 5, while an end 6.1 facing the first section 3.1 extends as far as the first section 3.1. The resistance element 6 fills almost the entire width of the web and is thus adjacent to both through-openings 4, 5. At the end 6.2, a second electrical contact 8 is arranged, which is also connected to the circuit 9.

[0049] The circuit 9 is closed between the first electrical contact 7 and the second electrical contact 8 by the conductive membrane 3 and the resistance element 6, against which the membrane 3 is in contact. Since the specific resistance of the resistance element 6 is significantly greater than that of the membrane 3, Fig. 1, the resistance element 6 is, in a sense, bridged by the membrane 3. Thus, the total resistance between the two electrical contacts 7, 8 is determined primarily by the resistance of the membrane 3. The resistance can be determined by a measuring device 10, which, for example, comprises a voltage source and measures the current in the circuit 9.

[0050] The membrane 3 consists of an elastic material, with the second section 3.2 in the Fig. 1 is pre-tensioned against the base body 2. However, it can be elastically deflected from the closed position by a fluid pressure acting from the through-openings 4, 5, so that it lifts off completely or partially from the surface 2.1 of the base body 2 and the resistance element 6. Such a state is in Fig. 3, which shows the check valve 1 in a first through-flow position. Here, the second section 3.2 is slightly elastically bent so that it is lifted off the surface 2.1. This exposes part of the through openings 4, 5, allowing fluid to flow through. A (generally non-linear) relationship between the exposed area and the flow rate can be determined, for example, experimentally. Because the second section 3.2 lifts off the surface 2.1, it also partially detaches from the resistance element 6. This, in turn, means that the part of the resistance element 6 that is no longer in contact with the membrane 3 is no longer bridged and thus contributes significantly to the overall resistance. A corresponding increase in resistance can be recorded by the measuring device 10.

[0051] In Fig. 4 shows another passage position, where the flow is Fig. 3 is increased, which is accompanied by a further detachment of the second section 3.2 from the surface 2.1 and the resistance element 6. On the one hand, this exposes a larger portion of the through-openings 4, 5, while on the other hand, the membrane 3 rests against an even smaller portion of the resistance element 6. Only this, in turn, smaller portion is thus bridged in the sense described above, which leads to a further increase in the overall resistance.

[0052] For the described case that the specific resistance of the resistance element 6 is significantly greater than that of the membrane 3, the total resistance at the Fig. 1-4 shown check valve 1 approximately proportional to the released area of ​​the through openings 4, 5. Fig. Figure 5 shows another embodiment of a check valve 1a in which this is not the case. Again, as in Fig. 2 the membrane 3 is omitted. This check valve 1a largely corresponds to the one in Fig. 1-4 and will not be described again in this regard. However, in this case, a resistance element 6a has an extension in the Y direction that changes along the X direction. As a result, the resistance element 6a has a substantially trapezoidal, even triangular shape, tapering toward the first section 3.1. Since the resistance contribution of the tapered parts is greater due to the smaller cross-section, the total resistance changes non-linearly with the exposed area of ​​the through-openings 4, 5. List of reference symbols: 1, 1a Check valve 2 base bodies 2.1 Surface 3 Membran 3.1 first section 3.2 second section 4, 5 passage opening 6, 6a resistance element 6.1, 6.2 End 7, 8 electrical contact 9 Circuit 10 Measuring device X X-direction Y Y-direction Z Z-direction

Claims

[1] Check valve (1, 1a) with - a base body (2) with at least one through opening (4, 5), - an electrically conductive membrane (3) which has, along an X-direction, a first section (3.1) fastened to the base body and having a first electrical contact (7), and a second, movable section (3.2), wherein the base body (2) has at least one electrode extending in the X-direction and is connected to a second electrical contact (8), and wherein, in a closed position, the membrane (3) covers the at least one through-opening (4, 5) and the second section (3.2) is arranged adjacent to the at least one electrode, wherein at least one resistance element (6, 6a) extending in the X-direction is arranged on the base body (2) as the electrode, wherein, in the closed position, the second section (3.2) bears against the resistance element (6, 6a). [2] Check valve according to claim 1, characterized by that the resistance element (6, 6a) is arranged in a Y-direction running transversely to the X-direction next to a through opening (4, 5). [3] Check valve according to claim 1 or 2, characterized by that an end (6.2) of the resistance element (6, 6a) facing away from the first section (3.1) extends in the X direction at least as far as the at least one through opening (4, 5). [4] Check valve according to one of the preceding claims, characterized by that an end (6.1) of the resistance element (6, 6a) facing the first section (3.1) extends in the X direction at least as far as the first section (3.1). [5] Check valve according to one of the preceding claims, characterized by that the base body (2) has at least two through openings (4, 5) between which the resistance element (6, 6a) is arranged. [6] Check valve according to one of the preceding claims, characterized by that the second section (3.2) can be elastically deflected from the closed position. [7] Check valve according to one of claims 1 to 5, characterized by that the second electrical contact (8) is arranged at an end (6.2) of the resistance element (6, 6a) opposite the first electrical contact (7). [8] Check valve according to one of the preceding claims, characterized by that at least one through-opening (4, 5) has a greater extent in the X-direction than in the Y-direction. [9] Check valve according to one of claims 1 to 5 or 7, characterized by that at least one resistance element (6, 6a) has an extension in the Y direction and / or in the Z direction which changes along the X direction.

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