Patent Application
20250172134
This application claims the benefit of German Application No. 102023132994.4, filed Nov. 27, 2023, the disclosure of which is incorporated by reference herein in its entirety.
The present invention relates to a membrane system, a membrane, and a metering diaphragm pump.
In metering diaphragm pumps, a membrane is used that has an outer section intended to be clamped, a central section, and a flexing section surrounding the central section, which connects both to the outer section and the central section. Inside the metering pump, the membrane is clamped at its outer section in such a way that it divides a cavity into a metering chamber, where the dosing fluid is drawn in through a suction inlet and expelled through a pressure outlet, and a working chamber.
The flexing section is designed to allow the central section to move back and forth relative to the outer section between a first position and a second position along a longitudinal axis.
An actuator engages with the central section, which moves the central section back and forth along the longitudinal axis. Since the outer section is clamped, the flexing section must deform to enable the back-and-forth movement of the central section. The membrane has a first side, which forms a wall of the metering chamber and is therefore intended to come into contact with the dosing fluid, and a second side, which is intended to not come into contact with the dosing fluid and forms a wall of the working chamber. The actuator engages with a core that rests against the second side at the central section.
To attach the membrane to the core, the membrane has a fastening section located on the second side. A clamping piece is provided, which holds the fastening section between the core and the clamping piece, allowing the central section, which rests against the core, to move back and forth between the two aforementioned positions as the core moves.
Expectations for such metering pumps, especially regarding the service life of the membrane and the increase in delivery capacity while maintaining a compact design, are continuously growing. Attempts have been made to increase the stroke length relative to the outer diameter of the flexing section to increase the dosing volume during a pressure stroke, i.e., during the movement of the core or the central section from the first to the second position. However, this has led to premature failure of the membrane, limiting the extent to which the stroke length can be increased. Similarly, increasing the membrane surface area is only feasible to a limited extent, as this would reduce the compactness of the metering pump.
Starting from this prior art, the object of the present invention is to provide a membrane system of the type mentioned at the outset, consisting of a membrane, a core, and a clamping piece, that allows for a larger stroke length without reducing the service life of the membrane system.
According to the invention, this object is achieved by providing a support element with a support surface, where the support surface comes into greater contact with the second side of the membrane in the area of the flexing section in the second position compared to the first position. It has been found that the greatest stress on the membrane occurs in the flexing area during the movement from the first to the second position, i.e., during the so-called pressure stroke, so that the membrane is supported by the support element during this movement. During the return movement, i.e., the movement from the second position back to the first position, the so-called suction stroke, the stress is significantly lower. Therefore, the membrane does not need to be supported here and can move away from the support element to allow for greater movement of the core relative to the outer section.
The support surface should not run parallel to the longitudinal axis. Furthermore, in a sectional view containing the longitudinal axis, the support surface preferably extends in a direction perpendicular to the longitudinal axis over a length that is greater than 10% of the extension of the flexing section in this direction.
In a preferred embodiment, the support surface is arranged on the clamping piece. For example, the core may have a section with an external thread, and the clamping piece may be screwed onto the external thread.
Especially when dosing environmentally harmful or health-hazardous substances, membranes are often used that have a protective layer covering the second side of the membrane, at least in the unclamped area and the area not in contact with the core. The protective layer is arranged such that, in the event of membrane fatigue, the dosing fluid penetrates through the now-leaking membrane into the space between the protective layer and the second side of the membrane, where it can be detected, usually leading to an immediate shutdown of the dosing process.
Especially when using such a protective layer, but also in cases where no protective layer is used, the constant contact and separation between the second side of the membrane (or the protective layer) and the support surface in this area leads to particularly high stresses.
Therefore, in a preferred embodiment, the support surface is at least partially made of an elastic material, preferably a plastic, and most preferably an elastomer such as EPDM (ethylene-propylene-diene rubber) or NBR (nitrile-butadiene rubber).
By providing an elastic support surface, the stress on the flexing section is significantly reduced, thereby increasing its service life. In a preferred embodiment, the support surface is convexly curved, meaning it bulges outward. This allows the dosing volume per stroke to be increased, as the flexing section is concavely curved in the first position and convexly curved in the second position. Since the flexing section lies at least partially on the support surface in the second position, the support surface is also convexly curved in this position.
In a preferred embodiment, the core is also convexly curved on the side resting against the central section. It is particularly preferred for the entire outer surface of the core to be convexly curved. However, in some embodiments, it may be sufficient for at least the edge areas of the central section, i.e., the areas closest to the support surface or facing it, to be convexly curved.
In another preferred embodiment, it is provided that the sum of the curvature radius of the support surface and the thickness of the membrane at the section in contact with the support surface, and the sum of the curvature radius of the convexly curved section of the core and the thickness of the membrane at the section in contact with the convexly curved section of the core, are substantially equal. If the membrane thickness is the same in both the central section and the flexing section, then the curvature radius of the support surface and that of the convexly curved sections of the core are also equal. However, if the thickness differs, the curvature radius is adjusted accordingly. It is advantageous for these two sums to be exactly equal. The smaller the difference between these sums, the greater the inventive effect.
When the difference between the sum of the curvature radius of the support surface and the membrane thickness at the section in contact with the support surface, and the sum of the curvature radius of the convexly curved section of the core and the membrane thickness at the section in contact with the convexly curved section of the core, is less than 25%, and preferably less than 15%, of the membrane thickness at the section in contact with the support surface, this is considered to be substantially equal.
This measure has the advantage that the membrane can roll particularly easily on the support surface, further extending the membrane's service life.
In another preferred embodiment, it is provided that the membrane has a thickness dR at the edge of the central section and a thickness dS at the section in contact with the support surface in the second position, where, in a sectional view, at least one edge of the central section and an imaginary line spaced from the support surface by the difference |dS−dR| run substantially along a continuous and inflection-free section of a mathematical function. Again, the situation is simplified when the membrane thickness in the central section and the flexing section are the same, as then both at least one edge of the central section and the support surface lie along a mathematical function. The mathematical function can be any type, but good results have been obtained with polynomial functions, trigonometric functions, ellipse functions, and circle functions. It is advantageous when the edge of the central section and the imaginary line lie exactly on a continuous and inflection-free section of a mathematical function. However, minor deviations only marginally reduce the inventive effect. Therefore, the edge of the central section and the imaginary line run substantially along a continuous and inflection-free section of a mathematical function if the deviations of the edge of the central section and/or the imaginary line from the mathematical function are no greater than 25%, preferably no greater than 15%, and particularly preferably no greater than 5% of the membrane thickness at the section in contact with the support surface.
In a preferred embodiment, the support surface is rotationally symmetrical or substantially rotationally symmetrical. This is especially advantageous for membranes that are essentially circular, as the flexing section is then evenly supported.
In a preferred embodiment, the fastening section is located at the boundary between the central section and the flexing section. Since the fastening section is intended to secure the membrane to the core, this position is particularly advantageous, as it ensures that all parts of the membrane located on one side of the fastening section are either firmly connected to the core or permanently supported by it, while the parts on the other side of the fastening section are part of the flexing section and thus movable relative to the core.
The invention also relates to a membrane for a membrane system of the type described. The membrane may be multi-layered. For example, the membrane may have two layers separated by a fabric.
Furthermore, it is possible, either alternatively or in combination, for the membrane to have a protective layer on its second side, which extends over the outer section, the flexing section, and the fastening section, but not over the central section. Preferably, the protective layer rests against the second side of the membrane, at least in the area where the protective layer may come into contact with the support surface, in both the first and second positions, but is not bonded to it. The protective layer is intended to capture dosing fluid that penetrates through a damaged membrane in the event of membrane rupture, i.e., a point-specific failure. A corresponding sensor may be provided between the protective layer and the membrane to detect the presence of dosing fluid, triggering a pump shutdown or at least signaling a fault. However, the sensor does not necessarily have to be located between the protective layer and the membrane. It could, for example, be located adjacent to the outer section. The sensor could be a liquid sensor or a pressure sensor that detects a bulging of the membrane caused by fluid entering between the protective layer and other membrane layers.
In another preferred embodiment, either as an alternative to or in combination with the multi-layer structure and/or the protective layer, it is provided that the second side has a groove-shaped recess on the side of the flexing section facing the central section. The groove-shaped recess allows the flexing section to better follow the support surface during the movement of the core between the first and second positions, increasing the membrane's service life in this area.
In another preferred embodiment, the first side of the membrane has a convexly curved section at the transition from the outer section to the flexing section, a convexly curved section at the transition from the central section to the flexing section, and a concavely curved section connecting the two convexly curved sections. In other words, the membrane has a bead on its first side, located in the flexing section, allowing the core to move a greater distance relative to the clamped outer section without requiring excessive elastic or plastic deformation of the membrane or its individual layers.
When the membrane is viewed in an unstressed state, i.e., in a state where no force is applied to the membrane via the core, in a preferred embodiment, a tangent to the inflection point between the convexly curved section positioned at the transition from the outer section to the flexing section and the concavely curved section forms an angle of less than 30° with the longitudinal axis. Alternatively or in combination, a tangent to the inflection point between the convexly curved section positioned at the transition from the central section to the flexing section and the concavely curved section forms an angle of less than 65° with the longitudinal axis.
This position of the inflection points further increases the movement range of the flexing section, allowing an even greater stroke and, consequently, a larger dosing volume per stroke.
The aim is to increase the dosing volume per stroke without increasing the lateral expansion of the membrane, and thus the dosing chamber, in this direction.
The present invention also relates to a metering diaphragm pump with a membrane system of the type described, or with a corresponding membrane, where the membrane is clamped at its outer section, and the metering diaphragm pump has a cavity that is divided by the membrane into a metering chamber and a working chamber. An actuator is provided, which moves the core back and forth between the first and second positions. Through the inventive measures, the metering diaphragm pump can be designed such that the ratio of the outer diameter of the flexing section to the distance between the first and second positions of the core is less than 15, preferably less than 12.5, particularly preferably less than 10, and greater than 5.
Further features, advantages, and applications of the present invention will become apparent from the following description of a preferred embodiment and the accompanying figures. The figures show:
The membrane (7, 8, 9) divides the cavity formed by the dosing chamber cover (4) and the working chamber element (5) into a dosing chamber (6) and a working chamber (12). The core (2) has a threaded hole (15) for attaching a push rod from an actuator. With the help of this actuator, the core (2) can be moved from its first position shown in
The membrane (7, 8, 9) has a first side facing the dosing chamber (6), which is intended to come into contact with the dosing fluid, and a second side facing the working chamber (12), which is not intended to come into contact with the dosing fluid. The central section (9) rests against the core (2). To attach and seal the membrane (7, 8, 9) to the core (2), a fastening section (10) is arranged on the second side of the membrane, which is clamped between the core (2) and a clamping piece (13).
A protective layer (11) is provided on the second side of the membrane (7, 8, 9), which is clamped together with the outer section (7) between the dosing chamber cover (4) and the working chamber element (5) and clamped together with the fastening section (10) between the clamping piece (13) and the core (2). A cavity (14) is formed between the second side of the membrane (7, 8, 9) and the protective layer (11). Should the membrane (7, 8, 9) rupture or be perforated during operation, dosing fluid may enter the cavity (14), where it can be detected as a failure state.
Furthermore, a spherical core (22) is provided, against which the central section (29) of the membrane rests. A flexing section (28) connects the outer section (27) with the central section (29). The side of the membrane facing right in
Additionally, a fastening section (30) is provided on the second side of the membrane, which is clamped and sealed between the core (22) and a clamping piece (23). To enhance the sealing effect, the clamping piece (23) features a sealing rib on its surface facing the fastening section (30), pressing the protective layer (31) against the fastening section (30), so that the fastening section (30) and the protective layer (31) are clamped between the clamping piece (23) and the core (22).
Compared to the clamping piece (13) from the prior art (see
To enhance this support effect, the second side of the membrane features a groove-shaped recess (37), located at the boundary between the central section (29) and the flexing section (28). The clamping piece (23) has a corresponding rib (38), on which the membrane rests.
The membrane in this embodiment is multi-layered and contains two layers, with a fabric layer embedded between them. A protective layer (31) is provided, which, unlike the known embodiment shown in
The support surface does not run parallel to the longitudinal axis. Furthermore, in the sectional view of
In this embodiment, the front surface of the core (22) and an imaginary line spaced from the support surface (39) by the difference in membrane thickness between the flexing section and the central section, lie on the same circle in the sectional view shown in
For embodiments where no protective layer (31) is provided, the surface of the support surface (39) and the front surface of the core (22), which contacts the central section (29), lie on the same circle. In the embodiment shown in
It is understood that the main effect of the invention is achieved through the transition between the central section (29) and the flexing section (28) rolling on the support surface (39). Therefore, it is not strictly necessary for the entire front surface of the core (22) to lie on the circle. It is sufficient if the edge areas adjacent to the flexing section (28) lie on the circle.
It is also not necessary for the front surface of the core and the imaginary line spaced from the support surface to lie on a circle. In principle, any mathematical function can be used, provided it is continuous and inflection-free in the section where the support surface (39) or the imaginary line spaced from the support surface (39) by the membrane thickness and the edge area of the front surface of the core (22) lie.
In the embodiment shown in
Following the path of the membrane in
A tangent (43) is also drawn at inflection point 41, between the convexly curved section positioned at the transition from the outer section to the flexing section and the concavely curved section. This tangent (43) forms an angle β with the longitudinal axis (16), which is less than 30°. Additionally, a tangent (44) is drawn at inflection point 42, between the convexly curved section positioned at the transition from the central section to the flexing section and the concavely curved section. This tangent (44) forms an angle α with the longitudinal axis (16), which is less than 65°. The position of the inflection points is independent of the choice of an elastic support surface, and is therefore also advantageous in an embodiment without an elastic support surface.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102023132994.4 | Nov 2023 | DE | national |
