Metering pump with metering diaphragm

Abstract

The invention relates to a metering pump having a metering chamber, a working chamber and a metering diaphragm, wherein the metering chamber and the working chamber are separated from each other by the metering diaphragm, wherein a device is provided for reciprocating the metering diaphragm between a first position and a second position, wherein the volume of the metering chamber in the first position is smaller than the volume of the metering chamber in the second position. A metering pump is provided, whose metering diaphragm has a longer service life and can be hydraulically operated as far as possible even at very low metering fluid pressures on the suction side; according to the invention, a prestressing device is provided, which prestresses the metering diaphragm in the direction of the first or second position.

Description

Technical Field

[0001] The present invention relates to a metering pump, which comprises a metering chamber, a working chamber and a metering diaphragm, wherein the metering chamber and the working chamber are separated from each other by the metering diaphragm. In addition, a device for reciprocating the metering diaphragm between a first position and a second position is provided, wherein the volume of the metering chamber in the first position is smaller than the volume of the metering chamber in the second position. Background Art

[0002] Usually, the metering chamber has two connections, namely a suction connection and a pressure connection, each connected to a non-return valve. During the suction stroke, i.e. the movement of the metering diaphragm from the first position into the second position, the non-return valve is connected to the pressure connection and the metering medium is sucked into the metering chamber at the suction connection via the non-return valve.

[0003] During the squeeze stroke, i.e. as soon as the direction of movement of the metering diaphragm is reversed and it moves from the second position to the first position, the volume of the metering chamber decreases and the pressure in the metering chamber increases, which results in the non-return valve at the suction connection closing and the non-return valve at the squeeze connection opening. The metering medium can then be pushed out of the metering chamber via the squeeze connection. The above procedure can be repeated as required in order to draw in metering medium via the suction connection and to convey metering medium via the pressure connection.

[0004] The movable metering diaphragm is held in some form. Usually, the metering diaphragm has an edge region, in which it is clamped or clamped between two components. Since the metering diaphragm is always bent or deformed alternately in one direction or the other, it is exposed to high loads in the immediate vicinity of the clamping or clamping region. This alternating bending creates a continuous change between tensile and compressive stresses in the material. As a result, the metering diaphragm can become grooved, cracked, etc. in the region adjacent to the clamped edge region, which can ultimately lead to premature rupture of the metering diaphragm.

[0005] Furthermore, in the case of hydraulic drive, the hydraulic fluid arranged in the working chamber oscillates under pressure, and although the movement of the metering diaphragm in the direction of the first position can be easily implemented by increasing the hydraulic pressure, the return movement to the second position is essentially achieved by means of the fluid pressure provided in the metering fluid to be delivered via the suction connection. This limits the application range of the pump, since there must be a given minimum pressure that is always applied at the suction connection in order to ensure a reliable return movement of the metering diaphragm into the second position and thus to ensure reliable operation of the pump. Summary of the invention

[0006] Based on the described prior art, the object of the present invention is therefore to provide a metering pump whose metering diaphragm has a longer service life and which can be operated hydraulically as far as possible even at very low metering fluid pressures on the suction side.

[0007] According to the present invention, an object is to provide a prestressing device which prestresses the metering diaphragm in the direction of the first position or the second position.

[0008] This has the result that even without a pressure difference between working chamber and metering chamber, a force is already exerted on the metering diaphragm and the latter is elastically deformed.

[0009] The prestress is preferably selected in such a way that, in contrast to the metering diaphragms of the prior art, the metering diaphragm is no longer in a released state, but only between two positions prestressed in the same direction. As a result, the alternating bending effect is eliminated and thus also the constant loading and unloading of the edge region of the metering diaphragm when the metering diaphragm is transitioned from an outwardly bent state to an inwardly bent state. In addition, the measures according to the invention ensure that during the suction stroke, a force is always exerted on the metering diaphragm in the direction of the second position, so that the metering pump can be hydraulically driven with very low metering fluid pressures. In other situations in which an alternating bending effect would normally occur, the metering fluid would even have to exert a force on the metering diaphragm in order to "topple" the metering diaphragm from a state displaced in the direction of the first position into a state displaced in the direction of the second position.

[0010] Particularly preferably, the prestressing device has such a design structure that the metering diaphragm is prestressed in the direction of the first position. In this way, the metering diaphragm is pushed in the direction of the first position at any time.

[0011] In another preferred embodiment, the device for reciprocating the metering diaphragm is a hydraulic device, wherein a hydraulic fluid is arranged in a working chamber, wherein the hydraulic device has such a design structure that it can act on the hydraulic fluid with hydraulic pressure to move the metering diaphragm in the direction of the first position.

[0012] Another preferred embodiment provides that the metering diaphragm comprises an elastic material, preferably a metal. Due to the prestressing of the metering diaphragm, the metering diaphragm is displaced in the direction of the first position until the return force of the elastic material compensates for the prestressing. In principle, the measure according to the invention means that the first and second positions of the metering diaphragm are displaced due to the provision of the prestressing device, so that the metering diaphragm is always prestressed or bent in the direction of the first position even in the second position with a larger volume of the metering chamber.

[0013] In a preferred further embodiment, the metering diaphragm comprises a flat metal foil. Such a flat metal foil has an edge region at which the metering diaphragm is held by a clamping device. By way of example, the clamping device can comprise two elements with mutually corresponding annular contact surfaces, between which the edge region of the metering diaphragm is arranged and clamped. When the metering diaphragm is held at its edge region, it can be moved in one direction or the other by a force acting on the central region of the metering diaphragm, so that the metering diaphragm bends in said direction.

[0014] In a particularly preferred embodiment, the clamping device is designed in such a way that it acts as a prestressing device.

[0015] This can be implemented, for example, by means of corresponding contact surfaces having a non-flat configuration. By way of example, they can have a curved configuration. In a particularly preferred embodiment, the corresponding contact surfaces are conical or have a conical surface, wherein the cone angle of the contact surface is preferably between 0° and 10°, optimally between 2° and 5°. If a flat metal metering diaphragm is clamped between such a curved or conical contact surface, this will automatically induce a prestress. Thus, an additional force-exerting element, such as a spring pressing on the diaphragm, can be omitted. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other advantages, features and possible uses will emerge from the following description of preferred embodiments and the associated drawings, in which:

[0017] Figure 1 A schematic cross-section through a membrane and a clamping device according to a first embodiment of the invention is shown. DETAILED DESCRIPTION

[0018] The basic structure of the described metering pump is known to the person skilled in the art. Figure 1 Only a sectional view of the metering diaphragm 5 is shown, which separates the metering chamber 1 from the working chamber 2. The metering diaphragm 5 is clamped at its edge region between the clamping devices 3, 4. The clamping devices 3, 4 comprise two cylindrical elements 3, 4 having contact surfaces facing each other, between which the edge region of the metering diaphragm 5 is clamped. Due to the conical configuration of the contact surfaces with a cone angle α, the edge region of the metering diaphragm 5 is clamped at the edge region of the metering diaphragm 5. Figure 1 In the case shown, the metering diaphragm 5 bends to the left when the two cylindrical elements 3, 4 of the clamping device are moved toward each other and the edge area of ​​the diaphragm is clamped. Figure 1 The clamped device is shown prestressed towards the left.

[0019] In a preferred embodiment, the working chamber 2 is filled with a hydraulic fluid, to which pressure can be applied by means of suitable means, such as a slave piston. When the pressure in the working chamber 2 rises above the pressure in the metering chamber 1, the metering diaphragm 5 moves still further to the left. This position is schematically indicated by the dashed line 5'. When the pressure in the working chamber 2 decreases, the diaphragm moves back to this position again, as indicated by the solid line 5.

[0020] The prestressing of the membrane according to the invention avoids alternating bending of the membrane. Microstructural changes occur in the case of alternating bending loads common in the prior art, which can lead to premature fatigue of the material. In the case of alternating bending, the force-travel diagram also does not exhibit the linear relationship usually expected for elastic materials (Hooke's law), but shows hysteresis in the area of ​​alternating bending.

[0021] Now the movement of the diaphragm always takes place in the same direction, so the prestressing prevents alternating bending.

[0022] Reference numerals list

[0023] 1 Measuring chamber

[0024] 2 Working chamber

[0025] 3 Clamping device

[0026] 4 Clamping device

[0027] 5 Metering diaphragm

Claims

1. A metering pump comprising a metering chamber, a working chamber and a metering diaphragm, wherein the metering chamber and the working chamber are separated from each other by the metering diaphragm, wherein means are provided for reciprocating the metering diaphragm between a first position and a second position, wherein the volume of the metering chamber in the first position is smaller than the volume of the metering chamber in the second position, It is characterized in that A prestressing device is provided, which prestresses the metering diaphragm in the direction of the first position, so that the metering diaphragm is no longer in a released state, but is only between two positions prestressed in the same direction, and the metering diaphragm is elastically deformed in the same direction even if there is no pressure difference between the working chamber and the metering chamber; The metering diaphragm comprises an elastic material, wherein the metering diaphragm is metal and, due to the prestress of the metering diaphragm, the metering diaphragm moves in the direction of the first position until a return force of the elastic material compensates for the prestress; The metering diaphragm has an edge region at which the metering diaphragm is held by a clamping device; The clamping device has two contact surfaces corresponding to each other, and the edge area of ​​the metering diaphragm is arranged between the two contact surfaces; The clamping device has such a design that it functions as the prestressing device.

2. The metering pump according to claim 1, characterized in that The device for reciprocating the metering diaphragm is a hydraulic device, and hydraulic fluid is arranged in the working chamber, wherein the hydraulic device has such a design structure that it can act on the hydraulic fluid with hydraulic pressure to move the metering diaphragm in the direction of the first position.

3. The metering pump according to claim 1, characterized in that The metering diaphragm is a flat metal foil.

4. The metering pump according to claim 1, characterized in that The corresponding contact surface has a non-planar configuration.

5. The metering pump according to claim 1, characterized in that The corresponding contact surface has a curved configuration.

6. The metering pump according to claim 1, characterized in that The corresponding contact surface is of conical configuration.

7. The metering pump according to claim 6, characterized in that The cone angle of the contact surface is between 0° and 10°.

8. The metering pump according to claim 6, characterized in that The cone angle of the contact surface is between 2° and 5°.

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