Valve unit, valve assembly and method for checking the closing state of a valve unit

Abstract

The invention relates to a valve unit (10) for metering a fluid, comprising: a fluid housing (12) having a valve seat (14); a fluid channel (16) extending from a fluid inlet (18) to the valve seat (14) and from the valve seat to a fluid outlet (20); a movably mounted valve closing body (24) for controlling or regulating a flow through the fluid channel (16); a first electrode (26) and a second electrode (28), wherein the first electrode (26) is arranged in the fluid channel (16) upstream of the valve seat (14) and the second electrode (26) is arranged in the fluid channel (16) downstream of the valve seat (14), wherein the two electrodes (26, 28) are spaced apart from each other by a maximum of 3 mm and / or the maximum distance of each electrode (26, 28) from the valve seat is a maximum of 1.5 mm. In addition, a valve assembly (50) and a method for checking the closed state of a valve unit (10) are provided.

Description

Technical Field

[0001] The invention relates to a valve unit for metering a fluid, a valve assembly having a valve unit and a method for checking a closed state of a valve unit. Background Art

[0002] Reliable closure of valve units is particularly important in sensitive areas where expensive reagents are often used, for example when metering fluids in medical technology. Leaky, leaking valve units can cause considerable damage, for example if reagents escape or become contaminated due to leaky valve units. It is therefore very important to be able to detect the presence of leaks.

[0003] When metering a fluid with a sufficiently high ion concentration, leaks can be determined from the conductivity of the fluid.

[0004] However, in fluids with low particle concentrations, known measuring methods do not work due to the low electrical conductivity of the fluid. Summary of the invention

[0005] It is therefore an object of the present invention to ensure a particularly reliable detection of leaks both when metering fluids with a high ion concentration and also in fluids with a low ion concentration, in particular deionized fluids.

[0006] This object is achieved according to the present invention by a valve unit for metering fluid, the valve unit comprising: a fluid housing having a valve seat; a fluid channel, the fluid channel extending from a fluid inlet to the valve seat and from the valve seat to a fluid outlet; a movably supported valve closing body, the valve closing body being used to control or regulate a flow through the fluid channel; and a first electrode and a second electrode, wherein the first electrode is arranged in the fluid channel upstream of the valve seat and the second electrode is arranged in the fluid channel downstream of the valve seat, wherein the two electrodes are spaced apart from each other by a maximum of 3 mm and / or the maximum distance between each electrode and the valve seat is a maximum of 1.5 mm.

[0007] If the valve unit no longer closes reliably and leakage occurs, for example due to wear of the valve closing body or due to other defects, a potential difference occurs at the valve seat. This potential difference is limited to a small area in the immediate vicinity of the valve seat.

[0008] In the case of a pressure-driven, slightly conductive fluid flowing through the valve seat, this potential difference occurs, especially when the gap that occurs is small enough. This is because the amplitude of the potential difference is related to the wall potential of the solid at the valve seat and the path length of the wall potential drop. If the valve unit is in the maximum open state, the fluid flows through the valve seat unhindered. Through a relatively large cross-section of, for example, 0.8mm to 2mm in the open state, the ions in the center of the channel are not subjected to the electrostatic repulsion caused by the wall potential of the channel wall and can pass through the valve seat unhindered. In this case, a so-called streaming potential is not formed. If the valve is completely closed, no potential difference occurs.

[0009] The potential difference at the valve seat occurs in particular when the double layer is greater than the gap at the valve seat or is about the same size as the gap due to the wall potential of the channel wall. The so-called Debye length of the double layer is here the path length from the channel wall into the fluid, in which the electrostatic field of the channel wall acts on the charge carriers present in the fluid. In deionized water, the ion concentration is particularly low due to the small amount of ions present. This causes the wall potential and thus the electrostatic repulsion to enter the fluid by several hundred micrometers. In fluids with a higher ion concentration, this path length is only 1 nm to 2 nm.

[0010] Typically, leakage at the valve seat is caused by a gap of a few micrometers. The gap is then smaller than the described Debye length, and a potential difference is formed at the valve seat in the pressure-driven flow in the fluid. This potential difference can be measured.

[0011] The potential difference occurs because even in deionized fluids there are small amounts of charge carriers, such as hydroxide ions, hydronium ions, carbonates (dissolved CO2) and / or impurities due to salt. In the event of a leak, if the gap that occurs is particularly small, the charge carriers with the same polarity as the channel wall gather at the valve seat, thereby generating a potential difference in the fluid. The potential difference thus generated in the fluid at the valve seat is called the streaming potential. The gathering of charge carriers with the same charge occurs in particular due to electrostatic interactions at the boundary surfaces of the fluid housing and the charge carriers in the fluid.

[0012] Due to the proximity of the electrodes to the valve seat, this potential difference can be measured. For this purpose, a voltage measuring device can be connected between the first and second electrodes.

[0013] In this way, leakage of the valve unit can be determined particularly reliably.

[0014] The invention is used in particular in microvalve units whose drives have a width of 6 mm to 10 mm.

[0015] If the fluid to be metered has a sufficiently high ion concentration, leaks can also be determined by conductivity measurement. For this purpose, only a suitable measuring device, in particular a conductivity measuring device, must be connected.

[0016] The distance between the electrodes can be less than 1 mm, preferably less than 0.8 mm.

[0017] The distance between the electrodes is measured in particular along the flow path of the fluid.

[0018] The minimum distance between the two electrodes is preferably 0.3 mm, in particular 0.5 mm. This makes it possible to reliably avoid contact between the electrodes due to position tolerances of the electrodes.

[0019] According to one embodiment, the valve unit has a metallic fluid interface arranged on the fluid inlet, wherein the fluid interface forms the first electrode. Such a fluid interface is usually made of metal. As a result, the fluid interface can be used as an electrode without further modifications and the structure of the valve unit can remain simple.

[0020] The fluid connection projects into the fluid housing, for example, and ends at a maximum of 1.5 mm upstream of the valve seat. As a result, the required maximum distance between the first and second electrodes can be reliably maintained.

[0021] In order to reliably position the second electrode, the fluid housing comprises a recess for receiving the second electrode. The recess is particularly shaped such that the second electrode can be inserted in a form-fitting manner.

[0022] Instead of subsequently placing the electrodes on the fluid housing, the first electrode and / or the second electrode can be firmly integrated in the fluid housing as an insert component. The first electrode and / or the second electrode can be injection molded, for example. In this way, the installation of the valve unit can be simplified, because the electrodes do not have to be installed when the valve unit is assembled. As a result, the positioning accuracy when positioning the electrodes can also be improved, because the position tolerances are smaller when the electrodes are injection molded than when they are installed after the fluid housing is manufactured.

[0023] The valve unit preferably has a contact element for contacting the first and / or second electrode, which extends from the electrode to the outside of the valve unit. Preferably, the contact element extends at a point outside the valve unit. In this way, the electrode can be integrated into the circuit in a simple manner.

[0024] According to one embodiment, the second electrode surrounds the valve seat. As a result, leakage can be reliably determined regardless of the direction in which the fluid undesirably escapes from the valve seat.

[0025] The area of ​​the fluid housing that contacts the medium is preferably made of a non-conductive material having a wall potential that is not equal to zero, in particular a negative wall potential. Such plastics are, for example, PMMA, nylon or polyamide. Since the wall potential of the area of ​​the fluid housing that contacts the medium is not equal to zero, a sufficiently strong potential can be formed when the same fluid is used. In particular, the greater the magnitude of the wall potential, the stronger the potential that occurs when a leak occurs.

[0026] Alternatively or additionally, the region of the fluid housing that is in contact with the medium is formed from a glass-fiber-reinforced plastic. This has the advantage that neutrally charged plastics can also be used. The glass fibers cause a strong negative surface charge, which facilitates the generation of a potential difference.

[0027] The object is further achieved by a valve assembly having a valve unit, which is designed as described above, and a voltage measuring device, which is connected in a circuit between a first electrode and a second electrode. With the aid of such a valve assembly, a low-cost measuring system for leaks can be realized, which also functions reliably in solutions with a low conductivity of less than 500 μS / cm, in particular less than 50 μS / cm. The valve assembly does not require complex additional electronics. In particular, only a circuit for voltage measurement is required, and the application of an external voltage, as is required when measuring conductivity, can be omitted. However, this does not exclude that a voltage can nevertheless be applied to measure conductivity.

[0028] Furthermore, the object is achieved by a method for checking the closed state of a valve unit when metering a fluid with a conductivity of less than 500 μS / cm, in particular less than 50 μS / cm, the valve unit being designed as described above, wherein a voltage is measured between two electrodes of the valve unit and a leakage of the valve is inferred from the measured voltage.

[0029] In particular, the potential difference between the fluid inlet and the fluid outlet is measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other advantages and features of the present invention are apparent from the following description and the accompanying drawings to which reference is made. In the accompanying drawings:

[0031] Figure 1 shows an exploded view of a valve unit according to the invention,

[0032] Figure 2 The principle of generating a potential difference is schematically shown,

[0033] Figure 3 Schematically shows the construction of the valve unit in the region of the valve seat,

[0034] Figure 4The measuring principle used in the valve unit according to the invention is schematically illustrated.

[0035] Figure 5 A diagram is shown for illustrating the potential difference,

[0036] Figure 6 shows the curve of the measured potential difference in relation to the occurrence of leakage when metering a fluid with low conductivity,

[0037] Figure 7 The measured conductivity is higher than that of Figure 5 The graph shows the change in the potential difference of the fluid relative to the leakage that occurs, and

[0038] Figure 8 The curve of the potential difference measured during operation of the valve unit according to the invention is shown. DETAILED DESCRIPTION

[0039] Figure 1 A valve unit for metering a fluid, for example a medicinal agent, is shown in an exploded view.

[0040] The valve unit 10 comprises a fluid housing 12 which has a valve seat 14. The valve seat 14 is preferably formed integrally in the fluid housing 12.

[0041] The valve seat 14 is arranged, in particular, in a recess 13 in the fluid housing 12 .

[0042] A section of the fluid channel 16 extends in the fluid housing 12 , which section extends from the fluid inlet 18 to the valve seat 14 and from the valve seat to the fluid outlet 20 .

[0043] exist Figure 1 In the valve unit 10 illustrated in FIG. 1 , the fluid housing 12 is arranged on an additional flange housing 15 . The fluid channel 16 is continued in the flange housing 15 , so that the fluid inlet 18 and the fluid outlet 20 are located on the flange housing 15 .

[0044] exist Figure 1 In the embodiment shown in , a flange housing 15 for a valve unit 10 is shown. However, in practice, a plurality of valve units 10 are often required in the metering process in order to meter different reagents. In this case, the flange housing 15 is usually enlarged so that a plurality of valve units 10 can be mounted on a one-piece flange housing 15.

[0045] The flange housing 15 thus enables simpler installation of the valve unit 10 in a metering installation.

[0046] However, it is also conceivable in principle for the flange housing 15 to be formed integrally with the fluid housing 12 .

[0047] A fluid connection 19 , 21 is connected to the fluid inlet 18 and to the fluid outlet 20 .

[0048] A drive unit 22 , for example a magnetic drive, is provided for opening and closing the valve unit 10 . Such a drive unit 22 for microvalves usually has a width of 6 mm to 10 mm, measured here into the plane of the drawing.

[0049] The drive unit 22 is connected to Figure 1 The valve closing body 24 which is not visible in the figure is coupled. However, the valve closing body Figure 2 Illustration in Chinese.

[0050] The valve closing body 24 controls or regulates the flow through the fluid passage 16. In the closed state of the valve unit 10, the valve closing body 24 sits on the valve seat 14 so that the fluid flow through the fluid passage 16 is prevented.

[0051] In the open state of the valve unit 10 , the valve closing element 24 is lifted from the valve seat 14 by means of the drive unit 22 , so that a fluid flow through the fluid channel 16 can take place for metering purposes.

[0052] In an ideal situation, only the two states mentioned above occur, namely completely closed or opened in a targeted manner for metering purposes.

[0053] However, it may also happen that the valve unit 10 or the valve closing element 24 does not close properly, for example due to wear phenomena, product defects or the like.

[0054] In this case, a gap or leakage occurs at the valve seat 14 in the maximum closed state of the valve unit 10. This is disadvantageous because in this case even only a small amount of the fluid to be metered can flow out of the fluid channel 16 unhindered or drip. Since the fluid to be metered is usually a very expensive reagent, even a small loss of fluid means an economic loss. In addition, there is the risk that foreign matter can enter the fluid due to the gap and contaminate it.

[0055] It is very difficult to determine such leakage in practice, since the valve unit 10 is partly very small and the valve seat 14 itself is not visible in the installed state of the valve unit 10. The amount of fluid that escapes in the event of a leakage is also very small and difficult to detect with the naked eye.

[0056] According to the invention, leakage is therefore determined by measuring the potential difference between the fluid inlet 18 and the fluid outlet 20 as a voltage.

[0057] For this purpose, the valve unit 10 comprises a first electrode 26 and a second electrode 28 , wherein the first electrode 26 is arranged in the fluid channel 16 upstream of the valve seat 14 and the second electrode is arranged in the fluid channel 16 downstream of the valve seat 14 .

[0058] By connecting the electrodes 26 and 28 to a voltage measuring instrument, the potential between the electrodes 26 and 28 can be measured.

[0059] exist Figure 1 In the embodiment illustrated in the figure, the first electrode 26 is formed by a metallic fluid interface 19, which is arranged on the fluid inlet 18. In this way, the first electrode 26 does not have to be realized by a separate component. However, it is quite feasible that the first electrode 26 is realized by another component.

[0060] The fluid connection 19 here passes through the flange housing 15 via a thin, tubular projection 29 and ends in the fluid housing 12 at most 1.5 mm upstream of the valve seat 14 , in particular 0.5 mm upstream of the valve seat 14 , but preferably at least 0.25 mm upstream of the valve seat 14 .

[0061] The second electrode 28 is arranged in the fluid housing 12 , wherein the second electrode 28 in particular surrounds the valve seat 14 .

[0062] Preferably, the second electrode 28 surrounds the valve seat 14 so that it is not important in which direction the fluid flows through the valve unit 10 , so that when connecting the valve unit 10 it is not necessary to pay attention to where the fluid inlet 18 and the fluid outlet 20 are arranged.

[0063] exist Figure 1 In the embodiment illustrated in FIG. 1 , the second electrode 28 is symmetrically designed and surrounds both the inlet 36 and the outlet 38 of the valve seat 14 .

[0064] For easier positioning of the second electrode 28 , a recess 32 is provided in the fluid housing 12 .

[0065] For contacting the second electrode 28, the valve unit 10 has a contact element 34 which extends from the electrode 28 to the outside of the valve unit 10. The contact element 34 is, for example, a metal wire.

[0066] As in Figure 1 As can be seen in FIG. 1 , a groove 40 is formed in the flange housing 15 on the outer side oriented toward the fluid housing 12 , in which groove the contact element 34 extends.

[0067] exist Figure 1In the embodiment illustrated in , the electrodes 26, 28 are mounted on the valve unit 10. However, it is also conceivable that the electrodes 26, 28 are firmly integrated as insert components in the fluid housing 12. The electrodes 26, 28 can be inserted into a mold for producing the fluid housing 12 and be injection-molded around, for example.

[0068] The two electrodes 26, 28 are spaced at a maximum of 3 mm from one another. Alternatively or additionally, the maximum distance of each electrode 26, 28 from the valve seat 14 is at most 1.5 mm. Only by such a small distance between the electrodes 26, 28 can the potential difference between the fluid inlet 18 and the fluid outlet 20 be reliably measured.

[0069] The minimum distance between the electrodes 26, 28 is, for example, 0.5 mm. Although a smaller distance between the electrodes 26, 28 is theoretically possible, tolerances must also be taken into account when positioning the electrodes 26, 28. If the distance is too small, there is the risk that a short circuit between the electrodes 26, 28 will occur if the tolerance position is unfavorable, and potential measurement will no longer be possible.

[0070] The fluid housing 12 is preferably made of an electrically non-conductive material and is in particular a plastic component, such as an injection molded part. By forming the fluid housing 12 and preferably also the flange housing 15 from plastic, the electrodes 26, 28 are insulated from one another by the fluid housing 12, that is, a complex insulation of the electrodes 26, 28 can be dispensed with. In particular, the fluid is the only potential electrical conductor between the electrodes 26, 28.

[0071] The flange housing 15 and the fluid connection 21 at the fluid outlet 20 are preferably also made of a non-conductive material such as plastic.

[0072] To install the valve unit 10 , the flange housing 15 , the fluid housing 12 and the second electrode 28 are placed below the drive unit 22 in a stacked and packaged manner and are firmly connected to the drive unit 22 , in particular screwed together.

[0073] The fluid connections 19 , 21 are pressed into the flange housing 15 or screwed thereto, for example, during assembly of the valve unit.

[0074] The two fluid connections 19 , 21 are designed in particular to receive hose connections having UNF screw connections.

[0075] exist Figure 1 The valve unit 10 shown in FIG. 1 serves only to illustrate a possible configuration; however, the design concept according to the invention can in principle be transferred to almost any valve.

[0076] Figure 2The principle of generating a potential difference which can be measured according to the invention to determine leaks, in particular when using fluids with a low electrical conductivity, for example less than 500 μS / cm, is illustrated by means of a greatly simplified partial view of a valve unit 10 with a valve seat 14 and a valve closing element 24 .

[0077] For components known from the above embodiments, the same reference numerals are used and reference is made to the above explanations in this regard.

[0078] exist Figure 2 1 shows the valve unit 10 in a slightly open position, which is intended to illustrate a leakage.

[0079] The fluid housing 12 has a negative charge 44 at its boundary surfaces 42 , in particular in the areas in contact with the medium.

[0080] Positive charge carriers 46 and negative charge carriers 48 are present in the fluid.

[0081] If a leak occurs at the valve seat 14, especially a small gap, an interaction occurs between the negative charge 44 at the boundary surface 42 of the fluid housing 12 and the charge carriers 46, 48 in the fluid. As a result, the negative charge carriers 48 are retained in front of the gap due to repulsive forces, while the positive charge carriers 46 can pass through the gap. As a result, an accumulation of negative charge carriers 48 occurs in front of the gap, i.e. upstream of the valve seat 14. Behind the gap, i.e. downstream of the valve seat 14, the positive charge carriers 46 increase or a dilution of the negative charge carriers 48 occurs.

[0082] The accumulation of charge carriers 48 in front of the gap, which normally only occurs during leakage, enables the measurement of the potential difference between the fluid inlet 18 and the fluid outlet 20 .

[0083] If already combined Figure 1 As described, electrodes 26 , 28 are provided for this purpose.

[0084] Figure 3 The functional principle is supplementarily illustrated by a greatly simplified partial view of a valve arrangement 50 according to the invention having a valve unit 10 according to the invention, as shown in FIG. Figure 1 The valve unit 10 shown in FIG. 1 is designed like the valve unit 10 shown in FIG.

[0085] exist Figure 3 A first electrode 26 upstream of the valve seat 14 and a second electrode 28 downstream of the valve seat 14 are schematically illustrated in FIG.

[0086] The valve assembly 50 also includes a voltage meter 42 connected in an electrical circuit 54 between the first electrode 26 and the second electrode 28 .

[0087] If already combined Figure 2As explained, when a leakage occurs, an accumulation of negative charge carriers 48 occurs in front of the gap and an accumulation of positive charge carriers 46 occurs behind the gap.

[0088] In this case, a voltage can be measured between the electrodes 26 , 28 , which voltage indicates a leakage.

[0089] In this case, the first electrode 26 acts as an anode and the second electrode 28 acts as a cathode.

[0090] In the closed or maximally open state of the valve unit 10 , no voltage can be measured, since in this case no accumulation of identically charged charge carriers 46 , 48 occurs upstream or downstream of the valve seat 14 .

[0091] In order to promote the accumulation of charge carriers 46 , 48 for the purpose of voltage measurement in the event of leakage, the region of the fluid housing 12 in contact with the medium has a wall potential which is not equal to zero.

[0092] exist Figure 2 4 illustrates negative charge carriers 44 at the boundary surface 42, that is, the part of the fluid housing that contacts the medium is composed of a material with a negative wall potential. Alternatively, the region that contacts the medium can also be composed of a material with a positive wall potential. In this case, positive charge carriers 46 accumulate in front of the gap and negative charge carriers 48 accumulate behind the gap.

[0093] A plastic with a negative wall potential is, for example, PMMA. A plastic with a positive wall potential is, for example, nylon or polyamide.

[0094] Another possibility for promoting the accumulation of charge carriers 46, 48 for the purpose of voltage measurement during leakage is to use plastic with glass fibers. Thus, neutrally charged polymers such as PEEK can also be used to produce the fluid housing 12. In particular, the area of ​​the fluid housing 12 that contacts the medium can be composed of glass-fiber reinforced plastic.

[0095] The conductivity can be determined with an identical design of the valve unit 10 by connecting a conductivity measuring device to the two electrodes 26 , 28 instead of the voltage measuring device 52 .

[0096] Figure 4 The diagram illustrates the electrical double layer which is advantageous for the measuring principle. The electrical double layer is formed at the phase boundary on the fluid side. The phase boundary can be a solid, another liquid or a gas.

[0097] Usually, at the phase boundary in the charged state two charge layers are situated opposite each other, which charge layers are of opposite sign, as in a capacitor.

[0098] The double layer consists not only of a fixed layer but also of a diffuse layer.

[0099] exist Figure 4 A solid is exemplarily illustrated in FIG. 4 , at which positive charge carriers 46 in the fluid accumulate.

[0100] The wall potential drops over the path length d of the entire double layer. The path length is often referred to as the Debye length. The Debye length is dependent, inter alia, on the ion concentration of the fluid and can be several hundred micrometers in deionized water.

[0101] The so-called Zeta potential is located at the beginning of the diffusion layer d, where the charge carriers 46, 48 in the fluid are mobile. The Zeta potential (also called ζ potential) is the potential at the shear layer of a particle moving in suspension.

[0102] Figure 5 Graph illustrating potential difference and ion concentration as a function of distance from the surface of a charged particle suspended in a dispersion medium.

[0103] Figure 6 The leakage in the valve unit 10 is illustrated in the form of flow (curve a) and, parallel thereto, the measured voltage (curve b). The measured voltage in volts is plotted on the left ordinate.

[0104] The fluid used was a 5 μM Tris / borate solution with a conductivity of 1.5 μS / cm and a pH of 8.

[0105] The leakage is simulated here in particular by opening the valve unit 10 in a defined manner by applying an actuator voltage to the valve unit 10, in particular to the drive unit 22, whereby a gap is generated between the valve closing element 24 and the valve seat 14. The actuator voltage in volts is plotted on the abscissa of the diagram.

[0106] With a higher actuator voltage, the degree of opening of the valve unit 10 increases, that is, as the actuator voltage increases, the gap also increases and the leakage increases. The flow rate through the valve unit in μl / min is plotted on the right ordinate in the diagram. At an actuator voltage of 1.8, a flow rate of 225 μl / min occurs in particular.

[0107] exist Figure 6 It can be seen from the potential curve illustrated in FIG that the potential curve is strongly correlated with the leakage curve. That is, the leakage at the valve seat 14 can be inferred based on the measured potential difference.

[0108] According to the method according to the invention, it is therefore possible to measure the voltage between the two electrodes 26 , 28 of the valve unit 10 when metering a fluid in the closed state of the valve unit 10 and to infer leakage of the valve unit 10 based on the measured voltage.

[0109] The measured potential profile also allows the flow velocity of the fluid to be inferred. The flow velocity can also be measured from this.

[0110] exist Figure 7 Another variation of the measured potential associated with a leak in the valve unit 10 is illustrated in FIG. Figure 6 Unlike the figure shown in Figure 7 The curve shown in FIG. 1 uses a 500 μM Tris / borate solution, which has a conductivity of 26.4 μS / cm.

[0111] As per Figure 7 As can be seen, the measurable potential difference is lower in the more concentrated solution than in the less concentrated solution. If the voltage values ​​are compared for the above solutions at an actuator voltage of 1.8 V and the same flow rate, a value of 9 V is reached in the less concentrated solution, compared to a value of 2.5 V in the more concentrated solution.

[0112] This means that the method according to the invention for measuring leakage based on potential difference is particularly suitable for fluids with low ion concentration and low conductivity, for example for fluids with conductivity less than 500 μS / cm, in particular less than 50 μS / cm.

[0113] At higher ion concentrations it may be advantageous to measure the conductivity.

[0114] Figure 8 The diagram illustrates the curve of the potential measured during operation of the valve unit 10 according to the invention. In particular, Figure 8 The potential difference is shown as a function of the time profile of the valve switching.

[0115] The potential increases briefly at the time O when the valve opens.

[0116] At the time C when the valve is closed, a higher signal is generated since the closing process caused by the mechanical return spring is slower than the opening process caused by the drive unit 22 .

[0117] Further information can also be obtained from the profile of the potential. For example, the quality of the actuator used can be inferred from the profile.

[0118] A possible rebound of the valve closing element 24 is also detectable, more precisely on the basis of the double peak D.

[0119] After the valve opening O, when the valve unit 10 is maximally opened, charge carriers cannot accumulate and no potential difference can be built up until the closing C.

[0120] In order to be able to build up a potential difference, the gap between the valve seat 14 and the valve closing element 24 is preferably smaller than the Debye length.

Claims

1. A valve unit (10) for metering a fluid, comprising: A fluid housing (12), the fluid housing having a valve seat (14); a fluid passage (16) extending from a fluid inlet (18) to the valve seat (14) and from the valve seat to a fluid outlet (20), a movably supported valve closing body (24) for controlling or regulating a flow through the fluid channel (16); and a first electrode (26) and a second electrode (28), wherein the first electrode (26) is arranged upstream of the valve seat (14) in the fluid channel (16), and the second electrode (28) is arranged downstream of the valve seat (14) in the fluid channel (16), wherein the first electrode (26) and the second electrode (28) are spaced apart from each other by a maximum of 3 mm and / or the first electrode (26) and the second electrode (28) are spaced apart from the valve seat by a maximum of 1.5 mm, It is characterized in that The valve unit (10) has a metallic fluid connection (19) arranged at the fluid inlet (18), wherein the fluid connection (19) forms the first electrode (26).

2. The valve unit (10) according to claim 1, characterized in that The distance between the first electrode (26) and the second electrode (28) is at least 0.3 mm.

3. The valve unit (10) according to claim 1, characterized in that The fluid connection (19) projects into the fluid housing (12) and ends at a maximum of 1.5 mm upstream of the valve seat (14).

4. The valve unit (10) according to claim 1 or 2, characterized in that: The fluid housing (12) comprises a recess (32) for accommodating the second electrode (28).

5. The valve unit (10) according to claim 1 or 2, characterized in that: The first electrode (26) and / or the second electrode (28) is / are firmly integrated in the fluid housing (12) as an inserted component.

6. The valve unit (10) according to claim 1 or 2, characterized in that: For contacting the first electrode and / or the second electrode (28), the valve unit (10) has a contact element (34) which extends from the first electrode (26) or the second electrode (28) to the outside of the valve unit (10).

7. The valve unit (10) according to claim 1 or 2, characterized in that: The second electrode (28) surrounds the valve seat (14).

8. The valve unit (10) according to claim 1 or 2, characterized in that: The region of the fluid housing (12) that is in contact with the medium is formed from a non-conductive material having a wall potential that is not equal to zero.

9. The valve unit (10) according to claim 1 or 2, characterized in that: The area of ​​the fluid housing (12) that comes into contact with the medium is composed of glass-fiber-reinforced plastic.

10. The valve unit (10) according to claim 8, characterized in that The non-conductive material has a negative wall potential.

11. A valve assembly (50) comprising a valve unit (10) according to any one of the preceding claims and a voltage measuring device (52), which is connected in an electrical circuit (54) between the first electrode (26) and the second electrode (28).

12. A method for checking the closed state of a valve unit (10) according to any one of claims 1 to 10 when metering a fluid with an electrical conductivity of less than 500 µS / cm, wherein a voltage is measured between the first electrode (26) and the second electrode (28) of the valve unit (10) and a leakage of the valve unit (10) is inferred from the measured voltage.

13. The method according to claim 12, characterized in that The conductivity is less than 50 μS / cm.

Images