DE102020119502A1 - METHOD OF OPERATING A DOSING PUMP IN A LIQUID SUPPLY SYSTEM - Google Patents

Abstract

The present invention relates to a method for operating a metering pump (3), which is designed to be self-priming only for a back pressure that is below a limit pressure, in a liquid supply system, in which it is determined whether the metering pump (3) is in a state ready for metering, by cyclically opening and closing a discharge valve (25), which is arranged between the outlet side of the metering pump (3) and a low-pressure area, during operation of the metering pump (3) and measuring the pressure on the outlet side in front of the discharge valve (25). , wherein the metering pump (3) is not yet in the metering-ready state when the measured pressure during the cyclical opening and closing of the discharge valve (25) is below a first pressure value that is lower than the limit pressure, and the pressure fluctuations are below a first fluctuation value lie.

Description

The present invention relates to a method for operating a metering pump, which is designed to be self-priming only for a back pressure that is below a limit pressure, in a liquid supply system.

In a liquid supply system for a car wash, various liquid additives are metered into the base liquid. A metering pump is used for each liquid additive, which pumps the liquid additive into a metering line. If the pressure in the metering line exceeds an opening pressure of the metering valve, this opens and the liquid additive reaches the feed line at an injection point, in which it mixes with the base liquid.

The problem here is that the metering pump in the metering line cannot generate enough pressure to open the metering valve when gas is sucked in by the metering pump, i. H. when the dosing pump pump head is dry. The dosing pump can also suck in gas or a gas/liquid mixture up to a certain back pressure, but if the back pressure exceeds a limit pressure, the dosing pump cannot further increase the pressure in the dosing line by sucking in the gas. A self-priming dosing pump is understood in this context to mean that the dosing pump designed for liquids can also pump gases to a certain extent and can build up a certain negative pressure for the purpose of suction. However, this is only possible up to a maximum suction height for the liquid to be pumped and only up to a certain back pressure. If a pressure that exceeds the limit pressure has to be generated in the dosing line, it is necessary to vent the dosing pump, i. i.e. it must be ensured that there is no more gas in the pump head of the dosing pump.

A bypass line is usually provided for venting, which branches off from the pressure line or metering line of the metering pump and which leads back into the reservoir. In this bypass line, a vent valve is arranged, which can be opened manually or electrically. When this valve is open, the dosing pump can first pump the gas or gas/liquid mixture in the pump without counter-pressure and suck in the liquid to be dosed. If the liquid is in the pump head of the pump, it is pumped back into the reservoir via the bypass line. If liquid has been pumped back into the reservoir, the dosing pump is vented and in a state ready for dosing. If it is switched on in this state, it immediately conveys the liquid to be dosed.

This method for venting the metering pump has the disadvantage that the metering pump has to be operated until a certain amount of liquid has been pumped back into the reservoir. It is not possible to draw any conclusions about the condition of the dosing pump during venting or in a state that may already have been vented.

The invention is therefore based on the object of specifying a method of the type mentioned at the outset, with which it can be determined whether the metering pump is in a state ready for metering. Furthermore, the dosing pump should be able to be put into this state ready for dosing if it has been determined that the dosing pump is not yet in the state ready for dosing.

According to the invention, this object is achieved by a method having the features of claim 1. Advantageous refinements and developments result from the dependent claims.

In the method according to the invention, it is determined whether the metering pump is in a state ready for metering, in which a discharge valve, which is arranged between the outlet side of the metering pump and a low-pressure area, is cyclically opened and closed during operation of the metering pump and during which the pressure on the outlet side is measured before the drain valve. The metering pump is not yet in the state ready for metering if the pressure measured during the cyclical opening and closing of the discharge valve is below a first pressure value that is lower than the limit pressure and the pressure fluctuations are below a first fluctuation value.

In the method according to the invention, it is advantageously not necessary to let the metering pump pump until it is evident that no liquid can be pumped, since the negative pressure generated by the metering pump is not sufficient to suck in liquid or the back pressure that builds up exceeds the limit pressure. Rather, in the method according to the invention it is sufficient to cyclically open and close the outlet valve during operation of the metering pump and to measure the pressure on the outlet side in the process. The cyclical opening and closing of the drain valve is also referred to as toggle in the following. In this way, an approach to the state ready for dosing can already be detected, even if no liquid has yet been conveyed by the dosing pump. Also can in this way it can also be detected that the dosing pump is already in a state ready for dosing.

In particular, the dosing pump is not yet ready for dosing when it is dry, i. i.e. if there is no liquid but gas or a gas/liquid mixture in the pump head of the dosing pump. Furthermore, if there is gas in the line on the outlet side of the metering pump, it is not yet in the metering-ready state. In this case, the gas is namely compressed during operation of the metering pump. In the method according to the invention, the connection between the measured pressure on the outlet side and the change in the state of the discharge valve during the toggle is utilized. When the drain valve is open, the outlet side of the dosing pump is connected to the low-pressure area. There is therefore no increase in pressure on the outlet side. When the drain valve is closed, the pressure on the outlet side increases. However, the course of the increase over time and the resulting pressure value depend on whether there is still gas in the line on the outlet side and whether there is gas or liquid in the pump head of the dosing pump. The first pressure value is set in advance in such a way that for the given volumes of the dosing pump and the subsequent line on the outlet side and depending on the period of cyclical opening and closing of the discharge valve, this first pressure value is not exceeded if there is still gas in the dosing pump and the line is located at the outlet side. Furthermore, in this case the pressure fluctuations are below the first fluctuation value, which has also been determined beforehand as a function of the volumes and the period of the cyclical opening and closing of the discharge valve.

Advantageously, it can thus be determined very quickly, in a very simple manner, whether the dosing pump is in a state ready for dosing.

According to a development of the method according to the invention, the metering pump is immediately before the metering-ready state if the measured pressure when the discharge valve is closed is above the first pressure value, which is lower than the limit pressure, and the pressure fluctuations are above the first fluctuation value. If, during further operation of the dosing pump, this liquid has been sucked in, which is then in the pump head, i. H. the dosing pump is no longer dry, there is an increase in pressure on the outlet side of the dosing pump. However, gas is still compressed in the line on the outlet side of the dosing pump if the discharge valve is in the closed state during toggling.

This results in a slight increase in pressure compared to the state in which the dosing pump is still dry. In this case, the pressure value that results when the drain valve is toggled is above the first pressure value. The pressure fluctuations also increase in this case, since the dosing pump is already pumping liquid. Advantageously, it can thus be determined in a simple and quick manner by cyclically opening and closing the drain valve when the metering pump is just before the metering-ready state.

In a further development of the method according to the invention, in the liquid supply system the metering pump is connected to a feed line via a metering line and a metering valve. Furthermore, a branch is arranged in the metering line between the metering pump and the metering valve, in which the drain valve is arranged. If, in the method according to the invention, the dosing valve is closed during the cyclical opening and closing of the drain valve and if it has been determined that the dosing pump is immediately before the state ready for dosing, the drain valve remains in an open state and the dosing pump delivers a specific first volume. Then the drain valve is closed and the metering valve is opened. Thereafter, the metering pump delivers a specific second volume, whereupon the metering pump is in a state ready for metering.

In this case, the dosing pump in a liquid supply system is put into a state ready for dosing by the method. It is established that the metering pump is just before the metering-ready state, in which the pump head of the metering pump is already filled with liquid, but the lines on the outlet side of the metering pump are still filled with gas. In the method, the knowledge of the volumes of the line system between the outlet side of the metering pump, the drain valve and the metering valve is used to initially displace the gas in the branch to the drain valve and then to displace the gas from the metering line. The metering valve can be opened, for example, by the pressure building up in the metering line. Even if this opening pressure is greater than the limit pressure of the dosing pump, the dosing pump can generate this pressure because in this case it is no longer dry, i. H. is already sucking in liquid and pumping it into the dosing line. After the gas in the metering line has also been completely displaced, the metering pump is in a state ready for metering and operation of the metering pump can be terminated. This means that the dosing valve also closes.

The metering pump's ready-to-meter state is characterized by the fact that when the metering pump is started up, liquid is delivered immediately and leads to an immediate increase in pressure in the metering line, which can lead to the metering valve opening, so that the liquid to be metered passes directly through the metering valve into the feed line .

According to another embodiment of the method according to the invention, the dosing pump is in the state ready for dosing when the pressure measured when the drain valve is closed is above a second pressure value. In this case, the dosing pump is ready for dosing under pressure control. If the measured pressure exceeds a second pressure value, the pump head of the dosing pump is filled with liquid and there is also no more gas in the lines on the outlet side of the dosing pump. In the liquid supply system described above, this second pressure value corresponds, for example, to the opening pressure of the metering valve. However, it is in particular greater than this opening pressure. If the pressure is measured at the metering pump, the pressure losses through the line and the pressure required for the flow of liquid through the metering line must be added to the opening pressure of the metering valve. If the second pressure value is measured, it is thus ensured that there is no longer any gas in the first metering line.

In the process according to the invention, the limit pressure is, for example, in a range from 700 mbar to 900 mbar. In the method according to the invention, the first pressure value is, for example, in a range from 400 mbar to 640 mbar, preferably in a range from 450 mbar to 600 mbar. The first pressure value is in particular 600 mbar. The fluctuation value for the pressure fluctuations is, for example, in a range from 140 mbar to 180 mbar, preferably in a range from 150 mbar to 175 mbar.

The second pressure value is in particular above the opening pressure of the metering valve. The opening pressure of the metering valve is, for example, in a range from 0.8 to 1.2 bar.

The pressure in the low-pressure area is, for example, lower than the limit pressure of the dosing pump. The pressure in the low-pressure area is 1013 mbar, for example. It corresponds, for example, to the ambient pressure.

The period of cyclic opening and closing of the metering pump is, for example, in a range from 0.5 sec to 10 sec, preferably in a range from 1 sec to 5 sec.

In a further development of the method according to the invention, when it has been determined that the dosing pump is in the state ready for dosing, the drain valve is closed and, in particular thereafter, the dosing pump is switched off. For dosing operation of the dosing pump, it is switched on again with the drain valve closed, and the dosing pump pumps liquid into a dosing line, which branches off between the drain valve and the outlet side of the dosing pump. Advantageously, the dosing pump is then completely vented and can start dosing the liquid immediately without gas being pumped first.

According to one embodiment of the method according to the invention, the pressure on the outlet side of the metering pump is measured by a pressure sensor which measures the pressure in an area between the outlet side and the outlet valve.

According to another embodiment, the pressure on the outlet side of the dosing pump is measured by a pressure sensor that is integrated into the dosing pump. Furthermore, the pressure can be determined indirectly via a drive of the metering pump. For example, a pressure detection element can be set up to detect the power consumption of the metering pump and to determine the pressure on the outlet side based on the power consumption.

• Die Figur zeigt den Aufbau des Ausführungsbeispiels des erfindungsgemäßen Flüssigkeitsversorgungssystems.

The invention will now be explained using exemplary embodiments with reference to the drawing:

• The figure shows the structure of the exemplary embodiment of the liquid supply system according to the invention.

The liquid supply system comprises a first reservoir 1, which can hold a first liquid additive. A first dosing pump 3 is provided for conveying the liquid additive received from the first reservoir 1 , which sucks in the first liquid additive via a first bottom suction valve 2 . The first metering pump 3 is designed in such a way that it is designed to be self-priming only for a back pressure that is below a first limit pressure. In the present exemplary embodiment, the first limit pressure is 800 mbar.

The first metering line 4 leads to a first metering valve 5 . The other side of the metering valve 5 is connected to a feed line 6 . The first liquid additive is thus metered into section 6 of the feed line at the first injection point 16 via the first metering valve 5 .

The first metering valve 5 is designed as a non-return valve, which is oriented such that it opens when the pressure on the side of the first metering line 4 is greater by the opening pressure of the first metering valve 5 than the pressure in section 6 of the feed line on the other side of the first metering valve 5. The opening pressure of the metering valve 5 is greater than the first limit pressure of the first metering pump 3. The opening pressure of the first metering valve 5 is 1 bar in the exemplary embodiment.

When the pump head of the first dosing pump 3 is dry, i. H., if gas, such. B. air, is in the pump head of the first metering pump 3, the first metering pump 3 cannot suck in any first liquid additive that is in the first reservoir 1, since the back pressure in the first metering line 4 exceeds the limit pressure up to which the first metering pump 3 is self-priming, will be exceeded, since the first metering valve 5 will only open above the limit pressure.

The section 6 of the feed line leads in the direction of flow behind the first injection point 16 into a distributor block 7 which comprises a plurality of spray valves 8 . The spray valves 8 are designed as 2/2-way valves. The distributor block 7 is coupled to control units 9, so that a first control unit 9-1 controls a first spray valve 8-1, a second control unit 9-2 controls a second spray valve 8-2 and a third control unit 9-3 controls a third spray valve 8-3 . If the first spray valve 8-1 is open, the base liquid is fed from the section 6 of the feed line into a first spray line 10-1. Similarly, when the second spray valve 8-2 is open, the base liquid is fed from the feed line section 6 into a second spray line 10-1, and when the third spray valve 8-3 is open, the base liquid is fed from the feed line section 6 into the third spray line 10-3 led. From the spray lines 10, which are also part of the feed line, the liquid reaches (not shown) spray openings of an ejection unit 34, via which it is sprayed onto a vehicle in a car wash. The spray lines 10 belong to the feed line, since washing liquid is conveyed to the spray openings of the washing system via these spray lines 10 .

The liquid supply system also includes a second reservoir 11, which accommodates a second liquid additive. This second liquid additive can be conveyed via a second bottom suction valve 12 by means of a second metering pump 13 into a second metering line 14 to a second metering valve 15 . Like the first metering pump 3, the second metering pump 13 is designed to be self-priming only for a back pressure that is below a second limit pressure. In the exemplary embodiment, the second limit pressure of the second metering pump 13 corresponds to the first limit pressure of the first metering pump 3. The second metering valve 15 also corresponds to the first metering valve 5. It is also a check valve with the same opening pressure.

The second liquid additive is thus metered into the third spray line 10 - 3 of the feed line at a second injection point 17 via the second metering valve 15 .

Correspondingly, the liquid supply system can include further reservoirs for further liquid additives, for which further dosing pumps can be provided which meter the corresponding liquid additive to further dosing valves in section 6 of the feed line or one of the spray lines 10 of the feed line. Such a liquid supply system is known per se.

In the liquid supply system according to the invention, a first branch 18 is arranged in the first metering line 4 between the first metering pump 3 and the first metering valve 5 . The first branch is designed as a Y-piece and leads into the first branch line 19 which leads to a first collector valve 20 . On the other side of the first collector valve 20 is a collector section 21.

The first collector valve 20 is designed as a non-return valve, with the passage direction leading from the first branch line 19 into the collector section 21 . The opening pressure of the first collector valve 20 is very low, so that it opens as soon as the pressure in the first branch line 19 exceeds the pressure in the collector section 21 . The opening pressure of the first collector valve 20 is lower, in particular very much lower, than the opening pressure of the first metering valve 15 ..

Likewise, a second branch 22 is arranged in the second metering line 14, which is also designed as a Y-piece. The second branch 22 leads into a second branch line 23 which leads to a second collector valve 24 . In the exemplary embodiment, the second collector valve 24 is designed in the same way as the first collector valve 20. The second collector valve 24 establishes a passage from the second branch line 23 into the collector section 21. The collecting section 21 is thus provided in common for the first metering pump 3 and the second metering pump 13 . Downstream of the collecting section 21, an electronically controllable outlet valve 25 is arranged, via which fluid from the collection section 21 can reach a drain line 26 . The drain line 26 carries fluid out of the liquid supply system, e.g. B. in the driving foot 33, from which it is derived. The drain line 26 is thus connected to a low-pressure area, namely the ambient pressure.

Further collecting valves for further pumps for further liquid additives can be arranged in the collecting section 21 .

Furthermore, a third branch 27 is arranged at section 6 of the feed line, at which the base liquid supplied via section 6 can be branched off into a flushing line 30 . The flushing line 30 leads to a flushing valve 28, which is also designed as a check valve. The opening pressure of the flushing valve 28 is selected such that the flushing valve 28 opens due to the pressure exerted by the supplied base liquid when the spray valves 8 are closed and the outlet valve 25 is open.

A pressure sensor 29 which measures the pressure in the collecting section 21 is arranged in the collecting section 21 . This pressure essentially corresponds to the pressure in the first metering line 4 and the first branch line 19 when the first collector valve 20 is open. Accordingly, the pressure sensor 29 measures the pressure in the second metering line 14 and the second branch line 23 when the second collector valve 24 is open.

In an alternative exemplary embodiment, instead of the pressure sensor 29, a pressure sensor is integrated into the dosing pumps 3 and 13, which detects the respective pressure on the outlet side.

In yet another embodiment, no pressure sensor is provided. In this case, the pressure on the outlet side of the respective metering pump 3, 13 can be determined indirectly via the power consumption of the metering pump 3, 13. Furthermore, a pressure sensor can also be arranged in the drive of the dosing pump. The pressure on the outlet side of the metering pump 3, 13 can then be calculated from the pressure measured by this pressure sensor.

The liquid supply system also includes a control unit 31 which is connected to the electrically controllable outlet valve 25, the pressure sensor 29 and the first and second metering pumps 3, 13 via data lines 32. The outlet valve 25 can be opened and closed by means of the control unit 31 , the pressure measured by the pressure sensor 29 can be received and the first metering pump 3 and the second metering pump 13 can be switched on and off. If a pressure sensor is integrated into the metering pumps 3, 13, the measured pressure can also be transmitted to the control unit 31 in this case.

• Zunächst wird geprüft, ob die erste Dosierpumpe 3 in einem dosierbereiten Zustand ist. In einem solchen dosierbereiten Zustand ist sie, wenn die Dosierpumpe 3 mit dem ersten Flüssigkeitszusatz aus dem Vorratsbehälter 1 gefüllt ist. Ferner wird sichergestellt, dass auch die erste Dosierleitung 4 und die erstes Abzweigungsleitung 19 mit dem ersten Flüssigkeitszusatz gefüllt sind. In diesem Zustand ist das erste Dosierventil 5 und das Auslassventil 25 geschlossen. Ferner ist auch das erste Sammlerventil 20 geschlossen.

Exemplary embodiments of the method according to the invention are explained below. Further details of the liquid supply system according to the invention are also explained. First, the basic process of the process for generating the washing liquid in the car wash is described:

• First, it is checked whether the first dosing pump 3 is in a state ready for dosing. It is in such a state ready for dosing when the dosing pump 3 is filled with the first liquid additive from the reservoir 1 . Furthermore, it is ensured that the first dosing line 4 and the first branch line 19 are also filled with the first liquid additive. In this state, the first metering valve 5 and the outlet valve 25 are closed. Furthermore, the first collector valve 20 is also closed.

If it has been determined that the first dosing pump 3 is not yet in a state ready for dosing, it is put into this state, as will be explained later.

Furthermore, it is determined whether the second dosing pump 13 is in such a state ready for dosing. If it is not yet in such a state, the second metering pump 13 is also put into this state ready for metering, as will be explained later.

It is then the base liquid, i. H. Fresh water or process water, funded via the section 6 of the feed line to the distributor block 7. The spray valves 8 are controlled via the control units 9 in such a way that the spray lines 10 required for cleaning the vehicle in the car wash are supplied with washing liquid or base liquid.

A first liquid additive is then pumped out of the first reservoir 1 via the first metering line 4 and the first metering valve 5 by means of the first metering pump 3 and metered into the feed line at the first injection point 16 . Likewise, the second metering pump 13 pumps a second liquid additive from the reservoir 11 via the second metering line 14 and the second metering valve 15 at the second injection point 17 into the third spray line 10-3 of the feed line. In this way, a mixture of the first and/or second liquid additive with the base liquid is produced as washing liquid in the spray lines 10 .

• Stromabwärts des Auslassventils 25 bei der Ablassleitung 26 ergibt sich ein Niederdruckbereich, der im Wesentlichen dem Umgebungsdruck entspricht. Das Ablassventil 25 ist somit zwischen der Auslassseite der ersten Dosierpumpe über die erste Abzweigungsleitung 19, das erste Sammlerventil 20, den Sammelabschnitt 21 einerseits und diesem Niederdruckbereich bei der Ablassleitung 26 andererseits angeordnet. Die erste Dosierpumpe 3 wird nun in Betrieb genommen. Das Auslassventil 25 wird dann, gesteuert von der Steuereinheit 31, zyklisch geöffnet und geschlossen. Es wird ein sogenanntes Togglen durchgeführt. Die Periode für das zyklische Öffnen und Schließen des Auslassventils 25 ist bei dem Ausführungsbeispiel 2 sec. Währenddessen wird mittels des Drucksensors 29 oder auf eine andere vorstehend beschriebene Weise der Druck auf der Auslassseite der ersten Dosierpumpe 3 vor dem Ablassventil 25 gemessen.

The following explains how a method for operating the first metering pump 3 is carried out in order to determine whether the first metering pump 3 is in the metering-ready state:

• Downstream of the outlet valve 25 in the outlet line 26 there is a low-pressure area which essentially corresponds to the ambient pressure. The drain valve 25 is thus arranged between the outlet side of the first metering pump via the first branch line 19, the first collector valve 20, the collector section 21 on the one hand and this low-pressure area in the drain line 26 on the other. The first metering pump 3 is now put into operation. The outlet valve 25 is then, controlled by the control unit 31, opened and closed cyclically. A so-called toggle is carried out. The period for the cyclical opening and closing of the outlet valve 25 is 2 seconds in the exemplary embodiment.

• Wird ein Druck gemessen, der unterhalb eines ersten Druckwerts liegt, der kleiner als der Grenzdruck der ersten Dosierpumpe 3 ist, und liegen die gemessenen Druckschwankungen unterhalb eines ersten Schwankungswerts, befindet sich die erste Dosierpumpe 3 noch nicht in dem dosierbereiten Zustand. Bei dem Ausführungsbeispiel liegt der erste Druckwert bei 500 mbar, und der erste Schwankungswert ist bei 170 mbar. In diesem Fall ist der Pumpenkopf der ersten Dosierpumpe 3 trocken, d. h., es befindet sich keine Flüssigkeit im Pumpenkopf. Wenn das Auslassventil 25 geöffnet ist, ergibt sich für die erste Dosierpumpe 3 kein Gegendruck, so dass sie Gas fördern kann. Im geschlossenen Zustand des Auslassventils 25 während des Togglens wird Gas in den Bereich zwischen der Auslassseite der ersten Dosierpumpe 3 und dem Auslassventil 5 komprimiert, so dass ein leichter Druckanstieg gemessen wird, der jedoch geringer als der erste Druckwert ist. In diesem Fall liegen die Druckschwankungen unterhalb des ersten Schwankungswerts. Die Steuereinheit erfasst in diesem Fall, dass die erste Dosierpumpe 3 noch nicht in dem dosierbereiten Zustand ist.

In this way, different states of the first metering pump 3 can be detected, as described below:

• If a pressure is measured that is below a first pressure value that is lower than the limit pressure of the first metering pump 3, and the measured pressure fluctuations are below a first fluctuation value, the first metering pump 3 is not yet in the state ready for metering. In the exemplary embodiment, the first pressure value is 500 mbar and the first fluctuation value is 170 mbar. In this case, the pump head of the first metering pump 3 is dry, ie there is no liquid in the pump head. When the outlet valve 25 is open, there is no back pressure for the first metering pump 3 so that it can pump gas. In the closed state of the outlet valve 25 during toggling, gas is compressed in the area between the outlet side of the first metering pump 3 and the outlet valve 5, so that a slight increase in pressure is measured, but this is lower than the first pressure value. In this case, the pressure fluctuations are below the first fluctuation value. In this case, the control unit detects that the first dosing pump 3 is not yet in the state ready for dosing.

If an increase in pressure is measured while the drain valve 25 is in the closed state when toggled, which exceeds the first pressure value and the pressure fluctuations are above the first fluctuation value, the dosing pump is immediately before the state ready for dosing. In this case, there is liquid in the pump head of the first metering pump 3. The first metering pump 3 sucks in the liquid additive in the reservoir 1, but compresses gas on the outlet side, which is still upstream of the outlet valve 25.

If a significant increase in pressure is measured, so that the measured pressure is above a second pressure value when the discharge valve 25 is closed during toggling, the dosing pump is in the state ready for dosing. In the exemplary embodiment, the second pressure value is 2 bar when the pressure at the first metering pump 3 is measured. At this pressure value, the first metering valve 5 opens so that no further increase in pressure is then possible. Depending on the throttling effect of the first metering valve, the pressure then remains constant.

In this way, the cyclical opening and closing of the first metering pump 3 and the measurement of the pressure on the outlet side of the first metering pump 3 can be used to determine the state in which the first metering pump 3 is located.

The status of the metering pump 13 can also be determined in the same way, with no separate outlet valve and no separate pressure sensor being required. The condition can also be determined using the outlet valve 25 and the pressure sensor 29 .

• Im Ausgangszustand ist das erste Dosierventil 5, das zweite Dosierventil 15, das erste Sammlerventil 20 und das zweite Sammlerventil 24 sowie das Auslassventil 25 geschlossen. Ferner ist auch das Spülventil 28 geschlossen.

The following describes how the procedure for generating the washing liquid in the washing system is carried out in order to put the first and the second metering pump 3, 13 into the state ready for metering if it has been determined that these metering pumps 3, 13 are not in are in this state:

• In the initial state, the first metering valve 5, the second metering valve 15, the first collector valve 20 and the second collector valve 24 and the outlet valve 25 are closed. Furthermore, the flushing valve 28 is also closed.

The outlet valve 25 is now opened and the first metering pump 3 is put into operation. The opening of the outlet valve 25 means that no pressure can build up on the outlet side during operation of the first metering pump 3 . The first metering pump 3 is therefore self-priming in this state; it can promote the gas that is in the pump head of the first metering pump 3 and possibly in upstream parts of the pump head.

The outlet valve 25 is now opened and closed cyclically, as explained above. The pressure is measured by the pressure sensor 29 and transmitted to the control unit 31 . If the outlet valve is in a closed state during this toggle, the control unit 31 detects a slight increase in pressure below the first pressure value. Furthermore, when the outlet valve 25 opens and closes, small pressure fluctuations that are below the first fluctuation value are detected. In the process, gas which is in the first metering pump 3 is conveyed via the first branch line 19 , through the then open first collector valve 20 , the collector section 21 and the outlet valve 25 into the drain line 26 .

As soon as the gas has been pumped out of the first metering pump 3 to such an extent that the first liquid additive, which is in the first storage container 1, has been pumped into the first metering pump 3 and the pump head of the first metering pump 3 is no longer dry, the control unit 31 records an increase in pressure. The measured pressure is above the first pressure value and the pressure fluctuations when opening and closing the outlet valve 25 are greater than the first fluctuation value. In this way, the control unit 31 detects that the first dosing pump 3 is just before the state ready for dosing.

The first dosing pump 3 now delivers the first liquid additive through the first branch line 19, the collecting section 21 and the outlet valve 25, if it is in the open state, into the outlet line 26. If there is no more gas in this line section up to the outlet valve 25, the Further operation of the metering pump 3 with the outlet valve 25 closed compresses gas which may be located between the first branch 18 and the first metering valve 5 in the first metering line 4 . Since the first metering pump 3 is no longer dry, it can increase the pressure in the first metering line 4 until the first metering valve 5 opens. The pressure which is measured by the pressure sensor 29 when the first metering valve 5 opens corresponds to the opening pressure of the first metering valve 5 when the outlet valve is in a closed state during toggling. In this case, the second pressure value is exceeded and the control unit 31 detects in this way that the first dosing pump 3 is in the state ready for dosing.

The outlet valve 25 is now closed and the operation of the first metering pump 3 is terminated by the control unit 31 .

In an alternative embodiment, when it has been detected by the control unit 31 that the first metering pump 3 is just before the state ready for metering, i. That is, if the pressure measured when the dump valve 25 is closed during the toggle is above the first pressure value, the dump valve 25 is placed in an open state. The control unit 31 now detects which volume is delivered by the first metering pump 3 . If a specific first volume has been delivered, which is stored in the control unit 31, the control unit 31 closes the drain valve 25. The pressure increase in the first metering line 4 then opens the first metering valve 5 and a specific second volume is pumped from the first metering pump 3 promoted. The value of this second volume is also stored in the control unit 31. Thereafter, the control unit 31 ends the operation of the first metering pump 3, whereupon the first metering valve 5 closes and the first metering pump 3 is in the metering-ready state.

The first liquid additive is now located in the collecting section 21 . In order to remove this from the collection section, the collection section 21 is rinsed. For this purpose, the outlet valve 25 is opened. At the same time, rinsing water, for example fresh water or process water, is supplied to section 6 of the feed line. The spray valves 8 are in a closed state, so that the flushing water builds up a pressure in the flushing line 30, which causes the flushing valve 28 to open. The flushing water now flushes through the collection section 21 and the outlet valve 25. It is discharged via the drain line 26.

After the collection section 21 and the outlet valve 25 have been sufficiently flushed, the outlet valve 25 is first closed. The supply of rinsing water is then stopped, so that the rinsing valve 28 closes.

Analogously to the first metering pump 3, the second metering pump 13 is now put into the state ready for metering. The second metering pump 13 is put into operation and the outlet valve 25 is first opened and then opened and closed cyclically. In this case, too, the pressure is measured by the pressure sensor 29 and the measured pressure is transmitted to the control unit 31 . As described above, the control unit 31 now detects the state of the second metering pump 13. If it is in the state ready for metering, the outlet valve 25 is closed and the operation of the second metering pump 13 is terminated.

Then, analogously to the previous rinsing process, the collection section 21, in which the second liquid additive is now located, is rinsed with rinsing water. If the collection section 21 and the outlet valve 25 have been completely rinsed, the outlet valve 25 is first closed and then the supply of rinsing water is stopped.

The liquid supply system is now in a state in which it can start operation in the car wash. If the liquid supply system is now to be put into operation, the base liquid is first conveyed into section 6 of the feed line. The flushing valve remains closed since the drain valve 25 is closed. There are then the spray valves 8 of the distributor block 7, if desired, opened. A flow pressure then arises in the feed line. Only then are the metering pumps 3 and 13 put into operation. A washing liquid is then produced in the feed line by dosing the first and the second liquid additive to the base liquid in the feed line. There is no longer the risk that the metering pumps 3 and 13 will need a certain amount of time before they can meter in the respective liquid additive, since they have not yet been vented. In addition, the system is pressurized in such a way that when the metering pumps 3 and 13 start operating, the metering valves 5 and 15 open immediately and the liquid additives are metered in at the injection points 16 and 17.

Reference List

1

first reservoir

2

first bottom suction valve/extraction valve

3

first dosing pump

4

first dosing line

5

first dosing valve

6

section of the feed line

7

distribution block

8th

Spray valves (2/2 way valve)

8-1

first spray valve

8-2

second spray valve

8-3

third spray valve

9

control units

9-1

first control unit

9-2

second control unit

9-3

third controller

10

Feed line spray lines

10-1

first spray line

10-2

second spray line

10-3

third spray line

11

second reservoir

12

second bottom suction valve/extraction valve

13

second dosing pump

14

second dosing line

15

second dosing valve

16

first vaccination site

17

second vaccination site

18

first turn

19

first branch line

20

first collector valve

21

collecting section

22

second turn

23

second branch line

24

second collector valve

25

Vent valve/exhaust valve

26

drain line

27

third Y piece

28

purge valve

29

pressure sensor

30

purge line

31

control unit

32

data lines

33

driving foot

34

ejection unit

Claims (12)

Method for operating a dosing pump (3), which is designed to be self-priming only for a back pressure that is below a limit pressure, in a liquid supply system, in which: it is determined whether the dosing pump (3) is in a state ready for dosing by a drain valve ( 25), which is arranged between the outlet side of the metering pump (3) and a low-pressure area, is cyclically opened and closed during operation of the metering pump (3) and during which the pressure on the outlet side before the drain valve (25) is measured, the metering pump (3) is not yet in the ready-to-dose state when the pressure measured during cyclic opening and closing of the Drain valve (25) is below a first pressure value that is less than the limit pressure, and the pressure fluctuations are below a first fluctuation value. procedure after claim 1 , characterized in that the dosing pump (3) is immediately before the ready-to-dose condition when the pressure measured when the discharge valve (25) is closed is above the first pressure value and the pressure fluctuations are above the first fluctuation value. procedure after claim 2 , characterized in that in the liquid supply system the metering pump (3) is connected to a feed line (6) via a metering line (4) and a metering valve (5) and in the metering line (4) between the metering pump (3) and the metering valve ( 5) a branch (18) is arranged, in which the drain valve (25) is arranged, wherein during the cyclic opening and closing of the drain valve (25) the metering valve (5) is closed, and when it has been determined that the metering pump ( 3) is immediately before the state ready for metering, the drain valve (25) remains in an open state and the metering pump (3) delivers a specific first volume, then the drain valve (25) is closed and the metering valve (5) is opened and then the Metering pump (3) promotes a specific second volume, whereupon the metering pump (3) is in a state ready for metering. procedure after claim 2 , characterized in that the dosing pump (3) is in the state ready for dosing if the pressure measured when the discharge valve (25) is closed is above a second pressure value. Method according to one of the preceding claims, characterized in that the first pressure value is in a range from 400 mbar to 640 mbar. Method according to one of the preceding claims, characterized in that the fluctuation value for the pressure fluctuations is in a range from 140 mbar to 180 mbar. Method according to one of the preceding claims, characterized in that the second pressure value is in a range from 0.8 to 1.2 bar. Method according to one of the preceding claims, characterized in that the period of cyclic opening and closing of the metering pump (3) is in a range from 0.5 sec to 10 sec. Method according to one of the preceding claims, characterized in that when it has been determined that the dosing pump (3) is in the state ready for dosing, the dosing pump (3) is switched off and the drain valve (25) is closed and the dosing pump ( 3) this is switched on again with the drain valve (25) closed and the dosing pump (3) pumps liquid into a dosing line (4), which branches off between the drain valve (25) and the outlet side of the dosing pump (3). Method according to one of the preceding claims, characterized in that the pressure on the outlet side of the metering pump (3) is measured by a pressure sensor (29) which measures the pressure in an area between the outlet side and the outlet valve (25). Procedure according to one of Claims 1 until 9 , characterized in that the pressure on the outlet side of the metering pump (3) is measured by a pressure sensor which is integrated into the metering pump (3). Procedure according to one of Claims 1 until 9 , characterized in that the pressure is determined indirectly via the dosing pump drive.

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