EP2877745B1 - Metering system and metering pump therefor - Google Patents

Description

The present invention relates to a metering system for metering a liquid metering medium with a suction line which is filled with a dosing medium with the liquid pressure p _s , and a pressure line which _is filled with the metering medium with the liquid pressure p _d , wherein the suction line via a metering pump trained dosing is connected to the pressure line. With the help of the dosing pump then dosing can be promoted from the suction line in the pressure line. For this purpose, the metering pump has a delivery chamber whose volume can be changed by means of a movable displacement element, for example a membrane, such that in a first position of the displacement element the delivery chamber has a minimum volume V _min and in a second position of the displacement element the delivery space has maximum volume V _max . In this case, the delivery chamber is connected via a pressure valve to the pressure line and a suction valve to the suction line, so sucked by an oscillating movement of the displacer in alternation dosing from the suction via the suction valve in the pumping chamber and dosing from the pumping chamber via the pressure valve in the Pressure line can be discharged.

Such metering systems and corresponding metering pumps have been known for a long time.

In the EP 1 546 557 B1 is described as a diaphragm pump metering pump described.

When dosing liquids, in particular outgassing pumped media, such as sodium hypochlorite (NaClO), air bubbles can form in the suction line connected to the suction and sucked into the dosing. It is also possible that air bubbles form in the delivery chamber. This is often the case after longer dosing breaks, for example after a weekend. Since the suction port is connected to a suction line, which is formed in the simplest case as a hose and ends in a reservoir, it may happen when replacing the reservoir, in particular when the pump is running, that the suction line is temporarily no longer connected to the fluid and Air sucks.

If there is too much gas in the delivery chamber of an oscillating feed pump, it can lead to disturbances of the metering process, if the own compressibility of the pump due to the trapped gas volume is insufficient to the pressure valve against the fluid pressure p _d and optionally against the return spring and the weight of the Open the closing body of the pressure valve. In other words, it may happen that, if the gas content in the pumping chamber becomes too high, despite the movement of the displacer from the second to the first position, the pressure in the pumping chamber is not increased sufficiently to open the pressure valve connected to the pressure port. The reason for this is the high compressibility of gas compared to liquids.

If, therefore, it is no longer possible for the displacer element to apply a sufficiently high pressure to open the pressure valve, the pumped medium is not pumped, that is to say the desired metering can not take place.

To get out of this error state, it is necessary to restore the compression capability to present at the pressure port back pressure p _d.

For this purpose, various approaches are known. In the simplest case, the metering pump has a screwable vent opening to the delivery chamber, which can be opened manually, so that the metering pump does not have to work against the liquid pressure p _d , but against the ambient pressure for a short time, so that the gas present in the delivery chamber can escape via the vent opening , Disadvantage of this method, however, is that a manual intervention is necessary.

Another solution is to equip corresponding vents with an actively controllable valve and to open this valve in periodic sections. However, this method has the disadvantage that the vent opening is also opened when there is no gas in the pumping chamber and therefore a certain leakage current of the pumped medium occurs.

When in the EP 1 546 557 B1 In contrast, an additional connection between delivery chamber on the one hand and pressure port on the other hand is provided, which is opened intermittently to allow liquid re-entry from the pressure line into the pumping chamber, which simultaneously gas can escape from the pumping chamber, so that the ratio between compressible gases and incompressible fluids again improved and, ideally, the pressure applied to the pressure port back pressure p _d in the delivery chamber can be achieved again.

However, this solution is relatively complex, since in addition to an additional bypass line, a valve closing this and a driving device for driving the valve must be provided. In addition, the intermittent opening of the bypass valve reduces the efficiency of the pump, since the opening takes place even if no gas is contained in the pumping chamber.

Based on the described prior art, it is an object of the present invention to provide a metering system and a metering pump adapted for this purpose, which has a high efficiency, shows no leakage current and which has a simple structure.

wobei k = 1,5 ist.With regard to the metering this object is achieved in that $\frac{V_{\mathrm{Max}}}{V_{\min }}>\sqrt[\kappa ]{\frac{p_d}{p_s}}.$

where k = 1.5.

The exponent k, also referred to as the adiabatic exponent, is a physical quantity that describes the ratio of the specific heat capacity of a medium at constant pressure to the specific heat capacity of the medium at constant volume. The value k is different for each gas and also temperature dependent. However, it has been found that a value of 1.5 can be used for k to capture all practically relevant use cases. As already mentioned, the displacement element must work against the back pressure, ie the pressure p _d on the pressure line. Since usually the delivery chamber is connected via a check valve to the pressure line, the displacer has to work against the spring of the check valve and optionally - depending on the arrangement of the closing body of the valve - against the weight of the closing body.

According to the invention, therefore, the ratio of the maximum volume V _max and the minimum volume V _{min of} the delivery chamber is chosen so large that even if the delivery chamber is completely filled with air, the necessary pressure p _d can be achieved. In most cases, the liquid pressure of the metering medium in the suction line p _{s will} correspond to the atmospheric pressure, but also applications are conceivable in which the suction line is already under positive or negative pressure.

The ratio between V _max and V _min thus depends on the expected fluid pressure p _d in the pressure line.

In a preferred embodiment, the metering in the pressure line, a liquid pressure p _d > 7 bar, preferably p _d > 10 bar and best p _d > 16 bar. Especially at such high liquid pressures is a reliable vent for accurate dosing advantage.

vorzugsweise $\frac{V_{\max }}{V_{\min }}\ge 6$

und am besten $\frac{V_{\max }}{V_{\min }}\ge 8.$

For typical applications, it is provided in a preferred embodiment that $\frac{V_{\mathrm{Max}}}{V_{\min }}\ge 4.$

preferably $\frac{V_{\mathrm{Max}}}{V_{\min }}\ge 6$

and best $\frac{V_{\mathrm{Max}}}{V_{\min }}\ge \mathrm{8th.}$

With the above conditions can be functionally reliable dosing systems for the vast number of applications to achieve.

vorzugsweise $\frac{V_{\max }}{V_{\min }}\ge 6$

und am besten $\frac{V_{\max }}{V_{\min }}\ge 8.$

With regard to the metering pump for use in the metering system according to the invention described, the object is achieved in that $\frac{V_{\mathrm{Max}}}{V_{\min }}\ge 4.$

preferably $\frac{V_{\mathrm{Max}}}{V_{\min }}\ge 6$

and best $\frac{V_{\mathrm{Max}}}{V_{\min }}\ge \mathrm{8th.}$

The appropriate choice of the ratio between the maximum volume and the minimum volume of the delivery chamber ensures that a dosing, in which the metering pump is used, ensures for most applications that even when completely filled with air delivery chamber, the inherent compressibility of the metering pump large enough is to promote the air from the delivery chamber against the liquid pressure p _{d of} the pressure line.

In a particularly preferred embodiment of the metering pump is provided that between the first position and the second position of the displacement element, a third position of the displacement element is provided, in which the delivery chamber has a working volume V _A , wherein V _min <V _A <V _max , and the metering pump has two modes of operation, wherein in a metering mode the displacer is reciprocated between the first and second positions or between the second and third positions and reciprocated in a bleed mode between the first and second positions ,

In other words, the maximum displacement (V _max - V _min ) is only achieved during the venting mode, wherein during the normal dosing mode, the displacement is only (V _max - V _A ) or (V _A - V _min ).

A smaller stroke volume and, concomitantly, a smaller stroke of the displacement element can, in particular when the displacement element is designed as a membrane, extend the service life of the displacement element. Therefore, in a preferred embodiment provided that the maximum stroke takes place only in the venting mode, while only a reduced stroke takes place in dosing mode.

In a preferred embodiment, therefore, a device is provided which switches the dosing pump at regular intervals for a short time in the venting mode. For example, the metering pump could be switched to the venting mode every fiftieth or every two hundredth stroke for one stroke, whereby any gaseous medium possibly located in the delivery chamber is reliably pushed out of the delivery chamber.

Alternatively, the metering pump may also have a device for detecting a gaseous medium in the delivery chamber, so that a control device may be provided which switches the metering pump in the venting mode when the detection device detects gaseous medium in the head.

• Figur 1 einen Querschnitt durch einen Dosierkopf einer erfindungsgemäßen Dosierpumpe und
• Figur 2 eine perspektivische Draufsicht auf die in Figur 1 dargestellte Ausführungsform.

Further advantages, features and possible applications will become apparent from the following description of a preferred embodiment and the accompanying figures. Show it:

• FIG. 1 a cross section through a dosing of a metering pump according to the invention and
• FIG. 2 a perspective top view of the in FIG. 1 illustrated embodiment.

In FIG. 1 is a sectional view through a dosing of an embodiment of a metering pump according to the invention shown. The dosing head 10 has a displacement element 1, which is connected to a membrane 2. Due to the movement of the displacement element 1, the membrane 2 is moved back and forth, so that the volume of the delivery chamber 3 changes. The delivery chamber 3 is connected to a suction port 5 via two series-connected check valves 8, 9, which form the suction valve. For example, a suction line of a dosing system can be connected to the suction connection 5, so that dosing medium is sucked out of the suction line into the delivery chamber 3, when the membrane 2 moves together with the displacement element 1 such that the volume of the delivery chamber 3 increases.

The delivery chamber 3 is also connected to a pressure port 4 via two check valves 6, 7 arranged in series, which together form the pressure valve. The pressure connection can be connected to the pressure line of a metering system, so that when the membrane 2 moves together with the displacement element 1 such that the volume of the delivery chamber 3 is reduced, metering via the two check valves 6, 7 and the pressure port 4 in the Pressure line is pressed.

In FIG. 2 is a perspective view of the dosing head 10 can be seen and one recognizes both the pressure port 4 and the suction port. 5

The delivery chamber 3 consists on the one hand of the space in which the membrane reciprocates and on the other hand from a pressure channel 11 which connects the membrane space with the check valve 7, and a suction channel 12 which connects the membrane space with the check valve 9. Both the pressure channel 11 and the suction channel 12 form part of the delivery chamber volume. The minimum volume V _{min of} the delivery chamber 3, which can be adjusted by means of the movable diaphragm 2, therefore consists at least of the volume of the pressure channel 11 and the volume of the suction channel 12.

In order to select the minimum volume V _{min of} the delivery chamber as low as possible, both the pressure channel 11 and the suction channel 12 are arranged transversely to the direction of movement of the displacement element 1, ie the direction of movement of the displacement element closes with the direction of movement of a closing element of the pressure valve and with the direction of movement a closing element of the suction valve at an angle of about 45 °.

In the embodiment shown, the ratio V _max / V _min is about 3. However, this ratio can be chosen to be even greater if the metering pump is to pump against high pressures.

LIST OF REFERENCE NUMBERS

1

displacement

2

membrane

3

delivery chamber

4

pressure connection

5

suction

6, 7

check valves

8, 9

check valves

10

dosing

11

pressure channel

12

suction

Claims (8)

1. Metering system for metering a liquid metering medium, with a suction line, which is filled with a metering medium at the liquid pressure p_s, and a pressure line, which is filled with the metering medium at the liquid pressure p_d, wherein the suction line is connected to the pressure line by a metering member configured as a metering pump, with which metering medium can be conveyed from the suction line into the pressure line, wherein the metering pump has a conveying chamber, the volume of which can be changed with the aid of a movable displacement element in such a way that, in a first position of the displacement element, the conveying chamber has a minimum volume V_min and, in a second position of the displacement element, the conveying chamber has a maximum volume V_max, the conveying chamber being connected by a pressure valve to the pressure line and by a suction valve to the suction line, so, by an oscillating movement of the displacement element, metering medium can alternately be sucked out of the suction line via the suction valve into the conveying chamber and metering medium can be discharged from the conveying chamber via the pressure valve into the pressure line, characterised in that $\frac{V_{\max }}{V_{\min }}>\sqrt[\kappa ]{\frac{p_d}{p_s}},$

   

   wherein κ = 1.5.
2. Metering system according to claim 1, characterised in that $\frac{V_{\max }}{V_{\min }}\ge 4,$

   

   preferably $\frac{V_{\max }}{V_{\min }}\ge 6$

   

   and at best $\frac{V_{\max }}{V_{\min }}\ge 8.$

   
3. Metering system according to claim 1 or 2, characterised in that the liquid pressure p_d > 7 bar, preferably p_d > 10 and at best p_d > 16.
4. Metering pump in a metering system according to claim 1 or 2, which has a conveying chamber, the volume of which can be changed with the aid of a movable displacement element in such a way that, in a first position of the displacement element, the conveying chamber has a minimum volume V_min and, in a second position of the displacement element, the conveying chamber has a maximum volume V_max, wherein the conveying chamber is connected by a pressure valve to a pressure connection for connection to a pressure line and is connected by a suction valve to a suction connection for connection to a suction line, characterised in that $\frac{V_{\max }}{V_{\min }}\ge 4,$

   

   preferably $\frac{V_{\max }}{V_{\min }}\ge 6$

   

   and at best $\frac{V_{\max }}{V_{\min }}\ge 8.$

   
5. Metering pump according to claim 4, characterised in that provided between the first position and the second position of the displacement element is a third position of the displacement element, in which the conveying chamber has a working volume V_A, wherein V_min < V_A < V_max, and the metering pump has two operating modes, wherein, in one operating mode, the displacement element is moved back and forth between the second and third position and, in a venting mode, it is moved back and forth between the first and the second position.
6. Metering pump according to claim 4, characterised in that a device is provided, which briefly switches the metering pump into the venting mode at regular time intervals.
7. Metering pump according to claim 4, characterised in that a device is provided for detecting a gaseous medium in the conveying chamber and a device is provided, which switches the metering pump into the venting mode when the detection device detects gaseous medium in the head.
8. Metering pump according to any one of claims 4 to 6, characterised in that the movement direction of the displacement element encloses an angle between 15° and 85°, preferably between 30° and 60° and at best between 40° and 50° with the movement direction of a closing element of the pressure valve and/or with the movement direction of a closing element of the suction valve.

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