EP3189234B1 - Displacement pump with fluid reservoir - Google Patents

Description

The present invention relates to a positive displacement pump with a delivery chamber, which is connected to a pressure and a suction port. The displacement pump furthermore has a displacement element which determines the volume of the delivery space and which can be moved back and forth between a first position in which the delivery space has a smaller volume and a second position in which the delivery space has a larger volume. The pressure connection is usually connected to the delivery chamber via a pressure valve designed as a check valve and the suction connection is connected to the delivery chamber via a suction valve which is likewise designed as a check valve.

In order to convey a medium, the displacer element, which may for example be a membrane, oscillates between the first and the second position. During the movement of the displacement element from the first to the second position, the so-called suction stroke, the volume of the delivery chamber is increased, as a result of which the pressure in the delivery chamber drops. As soon as the pressure in the delivery chamber falls below the pressure in a suction line connected to the suction connection, the suction valve opens and via the suction connection the medium to be delivered is sucked into the delivery chamber. As soon as the displacement element moves back from the second position in the direction of the first position (this is the so-called pressure stroke), the volume in the delivery chamber decreases and the pressure in the delivery chamber increases. The suction valve is closed to prevent backflow of the medium to be pumped into the suction line. As soon as the pressure in the delivery chamber exceeds the pressure in a pressure line connected to the pressure connection, the pressure valve is opened so that the delivery medium located in the delivery chamber can be pressed into the delivery line.

Such designed as a diaphragm pump positive displacement pump is in the EP 1 546 557 B1 shown and described.

When dosing liquids, in particular outgassing pumped media, such as sodium hypochlorite (NaOCl), gas bubbles can form in the suction line connected to the suction and sucked into the dosing. It is also possible that form gas bubbles in the delivery chamber. This is often the case after longer dosing breaks. Since the Suction connection 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 sucks gas ,

If there is too much gas in the dosing head of an oscillating feed pump, the dosing process may be disturbed, provided that the self-compression capability of the dosing head is insufficient to open the pressure valve against the return spring, the dead weight of the closing body and the system pressure due to the enclosed gas volume. 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 the opening of the pressure valve, the pumped medium is not pumped, i. the desired dosage can not be done.

In order to be able to leave this fault condition, it is necessary to restore the compressibility to the back pressure applied to the pressure port. This can be done by again bringing some liquid into the delivery chamber in order to improve the ratio of compressible to incompressible media so that the pressure built up by the movement of the delivery element can reach the counterpressure applied to the pressure connection again.

When in the EP 1 546 557 B1 Therefore, 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 fluid 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 counterpressure in the delivery chamber can be achieved again.

However, this solution is relatively expensive, since in addition to an additional bypass line, a valve closing this and a drive device for driving the valve must be provided.

Therefore, in the WO 2013/135681 has already been proposed to perform the pressure valve leaky so that even with the pressure valve closed, a return flow channel conveying chamber and pressure port connects, can get through the medium into the pumping chamber and / or gas can escape from the pumping chamber.

However, this embodiment has the disadvantage that the delivery characteristic depends on the pressure in the pressure line connected to the pressure port. In particular, when it is to be pumped against a very high pressure, the amount of delivery fluid, which flows back through the leaking pressure valve in the delivery chamber, increases significantly, so that the dosing is reduced. Another solution is in the EP 2728189 shown wherein a fillable with conveying fluid reservoir is connected via a degassing valve with the pumping chamber.

Against the background of the described prior art, it is therefore an object of the present invention to provide a positive displacement pump which is self-venting, has a simple design and, moreover, has a pressure-stable metering capacity even at high back pressures in the pressure line.

As defined in claim 1, this object is achieved, inter alia, in that a reservoir which can be filled with conveying fluid is connected to the delivery chamber via a degassing valve.

Under a reservoir while any cavity is understood, which is filled with conveying fluid and is optionally separated via valves both from the pumping chamber and from the pressure and suction port.

The degassing valve is designed such that it can be opened at least then during the suction stroke or automatically opens when too much gas in the pumping chamber, whereby conveying fluid is transferred from the reservoir into the pumping chamber and in the sequence during the next pressure stroke of the pressure in the delivery room continues to increase.

If the pressure rise in the pumping chamber is then still insufficient to open the pressure valve, during the next suction stroke again conveying fluid can be supplied from the reservoir into the pumping chamber, so that the pressure in the pumping chamber continues to rise during the pressure stroke. This can be continued until enough pressure builds up again in the pumping chamber to open the pressure valve, so that pumped fluid is optionally pumped together with gaseous components into the pressure line.

Therefore, the displacement pump is preferably designed such that conveying fluid from the suction port via the suction valve without flowing through the reservoir transported in the delivery chamber can be. Then it is possible during the suction stroke and then to conduct delivery liquid into the delivery chamber, if the pressure drop is insufficient to open the suction valve.

In a variant not claimed, the degassing valve in the direction from the reservoir to the delivery chamber has a flow coefficient which is smaller than the flow coefficient of the suction valve. For example, the flow rate coefficient of the degassing valve may be less than 1% or, preferably, even less than 0.2% of the flow coefficient of the suction valve. The flow coefficient is a measure of the achievable throughput of the fluid through the valve in question and is in principle also a measure of the effective cross section. In the context of the present invention, the absolute value of the flow coefficient does not matter, but only the ratio of the flow coefficient of the degassing valve to the flow coefficient of the suction or pressure valve. Alternatively, therefore, the effective cross section of the degassing valve is less than 1% and preferably even less than 0.2% of the effective cross section of the suction valve.

For example, as a definition of the flow coefficient of the conveying fluid flow rate of the valve (ml / min) at a pressure difference of 1 bar and a delivery fluid temperature of 25 ° C can be defined. The flow rate is determined in each case with the valve open.

By the corresponding reduction of the flow coefficient of the degassing valve, this can also be opened when there is no gas in the pumping chamber, so that a detection of the amount of gas is not absolutely necessary. Whenever the degassing valve is opened, a quantity of conveying fluid flows from the reservoir into the delivery space, which leads to a degassing of the delivery space. However, as a result, delivery fluid is also removed from the reservoir, so that it must be replenished. In addition, this reduces the delivery rate, as less delivery fluid is drawn through the suction port and pumped through the pressure port into the delivery line. Due to the large reduction in the flow coefficient, the printing performance is only minimally reduced. In particular, when the flow coefficient is less than 0.2% of the flow coefficient of the suction valve, the degassing valve may always be open or consist of a correspondingly sized throttle.

In an unclaimed variant, the degassing valve is designed as a throttle check valve, which provides a permanent, throttled connection and, if the pressure in the pumping chamber is greater than the pressure in the reservoir, an unthrottled connection. By virtue of this measure, the reservoir can also be filled again with delivery fluid when the delivery chamber is vented, since then a portion of the delivery fluid is pumped into the reservoir.

In a preferred embodiment, the throttle check valve in the unthrottled state, a flow coefficient which is smaller than the flow coefficient of the pressure valve, wherein preferably the flow coefficient of the unthrottled degassing valve is less than 15%, more preferably less than 5% of the flow coefficient of the pressure valve.

This measure ensures that only a small part of the delivery fluid is pumped into the reservoir in the reservoir and the greater proportion of the delivery fluid is transported into the pressure line.

According to the invention it is provided that the degassing valve is a check valve which opens when the pressure in the pumping chamber is less than the pressure in the reservoir. In particular, when the positive displacement pump is used in a metering, which provides only a low pressure, for example ambient pressure on the suction line, the embodiment with check valve is advantageous if the pressure in the reservoir is greater than the pressure in the suction line, then During the suction stroke fluid can be removed from the reservoir, even if the pressure in the delivery chamber does not fall below the pressure in the suction line.

In another variant not claimed, the reservoir is connected to the pressure port. In this case, the degassing valve is particularly preferably connected in series with the pressure valve, wherein the degassing valve is arranged closer to the delivery chamber.

In other words, delivery fluid, which is pumped from the delivery chamber into the pressure line, must first flow through the degassing valve and then through the pressure valve. The reservoir is then formed by the connecting line between the degassing valve on the one hand and the pressure valve on the other. Especially this embodiment has the advantage that the reservoir is automatically replenished, which must be done manually from the separate reservoir from and to. In this embodiment, the flow coefficient of the degassing valve from the delivery chamber into the reservoir should be approximately equal to the flow coefficient of the pressure valve.

In a further preferred embodiment, the reservoir is connected to an accumulator. An accumulator or hydraulic accumulator stores the fluid, i. the delivery fluid, under pressure.

For example, such an accumulator can be formed by a pressure vessel, the interior of which is divided by a movable partition member into two spaces, wherein in one space, a gas, which serves as a pressure accumulator, and in the other space, the conveying fluid is stored.

According to the invention, the positive displacement pump can be used in a metering system with a pressure line in which conveying fluid at a pressure p _{2 is} contained, and with a suction line in which conveying fluid is contained at a pressure p ₁ <p ₂ , the pressure line being connected to the pressure port and the suction line is connected to the suction port.

Particularly preferably, the delivery fluid is pressurized in the reservoir with a pressure p ₃ , where p ₁ <p ₃ <p ₂ .

This embodiment has the advantage that when there is too much gas in the pumping chamber and therefore no pumped fluid pumped via the pressure valve in the pressure line and at the end of the suction stroke no further pumping fluid through the suction line, the suction valve is sucked into the pumping chamber, instead during the suction stroke is introduced via the degassing valve conveying fluid from the reservoir into the pumping chamber, with the result that the pressure in the pumping chamber increases during the next pressure stroke.

Further advantages, features and applications of the present invention will become apparent from the following description of a preferred embodiment.

• Figur 1 eine schematische Darstellung einer Variante.

It shows:

• FIG. 1 a schematic representation of a variant.

In FIG. 1 is schematically shown a dosing with a positive displacement pump. The dosing system serves to pump a conveying fluid from a suction line 1, in which conveying fluid with the fluid pressure p _{1 is} contained, in a pressure line 6 in which conveying fluid is under a fluid pressure p ₂ , where p ₂ > p ₁ .

The positive displacement pump has a delivery chamber 3, in which a displacement element 11 designed as a membrane can be moved back and forth between two positions, wherein in the first position, which is shown in dashed lines in the figure and designated by the reference numeral 4 ', the delivery chamber has smaller volume, and in the second position, which is shown in solid lines and provided with the reference numeral 4, the delivery chamber has a larger volume.

If the membrane is moved from the position 4 'to the position 4, the volume of the delivery space 3 thus increases and the pressure in the delivery space drops. As soon as the pressure in the delivery chamber is smaller than the pressure p ₁ in the suction line 1, the suction valve 2 arranged between the suction line 1 and the delivery chamber 3 opens, which is designed as a check valve.

As a result, conveying fluid is transported from the suction line 1 into the conveying space 3.

Once the movement of the membrane is reversed, i. as soon as the membrane moves from the position 4 in the direction of the position 4 ', the volume of the delivery chamber 3 decreases and the suction valve 2 is closed.

The pressure in the delivery chamber 3 continues to increase until the pressure p ₂ in the pressure line 6 is reached or exceeded. In this case, the pressure valve 5 opens and delivery fluid is transported from the delivery chamber 3 into the pressure line 6.

It is now between the delivery chamber 3 and the pressure valve 5, which is also designed as a check valve, a reservoir 10 and a degassing valve 7 is provided. The reservoir 10 is formed by the connecting line between the degassing valve 7 and the pressure valve 5. The degassing valve 7 is designed as a throttle check valve, i. it consists of a throttled connection 9 and a check valve eighth

In normal operation, ie when there is no or little gas in the delivery chamber 3, the degassing valve 7 does not affect the functioning of the positive displacement pump. The advantages of the inventive arrangement of the reservoir and the degassing valve become clear only when, what can happen during operation or after a long standstill, the delivery chamber 3 contains too large a proportion of gaseous components. Because of the comparatively high compressibility of the gaseous constituents, this may in some circumstances mean that the movement of the membrane from position 4 into position 4 'is no longer sufficient to increase the pressure in the delivery chamber 3 to such an extent that the pressure p _{2 is} reached and the check valve 5 can be opened. In this state, although the membrane between the positions 4 and 4 'reciprocated, but there is neither an opening of the suction valve 2 nor an opening of the pressure valve. 5

In this situation, however, according to the invention, a small amount of the conveying fluid located in the reservoir 10 is guided back into the delivery chamber 3 via the throttle 9. As a result, the pressure in the delivery chamber 3 at the end of the pressure stroke, i. when the diaphragm is in position 4 ', rise until the check valve 8 opens and compressed gas is transferred to the reservoir 10. During the return movement of the membrane to position 4, the check valve 8 closes and the compressed gas in the reservoir 10 can expand only to a slight extent via the throttle 9.

Since the reservoir 10 now contains the gas in a compressed state, the pressure in the delivery chamber 3 will drop so much during the suction stroke that further delivery fluid from the suction line 1 via the suction valve 2 is sucked. This also leads to an increase in the pressure in the delivery chamber 3 at the end of the pressure stroke, since there is now more delivery fluid in the delivery chamber 3.

If the pressure and suction strokes are carried out repeatedly, the pressure in the delivery chamber 3 will rise until the gas can be compressed to such an extent that it is possible to open the pressure valve 5 and press the gas into the pressure line.

The degassing valve 7 may in principle be constructed in the same way as in the WO 2013/135681 A1 is described, that is, it may have a valve body and a valve seat, between which also in the closed position, a return flow channel, which is formed for example by a groove arises. Basically, the degassing valve is a leaking check valve. The structure described has the advantage that even when working against high pressures in the suction line 6, the dosing does not decrease, since the pressure line 6 is not permanently in contact with the degassing valve 7. This is also advantageous for safety reasons, since in the case of a diaphragm fracture there is no permanent connection between metering line 6 on the one hand and delivery chamber 3 on the other hand.

Claims (7)

1. A displacement pump comprising a delivery chamber (3) connected to a pressure (6) and a suction (1) connection, a displacer element (11) which determines the volume of the delivery chamber and which can be reciprocated between a first position (4') in which the delivery chamber is of a smaller volume and a second (4) position in which the delivery chamber is of a larger volume, wherein the pressure connection is connected to the delivery chamber by way of a pressure valve (5) and the suction connection is connected to the delivery chamber by way of a suction valve (2), characterised in that a reservoir which can be filled with delivery fluid is connected to the delivery chamber by way of a gas venting valve wherein the gas venting valve is a suction valve which opens if the pressure in the delivery chamber is less than the pressure in the reservoir.
2. A displacement pump as set forth in claim 1 characterised in that the displacement pump is so adapted that delivery fluid can be transported from the suction connection into the delivery chamber by way of the suction valve without flowing through the reservoir.
3. A displacement pump as set forth in one of claims 1 through 2 characterised in that the gas venting valve in the direction from the reservoir to the delivery chamber has a through-flow coefficient which is less than the through-flow coefficient of the suction valve, wherein preferably the through-flow coefficient of the gas venting valve is less than 1%, particularly preferably less than 0.2%, of the through-flow coefficient of the suction valve.
4. A displacement pump as set forth in one of claims 1 through 3 characterised in that the reservoir is connected to the pressure connection.
5. A displacement pump as set forth in one of claims 1 through 4 characterised in that the reservoir is connected to an accumulator.
6. A metering installation comprising a pressure line in which delivery fluid is contained at a pressure p₂, a suction line in which delivery fluid is contained at a pressure p₁ < p₂, and a displacement pump as set forth in one of claims 1 through 5, wherein the pressure line is connected to the pressure connection and the suction line to the suction connection.
7. A metering installation as set forth in claim 6 characterised in that the reservoir contains delivery fluid at a pressure p₃, wherein p₁ < p₃ < p₂.

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