EP0684383A1 - Fluid dosing pump - Google Patents

Abstract

The dosing pump has a pump chamber with a volume which is enlarged during the suction stroke and reduced during the compression stroke, with a venting valve (17, 18) at the upper end of the pump chamber. The response characteristics of the venting valve are dependent on the aggregate characteristics of the dosed medium. The venting value is preceded by a back-feed prevention valve (16, 18) in the flow direction from the pump chamber, the back-feed prevention valve normally held closed and only opened in response to the fluid flow from the pump chamber.

Description

The invention relates to a liquid metering pump with a pump chamber, the volume of which increases during a suction stroke and decreases during a pressure stroke, and at the upper end of which a vent valve device is arranged which has a flow-actuated vent valve, the response of which is determined by the physical state of the medium flowing through.

In a known metering pump of this type (DE 42 19 663 A1), the vent valve has a membrane as a valve element. The membrane can rest against a sealing surface and thus close the outlet from the pump chamber in the area of the vent valve device. However, the force to apply the membrane is only applied when liquid is present. As long as gas flows out, the dynamic pressure is not high enough to bring the membrane to close.

From CH 390 686 it is known that instead of a membrane, a ball also flows out as a valve element in a venting device. As long as gas is exerted, the forces exerted on the ball by the flow are not large enough to move the ball into a closed position. These forces are only applied when liquid flows out. However, this arrangement cannot be used with pumps that perform a suction stroke, as is typically the case with metering pumps.

With the liquid metering pump of the type mentioned above, the venting behavior can be controlled relatively precisely. The amount of liquid escaping through the vent valve is relatively small. However, this leads to a different effect. It has been shown that even if the pump chamber is completely filled with liquid during a pressure stroke, i.e. the gas quantities previously contained therein have escaped through the vent valve, and gas residues get back into the pump chamber during a subsequent suction stroke, although the aspirated liquid did not contain these gas quantities. One possible explanation for this behavior would be that the gas only gets behind the membrane when the pump chamber is vented. Since the membrane closes practically immediately as soon as liquid is present, the gas located there is no longer conveyed. During the next suction stroke, the membrane opens again and the gas behind it is sucked into the pump chamber. The check valve located behind the vent valve does not change this. This only prevents air or gas from being sucked in from the outside. However, it cannot prevent gas still located between the vent valve and the check valve from being sucked back into the pump chamber. The gas inclusions in the pump chamber change the metering behavior of the pump and are therefore undesirable. They will be pushed out of the pump chamber at the next pump play, but are still present behind the vent valve. The dead spaces of the known arrangement lead to inaccuracies, particularly in the case of small delivery quantities, a typical application of metering pumps.

The invention has for its object to improve the pumping behavior of a metering pump with a vent valve.

This object is achieved in a liquid metering pump of the type mentioned at the outset in that a back suction safety valve is connected upstream of the vent valve in the outflow direction from the pump chamber.

The fluid emerging from the pump chamber during the venting process is hereby prevented from re-entering the pump chamber during a suction stroke. This blocking is independent of whether the fluid is still gas or already liquid. Since the vent valve is only arranged in the flow direction behind the anti-suckback valve, in the area between the vent valve and the anti-suckback valve practically only liquid will be present at the end of the venting. This is a further safeguard against gas being sucked in during a suction stroke. This reliably closes a path with which parasitic gas residues can be sucked in. Undesired dead spaces are avoided.

Preferably, the back suction valve is normally closed and only opens when the fluid flows out of the pump chamber. The anti-suckback valve therefore does not require any backflow to be closed. Rather, it closes when there is no flow out of the pump chamber. During the backflow, which would otherwise be necessary until the back suction valve is closed, no further gas residues can be introduced into the pump chamber.

The vent valve and the anti-suckback valve advantageously have a common valve element. This measure ensures that the flow path between the anti-suckback valve and the vent valve is relatively short. The amount of liquid escaping, which is no longer immediately available for consumption due to the anti-return valve, remains small. This is particularly advantageous if the liquid to be dosed is toxic or aggressive. In this case, correspondingly small amounts of liquid have to be treated.

Preferably, the valve element is freely movable between a first valve seat, which is a component of the anti-suckback valve, and a second valve seat, which is a component of the vent valve, flow through the vent valve device being possible only in one position of the valve element between the first and second valve seats. In such a configuration, the back suction protection valve is opened as soon as a flow out of the pump chamber occurs. As long as gas flows out, the forces exerted by the flow on the valve element are not yet large enough to bring the valve element into contact with the second valve seat. The valve element is thus, so to speak, in a floating state or in an intermediate position between the first and the second valve seat. Only when liquid occurs do the forces acting on the valve element be large enough to bring the valve element against the second valve seat. This reliably closes the vent valve. The further pressure stroke then no longer leads to an escape of liquid from the pump chamber through the vent valve device, but rather through a metering outlet, which is normally closed with a preload valve. In this way, the metering accuracy of the pump can be increased with relatively simple measures.

The valve element is preferably designed as a ball. With a ball, the orientation of the valve element is practically irrelevant. Regardless of how the ball has rotated, it is always possible to seal against the first or the second valve seat. Rotation of the ball may even be desirable. As a result, a different point on the ball surface always comes into contact with the respective valve seats, so that the risk of leakage due to local wear remains relatively low.

The vent valve device advantageously has a valve housing with an interior in which the valve element is arranged and which tapers in the direction of the second valve seat arranged at its outlet. With the valve housing, the entire vent valve device with vent valve and anti-suckback valve can be implemented in a simple manner. The valve housing provides a guide for the valve element, i.e. the movements of the valve element transverse to the direction of flow are limited. The valve element is therefore always brought into contact with the respective valve seats with high reliability. The tapering of the interior towards the second valve seat counteracts the formation of dead spaces, so that no gases can accumulate here. These gases would be largely harmless because the back suction valve prevents them from being sucked back into the pump chamber. Such dead spaces are more critical for media that contain solids. These could deposit and sooner or later block the outflow path, which could impair the ventilation function.

The volume of the interior preferably has 1.5 to 3 times the volume of the valve element. The interior is larger than the valve element, so that the valve element can move freely. However, it is limited in size so that there cannot be excessive liquid here. This improves the operating behavior of the vent valve device.

It is also preferred that when the valve element rests on the first valve seat, the valve element essentially ends at a distance from the first valve seat at which the second valve seat begins. The distance that the valve element can travel between the first valve seat and the second valve seat is thus limited to the sum of the immersion depths of the valve element in the two valve seats. In this way you can achieve a very sensitive control of the vent valve. Only a very small gap remains between the valve element and the second valve seat. This gap is slightly reduced when the valve element lifts off the first valve seat. It is then only so large that, although gases can flow out without problems, liquids flowing past the valve element exert such large forces on the valve element that it is pressed practically directly against the second valve seat.

At least the first valve seat advantageously has a chamfer, which forms a contact surface for the valve element. With such a chamfer, the valve element can be better received and centered. This improves the tightness of the anti-suckback valve.

It is also preferred that at least the second valve seat has a broken edge with a predetermined roughness. This prevents the valve element from sticking to the second valve seat. This could prevent air or gas from being sucked back in from the outside. However, the gas volume enclosed between the first and the second valve seat could get back into the pump chamber during a suction stroke, which should be prevented.

The valve element preferably has a predetermined surface roughness and / or a predetermined roundness. These measures can also help to prevent the valve element from sticking, in particular to the second valve seat. The back suction safety valve always closes with great reliability as soon as the flow through the ventilation vents tileinrichtung is ended. There is no need for backflow to occur.

The first and the second valve seat are preferably formed in valve seat elements which are identical to one another. This simplifies production and spare parts inventory. In principle, the same components can be used both for the vent valve and for the back suction protection valve.

In a particularly preferred embodiment it is provided that a return line is connected to the vent valve device, which returns the liquid emerging from the vent valve device directly. No liquid can therefore be present at the outlet of the vent valve device, which could lead to a change in the closing or opening behavior of the vent valve device. Any liquid that escapes in one way or another when venting is drained off immediately. This is particularly advantageous in the case of toxic or aggressive liquids because there is no longer a need for a longer exposure time to areas of the pump behind the vent valve device.

The valve element advantageously has a specific weight that is greater than that of the liquid to be metered. If the difference is not too great, the valve element is then pressed against the second valve seat even with a smaller flow of the liquid. The vent valve is now closed. If the valve element has a larger specific weight - and thus a higher weight with the same size - you can also reliably vent liquids with a higher viscosity, which usually have a higher specific weight.

• Fig. 1 einen schematischen Schnitt durch eine Dosierpumpe und
• Fig. 2 eine Entlüftungsventileinrichtung.

The invention is described below with reference to a preferred embodiment in conjunction with the drawing. Show here:

• Fig. 1 shows a schematic section through a metering pump and
• Fig. 2 is a vent valve device.

A liquid metering pump 1 has a pump chamber 2 which is delimited by a housing 3 and a membrane 4. Instead of the membrane 4, a piston can also be used. The membrane 4 is moved back and forth via an actuating rod 5 by a drive, not shown. When moving to the left, the volume of the pump chamber 2 decreases. Such a movement is referred to below as the pressure stroke. When the diaphragm 4 moves to the right, the volume of the pump chamber 2 increases. Such a movement is referred to below as a suction stroke. An inlet connection 6 opens into the pump chamber 2 and can be connected via a screw connection 7 to a supply line (not shown in more detail). An inlet valve 8, which is designed as a gravity-operated check valve, is arranged between the pump chamber 2 and the inlet connection 6. During a suction stroke, the valve body shown as a ball is lifted from its seat and clears the way from the inlet connection 6 into the pump chamber 2. During a pressure stroke, the ball is pressed onto the valve seat and prevents the fluid in the pump chamber 2 from escaping into the inlet connection 6. The pump chamber is also connected to an outlet connection 9, which can be connected via a screw connector 10 to a metering line (not shown) . An outlet valve 11 is arranged between the outlet connection 9 and the pump chamber 2 and opens against the force of a spring 12 in the outlet direction. The spring 12 defines an opening pressure. The outlet valve 11 opens only when the opening pressure is exceeded. When the opening pressure in the pump chamber 2 falls below this, it closes again.

In the area of its uppermost point, a ventilation channel 13 leaves the pump chamber 2. The ventilation channel 13 leads to a ventilation valve device 14. The ventilation valve device 14 has a valve housing 15, which has a first valve seat 16 at its end facing the ventilation channel 13 and a second valve valve at its other end Has valve seat 17. The two valve seats 16, 17 are identical to one another. They are inserted into the valve housing from opposite sides.

Between the first valve seat 16 and the second valve seat 17, a ball 18 is freely movable as a valve element. The first valve seat 16 together with the ball forms a back suction valve. The second valve seat 17 forms the actual vent valve with the ball. An interior space 20 of the valve housing 15 is available for the ball 18 as the movement space. The valve housing 15 thus limits both the movements of the ball transverse to the direction of flow and - with the help of the two valve seats 16, 17 - in the direction of flow.

Both the ball 18 and the valve seats 16, 17 can consist of metals, in particular non-ferrous metals, plastics or elastomers. However, ceramic is preferably used, since there is high chemical resistance combined with high wear resistance.

The interior 20 tapers in the direction of the second valve seat 17. Since it is important for the function of the vent valve device 14 that it and thus also the second valve seat 17 is arranged approximately at the uppermost position as seen in the direction of gravity, the taper 21 results gases flowing through the possibility of escaping from the valve device 14 without accumulation of dead spaces.

Both the first valve seat 16 and the second valve seat 17 have a chamfer 22. This chamfer 22 forms a contact surface for the ball 18. Since the ball 18 is not precisely guided, that is to say can move transversely to the direction of flow, the chamfer 22 facilitates the centering of the ball when it contacts the respective valve seat 16, 17.

In the case of the second valve seat 17 in particular, the edge 23 having the chamfer 22 can be broken and have a defined roughness in order to prevent the ball 18 from sticking to the second valve seat 17. The ball 18 itself can also have a defined roughness 18 on its surface in order to prevent sticking to one of the two valve seats 16, 17.

The volume of the interior 20 is about 1.5 to about 2.5 times as large as the volume of the ball 18. Here, the distance between the first valve seat 16 and the second valve seat 17 is selected so that the ball 18 in contact with the first Valve seat 16 ends approximately where the second valve seat 17 begins. This is shown in Fig. 2 of the drawing. The path of movement of the ball 18 between the first valve seat 16 and the second valve seat 17 is then only as great as it corresponds to the sum of the two "immersion depths" of the ball 18 in the respective valve seats 16, 17. As a result, a gap 24 between the ball 18 and the second valve seat 17 can be kept relatively small. As soon as fluid flows through the valve housing 15, this gap 24 is narrowed anyway in that the ball 18 lifts off from the first valve seat 16.

A drain chamber 25 connects to the valve housing 15, from which a return line 19 extends. The return line 19 is arranged here so that practically no liquid can accumulate in the drain space 15. Any liquid that passes through the valve housing 15 flows practically directly through the return line.

The function of the vent valve device 40 can be briefly outlined as follows: During a pressure stroke of the membrane 4, gas that is located in the pump chamber 2 is compressed. Because of the high compressibility of the gas, the pressure in the pump chamber 2 will never rise so high that it can exceed the closing force of the spring 12 of the outlet valve 11.

The gas always collects at the highest accessible point due to the gravitational conditions. Since the ventilation duct 13 branches off from the pump chamber 2 at the uppermost point (seen in the direction of gravity), the gas will collect in the ventilation duct. In the event of a pressure stroke of the membrane 4, a pressure increase in the ventilation duct 13 occurs and thus a force on the ball 18 in the direction of the second valve seat 17. The ball is lifted by the first valve seat 16 under the effect of this force. There is a gap between the ball 18 and the first valve seat 16. The compressed gas flows around the ball 18 and escapes through the gap 24 between the ball 18 and the second valve seat 17.

When the pressure stroke of the diaphragm 4 ends, that is to say before the start of the suction stroke, the ball 18 falls back into the first valve seat 16 due to its own weight. No flow in the opposite direction is therefore required to bring the ball 18 into contact with the first valve seat 16. During the suction stroke of the diaphragm 4, the ball remains in the first valve seat 16 and thus prevents gas from flowing back into the pump chamber 2 above the first valve seat 16. This applies both to gas from the return line 19 and to gas located in the interior 20 of the valve housing 15.

With a suction stroke of the membrane 4, gas can no longer get back into the pump chamber 2. On the other hand, during the pressure strokes, all gas that is in the pump chamber 2 is gradually displaced from the pump chamber 2. As long as gas can flow out through the vent valve device 14, no appreciable pressure can build up in the pump chamber 2. No liquid, which may still contain gas, is therefore pumped through the output valve against the force of the spring 12. Rather, the entire pump output is used to drive the gas out of the pump chamber 2. This process is repeated until all of the gas is pumped out of the pump chamber 2 and the ventilation duct 13.

If the pump chamber 2 is completely filled with liquid, the ball 18 is lifted out of the first valve seat 16 during the pressure stroke. A partial flow of the liquid is conveyed out and flows off via the return line 19. However, this partial flow is relatively small. In the best case, it can even be made almost zero. The liquid present in the venting channel 13 presses the ball 18 very quickly against the second valve seat 17. The venting valve device 14 is thus closed. After a further movement of the membrane 4 in the pressure stroke, the pressure in the pump chamber 2 can then rise. It exceeds the opening pressure of the spring 12 in the outlet valve 11. The liquid can now be dispensed in doses. When the pressure stroke ends, ie before the start of the suction stroke, the ball 18 falls back into the first valve seat 16 due to its own weight.

If it is known which liquids are to be dosed, the weight of the ball 18 can be determined adjust to this. If a ball with a higher weight is used, liquids with a higher viscosity can also be vented. In general it can be said that the specific weight of the ball, i.e. its own weight divided by its volume, should be in the range of the specific weight of the liquid to be dosed. The specific weight can also be slightly larger or slightly lower. The flow forces required to move the ball 18 are then relatively low.

Claims (14)

1. Liquid metering pump with a pump chamber, the volume of which increases during a suction stroke and decreases during a pressure stroke, and at the upper end of which a vent valve device is arranged which has a flow-actuated vent valve, the response of which is determined by the state of matter of the medium flowing through, characterized in that Vent valve (17, 18) in the outflow direction from the pump chamber (2) is preceded by a back suction valve (16, 18). 2. Pump according to claim 1, characterized in that the back suction valve closes without backflow and opens only in the case of a fluid flow out of the pump chamber (2). 3. Pump according to claim 1 or 2, characterized in that the vent valve (17, 18) and the back suction valve (16, 18) have a common valve element (18). 4. Pump according to Anspurch 3, characterized in that the valve element (18) between a first valve seat (16), which is part of the back suction valve (16, 18), and a second valve seat (17), which is part of the vent valve (17, 18) is freely movable, with a flow through the vent valve device (14) being possible only in one position of the valve element (18) between the first and second valve seats (16, 17). 5. Pump according to claim 3 or 4, characterized in that the valve element (18) is designed as a ball. 6. Pump according to one of claims 3 to 5, characterized in that the vent valve device (14) has a valve housing (15) with an interior (20) in which the valve element (18) is arranged and which in the direction of the its outlet arranged second valve seat (17) tapers. 7. Pump according to claim 6, characterized in that the volume of the interior (20) has 1.5 to 3 times the volume of the valve element (18). 8. Pump according to one of claims 3 to 7, characterized in that when the valve element (18) bears against the first valve seat (16), the valve element (18) essentially ends at a distance from the first valve seat (16) in which the second Valve seat (17) begins. 9. Pump according to one of claims 3 to 8, characterized in that at least the first valve seat (16) has a chamfer (22) which forms a contact surface for the valve element (18). 10. Pump according to one of claims 3 to 9, characterized in that at least the second valve seat (17) has a broken edge (23) with a predetermined roughness. 11. Pump according to one of claims 3 to 10, characterized in that the valve element (18) has a predetermined surface roughness and / or a predetermined roundness. 12. Pump according to one of claims 3 to 11, characterized in that the first and the second valve seat (16, 17) are formed in valve seat elements which are identical to one another. 13. Pump according to one of claims 1 to 12, characterized in that a return line (19) adjoins the vent valve device (14) which drains liquid emerging from the vent valve device (14) directly. 14. Pump according to one of claims 3 to 13, characterized in that the valve element (18) has a specific weight which is greater than that of the liquid to be metered.

Images