EP0641935B1 - Hydraulically actuated membrane pump with limitation of the membrane stroke - Google Patents

Description

The invention relates to a hydraulically driven diaphragm pump according to the preamble of claim 1.

In the case of hydraulically driven diaphragm pumps, it is of great importance in order to maintain proper functioning that the intended amount of hydraulic fluid is always present in the hydraulic chamber, that proper diaphragm movement is ensured and stresses which could damage the diaphragm are avoided.

To compensate for a hydraulic fluid deficit in the hydraulic space, it is known from DE-A 23 33 876 to provide a leakage supplement device controlled by a membrane system. This means that the membrane itself takes over the actuation of a control valve, a control slide connected to the membrane, which is displaceably guided in the pump body, in the suction stroke end position of the membrane opening a connection from a reservoir for the hydraulic fluid to the hydraulic chamber. Leakage supplementation can and should only take place when the membrane has reached a predetermined limit position at the end of the suction stroke.

Further embodiments of such leakage supplement devices of diaphragm pumps are described in DE-A 28 43 054 and in FR-A 24 92 473.

Controlling the leakage supplementation through the membrane system offers a number of advantages compared to pressure-controlled leakage supplementation with a snifting valve. On the one hand, large suction heights can be overcome, the suction height being limited solely by the vapor pressure of the delivery fluid and hydraulic fluid. On the other hand, overloading of the hydraulic space, as can occur in the pressure-controlled leak replenishment due to vacuum peaks, is excluded. Such pronounced vacuum peaks preferably occur in large high-pressure diaphragm pumps at the beginning of the suction phase when the liquid column in the suction line is accelerated suddenly when the suction valve is opened. Finally, the diaphragm system-controlled leak supplement enables the sniffing of hydraulic fluid at a low differential pressure of, for example, less than 0.3 bar, i.e. the absolute pressure remains at around 0.7 bar. As a result, gas formation in the hydraulic space can be largely avoided, which provides corresponding advantages with regard to the delivery rate and the delivery accuracy. In contrast, the pressure-controlled leakage supplement requires a relatively high setting of the differential pressure at the snifting valve of, for example, 0.6 bar in order to ensure safe operation. The resulting pressure drop in the hydraulic chamber during the sniffing process to, for example, 0.4 bar absolute pressure leads to increased gas formation. This results in a reduced delivery rate and delivery accuracy.

In practice, however, it has been shown that these known diaphragm pumps still have certain weaknesses, the elimination of which is desirable. Before the pump is started up, it must be ensured that the diaphragm is never too far in the direction of the delivery chamber in relation to the piston is deflected. Only a predetermined amount of hydraulic fluid may remain in the hydraulic chamber, since an excessive amount of hydraulic fluid would cause the diaphragm to overstretch or even burst when the piston is first pressed. However, an incorrect amount of hydraulic fluid in the hydraulic chamber is always to be expected if a vacuum is present at the suction valve or pressure valve of the delivery chamber during a break in operation. The negative pressure prevailing at the suction valve, for example, can propagate via the suction valve, which is never completely static, into the delivery chamber and into the hydraulic chamber and then leads to hydraulic fluid, for example via the piston seal, being sucked from the reservoir into the hydraulic chamber.

In order to avoid that the membrane must be manually repositioned each time before the membrane pump is started in order to prevent membrane damage, it is already known from DE-A 41 41 670 that both the suction stroke position and the pressure stroke limit position of the membrane have a membrane stroke limitation to provide. This takes place in the suction stroke limit position in a purely mechanical manner, namely by means of a support plate against which the membrane lies in the suction stroke limit position. In the pressure stroke limit position, on the other hand, the diaphragm stroke limitation is effected purely hydraulically, in that a valve member, which is provided on the piston-side end of a control slide of a leakage supplement device, interrupts the hydraulic connection from the piston work chamber to the diaphragm work chamber, excess hydraulic oil being displaced into the reservoir space via a pressure relief valve.

However, the problem here is that the hydraulic diaphragm stroke limitation used is relatively complex and there are no display devices which would signal damage or bursting of the diaphragm.

In order to be able to monitor the membrane condition, it is already known in a diaphragm pump (DE-A 40 18 464) to design the diaphragm as a sandwich diaphragm, which consists of two individual layers held at a distance. The space between the individual layers is connected to a display device which responds as soon as the liquid pressure - either from the delivery space or from the pressure space - propagates into the membrane space when a single layer breaks. In order to avoid the mutual lifting of the individual layers, which occurs in particular in the suction stroke, in this known diaphragm pump, these are connected at a multiplicity of points, in particular by welding, but this is technically relatively complex and can lead to tearing of these connections at high negative pressures.

In order to avoid this disadvantage, it is known in a diaphragm pump of the generic type (US Pat. No. 3,354,831) to clamp the individual layers of the diaphragm at least in their central region between a coupling member on the delivery chamber side and a coupling member on the hydraulic chamber side and thereby mechanically connect them to one another. Here, the mechanical connection of the two coupling elements takes place either by means of a screw or a rivet, which is guided from the delivery space through corresponding through bores in the support plates and the membrane systems and is fixed either by means of a screw nut or by welding.

The disadvantage here, however, is that this type of attachment of the two coupling members can cause tension in the membrane systems, which is harmful at the high pressures of a hydraulic membrane pump. Furthermore, the screw or rivet used to fix the two support plates is exposed to a high impact load, which can lead to a loosening of this fastening. Such loosening leads to the fact that the entire composite, consisting of the two support plates and the intermediate Membrane systems, is no longer held together and is subject to increased wear during the rapid reciprocating movement.

Based on this prior art, the invention has for its object to design the diaphragm pump of the generic type in such a way that it has a high degree of functional reliability with little wear even after a long period of operation and ensures a secure holding together of the diaphragm systems in their central area.

The features of the invention created to achieve this object result from claim 1. Advantageous refinements thereof are described in the further claims.

In the diaphragm pump according to the invention, the coupling members are connected to a control slide of a diaphragm system-controlled leakage supplement device, which is displaceably guided in the pump body. Here, a simple mutual connection of the two coupling members is achieved in that the delivery chamber-side coupling member has a rod-like fastening part which passes through central through holes in the membrane and the hydraulic-side coupling member and is fastened to the control slide. This takes place in that the control slide also has a continuous longitudinal bore through which the rod-like fastening part passes, so that it can be fixed on the end of the control slide facing the displacement piston.

In the diaphragm pump according to the invention, there is no screw or rivet inserted from the delivery space, with which the two coupling members and thus the membrane systems located therebetween are clamped together. Rather, in the diaphragm pump according to the invention, the function of the screw or rivet is from the coupling member on the delivery chamber side itself taken over by being provided with a rod-like fastening part which extends through the control slide of a diaphragm system-controlled leakage supplement device and is fixed there at the opposite end.

As a result, the arrangement according to the invention has the advantage that the fastening device provided for clamping the membrane systems is not subjected to any pressure load. Deformations in the thread area, which occur with the known coupling screw and can lead to undesired loosening of the arrangement, are avoided in a simple manner. The membrane systems are thus reliably held together even with a long service life, and wear and tear is reduced. The stop surface of the coupling member on the delivery chamber can also be designed to be continuously flat and extensive, so that the compressive stresses between the stop surfaces and thus also wear phenomena occurring there can be reduced. The arrangement according to the invention can be produced in a very simple manner since only a central through-hole has to be made in the control slide of the leakage supplement device in order to be able to pass the rod-like fastening part of the coupling member on the delivery chamber side. It is thus included in the invention of the control slide of the leakage supplement device in the fastening of the coupling member, which results in a structural simplification.

The coupling members are expediently designed as stop elements which are connected both to the delivery chamber boundary wall of the pump cover and to that of the pump cover Have pump body interacting stop surfaces for a mechanical pressure stroke or suction stroke limitation of the membrane. Because of such an arrangement, the diaphragm stroke limitation is effected on both sides of the diaphragm in a purely mechanical manner, so that hydraulic stroke limitation means, for example for limiting the pressure stroke, are superfluous.

In an expedient embodiment of the invention, the coupling members are designed such that, in the pressure stroke or suction stroke limit position of the membrane, together with associated pump body or pump cover surfaces, they each form a support surface for the membrane that is adapted to the natural membrane geometry, at least essentially continuously. Such a configuration makes a significant contribution to protecting the membrane.

The coupling members are expediently designed as rotationally symmetrical support plates with, in particular, flat end faces. The flat end surface facing away from the membrane acts as a large-area stop surface in the pressure stroke or suction stroke limit position, while the flat end surface facing the membrane is designed as a large-area support surface for the membrane.

According to an advantageous embodiment of the invention, the coupling member on the delivery chamber side is covered with a plastic layer. This plastic layer protects the coupling member on the pressure stroke side from aggressive media on the one hand and on the other hand can be designed such that it acts as a damping element when the coupling member strikes the pump cover in the pressure stroke limit position.

A simple design results if the hydraulic coupling element is integral, i.e. in one piece, is formed with the control slide.

The radius of at least the coupling element on the delivery chamber side is expediently equal to or greater than half the radius of the membrane section located in the delivery chamber. As a result, large stop or support surfaces are achieved which reduce the mechanical pressure load on the coupling members, the pump body or pump cover and the membrane and at the same time ensure that the individual membrane systems are held securely together.

In a particularly advantageous embodiment of the invention, it is provided that the coupling member on the delivery chamber is dimensioned and arranged in such a way that it at least largely covers the mouths of the inlet and outlet channels. As a result, the membrane is also mechanically supported in the area of the inlet and outlet channels when the membrane is in the pressure stroke limit position, which can prevent the membrane from being pressed into the inlet or outlet channels and "shoot through" the membrane at these points he follows. It is therefore easily possible with such a configuration to dimension the inlet and outlet channels generously and to arrange them in such a way that they open into the delivery chamber in a region close to the center, ie in the region of the largest membrane stroke. This allows the pump's internal pressure losses to be reduced to a minimum and the efficiency of the pump to be increased, so that even highly viscous liquids can be pumped. In addition, the flow through the delivery chamber enforced via the separate inlet and outlet channels, so that the pump is also suitable for solids-laden liquids and for food use, in which the flow is essential for a good cleaning effect during the rinsing process.

Advantageously, the inlet and outlet channels open into the delivery chamber in such a way that their center point distance from the central axis of the delivery room is a maximum of 50% of the largest delivery chamber radius.

The pump-internal pressure losses can advantageously be further reduced in that the inlet and outlet channels are aligned parallel to the direction of movement of the membrane in the region of their orifices on the delivery chamber side.

Since the coupling members are generally dimensionally stable, it is advantageous if the individual membrane layers have a bead in the area between the coupling members and the clamping on the edge. On the one hand, this bead enables the desired mobility of the membrane and, on the other hand, it is expediently designed to be sufficiently rigid to prevent the individual membrane systems from lifting off from one another in the suction stroke.

A ventilation hole is expediently provided in the pump cover, which opens into the geodetically highest point of the delivery chamber and is connected to the outlet channel. This vent hole, which can be made relatively small in relation to the inlet or outlet channel, serves to vent the delivery chamber.

Furthermore, it is advantageous if a solid particle discharge hole is provided in the pump cover, which opens into the geodetically lowest point of the delivery chamber and is connected to the inlet channel. This hole is used to remove sedimented particles to prevent them from getting caught between the pump cover and the membrane and causing damage to the membrane.

The hydraulic chamber is expediently connected to a pressure relief valve since, as described at the beginning, it can happen when the pump starts up that the diaphragm or the coupling member bears against the pump cover. If the piston then moves further in the direction of its end of the pressure stroke or if a certain predetermined maximum pressure is exceeded, excess hydraulic oil is discharged into the reservoir via the pressure relief valve. Then the membrane works again in its normal working area.

Fig. 1

schematisch im Querschnitt eine Membranpumpe gemäß der Erfindung und

Fig. 2

eine vergrößerte schematische Darstellung der zwischen den Kopplungsgliedern eingespannten Membran, wobei das förderraumseitige Kopplungsglied mit Kunststoff ummantelt ist.

The invention is explained in more detail below with reference to the drawing, for example. This shows in

Fig. 1

schematically in cross section a diaphragm pump according to the invention and

Fig. 2

an enlarged schematic representation of the clamped between the coupling members, the coupling chamber-side coupling member is coated with plastic.

1 shows a hydraulically driven diaphragm pump which has a diaphragm 1 consisting of two separate individual layers 1a, 1b, in particular made of plastic. This is clamped at its edge between a pump body 2 and a pump cover 3 which is detachably attached to the end thereof and separates a delivery chamber 4 from a hydraulic chamber 5 filled with hydraulic fluid, which represents the piston working chamber.

The diaphragm pump has a hydraulic diaphragm drive in the form of an oscillating displacement piston 6, which sealed in the pump body 2 between the piston working space 5 and a storage space 7 for the hydraulic fluid. The piston working chamber 5 is connected via at least one axial bore 8 arranged in the pump body 2 to a diaphragm-side pressure chamber 9, which represents the diaphragm working chamber and together with the piston working chamber 5 forms the hydraulic chamber as a whole. As can be seen, the diaphragm working space 9 is delimited on the one hand by the diaphragm 1 and on the other hand by a rear (piston-side) calotte 10. This rear limitation cap 10 is formed by the correspondingly designed end face of the pump body 2 and represents part of the mechanical support surface on which the membrane 1 is applied at the end of the suction stroke.

Compared to the piston-side limiting cap 10, a front limiting cap 11 formed by the end face of the pump cover 3 is formed in the delivery chamber 4. The pump cover 3 is provided in the usual way with an inlet valve 12 (suction valve) and an outlet valve 13 (pressure valve). These two valves 12, 13 are connected via an inlet duct 14 and an outlet duct 15 to the delivery chamber 4 in such a way that the conveying medium during the suction stroke of the displacer 6 and thus the diaphragm 1 to the right according to FIG. 1 and thus the membrane 1 via the suction valve 12 and the Inlet channel 14 is sucked into the delivery chamber 4. In contrast, in the case of the pressure stroke of the membrane 1 to the left in accordance with FIG. 1, the pumped medium is discharged from the delivery chamber 4 in a metered manner via the outlet channel 15 and the pressure valve 13.

In order to prevent the occurrence of cavitation at the end of the membrane suction stroke and to ensure the leakage supplementation required due to the leakage losses, a leakage supplementation device is provided. This has a conventional spring-loaded sniffing valve 16, which via a channel 17 with the storage space 7 and via a channel 18 and the Connection channel 8 is connected on the one hand to the piston working space 5 and on the other hand to the membrane working space 9.

The leakage supplement is controlled by a control valve which has a control slide 19. This is axially displaceable with the displacement piston 6 in the area of the connecting channel 8 between the diaphragm working space 9 and the piston working space 5 in a corresponding bore of the pump body 2. At a certain point on the circumference of the control slide 19, a circumferential groove 20 is provided, which in the suction stroke end position of the membrane 1 establishes the connection between the snifting valve 16 of the leakage supplement device and the hydraulic chamber 5, 9 - via the channels 18, 8 -.

The individual layers 1a, 1b of the membrane 1 are rotationally symmetrical and have beads 21 in their area near the edge, which enable the layers 1a, 1b to move freely between their suction stroke and pressure stroke end positions. In the area of these beads 21, the individual layers 1a, 1b run at a distance from one another, so that an intermediate membrane space 22 is formed. In the event of a rupture of a membrane system 1 a, 1 b, this membrane space 22 is used for rapid membrane rupture signaling, by means of a corresponding display device 23, which is connected to the membrane space 22. The membrane space 22 is formed in that the membrane layers 1a, 1b are held at a distance in their edge-side clamping zone by a ring 24. This ring 24 is provided with one or more channels, not shown, which establish the connection between the membrane space 22 and the interior of the membrane rupture indicator device 23.

In contrast to their edge regions, the individual layers 1 a, 1 b of the membrane 1 do not run in their central region, but are instead arranged on both sides Coupling members in the form of disk-shaped support plates 25, 26 held close together. The support plates 25, 26 are essentially mirror images and are arranged centrally to the central axis 27 of the control slide 19.

The support plate 25 on the delivery chamber side has a flat end face 28 facing the pump cover 3, which lies parallel to a likewise flat end face 29 of the pump cover 3. This end face 29 of the pump cover 3 is located between the mouths of the inlet channel 14 and outlet channel 15 in the delivery chamber 4 and serves in the pressure stroke limit position of the membrane 1 as a stop surface for the support plate 25.

The diameter of the support plate 25 on the delivery chamber side, i.e. its extension in the radial direction is dimensioned such that the support plate 25 completely covers the mouths of the inlet and outlet channels 14, 15 in the radial direction, so that these mouths are closed by the support plate 25 in the pressure stroke limit position of the membrane 1. In this pressure stroke limit position, the support plate 25 lies in an axial bore 30 of the pump cover 3, so that the flat support surface of the support plate 25, which is in contact with the membrane 1, together with the radially outside region of the cap 11 of the pump cover 3, is an almost gap-free adapted to the natural membrane geometry Support surface forms.

The support plate 26 on the hydraulic chamber side, which is essentially a mirror image of this, enters an axial bore 31 of the pump body 2 in the suction stroke limit position of the diaphragm 1, the end face of the support plate 26 facing the displacer 6 striking an end face 41 of the pump body 2. The flat support surface of the support plate 26, which is in contact with the membrane system 1b, forms together with the radially outside membrane work space boundary surface the calotte 10 also has an almost gap-free support surface for the membrane system 1b which is adapted to the natural membrane geometry. The support plate 26 is formed integrally with the control slide 19, that is, integrally formed thereon.

The support plate 25 on the delivery chamber side is fastened to the support plate 26 on the hydraulic chamber side or on the control slide 19 by means of a rod-like fastening part 32 which extends through central through bores within the membrane systems 1a, 1b, the support plate 26 on the hydraulic chamber side and the control slide 19 and on which the displacement piston 6 facing end of the spool 19 is fixed by a nut 33.

In order not to restrict the movement space of the displacer 6, an axial bore 34 on the end face is provided in the displacer 6, the diameter of which is larger than that of the control slide 19. In this way, the displacer 6 can move beyond the projecting end of the control slide 19 in the direction of the membrane 1.

The inlet and outlet channels 14, 15 are oriented such that they run in the region of their mouths parallel to the central axis 27 of the control slide 19 and thus parallel to the direction of movement of the membrane 1. Since they are still arranged relatively close to the central axis 27, they lie in the region of the greatest stroke movement of the membrane 1, so that a forced flow through the delivery chamber 4 is achieved.

At the geodetically highest point of the delivery chamber 4, at least one pressure-resistant small bore 35 is provided, which opens into the outlet channel 15. This bore serves to vent the delivery chamber 4.

Furthermore, at the geodetically lowest point of the delivery chamber 4, at least one pressure-resistant small bore 36 is also provided, which opens into the inlet channel 14. This bore 36 serves to remove sedimented particles in order to prevent them from being pinched between the pump cover 3 and the membrane and causing damage to the membrane 1.

In normal operation, the membrane 1 works at a clear distance from the limiting cap 11 in the pump cover 3, so that the membrane 1 is not stressed by the mechanical system. When starting the pump, however, it can happen that the diaphragm 1 moves beyond its pressure stroke end position up to its pressure stroke limit position, in which the support plate 25 strikes the end face 29 of the pump cover 3 and the diaphragm 1 rests against the support surface in the pump cover 3. If the displacement piston 6 then moves further in the direction of its pressure stroke end position or if a certain predetermined maximum pressure is exceeded, excess hydraulic fluid is discharged into the storage space 7 via a channel 37 and via a pressure relief valve 38 connected to this and a channel 39. When the pump 1 starts up, the diaphragm 1 initially moves beyond its suction stroke end position to its suction stroke limit position, in which the support plate 26 strikes the end face 41 of the pump body 2 and the diaphragm 1 rests against the support face in the pump body 2, via the snifting valve 16 and the control slide 19 sucked hydraulic fluid from the storage space 7. In both limit positions, however, the membrane 1 is supported purely mechanically via the support plates 25, 26, which at the same time ensure a secure mutual connection of the membrane systems 1a, 1b.

In the embodiment shown in FIG. 2, the support plate 25 on the delivery chamber side is complete with a Sheathed plastic layer 40, which has a shock-absorbing effect on the end face 29 of the pump cover 3 when the support plate 25 stops and can also be designed in such a way that the support plate 25 is protected against aggressive media. In this embodiment too, the membrane systems 1a, 1b are held firmly against one another in their central region by means of the support plates 25, 26, so that they cannot become detached from one another during the suction stroke.

Claims (15)

1. Hydraulically driven diaphragm pump with a diaphragm which is clamped circumferentially between a pump element and a pump lid and comprises at least two individual layers, separates a conveying chamber comprising separate inlet and outlet ducts for a medium to be conveyed from a hydraulic chamber and can be reciprocated between a suction stroke end position and a pressure stroke end position by a hydraulic diaphragm drive in the form of an oscillating displacement piston, the individual layers (1a, 1b) of the diaphragm (1) being clamped at least in their central region between a coupling member (25) on the side facing the conveying chamber and a coupling member (26) on the side facing the hydraulic chamber and being thereby mechanically coupled with one another, characterised in that the coupling members (25, 26) are connected to a control pushrod (19) of a leakage compensating device which is controlled as a function of the diaphragm position, the control pushrod (19) being displaceably guided in the pump element (2), the coupling member (25) on the side facing the conveying chamber comprising a rod-like securing element (32), which passes through central through apertures in the diaphragm (1) and in the coupling member (26) on the side facing the hydraulic chamber and is secured to the control pushrod (19) in that it passes through a continuous longitudinal bore inside the control pushrod (19) and is secured to the end of the control pushrod facing the displacement piston (6).
2. A diaphragm pump according to claim 1, characterised in that the coupling members (25, 26) are constructed as abutment elements comprising abutment surfaces which cooperate with both the conveying chamber limiting wall of the pump lid (3) and the pump element (2) in order to mechanically limit the pressure stroke and suction stroke of the diaphragm (1).
3. A diaphragm pump according to claim 1 or 2, characterised in that the coupling members (25, 26) are constructed in such a manner that, together with associated pump element or pump lid surfaces, they each form a support surface for the diaphragm (1) in the pressure stroke or suction stroke limiting position of the diaphragm (1), which support surface matches the natural diaphragm geometry and is at least substantially continuous.
4. A diaphragm pump according to one of the preceding claims, characterised in that the coupling members (25, 26) are constructed as rotationally symmetrical support disks, more particularly with flat end faces.
5. A diaphragm pump according to one of the preceding claims, characterised in that the coupling member (25) on the side facing the conveying chamber is enclosed by a plastics material layer (40).
6. A diaphragm pump according to one of the preceding claims, characterised in that the coupling member (26) on the side facing the hydraulic chamber is integrally formed with the control pushrod (19).
7. A diaphragm pump according to one of the preceding claims, characterised in that the radius at least of the coupling member (25) on the side facing the conveying chamber is equal to or greater than half the radius of the diaphragm section lying in the conveying chamber (4).
8. A diaphragm pump according to one of the preceding claims, characterised in that the coupling member (25) on the side facing the conveying chamber is dimensioned and arranged in such a manner that it at least for the most part covers the openings of the inlet and outlet ducts (14, 15).
9. A diaphragm pump according to one of the preceding claims, characterised in that the inlet and outlet ducts (14, 15) open into the conveying chamber (4) in a region near the centre, the distance between the centre point of the inlet and outlet ducts (14, 15) and the central axis (27) of the conveying chamber (4) measuring at the most 50% of the maximum conveying chamber radius.
10. A diaphragm pump according to one of the preceding claims, characterised in that, in the region of their openings on the side facing the conveying chamber, the inlet and outlet ducts (14, 15) are aligned parallel to the direction of movement of the diaphragm (1).
11. A diaphragm pump according to one of the preceding claims, characterised in that the area of the conveying chamber limiting wall lying between the inlet and outlet ducts (14, 15) is constructed in particular as a flat abutment surface for the coupling member (25) on the side facing the conveying chamber.
12. A diaphragm pump according to one of the preceding claims, characterised in that the individual diaphragm layers (1a, 1b) comprise a corrugation (21) in the region between the coupling members (25, 26) and the circumferential clamping site.
13. A diaphragm pump according to one of the preceding claims, characterised in that a ventilation bore (35) is provided in the pump lid (3), which bore preferably opens into the conveying chamber (4) at the geodetically highest point of said chamber and is connected to the outlet duct (15)
14. A diaphragm pump according to one of the preceding claims, characterised in that a solid particle discharge bore (36) is provided in the pump lid (3), which bore preferably opens into the conveying chamber (4) at the geodetically lowest point of the said chamber and is connected to the inlet duct (14).
15. A diaphragm pump according to one of the preceding claims, characterised in that the hydraulic chamber (5, 9) is connected to a pressure limiting valve (38).

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