EP1736666B1 - Pump gear - Google Patents

Abstract

The pump transmission has each connecting rod (15) mounted on its own crank. The cranks are offset from each other by a present angle, which is selected, relative to the angle enclosing the cylinder axes, so that the phase displacements between each two successive pistons (13) as the crankshaft (12) rotates are equal to each other.

Description

The invention relates to a pump gearbox having a plurality of cylinders, the axes of which are arranged with predetermined angles enclosing a crankshaft, and whose pistons or diaphragms are each operatively connected to a connecting rod mounted on a separate crankshaft on the crankshaft, the crankshafts having a predetermined angular offset from each other, and this angular offset, in agreement with the angles which enclose the cylinder axes, is chosen such that the phase shifts between every two pistons of the cylinders successively actuated during one revolution of the crankshaft are the same.

Multi-cylinder pump transmissions are used in process pumps for conveying large flow rates or at high pressures. As pumpheads usually diaphragm pump heads are used. Since the membranes used in it are only limited deflection, diaphragm pump heads with very large diameter are required for large volumes. If such large diaphragm pump heads are to be operated with a multi-cylindrical gear, therefore, the distances between the pump head holder and the cylinder must be large enough. In conventional pump transmissions, the individual cylinders are usually arranged in parallel and horizontally mounted on a likewise horizontal crankshaft. In this case, a large cylinder spacing in the connection area for the pump heads also means a large bearing clearance on the crankshaft. With several cylinders and large pump heads, the crankshaft must be designed accordingly long. This in turn requires special properties of the crankshaft, in particular with regard to stability and flexural rigidity. This and the high space requirements result in high costs for production and warehousing. This is followed by efforts to develop efficient pump transmissions, which have a smaller footprint.

From the German Utility Model DE 8521520 U1 is known a multi-cylinder diaphragm pump in which the cylinder pistons on a single eccentric to a crankshaft are stored. The individual cylinders are arranged in a star shape around the crankshaft. The crankshaft itself is therefore comparatively short. In order to achieve a uniform superposition of the partial flow rates of the individual cylinders, the angles at which the cylinders are mutually distributed, evenly distributed over 360 °. However, the star-shaped arrangement of the cylinder is associated with considerable disadvantages. On the one hand, the entire pump is relatively expansive, and the footprint of the pump is still unsatisfactory, on the other hand, the accessibility of the rear-side cylinder is significantly reduced in a built-in pump. In addition, the piping requires a special effort.

From the US 4,264,286 A Considered as the closest prior art is a high pressure piston pump and a low pressure piston pump in a system for different liquids, each comprising a plurality of cylinders arranged in series with pump heads, the two pump head groups on crossheads and respective different length connecting rods and a common crankshaft are driven. All pump cylinder axes are parallel to each other in a plane. The crankshaft cranks are arranged equiangularly with respect to each other and equidistant from each other along the crankshaft axis for each pump head group, which produces a reduction in the vibrations of the pump. The phase of the low-pressure piston pump is offset by 30 ° to the phase of the high-pressure piston pump

The DE 199 18 161 A1 discloses a compressor of a refrigerant compressor plant, wherein the cylinders are arranged at a V-shaped angle less than 90 ° to each other. The compressor shaft is mounted at its two ends in corresponding bearings. Eccentric are arranged between the bearing sections of the compressor shaft, wherein for each individual piston in each case an eccentric is provided, which is arranged at a distance from the other individual eccentric for the respective other piston. Again, no optimal space utilization or compactness and no optimized quiet running of the pump gear is reached.

Against this background, it is an object of the invention to provide a pump gear, which is particularly compact and at the same time good accessibility of the individual cylinders has a short crankshaft and optimal running behavior.

The object is achieved by a pump gearbox having a plurality of cylinders, the axes of which are arranged predetermined angles enclosing a crankshaft, and whose pistons are each articulated by a crankshaft mounted on a crankshaft connecting rod, each connecting rod is mounted on its own Kurbelkröpfung, and the crankshafts have a predetermined angular offset from each other. The angular offset of these crankcases is according to the invention in vote to the angles which include the cylinder axes, chosen so that the phase shifts between each two successive actuated at a revolution of the crankshaft piston of the cylinder are the same size. The sum of all angles which enclose the cylinder axes is inventively less than or equal to 180 ° and the cylinder axes are all in a plane perpendicular to the crankshaft or their mutual height offset in the direction of the crankshaft axis corresponds to a maximum of Pleueldicke.

The angles which enclose the cylinder axes are to be seen in projection on a plane perpendicular to the longitudinal axis of the crankshaft. In fact, the cylinder axes do not intersect, as the points of engagement of the connecting rods are offset at the respective crankshafts along the longitudinal axis of the crankshaft. In the projection, however, the cylinder axes intersect in the crankshaft and radiate from this. The angular distribution between the cylinder axes can be chosen almost arbitrarily around the crankshaft. Only the minimum angle between two adjacent cylinder axes is given by the dimensions of the cylinder and the pump heads to be connected and the sum of all included angles must not exceed 180 °. Both symmetrical arrangements with regular angular distances of the cylinders and asymmetric arrangements are possible. The multiple possibilities of geometric arrangement have the advantage that the pump can be adapted to many different structural conditions, for example when it is to be integrated into a more complex system.

In the pump transmission according to the invention, the cylinders are arranged so that the sum of the included by the cylinder axes angle is less than or equal to 180 °. The cylinder axes are therefore not distributed around the crankshaft, but protrude from the crankshaft only in a half-space. That is, there are preferably two outermost cylinders whose axes enclose an angle smaller than 180 ° with each other, or which extend in parallel in opposite directions from the crankshaft. In the event that the pump gear has more than these two outermost cylinders, they are fan-shaped distributed between the two outermost cylinders, while in the second half space no cylinder axes protrude. The asymmetric cylinder distribution is taken into account by the angular offset of the crankshafts, so that nevertheless a uniform flow rate is achieved. When installing the pump in a system, the restriction of the space for cylinder connections to 180 ° has the advantage that all cylinders, for example for maintenance, are accessible from one side.

Thus, despite an asymmetric arrangement of the cylinder around the crankshaft, a torque curve as uniform as possible during one revolution of the crankshaft is achieved, the angles at which the cranks are each other, adapted to the angular distribution of the cylinder. The crankshafts, on which the connecting rods of the individual cylinders are mounted, must therefore be offset from each other by certain angles about the axis of the crankshaft. The angular offset between the crankcasters is then chosen so that the phase shifts between the cycles of two successively actuated pistons are the same size. In a three-cylinder gear, the phase difference between the duty cycles of two cylinders, regardless of the spatial arrangement of the cylinder, so each 120 °. In a four-cylinder gear, the phase difference is 90 ° for two consecutively actuated cylinders. In this way it is ensured that the partial flow rates of the individual cylinders overlap uniformly and no excessive pressure pulsations occur. Due to the angular offset of the crankshafts can therefore be a uniform flow with any angular positions of the cylinder axes.

The inventive pump transmission is particularly suitable for the cultivation of piston diaphragm pump heads. For trouble-free operation of piston diaphragm pump heads, horizontally located piston axes with vertically aligned superimposed valve connections are to be preferred. The crankshaft is therefore expediently mounted vertically standing, wherein the cylinder axes point horizontally radially away from this.

The articulation of the piston through the connecting rods is preferably carried out via a crosshead, which receives the transverse portions of the outgoing from the crankshaft rotational movement of the connecting rod.

The crankshafts for the individual connecting rods and cylinders are distributed along the longitudinal axis of the crankshaft. In the case of a vertically mounted crankshaft, this means that the connecting rod main bearings, with which the connecting rods are each mounted on a separate crank throw, are offset in height relative to one another. In a preferred embodiment, this height offset corresponds to the thickness of the connecting rod. The crankshafts are so close together that the connecting rods slide on each other without appreciable spatial separation. If the connections from the connecting rod to the crosshead and from the crosshead to the cylinder piston are centered, this also results in a corresponding height offset of the cylinder axes by one connecting rod thickness. The cylinder axes are then, in fact, fan-like or similar to the steps of a spiral staircase from the crankshaft.

Preferably, the pump gear according to the invention has three cylinders. In a distribution of the cylinder axes to 180 °, these can each be at an angle of 90 ° to each other.

In a particularly preferred embodiment, however, the three cylinder axes are distributed only over an angular range of 90 ° and the individual cylinders are then at an angle of 45 ° to each other. This arrangement allows an even more compact design of the pump. The accessibility from one side is further improved. Depending on the specific requirements, however, it is also possible, for example, to arrange at angles of 30 ° and 60 ° or other angle combinations.

The pump gearbox can be driven, for example, with a worm gear or an external geared motor which can be coupled directly to the crankshaft. Therefore, in a preferred development, the crankshaft has both a clutch for such an external transmission and a connecting device for a worm gear. If the pump gear is surrounded by a housing, both drive options are expediently possible with the same base variant of a housing. The worm gear can then be integrated into the housing, while the external gear can be mounted in extension of the crankshaft outside of the housing. The drive motor is then either mounted to the drive via the worm gear directly to the side of the housing, or to the drive via the external gear following it. With both types of drive, a stroke frequency suitable for diaphragm pumps can be generated. Such a frequency is usually less than 250 strokes per minute. The drive of the pump gear via a worm gear has the advantage that a plurality of pump gear can be chained horizontally via a compound of the screw shafts. A vertical linking of several pump transmissions is possible with both types of drive. For this purpose, the crankshafts of several pumps can be coupled to each other. Both an equal and a mutual arrangement of the pump heads is possible.

In a preferred embodiment of the pump transmission with three cylinders, which enclose a total of 90 °, the crankshaft is driven by a worm gear. Preferably, the drive motor, whose axis is naturally perpendicular to the crankshaft, mounted so that its axis with the axis of the middle cylinder forms an angle of less than or equal to 135 °. Cylinder and drive motor are then arranged fan-shaped around the crankshaft. If the worm engages in the vicinity of the crankshaft crankshaft, the crankshaft can be designed correspondingly short, and a particularly compact flat design of the pump is possible.

In all the aforementioned embodiments, the cylinders are each offset by a connecting rod thickness, in the direction of the longitudinal axis of the crankshaft, and are not in one plane. This may require an increased effort when connecting the pump, for example in the piping. This constructive disadvantage can be avoided in a preferred embodiment by one or more connecting rods are angled so that the crankshaft remote from the outer ends of all connecting rods lie in one plane, while the other ends naturally next to each other or, for a vertical crankshaft, one above the other on the crankshaft are stored. For a three-cylinder pump, at least two such angled connecting rods are necessary so that all connecting rod ends facing away from the crankshaft can lie in one plane. In another preferred variant, the height offset of the cylinder axes is circumvented by the fact that either the connecting rods on the crossheads or the crossheads on the pistons engage eccentrically. In this way, the crosshead tracks, or at least the cylinder pistons, can already be brought into a plane. It is also appropriate to combine both measures.

For the assembly of the connecting rod on the crankshaft, this is preferably composed lengthwise of at least two parts. The division is expediently in the range of crankcases. The torque transmission is then ensured by a positive shaft-hub connection. Possible embodiments include a multi-tooth or polygonal profile or a feather key. A split crankshaft allows the use of several similar connecting rods, but at least of connecting rods with the same shaped closed main bearings, for all cylinders. As a result, warehousing and production costs can be reduced or kept low. For three- or four-cylinder pump transmissions, the crankshaft must be composed of at least two parts. With a larger number of cylinders correspondingly more parts are necessary.

When using an undivided crankshaft for a pump transmission having at least three cylinders, preferably at least one main bearing of a connecting rod on a split bearing shell. In a three-cylinder gearbox then expediently carried the middle Pleuelhauptlager divided. The assembly of more than two connecting rods on an undivided crankshaft can alternatively also by different diameter of the connecting rod main bearings are made possible. In particular, for pump gearbox with a larger selection of cylinders and the combination of a split crankshaft with split con rod main bearings or conrod bearings of different diameters may be useful. The crankshaft itself is preferably mounted at its ends, on both sides of the crank cranks, in at least two main bearings. Here, both sliding and rolling bearing technology can be used.

Conveniently, the pump gearbox is installed in a housing. The housing is preferably made of one part and equipped for installation, each with a closable opening in the bottom and rear wall. Through these openings, the inner workings of the pump, so the one- or multi-part crankshaft and the connecting rods are mounted.

In a preferred embodiment, the crosshead lift tracks of the cylinder and the pump head holder are integrated into the housing. The individual pump head holders can then be interconnected. This has the advantage that pressure differences in the housing, which arise from the oscillating movements of the crossheads and pistons, even with sealed housing openings can be compensated because the required air mass balance between the cylinders can take place. In addition, the interconnected housing volumes can be used in special construction variants of diaphragm pump heads as a reservoir for hydraulic oil.

The object of the invention is also achieved by a pump with a pump transmission according to the invention. Preferably, diaphragm pump heads are connected to the pump head holders of the cylinder.

Fig. 1:

Pumpengetriebe mit drei Zylindern und eingezeichneter Winkelverteilung um die Kurbelwelle;

Fig. 2:

Pumpengetriebe mit drei Zylindern und senkrecht stehender Kurbelwelle im horizontalen Schnitt;

Fig. 3:

Pumpengetriebe aus Fig. 2 im vertikalen Schnitt;

Fig. 4:

Kurbelwelle mit Kröpfungen im vertikalen Schnitt entlang der Längsachse der Kurbelwelle;

Fig. 5:

Kurbelwelle in Draufsicht mit eingezeichnetem Winkelversatz der Kurbelkröpfungen;

Fig. 6:

Dreizylinderpumpengetriebe mit symmetrischer Winkelverteilung der Zylinderachsen und angebauten Membranpumpenköpfen in Frontalansicht auf die Stirnseite des mittleren Zylinders;

Fig. 7:

Kurbelwelle mit abgewinkelten Pleueln im Schnitt entlang der Längsachse der Kurbelwelle;

Fig. 8:

Kurbelwelle mit abgewinkelten Pleueln in Draufsicht auf die Stirnseite der Kurbelwelle;

Fig. 9:

Vertikaler Schnitt durch ein mehrzylindrisches Pumpengetriebe mit vertikaler Kurbelwelle und horizontal in einer Ebene liegenden Zylindern;

Fig. 10:

Detailansicht der Verbindung von Pleuel zu Kreuzkopf in drei verschiedenen Positionen;

Fig. 11:

Detailansicht der Verbindung von Kreuzkopf zu Kolben in drei unterschiedlichen Positionen;

Fig. 12:

Vertikaler Schnitt durch ein Pumpengetriebe mit senkrecht stehender Kurbelwelle und direkt an die Kurbelwelle gekuppelten externem Getriebe und Antriebsmotor;

Fig. 13:

Teilbare Kurbelwelle im vertikalen Schnitt durch die Längsachse;

Fig. 14:

Pumpengetriebe mit in das Gehäuse integrierten Kreuzkopflaufbahnen und Pumpenkopfhaltern im horizontalen Schnitt.

In the following the invention will be explained with reference to embodiments illustrated in the drawings. They show schematically:

Fig. 1:

Pump gearbox with three cylinders and marked angular distribution around the crankshaft;

Fig. 2:

Pump gearbox with three cylinders and vertical crankshaft in horizontal section;

3:

Pump gearbox off Fig. 2 in vertical section;

4:

Crankshaft with cranks in vertical section along the longitudinal axis of the crankshaft;

Fig. 5:

Crankshaft in plan view with marked angular offset of the crankshafts;

Fig. 6:

Three-cylinder pump gearbox with symmetrical angular distribution of the cylinder axes and mounted diaphragm pump heads in front view on the front side of the middle cylinder;

Fig. 7:

Crankshaft with angled connecting rods in section along the longitudinal axis of the crankshaft;

Fig. 8:

Crankshaft with angled connecting rods in plan view of the end face of the crankshaft;

Fig. 9:

Vertical section through a multi-cylindrical pump gearbox with vertical crankshaft and horizontally in-plane cylinders;

Fig. 10:

Detail view of connecting rod to crosshead in three different positions;

Fig. 11:

Detail view of the connection from crosshead to piston in three different positions;

Fig. 12:

Vertical section through a pump gearbox with vertical crankshaft and external gearbox and drive motor coupled directly to the crankshaft;

Fig. 13:

Divisible crankshaft in vertical section through the longitudinal axis;

Fig. 14:

Pump gearbox with crosshead tracks integrated into the housing and pump head holders in horizontal section.

Fig. 1 shows a possible geometric arrangement of the pump gear 10 according to the invention with three cylinders 11 seen from above. These cylinders 11 point horizontally radially away from the vertically oriented crankshaft 12. They are arranged symmetrically in this embodiment and include in the projection shown on a plane perpendicular to the crankshaft 12 in each case an angle W _Z with each other. In Fig. 2 a pump transmission 10 is shown in more detail with the same geometry. The sectional plane of the drawing passes through the uppermost mounted connecting rod 15. The other two connecting rods 15 are mounted without a distance directly below the uppermost connecting rod 15 on the crankshaft 12. The vertical crankshaft 12 is driven by a horizontal worm gear 18 with a drive motor 19. On the crankshaft 12, the three connecting rods 15 are each mounted on a separate crank 14. At their other, the crankshaft 12 facing away from the end, they are hinged to a crosshead 16. This converts the rotational movement of the connecting rod 15 in a linear movement. This movement is transmitted via a piston rod to a piston 13. This in turn directs the membranes of the connected pump heads 22. The same embodiment is in Fig. 3 shown in vertical section. Here, the distance from one another superimposed on the crankshaft 12 connecting rod 15 are visible. The crankshaft 12 with the directly superimposed cranks 14 is in Fig. 4 again shown in detail in side view. The cranes appear horizontally shifted in this view, but in fact they have an angular offset W _K to each other, as in Fig. 5 can be seen in the plan view. This angular offset W _K is adapted to the angle between the cylinder W _Z. In the symmetric, in the Fig. 1 and 2 illustrated embodiment with three cylinders is the context W _K = 120 ° - W _Z , where W _K denotes the angular offset of the crank cranks 14 and W _Z the intermediate angle of the cylinder 11. At gleichgeformten connecting rod and identical cultivation of Kreuzkopaufaufbahnen 25, piston 13 and pump heads 22nd have the pump heads 22 to each other a height offset b, which corresponds to the thickness of the connecting rod. Fig. 6 shows this height offset in a variant according to Fig. 1 and 2 seen from the perspective of the middle pump head. This height offset of the cylinder complicates the installation of the pump gear according to the invention and also unnecessarily causes an increased space requirement in the vertical direction. In order to avoid this disadvantage, one or more connecting rods 15 can be designed angled, so that the connecting rod ends facing away from the crankshaft 12 all lie in a horizontal plane. Fig. 7 shows a vertical crankshaft 12 with three connecting rods mounted thereon, wherein the middle connecting rod is straight and both the upper and the lower connecting rod 15 are angled such that the ends are all on the plane AA of the central connecting rod 15. In Fig. 8 This is again shown in plan view of the vertical crankshaft 12. The kinks in the two outer connecting rods are represented by lines 24.

Another way to compensate for the height offset b comes in the Fig. 9 to 11 shown developments are used. Fig. 9 again shows a pump gear in vertical section. In the center, a cross-head track 25 can be seen in section and behind perspective the opening to an adjacent cross-head track. Both Kreuzkopraufbahnen are at the same height despite superimposed on the crankshaft 12 mounted un-angled connecting rod 15. The height offset b is here compensated by the fact that the connecting rods on the crosshead not centrally attack, but, depending on the position on the crankshaft, either below or above the center of the crosshead 16. The bottom of the lowest crank 14 mounted connecting rod 15 then attacks below the center of the crosshead 16 at. This is in detail in Fig. 10 on the far left. In the middle in Fig. 10 is the middle connecting rod 15, which acts in the center of the crosshead 16 to see. Right attacks the uppermost connecting rod 15 accordingly above the center of the crosshead 16.

Fig. 11 shows another embodiment in which the Kreuzkopflaufbahnen 25 still have a height offset. This is compensated only in the transmission of the movement of the piston 13, in which this is articulated according to above or below the crosshead center.

The drive of the pump gear 10 can be done either via a worm gear 18 or via a directly coupled to the crankshaft 12 external gear 17 with drive motor 19. Fig. 12 shows a pump gear according to the embodiments in Fig. 2 and 3 in vertical section, but here with an external gear 17. This is coupled to the upper end of the vertically mounted crankshaft 12. This is followed by the drive motor 19.

Thus, more than two similar connecting rods 15 can be mounted on the crankshaft 12, the crankshaft 12 is designed to be divisible in a specific embodiment. Fig. 13 shows such a crankshaft 12 in longitudinal section. The pitch is in the range of crankcases 14. The illustrated crankshaft 12 is composed of three parts 12.1, 12.2 and 12.3.

Fig. 14 shows a compact pump gear 10 in a housing 20. The individual Kreuzkopflaufbahnen 25 are connected via housing openings 23 with each other. This variant has, as well as in Fig. 1-3 shown, a symmetrical angular distribution of the cylinder over 90 °. The drive motor is additionally arranged at an angle of 135 ° relative to the middle cylinder. This special arrangement allows a particularly compact design of the pump gear according to the invention. Depending on the size of the pump heads used, the angle between the cylinders and the drive motor can be chosen even lower.

Claims (19)

1. Pump mechanism (10) having multiple cylinders (11), whose axes are situated around a crankshaft (12) to enclose predetermined angles (W_z), and whose pistons (13) are each functionally connected to a connecting rod (15) mounted on its own crank (14) on the crankshaft (12),
   the cranks (14) having a predetermined angular offset (W_K) to one another, and this angular offset (W_K) is selected in accordance with the angle (W_Z), which the cylinder axes enclose, in such a way that the phase shifts between each two pistons (13) of the cylinders (11) actuated in sequence during a rotation of the crankshaft (12) are equally large,
   characterized in that the sum of the angles (W_Z) enclosed by the cylinder axes is less than or equal to 180° and that all cylinder axes lie in a plane perpendicular to the crankshaft (12) or their offset in height to one another in the direction of the crankshaft corresponds to the thickness of a connecting rod.
2. Pump mechanism according to claim 1,
   characterized in that the pistons (13) are connected to the connecting rods (15) via a crosshead (16).
3. Pump mechanism according to one of the preceding claims,
   characterized in that neighboring connecting rods (15) are mounted in the direction of the longitudinal axis of the crankshaft (12) in such a way that they slide on one another without spatial separation.
4. Pump mechanism according to one of the preceding claims,
   characterized in that it has three cylinders (11).
5. Pump mechanism according claim 4,
   characterized in that the axes of two neighboring cylinders (11) each enclose an angle (W_Z) of 45° and the axes of the two outer cylinders (11) enclose an angle of 90°.
6. Pump mechanism according to one of the preceding claims,
   characterized in that the crankshaft (12) has both a coupling to the drive via an external transmission (17) to an external drive motor (19) and also a connection device for the drive using a worm gear pair (18).
7. Pump mechanism according to claim 6,
   characterized in that it is equipped with a worm gear pair (18) for driving the crankshaft (12), whose drive motor (19) is mounted in such a way that its axis is perpendicular to the longitudinal axis of the crankshaft and encloses an angle of less than or equal to 135° with the axis of the middle cylinder.
8. Pump mechanism according to one of the preceding claims,
   characterized in that at least one connecting rod (15) is bent in such a way that the ends of at least two connecting rods (15) facing away from the crankshaft (12) lie in a plane perpendicular to the longitudinal axis of the crankshaft.
9. Pump mechanism according to one of the preceding claims,
   characterized in that at least one connecting rod (15) is linked to the crosshead (16) outside the crosshead center.
10. Pump mechanism according to one of the preceding claims,
    characterized in that at least one piston (13) is linked to the crosshead (16) outside the crosshead center.
11. Pump mechanism according to one of the preceding claims,
    characterized in that the crankshaft (12) may be assembled along its length from at least two parts, which are connectable to one another in a formfitting way in the area of the cranks.
12. Pump mechanism according to one of the preceding claims,
    characterized in that at least one connecting rod main bearing has a divided bearing shell.
13. Pump mechanism according to one of the preceding claims,
    characterized in that the connecting rod main bearings have different diameters.
14. Pump mechanism according to one of the preceding claims,
    characterized in that the crankshaft (12) has at least two main bearings, which are situated on both sides of the cranks (14).
15. Pump mechanism according to one of the preceding claims,
    characterized in that it is installed in a housing (20).
16. Pump mechanism according to Claim 15,
    characterized in that the housing (20) is manufactured in one part and is equipped with a closable opening in each of the floor and the rear wall for mounting.
17. Pump mechanism according to one of Claims 15 or 16,
    characterized in that the crosshead tracks (25) and pump head holders (21)are integrated in the housing (20) and the volumes of the individual pump head holders (21) are connected to one another.
18. Pump having a pump mechanism according to one of the preceding claims.
19. Pump according to Claim 18,
    characterized in that diaphragm pump heads (22) are connected to the pump head holders (21).

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