EP1752662B1 - Apparatus to concentrate a fluid and a multiple chamber pump - Google Patents

Abstract

The device has a drive shaft (12) and a differential piston pump. The differential piston pump is driven by the drive shaft and a valve control unit (18) is arranged for operating an inlet and outlet valve arrangement. A tappet is arranged on the drive shaft for a differential piston (K) and the valve control unit. The differential piston and the valve control unit are coupled with a pressure coupling directly at the tappet. An independent claim is also included for a differential piston pump for a fluid.

Description

The invention relates to a device specified in the preamble of claim 1. Art and a differential piston pump according to the preamble of claim 2.

When concentrating liquids, for example, in seawater desalination (reverse osmosis) or fruit juice production process-related much primary energy is needed to pump the liquid, the resulting concentrate is obtained with relatively high residual pressure. Especially in seawater desalination, the high demand for primary energy is a long-known disadvantage that has been known in the past and in view of the high energy costs, e.g. This is minimized by using the energy contained in the concentrate thanks to the residual pressure to assist the differential piston pump in pumping, thus saving primary energy.

At the EP 0 450 257 B1 known device for seawater desalination and in the in EP 0 450 257 B1 . Fig. 5 , Differential piston pump shown, the differential piston with the piston rod remote side pumps the liquid to be concentrated, eg seawater, controlled by inlet and outlet valves on the acting, for example, as the principle of reverse osmosis membrane, behind the concentrate with high residual pressure and permeate. The residual pressure concentrate is cycled to the piston rod side of the differential piston, controlled by the inlet and outlet valve assembly, to assist in pumping directly by the residual pressure before the concentrate is substantially depressurized. The linear guided shaft of the differential piston is coupled via a connecting rod with a crank pin of the drive shaft designed as a crankshaft. The inlet and outlet valve assembly of the pressure chamber on the piston rod side of the differential piston has separate inlet and outlet valves, which are actuated via linearly guided ram of arranged on the drive shaft control cam against spring force.

Because the springs are strong and progressive, they produce an undesirable loss of power. The crankshaft / connecting rod arrangement not only leads to large size of the differential piston pump, but due to e.g. due to the Pleuelauslenkung a little harmonic piston stroke, resulting in the further power losses and pulsations in the pumped liquid.

The invention has for its object to provide a operable with minimal use of primary energy device of the type mentioned, and to provide a compact and extremely efficient differential piston pump.

The stated object is achieved with the features of claim 1 or claim 2.

In the device, the radial piston pump concept results in a small size, in pulsation-poor performance and thanks to the tensile and compressive couplings in high efficiency with minimal losses, so that very little primary energy sufficient and the energy contained in the concentrate is used optimally and above all directly. The tensile and compressive couplings lead to an extremely harmonious stroke of the differential piston and the valve control member. The control of the inlet and outlet valves to the pressure chamber in optimal adaptation to the stroke of the differential piston and with minimal wear over long periods. The radial piston pump concept allows seawater desalination to create and deploy compact devices tailored to the needs of individual buildings or groups of buildings, with even primary DC power from solar panels delivering high throughput rates, for example in sunny and marginal areas, due to the low primary energy input. Thus, such compact devices can be used without mains connection or in areas where electricity is not or rarely available or would be too expensive for domestic use.

Thanks to its compact size and high efficiency, the differential piston pump with the radial piston concept without connecting rods and above all without energy-consuming, powerful valve springs is ideal for all applications, not only for seawater desalination. suitable in which a liquid is to pump, and the same or the concentrated or another liquid with significant residual pressure is available.

In an expedient embodiment, a single valve control member is provided for each of an exhaust and an intake valve to minimize energy losses. Thanks to the pressure and traction coupling with the eccentric on the drive shaft accounts for energy-consuming valve springs, which benefits the efficiency and durability, since the inlet and outlet valve assembly operates relatively low power and contains no damage-prone components.

In an expedient embodiment, a rotatably mounted on the eccentric towed body is provided, with which the shaft end is positively coupled so that the orbital motion of the eccentric is transmitted in a harmonious manner. The sliding guide allows the transverse displacement movements between the rotating eccentric and the linearly movable shaft without significant wear and without noise or vibration.

Appropriately forms the sliding guide, which mediates between the rotating eccentric and the linearly guided shaft, a rotation of the shaft. Alternatively, however, the sliding guide can also be designed so that the shaft can rotate for distribution of wear.

Conveniently, the towed body is either made of assembled halves from assembled halves or even integrally formed, and so that it has an outwardly open pocket for the shaft, which is narrower for the positive locking than the outer width of the shaft. The interlocking interaction takes place between relatively large sized surfaces, which avoids local wear.

In order to exclude transverse loads on the shaft during operation, it may be advantageous to arrange the shaft in a housing-fixed sliding guide. The sliding guide can be an inserted sliding bushing. Furthermore, the sliding guide should be molded with Sliding support shells into the pocket with a sliding fit to support the shaft over as long a length as possible.

For assembly reasons, it is expedient here if either the shank or the support shells, or both, axially position the towed body on the eccentric.

A base of the pocket should form a pressure surface for the shaft end (pressure coupling), which is longer because of the required sliding movement than the outer width of the shaft end. At a distance from the shank end, parallel grooves are formed in the shank defining a width approximately corresponding to the inside width of the pocket and forming outboard stems on the shank end as engagement members (on one or both sides of the shank) which engage undercuts in the pocket (pull coupling). The sliding movement between the shaft end and the towed body takes place optimally close to the eccentric, which benefits the smoothness.

In an expedient embodiment, the undercuts in the pocket extend parallel to a tangent to the eccentric, wherein the undercuts in this direction are longer than the drivers in order not to hinder the relative sliding movement. The undercuts can be formed continuously, which can simplify the mounting of the shaft end in the towed body, so that the towed body if necessary. Can be integrally formed.

In order to act on the piston rod side of the differential piston via the delivery stroke exactly controlled with the residual pressure, however, reduce the residual pressure promptly during the return stroke of the differential piston, it is important that the eccentric for the valve control member of a differential piston associated exhaust and inlet valve assembly relative to the eccentric for this differential piston is offset by 90 ° about the axis of the drive shaft and in the drive direction of rotation leading.

With regard to a low-noise and low-pulsation run, it is expedient to distribute three or more differential piston star-shaped regularly around the axis of the drive shaft and for this differential piston a common eccentric and to provide a common towed body. As a result, the moving masses can be reduced and space is saved. It is possible to arrange several such differential piston groups along the drive shaft.

The valve control members for the outlet and inlet valve arrangements of the plurality of differential pistons are also expediently distributed in a star shape around the axis of the drive shaft, wherein a common eccentric and a common towed body should be provided for the valve control members for constructional reasons.

In an expedient embodiment, the exhaust and intake valve assembly includes an intake valve seat and an exhaust valve seat fixed radially to the axis of the drive shaft and coaxial with the exhaust valve seat suitably closer to the drive shaft than the intake valve seat. As a result of this placement, the area in which high residual pressure acts for a longer time is as far away as possible from the drive shaft, and the seal between the inlet valve seat and the drive shaft is exposed to the high residual pressure barely or only for a short time. The arrangement of the valve seats takes up little space in the direction of the axis of the drive shaft.

The valve control member should extend through the exhaust valve seat with sufficient clearance into the intake valve seat, with a sealing area provided between the valve seats, and also with respect to the drive shaft. First and second shoulders on the valve control member serve to lift the respective valve body from their seats, wherein the lift-off movements of the valve body take place in opposite directions. That is, the valve control member opens the intake valve when lifting, while when lowering, the exhaust valve opens.

Mounting technology favorable, the shoulder of the ends of a set on the valve control member, preferably screwed tube formed in order to achieve the largest possible contact areas.

The valve bodies are urged to their seats by only weak springs, with the inlet valve body being a disc or plate which can be centered by the spring. The exhaust valve body, however, is an annular disc or an annular plate which is guided on the valve control member and can move relative thereto. Appropriately, a mechanical seal between the valve control member and the Auslaßventilkörper is provided here to avoid a discharge valve body immediate leakage into the exhaust valve seat.

With regard to perfect sealing conditions with attached valve bodies conical or spherical sealing surfaces could be provided on the valve bodies, and also the valve seats could be formed with conical or spherical sealing surfaces.

To ensure that no overlap occurs between the exhaust and intake valves, i. each valve opens only when previously closed the other valve, it is important to make the distance between the shoulders in the longitudinal direction of the valve control member smaller than the distance between the attached valve bodies. Preferably, the dimensioning is carried out here so that both valve bodies are placed at the top and bottom dead center of the differential piston and the valve control member is a match to each shoulder. This game can for example be between about 0.1 and 0.4 mm.

The valve control member is expediently guided repeatedly over its length.

The valve seats and a guide for the valve control member may be arranged in sleeve bodies, which are clamped in a housing chamber between a housing wall adjacent the drive shaft and a housing cover. These sleeve bodies may have an inlet and two outlets while another inlet is disposed in the wall of the housing chamber. This concept simplifies installation and makes it possible to place the intake and exhaust valves close to each other to save space.

In an advantageous embodiment, the eccentric for the differential piston and the valve control member are the same size and formed with the same eccentricity.

In a particularly advantageous embodiment, the eccentricity of the eccentric can be adjusted relative to the axis of the drive shaft in order to adjust the flow rate and / or performance as needed. This could be realized, for example, by virtue of the fact that the eccentric consists of two eccentric sleeves which are set into one another and can be fixed relative to one another and which can be fixed in any desired relative position. Alternatively, the eccentric could also be replaceably mounted on the drive shaft, so that a change in the eccentricity can be accomplished by replacing the eccentric.

Fig. 1

eine Vorrichtung zum Aufkonzentrieren einer gepumpten Flüssigkeit, in Schemadarstellung, mit einer Radialkolbenpumpe, die in einem Teilachsschnitt gezeigt ist, wobei ein Differentialkolben den oberen Totpunkt einnimmt,

Fig. 2

die Radialkolbenpumpe beim Ansaughub,

Fig. 3

die Radialkolbenpumpe beim Förderhub,

Fig. 4

einen Querschnitt eines Ausführungsdetails der Radialkolbenpumpe, in der Schnittebene IV-IV von Fig. 5,

Fig. 5

einen Achsschnitt des Details von Fig. 4, in der Schnittebene V-V,

Fig. 6

schematisch eine weiteres Ausführungsdetail, und

Fig. 7

ein weiteres Ausführungsdetail.

Reference to the drawings, embodiments of the subject invention will be explained. Show it:

Fig. 1

a device for concentrating a pumped liquid, in schematic representation, with a radial piston pump, which is shown in a partial axis section, wherein a differential piston assumes the top dead center,

Fig. 2

the radial piston pump during the intake stroke,

Fig. 3

the radial piston pump during the delivery stroke,

Fig. 4

a cross section of an embodiment of the radial piston pump, in the section plane IV-IV of Fig. 5 .

Fig. 5

an Axis cut of the detail of Fig. 4 , in the section plane VV,

Fig. 6

schematically another Ausführungsdetail, and

Fig. 7

another execution detail.

An in Fig. 1 schematically shown device V for concentrating a liquid F in a concentrate or a concentrated liquid F _K , for example, with simultaneous formation of pure liquid F _R , could be operating on the principle of reverse osmosis seawater desalination plant, or a plant for concentrating fruit juice, or like. More. Basically, it is provided in the device V, to promote the liquid F with a radial piston pump R and to pressurize, to pass through a concentrator 3, from which the concentrated liquid F _{K is obtained} with considerable residual pressure, while the pure liquid F _R substantially depressurized eg as pure water permeate in seawater desalination, is collected. The concentrated liquid F _K with the considerable residual pressure is used in the radial piston pump R, with the energy directly support the promotion of the liquid F to the operation of the radial piston pump R only a little primary energy, such as electric power or the power of a motor P, too consume. In the case of seawater desalination, the concentrator 3 would be, for example, a membrane system that operates on the principle of reverse osmosis.

The radial piston pump R in Fig. 1 sucks the liquid F, which is optionally provided with a small pre-pressure, via a line 1 and a supply valve 16 by means of at least one differential piston K (intake stroke), and promotes the delivery cycle via a discharge valve 17 in a line 2. The line 2 leads to the concentrator 3, from which the pure liquid F _R emerges and in a line 4, the concentrated liquid F _{K is} conveyed under the residual pressure to an inlet 5. After the concentrated liquid F _{K has been used} in a pressure chamber 36 for acting on the differential piston K during the delivery cycle, it flows from an outlet 6 substantially without pressure.

In order to simplify the start-up of the device, a valve device 7 may be provided in the line 2, which promotes via a line 8 directly in de inlet 5, but is hardly or only used under certain circumstances in normal operation.

The radial piston pump R has a housing wall 10 which separates the conveying and working area of a chamber 11 of a drive shaft 12, and, for example, a removable housing cover. 9

On the drive shaft 12, an eccentric 13 for driving the differential piston K and another eccentric 14 for actuating an inlet and outlet valve assembly A are arranged, the eccentric 14 in the drive direction of rotation 40 about an axis 38 of the drive shaft 12 relative to the eccentric 13 by about 90 ° is offset. In the embodiment shown, the two eccentrics 13 are dimensioned differently sized and arranged with different eccentricities on the drive shaft 12. However, it would be quite possible to dimension both eccentrics 13, 14 equal and to arrange with the same eccentricities. The eccentrics 13, 14 may be fixedly formed on the drive shaft 12 or interchangeable wedged thereon. In an alternative, not shown, the eccentricity of each eccentric relative to the axis 38 of the drive shaft 12 can be changed, for example by replacement or by each eccentric 13 or 14 consists of two rotatable relative to each other and definable in selectable relative positions eccentric sleeves. In Fig. 1 the axis of the eccentric 13 with 37 and the eccentric 14 are designated 39.

The differential piston K has on the piston rod side a shaft 15 which is connected via a train-pressure coupling directly to the eccentric 13, in the housing wall directly or indirectly guided linearly at 37, and sealed. The differential piston K includes a sealing arrangement that separates a pumping chamber from the pressure chamber 36.

The intake and exhaust valve assembly A includes an intake valve of a valve body 32 and a valve seat 27, and an exhaust valve of a valve body 29 and a valve seat 28. The valve seats 27, 28 are radially aligned with the axis 38 of the drive shaft 12 and coaxial, wherein the Outlet valve seat 28 to the drive shaft 12 has and is disposed closer to this, as the inlet valve seat 27 facing away from the drive shaft 12. Both valves associated with a common valve control member 18 which is at least once in the housing wall 10 directly or indirectly linearly guided and sealed, and is articulated directly to the eccentric 14 via a compression and traction coupling S, wherein a shaft 19 of the valve control member 18 extends from the coupling S through the outlet valve seat 28 with radial clearance up to the inlet valve seat 27. The seals 29 seal between the outlet valve and the chamber 11 and between the outlet 6 and the inlet valve seat 27, respectively. Further, a further guide 21 is provided for the valve control member 18 between the valve seats. On a stepped shaft portion of the valve control member 18, a tube 22 is fixed, for example screwed, which forms a first, to the outlet valve body 29 facing shoulder 23 and a second, the inlet valve body 32 facing shoulder 24. The distance between the shoulders 23, 24 is smaller than the distance between the valve bodies 29, 32, when they are placed on their valve seats 27, 28, such that with the valves closed, for example, between each shoulder 23 or 24 and the adjacent valve body 32 or 29 a game between 0.1 to about 0.4 mm is present. The inlet valve body 32 may be a disc or a plate and is centered by a weak spring 33 and applied to the inlet valve seat 27. The valve body 29 may be an annular disc or an annular plate, which is acted upon by a spring 31 against the outlet valve seat 28. Between the outlet valve body 29 and the stem 19 of the valve control member 18, a mechanical seal 30 may be provided. The valve bodies 32, 29 may have tapered or rounded seating surfaces, as may the valve seats 27, 29. The inlet valve seat 27 may be formed in a sleeve member 25 while the guide 21 and seal 29 and outlet valve seat 28 are in another Sleeve member 26 may be formed. The sleeve body 25, 26 are clamped in the housing between the housing wall 10 and the housing cover 9. Downstream of the inlet valve seat 27, an outlet in the sleeve body 26 leads to an inlet 35 to the pressure chamber 36. The inlet 35 is simultaneously connected to a chamber located below the sleeve body 26 and containing the outlet valve body 29 at the outlet valve seat 28.

Function:

The drive shaft 12 is driven by the primary drive source P, for example an electric motor or an internal combustion engine, in order to drive the differential piston K and the valve control member 18 back and forth via the couplings S. The differential piston K sucks in the intake stroke over the piston rod far side liquid F via the open feed valve 16 at. During the intake stroke, the intake valve 32, 27 is closed and the exhaust valve 29, 28 is open. The concentrated liquid F _K is pushed out of the pressure chamber 36 through the outlet 6 substantially without pressure. Shortly before reaching or generally in the region of the bottom dead center of the differential piston K, the outlet valve 29, 28 is closed and then, without valve overlap, the inlet valve 27, 32 is opened. At the beginning of the delivery cycle, the concentrated liquid F _K under the residual pressure in the pressure chamber 36 pressurizes the piston rod side of the differential piston K to cooperate with the delivery cycle. Shortly before or in the region of the top dead center of the differential piston K, the inlet valve 32, 27 is closed again and only then the outlet valve 29, 28 opens without valve overlap.

Expediently, a plurality of differential pistons K and also a plurality of inlet and outlet valve arrangements A are distributed in a star shape and regularly around the drive shaft 12, for example at least three or more.

Thanks to the assistance of the concentrated liquid F _K with their residual pressure so little primary energy is required to operate the radial piston pump R that the device V for seawater desalination can be operated autonomously, for example, for the drinking water needs of a building or a system via a DC motor of solar panels.

The area ratio between the rod side remote and the piston rod side of the differential piston K is adjusted to the proportions between the liquid to be pumped and the concentrated liquid so that the energy in the concentrated liquid can be optimally utilized for assistance. In this case, the pressure difference at the sealing device of the differential piston K is relatively low, and also the sealing region 20 is acted upon only for a short time during the conveying cycle with the residual pressure. In the housing chamber 11 may be provided an oil bath.

Fig. 2 illustrates the intake stroke of the differential piston K in the radial piston pump R. The concentrated fluid F _K in the pressure chamber 36 is above the open Exhaust valve 28, 29 relaxed and is ejected into the outlet 6, while in the inlet 5 with closed inlet valve 27, 32, the residual pressure is present. The shoulder 23 holds the outlet valve 28, 29 open while the shoulder 24 is away from the inlet valve body 32. At a residual pressure of, for example, 68 bar in the inlet 5 prevails in the pressure chamber 36 only a pressure of about 1 bar. Downstream of the closed discharge valve 17 there is a delivery pressure of about 70 bar, while the suction pressure with open supply valve 16 is about 1 bar. Thus prevails on both sides of the differential piston K in about the same pressure.

Fig. 3 illustrates the delivery stroke of the radial piston pump R, in which the differential piston K moves toward top dead center. The valve control member 18 has the inlet valve 32, 27 open while the outlet valve 28, 29 is closed. The concentrated liquid F _K flows with the residual pressure of for example 68 bar into the pressure chamber 36 and assists the differential piston K. The outlet valve 28, 29 is kept closed with this pressure. The liquid to be pumped is under a pressure of about 70 bar, the supply valve 16 is closed and the discharge valve 17 is opened. The pressure difference at the sealing device of the differential piston K is only about 2 bar.

The 4 and 5 illustrate an embodiment of the coupling S, for example, between the shaft 15 and the eccentric 13. In the 4 and 5 the leadership will be 37 of the Fig. 1 formed by a sliding bush 41 in the housing wall 10, which dips with two support shells 42 in the chamber 11 and the shaft 15 is supported in the direction of rotation of the eccentric 13 against transverse forces and leads. The support shells 42 engage in a pocket 45 of a towed body 44, which is rotatably mounted on a plain bearing bush or a needle bearing 43 on the eccentric 13 and axially positioned on the eccentric 13, for example by the shaft 15 and / or the support shells 42. The pocket 45 has an inner width which approximately corresponds to the outer dimension of the support shells 42, so that a slight sliding fit is created here. In the pocket 45, a lower pressure surface 49 for the shaft end (pressure coupling) and in undercuts 46 in the side walls of the pocket 45 traction surfaces 50 (train coupling) are formed for the shaft end. The shank end contains two mutually parallel grooves 47, so that two outwardly extending drivers 48 are formed on the shaft end, which engage in the undercuts 46. The undercuts 46 are longer than the outer width of the end of the shaft 15 and optionally extend to the periphery of the towed body 44th

The towed body 44 may be formed in one piece, or ( Fig. 5 ) are assembled from two halves 44a and 44b. Optionally, the grooves 47 are combined in a circumferential groove and also form the two drivers 48 has a circumferentially round collar, so that the shaft 15 in the Coupling S can twist.

In the simplified embodiment of Fig. 6 At the end of the shaft 15, a widening is formed, which forms one or two drivers 48 ', and engages in the undercut 46' of the towed body 44. In the transverse direction in Fig. 6 is between the dogs 48 'and the undercut 46' and between the shaft 15 and the inlet to the undercut 46 'sufficient clearance provided to allow the indicated by a double arrow sliding movement of the shaft 15 during the orbital movement of the eccentric 13 about the axis 37.

In the embodiment in FIG Fig. 7 are on the towed body 44 bearing blocks 51 integrally formed in which a sliding pin 52 is seated, which passes through the end of the shaft 15. Between the bearing blocks 51 enough clearance is provided to the in Fig. 7 indicated by a double arrow sliding movement in the sliding guide of the shaft 15 during the orbital movement of the eccentric about the axis 37 allow.

Claims (23)

1. Device (V) for concentrating a fluid (F) pumped by a differential piston pump through a concentrating means (3), which fluid acts, as concentrate (F_K) under residual pressure, directly on the at least one differential piston (K) in such a manner as to assist the delivery stroke, the differential piston (K) being driven by a drive shaft (12) which actuates at least one linearly guided valve control member (18) of an inlet and outlet valve arrangement (A), characterized in that the differential piston pump is a radial piston pump (R), in that eccentrics (13, 14) for the differential piston (K) and the valve control member (18) are arranged on the drive shaft (12), and in that the differential piston (K) and the valve control member (18) are coupled directly to the eccentrics (13, 14) with push and pull couplings (S).
2. Differential piston pump for fluids (F), having a housing comprising an inflow and an outflow for the fluid (F) to be pumped and an inlet (5) and an outlet (6) for fluid (F_K) under residual pressure, at least one differential piston (K) delivering the fluid (F) from the inflow into the outflow, which differential piston may be driven by a drive shaft (12) and during the delivery stroke also directly by the residual pressure and separates a pump chamber from a pressure chamber (36), at least one inlet and outlet valve arrangement (A) for the pressure chamber (36), and at least one linearly guided valve control member (18), actuated by the drive shaft (12), of the inlet and outlet valve arrangement (A), characterized in that the differential piston pump is a radial piston pump (R), in that eccentrics (13, 14) for the differential piston (K) and the valve control member (18) are arranged on the drive shaft (12), and in that the differential piston (K) and the valve control member (18) are coupled directly to the eccentrics (13, 14) with push and pull couplings (S).
3. Differential piston pump according to Claim 2, characterized in that a single valve control member (18) is provided for the inlet and outlet valve arrangement (A).
4. Differential piston pump according to Claim 2, characterized in that the push and pull coupling (S) comprises a draw body (44) mounted rotatably on the eccentric (13, 14) and at least one engaging member (48) provided at one end of a shaft (15, 19) of the differential piston (K) or of the valve control member (15), and in that between the engaging member (48) and the draw body (44) there are provided a substantially radially active form-fitting engagement and, in the circumferential direction, preferably parallel to a tangent to the eccentric (13, 14), a slideway.
5. Differential piston pump according to Claim 4, characterized in that the slideway provides protection against rotation for the shaft (15, 19).
6. Differential piston pump according to Claim 4, characterized in that the draw body (44), which, preferably, consists of two axially assembled halves (44a, 44b) or is in one piece, comprises for the shaft (15, 19) an externally open pocket (45) undercut in the slideway, whose internal width, when viewed in the axial direction, is less than the external width of the shaft (15, 19).
7. Differential piston pump according to Claim 6, characterized in that the shaft (15, 19) of the differential piston (E) and/or of the valve control member (18) is arranged in a slide guide (37) fixed to the housing, in that the slide guide (37) comprises a sliding bushing (41), and in that the sliding bushing (41) engages with formed-on supporting shells (42), oriented towards one another in the direction of rotation of the eccentric (13, 14), with a sliding fit between side walls of the pocket (45).
8. Differential piston pump according to Claim 6, characterized in that the draw body (44) is positioned axially on the eccentric (13, 14) via the slideway and/or the supporting shells (42).
9. Differential piston pump according to Claim 6, characterized in that a bottom of the pocket forms a pressure surface (49) for the shaft end, which surface is longer than the external width of the shaft end, in that, at a distance from the shaft end, two diametrically opposing parallel grooves (45) or a circumferential groove are formed in the shaft, which grooves define a width approximately corresponding to the internal width of the pocket (45), and in that the shaft end adjoining the grooves or groove forms as engaging member (48) at least one externally protruding driver, which engages in an undercut (46) formed in a pocket side wall.
10. Differential piston pump according to Claim 9, characterized in that the undercut (46) extends parallel to a tangent to the eccentric (13, 14) and is longer in this direction than the driver.
11. Differential piston pump according to Claim 2, characterized in that the eccentric (14) for the valve control member (18) of the outlet and inlet valve arrangement (A) assigned to a differential piston (K) is offset relative to the eccentric (13) for this differential piston (K) by approximately 90° about the axis (38) of the drive shaft (12) and in a leading manner in the driving direction of rotation (40).
12. Differential piston pump according to Claim 2, characterized in that three or more differential pistons (K) are distributed in a stellate arrangement about the axis (38) of the drive shaft (12), and in that a common eccentric (13) and a common draw body (44) are assigned to the differential pistons (K).
13. Differential piston pump according to Claim 12, characterized in that the valve control members (18) for the outlet and inlet valve arrangements (A) of the differential pistons (K) are distributed regularly in a stellate arrangement about the axis (38) of the drive shaft (12), preferably with a respective offset of approximately 90° relative to the differential pistons (K), and in that a common eccentric (14) and a common draw body (44) are assigned to the valve control members (18).
14. Differential piston pump according to Claim 2, characterized in that the outlet and inlet valve arrangement (A) comprise, fixed to the housing, an inlet valve seat (27) and an outlet valve seat (28), which are oriented radially relative to the axis (38) of the drive shaft (12) and are coaxial, in that the outlet valve seat (28) is positioned closer to the drive shaft (12) than the inlet valve seat (27), and in that the outlet valve seat (28) points towards the drive shaft (12) and the inlet valve seat (27) points away from the drive shaft (12).
15. Differential piston pump according to Claim 14, characterized in that the valve control member (18) extends in each case with radial spacing through the outlet valve seat (28) as far as into the inlet valve seat (27), is sealed relative to the drive shaft (12) and between the valve seats (27, 28), and comprises a first shoulder (23) for lifting an outlet valve body arranged movably on the side of the outlet valve seat (28) pointing towards the drive shaft (12) and a second shoulder (24) for lifting an inlet valve body arranged movably on the side of the inlet valve seat pointing away from the drive shaft (12).
16. Differential piston pump according to Claim 15, characterized in that the shoulders (23, 24) are formed by the ends of a tube (22) fixed, preferably screwed, to the valve control member (18).
17. Differential piston pump according to Claim 15, characterized in that the inlet valve body (32) is a disc loaded by a spring (33) towards the inlet valve seat (27), preferably centred by the spring (33), and in that the outlet valve body (29) is an annular disc loaded by a spring (31) towards the outlet valve seat (28) and guided movably on the valve control member (18), preferably with a sliding ring seal (30) arranged between the valve control member (18) and the annular disc.
18. Differential piston pump according to Claim 17, characterized in that the annular disc and the disc comprise conical or spherical seat surfaces, and, preferably, the valve seats (27, 28) are of conical or spherical construction.
19. Differential piston pump according to Claim 15, characterized in that the distance, when viewed in the longitudinal direction of the valve control member (18), between the shoulders (23, 24) is smaller than the distance between the valve bodies positioned on the valve seats (27, 28), preferably in such a way that, at the top and bottom dead centres of the differential piston (K) assigned to the outlet and inlet valve arrangement (A), both valve bodies are seated and play is present relative to the respective shoulder (23, 24), preferably in each case of approx. 0.1 to 0.4 mm.
20. Differential piston pump according to Claim 15, characterized in that the valve control member (18) extends between the outlet valve seat (28) and the drive shaft (12) and between the valve seats (27, 28) through guides (21, 37) fixed to the housing.
21. Differential piston pump according to Claim 14, characterized in that the valve seats (27, 28) and the one guide (21) are arranged in sleeve members (25, 26), which are mounted in a housing chamber between a housing wall (10) adjacent to the drive shaft (12) and a housing cover (9) and comprise an inlet (5) and two outlets (34, 6), and in that a further inlet is arranged in the housing wall (10).
22. Differential piston pump according to at least one of preceding Claims 2 to 21, characterized in that the eccentric (13) for the differential piston (K) and the eccentric (14) for the valve control member present at least substantially identical dimensions and with identical eccentricities (C).
23. Differential piston pump according to at least one of preceding Claims 2 to 22, characterized in that the extent of the eccentricity (C) of the eccentric (13, 14) is adjustable and/or the eccentric (13, 14) is arranged replaceably on the drive shaft.

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