US20100183454A1

US20100183454A1 - Rotary displacement pump

Info

Publication number: US20100183454A1
Application number: US12/687,230
Authority: US
Inventors: Klaus Lübke; Sven Borghoff; Sebastian M. Siegmund; Andreas Klomfass
Original assignee: Gather Industrie GmbH
Current assignee: Gather Industrie GmbH
Priority date: 2009-01-16
Filing date: 2010-01-14
Publication date: 2010-07-22
Also published as: EP2208890A3; DE202009000690U1; EP2208890A2

Abstract

A rotary displacement pump (2) for pumping a medium, having a pump housing (3); a reception chamber (4) which is formed in the pump housing (3), with an inlet area (26) and an outlet area (27); at least one rotary displacement element (5, 6) which is accommodated in the reception chamber (4), and which is rotatably attached by means of at least one bearing (40, 41, 56) in the pump housing (3), and which presents at least one delimitation surface (21), by means of which it delimits at least one work space (19) of the pump (2); and a bypass (59) which allows the return flow of a part of the pumped medium from the outlet area (27) into the inlet area (26). The rotary displacement element (5, 6) and/or a rotating part (35) which is connected to the rotary displacement element can present at least one counter surface (64) which delimits the bypass (59), and whose counter surface normal (65) has at least one component which is directed opposite to the delimitation surface normal (66) of the delimitation surface (21).

Description

The invention relates to a rotary displacement pump for pumping a medium, with a pumping housing, a reception chamber with an inlet area and an outlet area, which chamber is formed in the pump housing, and at least one rotary displacement element which is accommodated in the reception chamber, and attached rotatably by means of a bearing in the pump housing, and which presents at least one delimitation surface by means of which it delimits at least one work space of the pump.
In rotary displacement pumps, the medium is conveyed by the rotary movement of a displacement element, respectively several displacement elements, through a work space that is closed on itself, from an inlet area into an outlet area. Unless there are leaks resulting from the construction, the medium cannot flow through this work space—even if the pump is at stand still—in the reverse direction, i.e., from the outlet area into the inlet area. As a result of the compaction of the medium in the work space of the pump, considerable pressure is generated on a delimitation surface of the rotary displacement element, particularly in the outlet area. Because this rotary displacement element is attached rotatably by means of a bearing, respectively several bearings, in the pump housing, this bearing must absorb strong forces.
The invention is therefore based on the problem of reducing the total force, which is the resultant of the superposition of the applied forces, on the rotary displacement element, respectively on the bearing.
To solve this problem, the rotary displacement pump presents at least one bypass which allows the return flow of a part of the pumped medium from the outlet area into the inlet area, where the rotary displacement element and/or a rotating part that is connected to the rotary displacement element present(s) at least one counter surface which delimits the bypass and whose counter surface normal has at least one component that is directed opposite to the delimitation surface normal of the delimitation surface. As a result of the pressure in the work space of the pump, a resultant force acting on the rotary displacement element along the delimitation surface normal is generated. This force is compensated—at least partially—by a counter force which bears on the counter surface as a result of the pressurized medium in the bypass. Due to the superposition of the force applied to the delimitation surface, which force results from the pressure in the work space, and of the corresponding counter force due to the pressure in the bypass, the resulting total force acting on the rotary displacement element, respectively its bearing, is reduced. The bearing can accordingly be designed to be smaller. The rotary displacement element is attached in the housing directly via the bearing, or via the bearing and at least an additional intermediate element, particularly the rotating part. The bypass is particularly a bypass that runs within the pump housing. The medium is preferably a liquid medium.
In particular, it is provided for the delimitation surface to constitute an axial delimitation surface which delimits the work space axially. The rotary displacement element is attached rotatably with respect to the pump housing, usually by a bearing designed as a radial bearing.
Such a radial bearing is usually not suitable for absorbing stronger axial forces. However, such forces occur if the rotary displacement element presents an axial delimitation surface. To reduce the resulting axial total force, the counter surface presents a counter surface normal which has a component that is directed opposite to the axial delimitation surface normal of the axial delimitation surface. As a result of the compensation of the resulting axial forces, a reduction of the axial total force on the rotary displacement element, the rotating part which is connected to the rotary displacement element, and/or the bearing is achieved,.
According to a variant of the invention, it is provided for the counter surface to be arranged so it faces the delimitation surface. The pressure of the medium in the work space, which acts on the delimitation surface, is compensated—at least partially—by the counter pressure which the medium exerts in the bypass on the counter surface, in such a way that no additional moment of tilt acts on the rotary displacement element, the rotating part and/or the bearing.
According to an advantageous variant of the invention, it is provided for the bypass to present a valve for the control and/or regulation of the flow of the return-flow medium through the bypass. The valve here serves as a counter pressure delimitation. The volume flow rate of the medium on/in the valve is determined by means of a sensor. By means of the valve, a variable counter pressure is generated on the counter surface, pressure which corresponds to the volume flow rate, and which is regulated if necessary.
In particular, it is provided for the rotary displacement element to be designed as a rotary piston. A rotary displacement pump with a rotary piston is particularly a rotary displacement piston pump. Rotary displacement piston pumps are rotary piston pumps, rotary vane pumps, circumferential piston pumps, and toothed wheel pumps.
In an advantageous embodiment of the invention, it is provided for one of the rotary displacement elements to be designed as a housing element which encloses eccentrically a rotary displacement element designed as an inner rotary displacement element. Together, the housing element which is attached rotatably and the inner rotary displacement element form a displacement element set. A rotary displacement pump with such a displacement element is called, for example, an inner toothed wheel pump, also called crescent pump, or a toothed ring pump, also called gerotor pump. In the case of the inner toothed wheel pump and the toothed ring pump, the inner rotary displacement element, which is designed as a toothed wheel (front wheel), engages with its teeth in the tooth gaps (chambers) of an inner toothing of the housing element that is attached rotatably. The housing element is designed as a toothed ring or it presents a toothed ring. In the case of the inner toothed wheel pump, the medium to be conveyed is conveyed in the spaces between the tooth gaps of the toothed wheel and of the toothed ring, where the teeth are sealed by means of a crescent-shaped intermediate element. In the toothed wheel pump, on the other hand, the medium is conveyed through the work space—whose volume changes—between the tooth gaps and the teeth of the two rotary displacement elements.
In an advantageous embodiment of the invention, it is provided for the housing element to be designed as a hypotrochoid housing with n chambers, and for the additional inner rotary displacement element to present n-1 corresponding teeth for engagement in the chambers. The chambers and teeth are designed here with mutual adjustment so that they determine, without any additional element, the shape and the volume of the work space, respectively the volumes of the work space. The inner rotary displacement element here presents precisely one tooth less than the housing element has chambers. The volume of the work space is changed in such a manner by the movement of the two rotary displacement elements (of the displacement element set) that the pump sucks the medium in the inlet area, compacts it on the way to the outlet area, and expels it there. For this purpose, the volume of the work space between the inlet area and the outlet area is first enlarged by the movement of the rotary displacement element, and then decreased again. The number n of the chambers is preferably seven (n=7).
It is advantageous to provide for the bearing to be a rolling element bearing or a slide bearing. If the bearing is a radial bearing, then it is a radial bearing in the form of a rolling element bearing or a slide bearing for the radial attachment of the rotary displacement element. Alternatively, or additionally, the bearing is an axial bearing. In particular, the axial bearing is a combined axial/radial bearing. If the bearing is a rolling element bearing, then it is preferably a ball bearing, a roller bearing or a needle bearing. If the bearing is designed as a slide bearing, then it presents an annular, closed bearing sleeve, or a bearing sleeve composed of bearing shells.
It is provided for the rotating part to be a shaft or to present a shaft. In this case, the rotary displacement element is preferably attached rotatably in the housing by means of this shaft. Here, it is provided in particular for the shaft to contribute to the formation of the bypass. The shaft is preferably a hollow shaft which forms an axial channel.
In a preferred embodiment of the invention, it is provided for the rotary displacement element to be a rotary displacement element which can be driven by an associated driving motor. The driving motor drives the rotary displacement element preferably via the rotating part, particularly the shaft. Such a drive shaft is a drive shaft of the pump. Here, it is provided particularly for the arrangement of a coupling, particularly a magnetic coupling, between the shaft and the driving motor. By means of the interconnected coupling, the output of the driving motor and the shaft are not connected permanently to each other; rather they can be connected rotatably. In particular, it is provided for the coupling to contribute to the formation of the bypass.
According to an advantageous variant of the invention, the valve presents a valve-internal mechanism for the valve-internal control of the pressure difference Δp of the medium as a function of the pressure exerted at the inlet side of the valve.
It is advantageous to provide for the pump to be designed as a rotary displacement pump without moving seal. A moving seal is a dynamic seal which is arranged between two mutually moving parts.
In an advantageous embodiment of the invention, it is provided for the pump housing and/or the shaft to consist of a stainless steel and/or a Hastelloy nickel based alloy and/or titanium. These materials guarantee a high mechanical strength and a high resistance to corrosion at temperatures ranging from −20° C. to +200° C.
Finally, it is advantageous for the bearing and/or the rotary displacement elements to consist—at least partially—of the materials Teflon and/or carbon and/or Peek and/or non galling alloys. These materials (Teflon, carbon, Peek, and non galling alloys) are materials that cannot become welded to the above-mentioned materials (stainless steel, Hastelloy nickel based alloy, and titanium) during the operation of the pump.

The invention is explained in greater detail in reference to the figures, which show:

FIG. 1 a schematic representation of the essential construction of a rotary displacement pump designed as a gerotor pump,

FIG. 2 a longitudinal section through a gerotor pump according to a preferred embodiment example of the invention, and

FIG. 3 in the upper area, a top view of the gerotor pump, and, in the lower area, a cross-sectional representation through the gerotor pump of FIG. 2.

FIG. 1 shows the essential structure and [sic] of a rotary displacement pump 2 which is designed as a gerotor pump 1, with a pump housing 3, and a cylindrical reception chamber 4 arranged in the pump housing 3. In the reception chamber 4, two rotatably attached rotary displacement elements 5, 6 are accommodated, which together form a displacement element set 7.
The first rotary displacement element 5 is designed as a housing element 8 which is attached rotatably about a rotation axis 9. This housing element 8, which is designed as a hypotrochoid housing 10, presents two parts: a ring part 11, and an axially connected wall part 12. The ring part 11 presents, on its inner periphery 13, seven chambers 14 which are distributed evenly along the circumference. In the rotatably attached housing element 8, the second rotary displacement element 6 is arranged, which is designed as a star-shaped inner rotary displacement element 15; it presents six teeth 17 on its outer periphery 16. The inner rotary displacement element 15 is attached rotatably about a rotation axis 18 which does not coincide with a rotation axis 9 of the housing element 8. The rotation axes 9 and 18 are separated from each other in such a way that a part of the teeth 17 engages in a part of the chambers 14, and work spaces 19 form between the remaining teeth 17 and chambers 14. Each one of the work spaces 19 is delimited by a part of the inner periphery 13 of the ring part 11 which is part of the housing element 8, by a part of the outer periphery 16 of the inner rotary displacement element 15, and by a delimitation surface 21—which is designed as an axial delimitation surface 20—of the wall part 12 which is part of the housing element 8. A given part of the inner periphery 13 and of the outer periphery 16 thus also forms a delimitation surface 21. An additional second axial delimitation surface (not shown) facing the axial delimitation surface 20 of the wall part 12 is formed by a pump cover 22.
On facing sides of the pump cover 22, an inlet channel 23 and an outlet channel 24 of the pump 2 are located. The inlet channel 23 is connected via an inlet port 25 to an inlet area 26 of the reception chamber 4. An outlet area 27—which faces the inlet area 26—of the reception chamber 4 is connected to the outlet channel 24 via an outlet port 28 formed in the pump cover.
The resulting functioning of the pump 2 is as follows: When the housing element 8 rotates (arrow 29), as a result of the engagement of the teeth 17 of the inner rotary displacement element 15 into the chambers 14 of the housing element 8, the inner rotary displacement element 15 rotates simultaneously (arrow 30). As can be seen in the instantaneous view according to FIG. 1, the teeth 17 engage completely into the chambers 14 only over a certain angular range—in the lower area of FIG. 1—, whereas in a diametrically opposite angular area—top of FIG. 1—the teeth 17 of the inner rotary displacement element 15 do not engage into the chambers 14 of the housing element 8.
During the rotation (arrows 29, 30) of the displacement element set 7, the teeth 17 move past the chambers 14 in the last-mentioned angular area in the rotation direction (arrow 26). During the process of rotating out of the first-mentioned angular area of engagement, one of the work spaces 19, which moves simultaneously and becomes increasingly enlarged during the rotation of the displacement element set 7, forms in each case between two adjacent teeth 17 of the inner rotary displacement element 15 and a chamber 14 of the housing element 8, which space then becomes smaller again as the first-mentioned angular area of engagement of the toothing is approached, and finally vanishes. During the phase of the enlargement of the work space 19, the latter moves past the inlet port 25 in the inlet area 26, so that the medium which is conveyed in the inlet channel 23 is sucked into the respective work space 19. During the phase of reduction of the size of the respective work space 19, the latter moves past the outlet port 28 in the outlet area 27, so that the medium is expelled via the outlet port 28 to the outlet channel 24. In this way, by means of the rotation of the housing element 8 respectively of the inner rotary displacement element 15—i.e., at least one of the rotary displacement elements 5, 6—, a continuous pump operation is achieved.
FIG. 2 shows an embodiment according to the invention of the rotary displacement pump 2 designed as a gerotor pump 1. The rotary displacement pump 2 extends from a drive-side first end 31 along its longitudinal axis 32 to a pump-side second end 33. The longitudinal axis 32 is simultaneously the rotation axis 9 of the first rotary displacement element 5 which is designed as a housing element 8. The wall part 12 of the housing element 8 is connected so as to form one piece to the rotating part 35 which is designed as a shaft 34. The shaft 34 extends from the wall part 12 of the housing element 8 to a coupling 37 which is designed as a magnetic coupling 36. The coupling 37 is located in a pump carrier housing 39 which is attached with the attachment screws 38 to the pump housing 3. The shaft 34 is attached rotatably via two bearings 40, 41, which are axially separated with respect to the rotation axis 9, in the pump housing 3. The bearings 40, 41 are radial bearings. The first bearing 40 is here designed as an inclined ball bearing 42, which is designed in two parts, and the second bearing 41 is designed as a cylinder roller bearing 43.
The magnetic coupling 36 consists of an external magnet 44 which encloses ideally an internal magnet 45. The internal magnet 45 is connected rotatably to a shaft 34, via an associated hub 46 (magnetic hub) and an attachment screw 47. The hub 46 is centered by means of a centering pin 48 which is arranged between the hub 46 and the shaft 34. Between the external magnet 44 and the internal magnet 45, a fixed cap 50 is arranged on the pump housing 3 by means of the attachment screws 49. The cap 50 here separates a pump inner space 51 of the pump housing 3, of which the reception chamber 4 is also a part, from an internal space 52 of the pump carrier housing 39 in which the external magnet 44 is located. The external magnet 44 is connected rotatably to a magnet carrier 53 which presents an intake 54 for the output shaft of a driving motor which is not shown. The driving motor is preferably an electro motor. If the shaft 34 is driven by the driving motor, then the shaft 34 is a drive shaft of the driven rotary displacement element 5.
The inner rotary displacement element 15, which is enclosed eccentrically by the rotatably attached housing element 8, is attached rotatably on the pump cover 22 (housing cover) via a bearing 56 which is designed as a cylinder roller bearing 55. A corresponding bearing axis 57, which is fixed by means of an attachment screw on the pump cover 22, presents centering pins 58 for centering.
In the pump internal space 51, a bypass 59 extends which connects the outlet area 27 to the inlet area 26, allowing in this way—independently of the conveyance through the work spaces 19—the return of a part of the medium from the outlet area 27 into the inlet area 26. The bypass 59 allows volume flow of the medium along the subsequent bypass path: Through a leakage channel which is not shown, the return-flow medium flows from the outlet area 27 of the reception chamber 4 through the cylinder roller bearing 55, which is associated with the inner rotary displacement element 15, into a channel 60 which runs within the shaft 34, and through the attachment screw 47, which is designed as a hollow screw, into the cap internal space 61 of the cap 50. Then, the medium flows back along the inner surface of the cap 50 to the external area 62 of the shaft 34, it traverses an axial fixation 63, as well as the two bearings 40, 41 which are arranged in the pump internal space 51. Then, the medium flows along a counter surface 64 of the first rotary displacement element 5 (housing element 8) into an external area 62—which encloses the ring part 11 of the housing element 8—of the reception chamber 4. From there, the medium reaches the inlet area 26 of the reception chamber 4. The counter surface 64 of the first rotary displacement element 5 delimits the bypass 59, where its counter surface normal (arrow 65) has a component which is directed opposite to the delimitation surface normal (arrow 66) of the delimitation surface 21.
In this embodiment example, an axial delimitation surface 20, which delimits the work spaces 19 axially, is [sic] into the delimitation surface 21. Moreover, in this embodiment example, the counter surface 64 is arranged so it faces the delimitation surface 21.
The resulting functioning of the bypass 59 is as follows: By means of the opposing orientation of the counter surface normal (arrow 65) and of the delimitation surface normal (arrow 66), the axial forces which are generated by the pressure of the medium in the work space 19 and by the pressure in the bypass 59 on the mutually facing surfaces 21, 64 compensate each other at least partially. As a result of the clearly reduced axial total force, the bearings 40, 41, which are designed as radial bearings, can be designed to be smaller, and they do not absorb strong axial surfaces; rather, they receive primarily radial surfaces.
The pressure in the interior of the bypass 59 can be controlled and/or regulated by means of a valve 67 shown in FIG. 3. This valve 67 is attached on the external surface of the pump cover 22. As far as fluid engineering is concerned, it is arranged, for example, in the bypass 59 between the outlet area 27 and the leakage channel, and it serves as a counter pressure delimitation. The valve 67 can be controlled externally, and it presents preferably a sensor for the determination of the volume flow rate through the valve 67. By means of a determination of the volume flow rate at the valve 67, a variable counter pressure can be generated, which can be regulated as needed.
Alternatively, the valve 67 presents a valve-internal mechanism which controls a valve-internal control of the pressure difference Δp of the medium as a function of the pressure exerted at the inlet side of the valve 67.
Moreover, the forces resulting from the pressure difference Δp between the inlet area 26 and the outlet area 27 can be set, particularly reduced, by setting this pressure difference Δp of the valve 67 via the bypass 59.
As a result of the adjusted rotary movement of the rotary displacement elements 5, 6, i.e., of the housing element 8 or of the inner rotary displacement element 15, the conveyance of the medium is low pulse. Moreover, the medium is not squeezed [sic] the good adjustment of the rotary movement function between the inlet port 26 and the outlet port 28 in the cover 22.
In an embodiment, the axial fixation 63 functions simultaneously as an orifice plate for pressure reduction and thus also for force reduction between the internal space of the cap 50 and the pump internal space 51 in the external area 62 of the shaft 34.
The bypass 59 of the pump 2 shown in FIG. 2 runs in a closed-off area of the pump 2, which extends in the direction of the longitudinal axis 32 from the pump cover 22 to the cap 50 which encloses the internal magnet 45 of the magnetic coupling 36. The force transfer to the driving motor occurs by magnetic transmission of force between the internal magnet 45 within the closed off area and the external magnets 44 of the magnetic coupling 36, which are arranged outside of this closed off area. No rotating part 35 which is attached rotatably with respect to the pump housing 3, such as for example the shaft 34, is led out of the closed off area. As a result, it is not necessary to provide a seal for the closed off area with respect to its environment using a dynamic seal (moving seal), particularly a rotary seal, such as, for example, a rotary shaft seal which encloses the rotating part 35 circumferentially. The rotary displacement pump 2 is thus preferably a rotary displacement pump 68 without moving seal. A rotary displacement pump 68 without moving seal can be used for a maximum medium pressure in the inlet area 26 and/or in the outlet area 27 in a range above 20 bar, preferably in a range above 50 bar.
Besides reducing the axial forces, the bypass 59 also functions to cool the above-mentioned components around and through which it [sic] flows, i.e., the bearings 40, 41, 56, the shaft 34, the coupling 37, the pump internal space 51, and the rotary displacement elements 5, 6 of the pump 2. If the medium has sufficient lubrication properties, then the bypass 59 also serves to lubricate these components of the pump 2.
If the above-mentioned moving components 5, 6, 40, 41, 56, 34, 37, 51, around and through which the medium flows, are furthermore low-wear components with high chemical resistance, then the pump 2 is a pump 2 for conveying non-lubricant and/or corrosive media. The pump housing 3 and/or the shaft 34 is(are) preferably made of stainless steel (material No. 1.4404 or 1.4571) and/or Hastelloy (C-276, material No. 2.4819) and/or titanium (grade 2, material No. 3.7035). The bearings 40, 41, 56 and/or the rotary displacement elements 5, 6 are—at least in part—manufactured from the materials Teflon and/or carbon and/or Peek and/or non galling alloys. The non galling alloys do not become welded during the operation of the pump to the stainless steel, Hastelloy or titanium of the pump housing 3 and/or of the shaft 34.

LIST OF REFERENCE NUMERALS

1 Gerotor pump
2 Rotary displacement pump
3 Pump housing
4 Reception chamber
5 Rotary displacement element
6 Rotary displacement element
7 Displacement element set
8 Housing element
9 Rotation axis
10 Hypotrochoid housing
11 Ring part
12 Wall part
13 Inner periphery
14 Chamber
15 Inner rotary displacement element
16 Outer periphery
17 Tooth
18 Rotation axis
19 Work space
20 Axial delimitation surface
21 Delimitation surface
22 Pump cover
23 Inlet channel
24 Outlet channel
25 Inlet port
26 Inlet area
27 Outlet area
28 Outlet port
29 Arrow
30 Arrow
31 First end
32 Longitudinal axis
33 Second end
34 Shaft
35 Rotating part
36 Magnetic coupling
37 Coupling
38 Attachment screw
39 Pump carrier housing
40 Bearing
41 Bearing
42 Inclined ball bearing
43 Cylinder roller bearing
44 External magnet
45 Internal magnet
46 Hub
47 Attachment screw
48 Centering pin
49 Attachment screw
50 Cap
51 Pump internal space
53 Magnet carrier
54 Intake
55 Cylinder roller bearing
56 Bearing
57 Bearing axis
58 Centering pin
59 Bypass
60 Channel
61 Cap internal space
62 External area
63 Orifice plate
64 Counter surface
65 Counter surface normal
66 Delimitation surface normal
67 Valve
68 Rotary displacement pump without moving seal

Claims

1. Rotary displacement pump (2) for pumping a medium, with

a pump housing (3),

a reception chamber (4) which is formed in the pump housing (3), with an inlet area (26) and an outlet area (27), and

at least one rotary displacement element (5, 6) which is accommodated in the reception chamber (4), and which is rotatably attached by means of at least one bearing (40, 41, 56) in the pump housing (3), and which presents at least one delimitation surface (21), by means of which it delimits at least one work space (19) of the pump (2), and

a bypass (59) which allows the return flow of a part of the pumped medium from the outlet area (27) into the inlet area (26),

where the rotary displacement element (5, 6) and/or a rotating part (35) which is connected to the rotary displacement element present(s) at least one counter surface (64) which delimits the bypass (59), and whose counter surface normal (65) has at least one component which is directed opposite to the delimitation surface normal (66) of the delimitation surface (21).

2. Rotary displacement pump according to claim 1, wherein the delimitation surface (21) is an axial delimitation surface (20) which delimits the work space (19) axially.

3. Rotary displacement pump according to claim 1, wherein the counter surface (64) is arranged so it faces the delimitation surface (21).

4. Rotary displacement pump according to claim 1, wherein the bypass (59) presents a valve (67) for the control and/or regulation of the flow of the return-flow medium through the bypass (59).

5. Rotary displacement pump according to claim 1, wherein one of the rotary displacement elements (5) is designed as a housing element (8) which encloses eccentrically a rotary displacement element (6) designed as an inner rotary displacement element (15).

6. Rotary displacement pump according to claim 5, wherein the housing element (5) is designed as a hypotrochoid housing (10) with n chambers, and the inner rotary displacement element (15) presents n-1 corresponding teeth (17) for engagement in the chambers.

7. Rotary displacement pump according to claim 1, wherein the rotating part (35) is a shaft (34) or presents a shaft (34).

8. Rotary displacement pump according to claim 7, wherein the shaft (34) contributes to the formation of the bypass (59).

9. Rotary displacement pump according to claim 1, wherein the rotary displacement element (5) is a rotary displacement element (5) which can be driven by an associated driving motor.

10. Rotary displacement pump according to claim 9, wherein a coupling (37), particularly a magnetic coupling (36), which is arranged between the shaft (34) and the driving motor.

11. Rotary displacement pump according to claim 10, wherein the coupling (37) contributes to the formation of the bypass (59).

12. Rotary displacement pump according to claim 4, wherein the valve (67) presents a valve-internal mechanism for the valve-internal control of the flow through the bypass (59) as a function of the pressure exerted at the inlet side of the valve (67).

13. Rotary displacement pump according to claim 1, wherein the pump (2) is designed as a rotary displacement pump (68) without moving seal.

14. Rotary displacement pump according to claim 1, wherein the pump housing (3) and/or the shaft (34) consist(s) of stainless steel and/or a Hastelloy nickel based alloy and/or titanium.

15. Rotary displacement pump according to claim 1, wherein the bearings (40, 41, 56) and/or the rotary displacement elements (5, 6) consist(s)—at least in part—of the materials Teflon and/or carbon and/or Peek and/or non galling alloys.