ECCENTRIC SCREW PUMP

Abstract

An eccentric screw pump with a rotor (2) and with a rotationally fixed stator (6; 6′) surrounding the rotor (2). The rotationally fixed stator includes at least one elastomeric portion, wherein a pressure chamber (16) is arranged on this elastomeric portion of the stator (6; 6′) at a side facing away from the rotor (2). The pressure chamber (16) is connected to a pressure region of the eccentric screw pump such that the at least one elastomeric portion of the stator (6; 6′) is subjected to a pressure produced by the eccentric screw pump.

Claims

1. An eccentric screw pump comprising: a rotor; and a stator surrounding the rotor, the stator comprising at least one elastomeric stator portion and a pressure chamber formed on a radial outer side of said elastomeric stator portion, the radial outer side facing away from said rotor, wherein said pressure chamber is connected to a pressure region of the eccentric screw pump in such that the at least one elastomeric stator portion is subjected to a pressure produced by the eccentric screw pump.

2. An eccentric screw pump according to claim 1, wherein said pressure chamber is connected to the pressure region in the flow path for the fluid pumped by the pump, wherein the pressure chamber is connected to said pressure region preferably via at least one pressure channel.

3. An eccentric screw pump according to claim 1, wherein the stator is arranged in a casing and the pressure chamber is formed between the casing and the at least one elastomeric stator portion.

4. An eccentric screw pump according to claim 1, wherein the rotor is formed of a material with a lower elasticity than the elastomeric stator portion.

5. An eccentric screw pump according to claim 1, wherein the pressure chamber is connected to the pressure region via at least one pressure channel comprising valve means positioned and configured to vary the cross section of the pressure channel.

6. An eccentric screw pump according to claim 1, wherein the pressure chamber is connected to the pressure region via at least one pressure channel connected to a pump cavity between the rotor and the stator or connected to a delivery channel of the eccentric screw pump.

7. An eccentric screw pump according to claim 1, further comprising reinforcement elements arranged in the pressure chamber.

8. An eccentric screw pump according to claim 7, wherein the reinforcement elements extend in a radial direction with respect to the axial direction of the rotor.

9. An eccentric screw pump according to claim 7, wherein the reinforcement elements extend between the at least one elastomeric stator portion and a surrounding casing.

10. An eccentric screw pump according to claim 7, wherein the reinforcement elements are integrally formed with the stator.

11. An eccentric screw pump according to claim 7, wherein a distance between two proximate reinforcement elements in a first region of the stator is closer than in at least a second region of the stator.

12. An eccentric screw pump according to claim 1, wherein the pressure chamber extends around the stator over a whole periphery thereof.

13. An eccentric screw pump according to claim 1, wherein the pressure chamber extends in the axial direction over a part region or over the complete axial length of the stator, wherein the pressure chamber preferably extends over at least 75% of the axial length of the stator.

14. An eccentric screw pump according to claim 1, wherein the elastomeric stator portion of the stator has a varying thickness over an axial extension thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the drawings:

[0028] FIG. 1 is an eccentric screw pump according to the prior art;

[0029] FIG. 2 is a schematic cross sectional view of an eccentric screw pump according to a first embodiment; and

[0030] FIG. 3 is a schematic cross sectional view of a helical screw pump according to a second embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] Referring to the drawings, FIG. 1 shows an eccentric screw pump device as known in the prior art. The pump device comprises the eccentric screw pump P and an electric drive motor M coupled the pump P via a coupling device C. The coupling device C transfers the rotational movement of the drive motor M onto the rotor 2 of the pump allowing a superimposed radial movement of the rotor 2 to achieve a resulting eccentric movement of the rotor 2 inside a surrounding stator 6. The rotor 2 comprises a helix on its outer circumference and the stator 6 comprises a helix on its inner circumference, wherein in this embodiment the rotor 2 has a double helix and the stator has a single helix. However, this may be arranged vice versa.

[0032] FIGS. 2 and 3 show the eccentric screw pump without the drive. The drive may be a conventional drive motor, in particular an electric motor which is coupled to the rotor 2 in such a way that the rotor 2 fulfils the necessary eccentric motion, i.e. a rotational movement with a superimposed radial movement as it is commonly known for eccentric screw pumps and shown for example in FIG. 1.

[0033] The rotor 2 in both embodiments is made from a rigid material, like metal, for example stainless steel. According to the usual configuration of eccentric screw pumps the rotor 2 has a thread or helix 4 on its outside. A surrounding stator 6 in FIGS. 2 and 6′ in FIG. 3 is made from an elastic material and encircles the rotor 2. On its inner circumference also the stator 6, 6′ has a thread or helix 8 according to the common configuration of eccentric screw pumps. The rotor 2 and the stator 6, 6′ are dimensioned such that the protruding portions of the helix 4 on the outer circumference of the rotor 2 come into contact with the protrusions of the helix 8 of the stator 6, 6′. By this pump cavities 10 are formed between the rotor 2 and the surrounding stator 6, 6′.

[0034] The shown pump has a suction end 12 and a delivery end 14. The fluid or medium to be pumped enters the pump cavities on the suction end 12 and is feed through the pump towards the delivery end 14 with an increase in pressure.

[0035] According to the invention there is provided a pressure chamber 16 surrounding the outside of a middle portion of the stator 6, 6′. The pressure chamber 16 is provided between the outer circumference of the stator 6, 6′ and the inner side of a surrounding casing 18. The casing 18 is also made from a rigid material as metal, in particular steel. The pressure chamber 16 is, thus, arranged on an outer side of the stator 6 facing away from the rotor 2, i.e. opposite to the rotor 2. In this example the pressure chamber 16 extends over approximately 75% of the axial lengths of the pump in the axial direction x of the rotor 2. The pressure chamber 16 is connected via pressure channels 20 to the pump cavity 10 between rotor 2 and stator 6, i.e. to the flow path for the fluid to be pumped, near the delivery end 14. In this pressure region on the exit or delivery side of the pump the pumped fluid has an increased pressure, i.e. substantially the delivery pressure of the pump. This pressure is transferred via the pressure channel 20 into the pressure chamber 16. The pressure acting inside the pressure chamber 16 produces a force acting onto the elastomeric stator on the inner circumference of the pressure chamber 16 in radial direction with respect to the longitudinal axis X of the rotor 2. Due to the elasticity of the stator 8 or a respective elastomeric stator portion the protruding portions of the helix 8 formed on the inner circumference of the stator 6, 6′ are pressed against the outer circumference, in particular the protruding portions of the helix 4 of the rotor 2. This ensures a close or sealing contact between rotor 2 and stator 6, 6′ sealing the pump cavities 10 and ensuring higher efficiency and functionality of the pump even under higher pressure. However, when starting the pump there is nearly no exit or delivery pressure in the cavity 10 on the delivery end 14 and, thus, there is also no increased pressure inside the pressure chamber 16. By this the radial force acting on the stator 6, 6′ or an elastomeric stator portion, respectively, is reduced which reduces the friction between stator 6, 6′ and rotor 2 during start of the pump.

[0036] To ensure a sufficient stiffness of the stator 6, in particular during starting operation, when there is no increased pressure inside the pressure chamber 16, according to the first embodiment in FIG. 2 the stator 6 has a wall thickness increasing towards the suction end 12 of the pump. The thickness of the wall of the stator 6 decreases from the suction end 12 towards the delivery end 14 along the longitudinal extension of the pressure chamber 16. This ensures a higher stiffness on the inlet or suction end of the stator 6 which is advantageous when starting the pump. Towards the delivery end 14 the thickness of the wall of the stator 6 is reduced such that the flexibility is increased. This ensures a high flexibility of the wall of the stator 6 in the region of higher pressure so that during operation of the pump in particular in this region the stator wall by the pressure acting inside the pressure chamber 16 is pressed towards the outer circumference of the rotor 2.

[0037] FIG. 3 shows a different solution for supporting the wall of the stator 6′ or an elastomeric stator portion, respectively. In this embodiment the wall of the stator 6′ along the pressure chamber 16 has a constant thickness. However, inside the pressure chamber 16 there are arranged reinforcement elements 22 extending in radial direction between the inner wall of the stator 6′ and the surrounding casing 18. By this the stator 6′ is supported on the casing 18 via the reinforcement elements 22. The reinforcement elements 22 in this embodiment are integrally formed with the entire stator 6′. However, it would also be possible to configure the reinforcement elements 22 as separate elements. In this embodiment the reinforcement elements 22 are formed as ribs extending in radial or circumferential direction perpendicular to the longitudinal axis X. Alternatively, it would be possible that the reinforcement elements 22 are shaped as posts or pillars extending between the stator 6′ and the inner wall of the casing 18. In either case the reinforcement elements 22 should be configured such that they allow a pressure exchange between the cavities or portions between the reinforcement elements 22 inside the pressure chamber 16 so that a uniform pressure can be ensured inside the pressure chamber 16 over the entire circumference and the entire longitudinal extension of the pressure chamber 16.

[0038] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

REFERENCE CHARACTERS

[0039] 2 rotor [0040] 4 helix [0041] 6, 6′ stator, elastomeric stator portion [0042] 8 helix [0043] 10 pump cavity [0044] 12 suction end [0045] 14 delivery end [0046] 16 pressure chamber [0047] 18 casing [0048] 20 pressure channels [0049] 22 reinforcement elements [0050] x axial direction/longitudinal axis