Description

[01 ] The invention refers †o an eccentric screw pump.

[02] Eccentric screw pumps or Moineau-pumps are for example known from EP 1 308 624 B1 or DE 31 19 568 Al . These pumps consist of a helical rotor and a surrounding sfafor. The rotor performs a movement inside the sfafor which is a combination of a rotational movement and a superimposed radial movement. If is known †o make the sfafor from an elastic material and the rotor from a non-elasfic material.

[03] Pumps of this type are especially suitable for high pressure and low flow applications making them advantageous for use in more re- mote locations or in applications relying on solar or wind power as a primary source of power. A disadvantage with this type of pump is the large starting torque required †o overcome the frictional forces be tween the rotor and the sfafor. This sets a limit †o the size of the pump or would necessitate a frequency converter which however would in- crease the cos† of the pump.

[04] In view of this i† is the object of the invention †o provide an im proved eccentric screw pump having a reduced starting torque.

[05] This object is achieved by an eccentric screw pump having the features defined in claim 1 . Preferred embodiments are known from the dependent subclaims, the following description and the accompany ing drawings. [06] The eccentric screw pump or Moineau-pump according to the invention comprises a rotor and a surrounding stator. The stator com prises at least one rotationally fixed elastomeric stator portion and pref erably is completely made from an elastomeric material. The rotor preferably is made from a material having a lower elasticity and further preferably is made form metal. For adjusting the contact pressure be tween rotor and stator there is formed a pressure chamber on a radial outer side of said elastomeric sfafor portion, i.e. on a side facing away from said rotor. This allows †o apply a pressure, in particular a fluid pres sure †o the pressure chamber which effects a radial force between the elastomeric portion of the sfafor and the rotor inside the sfafor. The sfa for and the rotor may have a conical design according †o which the diameter of the sfafor and the rotor decreases from one axial end to wards the opposite second axial end of the sfafor. However, according to a preferred embodiment the rotor and the sfafor have a non-conical design with a constant cross section beside the helical grooves on the outside of the rotor and the inner surface of the sfafor.

[07] Preferably, there is provided a drive device whose connection †o the rotor and design is such that if effects a rotating movement of the rotor with a superimposed radial movement. This is a conventional mo tion of the rotor in an eccentric screw pump. The eccentric movement may be achieved by a suitable gear box or a flexibility of the rotor shat† in radial direction. In such a design the rotor may be guided inside the sfafor when driven by a rotating drive. [08] According †o the invention said pressure chamber is connected

†o a pressure region of the eccentric screw pump, i.e. †o a region of a flow path for the fluid or medium †o be pumped having an increased pressure, i.e. a region downwards the suction or inlet side of the pump. This is the region in which the fluid pumped by the pump has an in- creased pressure, preferably corresponding †o or close †o the delivery pressure of the pump. The pressure chamber is connected †o this pres sure region in a manner such that the a† leas† one elastomeric stator portion is subjected to a pressure which is produced by the eccentric screw pump itself. By this design an additional pressure supply, in par- ticular a pressurized air supply can be omitted. Furthermore, by this de sign a pressure control device becomes superfluous, since the pressure control is effected automatically by the delivery pressure of the pump. With increasing the delivery pressure or increasing pressure in the pres sure region the pressure acting on the at least one elastomeric portion automatically increases. Thus, the contact force between stator and rotor in the region of the elastomeric portion automatically increases with increasing pressure inside the pump. This has the advantage that when starting the pump the pressure acting inside the pressure cham ber onto the elastomeric portion is substantially zero so that there is a reduced contact force between the stator and the rotor in radial direc tion effecting a reduced friction during starting. Thus, the starting torque is reduced. This for example allows to use a drive motor of smaller size or power which may be advantageous for use with a limited electric power supply. Alternatively, a pump of larger size may be driven by the same motor without increasing the input power of the motor. With in creasing pressure in the pressure region, preferably in the delivery re gion, also the pressure acting inside the pressure chamber on the elas tomeric stator portion increases. This effects a higher contact force be tween the elastomeric portion and the rotor to improve the sealing contact between rotor and stator.

[09] Said at least one elastomeric stator portion is a portion of the stator comprising at least a portion of the stator helix being in contact with the outer circumference of the rotor. Thus, this portion of the stator by the pressure inside the pressure chamber is pressed against the outer circumference of the rotor, i.e. the outer circumference, i.e. the helical protrusions of the rotor helix. [10] Preferably, said pressure chamber is connected †o a pressure region in the flow path for the fluid pumped by the pump and prefera bly †o a pressure region of the delivery end of the pump, wherein the pressure chamber is connected †o said pressure region preferably via of leas† one pressure channel. This means the pressure channel extends from the pressure region †o the pressure chamber such that the pressure in the pressure region is transferred †o the inside of the pressure cham ber and inside the pressure chamber there is acting a pressure onto the elastomeric sfafor portion so that a radial force between the sfafor and the rotor is effected in this region of the sfafor. The pressure region is a region of the flow path having an increased pressure which is pro duced by the pump itself. In particular the pressure region is a region with a pressure higher than the pressure inside af leas† a portion of the sfafor in the region of the pressure chamber. Thus, a higher pressure in side the sfafor is transferred †o the outside of the elastomeric portion of the sfafor surrounding a region of lower pressure inside the pump. Pref erably if is a region af the delivery end or close †o the delivery end of the pump. In this region the fluid pressure corresponds †o the delivery pressure of the pump or nearly reaches the delivery pressure. If this pres sure is transferred †o the pressure chamber, preferably via the af leas† one pressure channel, inside the pressure chamber there is a pressure preferably higher than the pressure between the elastomeric sfafor por tion and the rotor, i.e. inside a pump chamber between rotor and sfa for. This ensures a contact force holding the elastomeric sfafor portion in sealing contact with the outer circumference of the rotor, i.e. of the rotor helix.

[1 1 ] According †o a preferred embodiment there is provided af leas† one pressure channel. However, if would also be possible †o arrange more than one, i.e. several pressure channels †o connect a pressure region in the flow path of the pump †o the pressure chamber. [12] According †o a further preferred embodiment the sfafor is ar ranged inside a casing or housing and the pressure chamber is formed between this casing and the af leas† one elastomeric stator portion, wherein the casing preferably has a lower elasticity than the elastomer- ic stator portion and further preferably is made from metal. For example the casing may be made from steel. By applying the pressure inside the pressure chamber between the surrounding casing and the elastomeric stator portion a force in radial direction acting on the elastomeric stator portion is produced. To increase this force it is preferred that the casing has a higher stiffness than the elastomeric stator portion, preferably the casing is substantially not deformed by the pressure. This can in particu lar be achieved by a casing made from metal like steel. The elastomer ic stator portion, however, can be deformed by the pressure acting onto the outside of the elastomeric stator portion such that the elasto- meric stator portion is pressed against the outer circumference of the rotor, i.e. the rotor helix, to ensure a tight contact between stator and rotor in the region of the elastomeric stator portion.

[13] According to a further preferred embodiment the rotor is formed of a material with a lower elasticity than the elastomeric stator portion. In a preferred embodiment the rotor is formed from metal, for example steel or stainless steel.

[14] According to a further possible embodiment the at least one elastomeric stator portion annularly surrounds the rotor and is loaded by the pressure inside the pressure chamber from its outer peripheral side which is away from the rotor. This means the pressure inside the pressure chamber acts onto the outer side of the elastomeric stator portion such that it produces a force radially inwardly. By this the elastomeric stator portion over the entire circumference is pressed onto the outer surface of the rotor helix to ensure a tight contact. [15] Preferably said pressure chamber is connected †o the pressure region via a† leas† one pressure channel comprising valve means posi tioned and designed to vary the cross section of the pressure channel and preferably to close the pressure channel in at least one operation al condition of the pump. In case that more than one pressure channel should be provided such valve means may be arranged inside each pressure channel or only in one or a part of the pressure channels. The valve means may be positioned and designed to close the pressure channel in certain operational conditions or to vary the cross section, for example depending on the pressure. The valve means may be pro vided by a deformable portion of an elastic material, wherein a defor mation preferably may be caused by an increase of pressure. Thus, the valve means may be designed to vary the cross section of the pressure channels dependent on the pressure produced by the pump and transferred to the pressure chamber. In particular it may be possible to reduce the cross section with increasing pressure to avoid an overload of the elastomeric portion by the pressure inside the pressure chamber. Alternatively, the valve means may be designed such that it opens at a certain pressure such that the pressure in said pressure chamber may be reduced for operational conditions with lower pressure or during start of the pump. In an alternative embodiment the valve means may be valve means which are actively controlled by a suitable control means.

[16] According to a further possible embodiment the pressure cham ber is connected with the pressure region via at least one pressure channel connected to a pump cavity which is situated between the rotor and the stator or is connected to a delivery channel of the eccen tric screw pump, i.e. to a flow path on the outlet side of the pump. Also, in this design it would be possible to provide more than one pressure channel, i.e. several pressure channels. The at least one pressure chan nel transfers the pressure, i.e. the fluid pressure, produced by the pump inside the pump cavity or on the outlet side of the pump info the pres sure chamber †o provide an increasing pressure onto the elastic or elastomeric stator portion with increasing pressure produced by the pump. By this a low friction during start of the pump and also a fight contact between stator and rotor during operation under higher pres sure can be achieved.

[17] According †o a further possible embodiment there may be rein forcement elements arranged inside the pressure chamber, which rein forcement elements preferably extending in a radial direction with re- spec† †o the axial direction of the rotor. The reinforcement elements ensure a certain stiffness of the elastomeric s†a†or portion, preferably in radial direction, in those operational conditions in which a lower or sub stantially no pressure is acting onto the outside of the elastomeric por tion, i.e. inside the pressure chamber. By this design it is avoided †ha† the elastomeric s†a†or portion can be deformed in radial direction due †o the pressure acting between rotor and s†a†or, i.e. between rotor and the elastomeric s†a†or portion inside a pump cavity. This ensures a tight contact between the s†a†or, i.e. the elastomeric portion of the s†a†or, and the rotor also in the operational conditions with low pressure pro- duced by the pump, in particular during star† of the pump.

[18] Preferably said reinforcement elements extend between the a† leas† one elastomeric s†a†or portion and a surrounding casing. By this the elastomeric s†a†or portion is supported on the casing via the rein forcement elements. Forces acting in radial direction from the inside onto the elastomeric s†a†or portion are transferred via the reinforce ment elements onto the casing. Preferably the reinforcement elements and the casing are designed such †ha† substantially no deformation occurs and the shape of the elastomeric s†a†or portion is maintained, thus, ensuring a tight contact between the elastomeric s†a†or portion and the rotor even in operational conditions in which the pressure in side the pressure chamber is not high enough.

[19] The reinforcing elements for example may be designed as col umns or pillows respectively, webs and/or ribs extending from the elas- fomeric sfafor portion outwardly, preferably in radial direction.

[20] According †o a further preferred embodiment the reinforcement elements may be integrally formed with a† leas† a par† of the s†a†or, preferably a† leas† with the elastomeric s†a†or portion and further pref erably with the entire s†a†or. The reinforcement elements may be made from the same material as the connected parts of the s†a†or and in par ticular the elastomeric s†a†or portion. Furthermore, it would be possible †o form the reinforcement elements from a different material connect ed with the other parts of the s†a†or, in particular with the elastomeric portion of the s†a†or. The reinforcement elements for example may be connected †o the elastomeric s†a†or portion during a moulding process of the elastomeric portion and/or of the reinforcement elements. This may be achieved for example by a multi-component injection mould ing process.

[21 ] According †o a further possible embodiment the distance be- tween proximate reinforcement elements in a firs† region of the s†a†or is closer than in a† leas† a second region of the s†a†or, wherein preferably the distance becomes closer towards one axial end of the s†a†or. Fur thermore, it would be possible †o vary the number of reinforcement el ements and/or the stiffness of the reinforcement elements due †o their design over the axial lengths of the s†a†or, in particular over the axial length of the elastomeric s†a†or portion. For example, there may be ar ranged more reinforcement elements or reinforcement elements closer †o one another in a region of higher pressure of the s†a†or †o ensure a required stiffness of the elastomeric s†a†or portion in radial direction. [22] According †o a further preferred embodiment said pressure chamber extends around the stator over the whole periphery. This en sures forces acting on the elastomeric stator portion in radial direction over the entire circumference of the rotor to achieve the tight contact between stator and rotor. Furthermore, by this an equal application of forces can be achieved.

[23] According to a further preferred embodiment said pressure chamber in the axial direction extends over a part region or over the complete axial lengths of the stator, wherein the pressure chamber preferably extends over at least 75% of the axial length of the stator. This ensures a high or close contact between rotor and stator in sub stantially the entire contact region between stator and rotor.

[24] According to a further possible embodiment the elastomeric sta tor portion has a varying thickness over its axial extension, wherein the thickness preferably decreases from the suction side to the delivery side of the eccentric screw pump. Such a design ensures a higher stiffness of the elastomeric stator portion close to the suction side which is advan tageous during start of the pump when the produced pressure acting inside the pressure chamber is low. By the reduced thickness of the elas- tomeric stator portion towards the delivery or pressure side of the screw pump a higher flexibility of the elastomeric portion is achieved, so that the pressure acting inside the pressure chamber can effect a defor mation of the elastomeric portion in radial direction to press the elas tomeric portion onto the outer side of the rotor for an improved or clos- er contact.

[25] In the following the invention is described by example with refer ence to the accompanying drawings. In this: Fig. 1 shows an eccentric screw pump according to the prior art,

Fig. 2 shows a schematical cross section of an eccentric screw pump according †o a firs† embodiment, and

Fig. 3 shows a schemafiacl cross section of a helical screw pump according to a second embodiment.

[26] Figure 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 move ment 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 ar ranged vice versa.

[27] Figures 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 ec centric screw pumps and shown for example in Fig. 1 .

[28] The rotor 2 in both embodiments is made from a rigid material, like metal, for example stainless steel. According to the usual design of eccentric screw pumps the rotor 2 has a thread or helix 4 on its outside. A surrounding s†a†or 6 in figure 2 and 6’ in figure 3 is made from an elas tic material and encircles the rotor 2. On its inner circumference also the sfafor 6, 6’ has a thread or helix 8 according †o the common design of eccentric screw pumps. The rotor 2 and the stator 6, 6’ are dimen- sioned such that the protruding portions of the helix 4 on the outer cir cumference 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’.

[29] 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.

[30] 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 trans ferred via the pressure channel 20 into the pressure chamber 16. The pressure acting inside the pressure chamber 16 produces a force act ing onto the elastomeric stator on the inner circumference of the pres- sure chamber 16 in radial direction with respect to the longitudinal axis X of the rotor 2. Due †o the elasticity of the stator 8 or a respective elas tomeric 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 sta tor 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 re duced which reduces the friction between stator 6, 6’ and rotor 2 dur ing start of the pump.

[31] To ensure a sufficient stiffness of the stator 6, in particular during starting operation, when there is no increased pressure inside the pres sure chamber 16, according to the first embodiment in figure 2 the sta tor 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 suc tion end 12 towards the delivery end 14 along the longitudinal exten- sion 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 sta tor wall by the pressure acting inside the pressure chamber 16 is pressed towards the outer circumference of the rotor 2.

[32] Figure 3 shows a different solution for supporting the wall of the stator 6’ or an elastomeric staor portion, respectively. In this embodi- men† the wall of the stator 6’ along the pressure chamber 16 has a con- stem† thickness. However, inside the pressure chamber 16 there are ar ranged reinforcement elements 22 extending in radial direction be tween 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, if would also be possible †o design 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 †o the longitudinal axis X. Alternatively, if would be possible that the rein forcement elements 22 are shaped as posts or pillars extending be tween the stator 6’ and the inner wall of the casing 18. In either case the reinforcement elements 22 should be designed 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.

References

2 rotor

4 helix

6, 6’ stator, elastomeric stator portion 8 helix

10 pump cavity 12 suction end 14 delivery end 16 pressure chamber 18 casing 20 pressure channels 22 reinforcement elements x axial direction/longitudinal axis