Patent Grant
8613608
This invention relates to a progressive cavity pump with inner and outer rotors intended for relatively high rotational speeds and great lifting heights with small vibrations. The invention indicates a possible standardization with a few versions of the main elements of the pump and a number of exchangeable rotor elements with standardized interfaces but with external and/or internal helical cross section(s) adapted for the characteristic viscosity, lifting height and chemical composition of the pumping medium of the most relevant application at any time. From the invention appears a method of limiting the necessary inner diameters of the dynamic seals and bearings of the outer rotor as well.
Progressive cavity pumps, also called Mono pumps, PCP pumps, or Moineau pumps, are a type of displacement pumps which are commercially available in a number of designs for different applications. In particular, these pumps are popular for pumping high-viscosity media. Typically, such pumps include a usually metallic helical rotor (in what follows called the inner rotor) with Z number of parallel threads (in what follows called thread starts), Z being any positive integer. The rotor typically runs within a cylinder-shaped stator with a core of an elastic material, a cavity extending axially through it being formed with (Z+1) internal thread starts. The pitch ratio between the stator and rotor should then be (Z+1)/Z, the pitch being defined as the length between adjacent thread crests from the same thread start.
When the geometric design of the threads of the rotor and stator is in accordance with mathematical principles written down by the mathematician Rene Joseph Louis Moineau in, for example, U.S. Pat. No. 1,892,217, the rotor and stator together will form a number of fundamentally discrete hollows or cavities by there being, in any section perpendicular to the centre axis of the rotor screw, at least one point of full or approximately full contact between the inner rotor and the stator. The central axis of the rotor will be forced by the stator to have an eccentric position relative to the central axis of the stator. For the rotor to rotate about its own axis within the stator, also the eccentric position of the axis of the rotor will have to rotate about the centre axis of the stator at the same time but in the opposite direction and at a constant centre distance. Therefore, in pumps of this kind there is normally arranged an intermediate shaft with 2 universal joints between the rotor of the pump and the motor driving the pump.
The pumping effect is achieved by said rotational movements bringing the fundamentally discrete cavities between the inner surfaces of the stator and the outer surfaces of the rotor to move from the inlet side of the pump towards the outlet side of the pump during the conveyance of liquid, gas, granulates etc. Characteristically enough, internationally these pumps have therefore often been termed “PCPs” which stands for, in the English language, “Progressive Cavity Pumps”. This is established terminology also in the Norwegian oil industry, for example.
The volumetric efficiency of the pump is determined mainly by the extent to which these fundamentally discrete cavities have been formed in such a way that they actually seal against each other by the relevant rotational speed, pumping medium and differential pressure, or whether there is a certain back-flow because the inner walls of the stator yield elastically or because the stator and rotor are fabricated with a certain clearance between them. To increase the volumetric efficiency, progressive cavity pumps with elastic stators are often constructed with under-dimensioning in the cavity, so that there will be an elastic squeeze fit.
Not very well known and hardly used industrially to any wide extent—yet described already in said U.S. Pat. No. 1,892,217—are designs of progressive cavity pumps in which a part, like the one termed stator above, is brought to rotate about its own axis in the same direction as the internal rotor. In this case the part with (Z+1) internal thread starts may more correctly be termed an outer rotor. At the same time it will then be natural to use the term inner rotor about the part which corresponds to the more usual rotor with an external screw and Z thread starts. By a definite speed ratio between the outer rotor and the inner rotor, both the inner rotor and the outer rotor may be mounted in fixed rotary bearings, provided the rotary bearings for the inner rotor have the correct shaft distance or eccentricity measured relative to the central axis of the bearings of the outer rotor.
A limitation to the gaining of ground of such early-described solutions has probably been that an outer rotor needs to be equipped with dynamic seals and rotary bearings, which is avoided completely when a stator is used. It is also likely that the potential increase in rotational speed and consequent increase in capacity enabled by the fact that the mass centres of both rotors will lie near the rotary axis have been overlooked or underestimated. Besides, an intermediate shaft and universal joints may, in principle, be avoided when the stator is replaced with an outer rotor.
In U.S. Pat. No. 5,407,337 is disclosed a Moineau pump (here called a “helical gear fluid machine”), in which an outer rotor is fixedly supported in a pump casing, an external motor has a fixed axis extending through the external wall of the pump casing parallel with the axis of the outer rotor in a fixed eccentric position relative to it, and the shaft of the motor drives, through a flexible coupling, the inner rotor which has, beyond said coupling, no other support than the walls of the helical cavity of the outer rotor, the material assumedly being an elastomer. In this case the rotation of the outer rotor is driven exclusively by movements and forces at the contact surfaces of the inner cavity against the inner rotor. A drawback of this solution is that if there is considerable clearance at or elastic deflection of the contact surface, the inner rotor or the outer rotor will be moved more or less away from its ideal relative position. Further, by increasing load, the driving contact surface between the inner and outer rotors will be moved constantly closer to the motor and thereby force the inner rotor more and more out of parallelism relative to the axis of the outer rotor, so that over the length of the outer rotor, the inner rotor will contact the outer rotor on diametrically opposite sides with consequent friction loss, wear on rotors and motor coupling and also possible signs of wedging. Vibrations, erratic running and reduced efficiency may also be expected.
In U.S. Pat. No. 5,017,087 as well as WO99/22141 inventor John Leisman Sneddon has shown designs of Moineau pumps, in which the outer rotor of the pump is enclosed by and fixedly connected to the rotor of an electromotor whose stator windings are fixedly connected to the pump casing. In these designs the outer and inner rotors of the pump are both fixedly supported at both ends radially in the same pump casing, so that the outer and inner rotors of the pump function together as a mechanical gear, driving the inner rotor at the correct speed relative to the outer rotor which, in turn, is driven by said electromotor. In this case as well, signs of wedging between the inner and outer rotors may arise, in particular if solid, hard particles seek to wedge between the inner and outer rotors where these have their driving contact surfaces. Besides, a disadvantage of an inner rotor fixedly supported at both ends is that if the pumping medium is of a kind which must be separated from contact with the bearings, independent dynamic seals will be needed at both ends for both the inner rotor and the outer rotor, as these do not have a common rotary axis.
In U.S. Pat. No. 4,482,305 is shown a pump, flow gauge or similar according to the PCP principle with inner and outer rotors. Here is used a wheel gear outside the pump rotors which ensures a stably correct relative rotational speed between the inner and outer rotors, independently of internal contact surfaces between them. This ensures smoother running, in particular by great pressure differences and/or spacious clearances—which may be necessary to achieve a gradual pressure increase when compressible media are pumped. However, it is assumed here as well that there are dynamic seals and radial bearings at both ends of the inner rotor. The dynamic seal for the outer rotor is also complicated by the diameter of the sealing surface having to be large enough to allow an internal passage for both the pumping medium and the bearing shaft on the extension of the active helical part of the inner rotor.
In the Norwegian patent application No. 20074591 is indicated a method of stabilizing the flow rate and outlet pressure in a progressive cavity pump with internal and external rotors intended for pumping compressible media. According to this document, signs of sudden cyclical back-flows of pumping medium in consequence of compression during the adjustment to the outlet pressure can be effectively limited by letting the defined pump cavity which is, at any time, the closest to the outlet side be allowed to have a substantially larger continuous leakage flow than the other pump cavities. To be as effective as possible, this leakage flow must be planned and be built into the construction of the outer and/or inner rotor(s) in each individual case. The document does not indicate a way of limiting the costs of this adaptation through, for example, letting it affect as few and as inexpensive parts as possible.
In most known designs of progressive cavity pumps with inner and outer rotors is required—unless the pumping medium is of a kind which may be allowed to penetrate into the bearings of the outer rotor or even function as an active component in hydrodynamic bearings—a large diameter on the dynamic seals of the outer rotor with consequent relatively large leakage, frictional moment and hydrostatic axial forces on the bearings of the outer rotor. A reason for the big seal diameter is that the seal normally surrounds the entire helical cavity with Z+1 thread starts and that this cross section cannot be reduced towards the seal if the inner rotor is to be installable from the same side as the seal and if the outer rotor is to be made in one piece. With this typical construction there will also be an unfavourable flow pattern as pumping medium is let in and out, because the medium meets the plane end surface of the outer rotor as an obstruction vertically to the direction of flow.
The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art.
The object is achieved through features which are specified in the description below and in the claims that follow.
Thus, the invention provides an outer rotor of such construction that the diameter of dynamic seals and bearings may be reduced, flow transitions smoothed, application adaptations simplified and wear parts replaced more easily and more inexpensively. The invention also enables a relatively simple, quick and inexpensive testing of alternative adaptations between the inner and outer rotor, so that, among other things, pressure build-up from step to step by the relevant gas volume percentage and viscosity can be optimized for a specific application.
This is achieved by an outer rotor being assembled from a rigid rotor sleeve adapted to the rotary bearings of the outer rotor at both ends, by the sleeve closely surrounding a number of exchangeable, concentric rotor inserts closely adjoining each other in an axial direction, by the sleeve having a detachable end piece at least at one end, by this end piece being adapted for maintaining the axial position of alternative sets of rotor inserts, by the sleeve and/or its end piece(s) having, at a respective end, a through hollow which forms a transition between round cross sections nearest to the inlet side or the outlet side and principally wing-shaped cross sections with Z+1 wings corresponding to and abutting the helical cavity having Z+1 thread starts extending through every rotor insert.
An outer rotor in a progressive cavity pump comprising at least one inner helical rotor with Z external thread starts and at least one adapted outer rotor with a helical cavity with Z+1 internal thread starts may be characterized by at least an outer rotor being assembled from several concentric rotor inserts following closely one after another axially and having helical cavities and Z+1 internal thread starts, each rotor insert being closely surrounded by and concentrically fixed in a common rigid rotor sleeve, and there being detachably connected to the rotor sleeve at least one removable end piece with a principally concentric cavity extending axially through it, and by the through hollow of the end piece or end pieces forming a gradual transition between a principally circular cross section furthest out and a cross section adapted to the helical cavities of the rotor inserts nearest to them.
The outer rotor may have at least one detachable end piece which rotates in a surrounding bearing for the outer rotor and the through hollow surrounded in the axial position by the bearing has a principally circular cross section with its longest diagonal substantially smaller than the longest diagonal in the helical cross sections of the rotor inserts.
Nearest to the inlet and/or outlet of the outer rotor, the outer rotor may have room installed or arranged for a mechanical or other dynamic seal—or a seat for this, with a diameter for the sealing surface which is smaller than the longest diagonal for the helical cavities of adjacent rotor inserts.
The outer rotor may be formed in such a way that the rotor sleeve has a through hollow with a principally constant cross section adapted for the tight installation of rotor inserts having principally the same external cross section, retained between two detachable end pieces.
The outer rotor may be formed in such a way that the outer rotor has a detachable end piece only on one side of the rotor sleeve, that in the rotor sleeve, from the side of the detachable end piece, extends an axial cavity of a principally constant cross section and depth adapted for the tight installation of a number of axially measured-out rotor inserts, that the constant cross section suddenly changes into a smaller cross section adapted to the helical cavity of the rotor inserts, and that, from here, there is arranged a through flow channel which merges gradually into a principally circular shape at the outlet.
The outer rotor may be formed in such a way that at least one rotor insert has a length divisible by P/Z, P being the thread pitch of the inner rotor and Z being the number of thread starts on the inner rotor.
The outer rotor may be formed in such a way that several of the inserts have a certain rotation relative to each other, freely adjusted to minor deviations from the ideal ratio between the thread pitches of the inner and outer rotors.
The outer rotor may be formed in such a way that the rotor sleeve is fixed against rotation relative to at least one end piece and at least one rotor insert with a helical cavity adapted for driving contact with the inner rotor.
The outer rotor may be formed in such a way that all the rotor inserts are fixed against rotation relative to each other and against rotation relative to the rotor sleeve.
The outer rotor may be formed in such a way that for fixing rotor inserts against rotation relative to each other there are used dowels in corresponding bores.
The outer rotor may be formed in such a way that in mutual-contact surfaces between the rotor inserts are arranged elastic seals in adapted grooves in at least one of the contact surfaces, that these grooves relatively closely surround the helical cavity cross section, and that the depth of the grooves is adapted in such a way that the elastic seal will have the right pre-tensioning when the gap between the plane end surfaces of adjacent rotor inserts is completely neutralized.
The outer rotor may be formed in such a way that all the rotor inserts have a cylindrical outer surface with principally the same diameter and easy-running fit relative to the rotor sleeve, that near the middle of the cylinder surface is arranged a cylindrical groove with an exact internal diameter adapted for guide bushes which are arranged, when mounted together with the rotor insert, to run tightly in the rotor sleeve but allow close contact between adjacent inserts with a compensation for possible minor angular deviations at the end surfaces relative to the vertical on the rotary axis.
The outer rotor may be formed in such a way that the rotor insert located nearest to the outlet side has a helical cavity length fundamentally equaling P/Z, P being the thread pitch of the inner rotor, and that on the upstream end surface of said insert is made a recess in the form of a local substantial increase of the cavity cross section, that this increased cavity cross section provides substantially increased clearance locally between the inner and outer rotors, that this increased clearance varies with the relative angular positions of the inner and outer rotors, and that, in each individual case, the varying clearance is sought to be adjusted in such a way that the transversal leakage flow from the last cavity, which is open or shortened towards the outlet side, up to the last, fundamentally discrete full-length cavity will cause a gradual compression of the fluid in the last full-length cavity, so that the pressure difference towards the outlet will decrease approximately linearly down to an acceptable minimum before the last full-length cavity suddenly opens wide as it reaches the outlet of the screw.
The outer rotor may be formed in such a way that said recess has been milled out at a constant depth, so that the adaptation has been done only by calculating the shape of the cross section, and that there is a seal between the transversal contact surfaces of the inserts outside said recess.
The outer rotor may be formed in such a way that the rotor sleeve and at least one of the rotor inserts are made of a metallic, thermally conductive material and are in metallic connection with each other.
The outer rotor may be formed in such a way that at least one of the inserts, preferably nearest to the inlet side, is made of a viscoelastic material, for example rubber, and that the cavity of this insert is made with a nominal squeeze fit relative to the helical part of the inner rotor.
The outer rotor as described above may be formed in such a way that the rotor sleeve has a sufficient diameter for accommodating rotor inserts with considerable variation in the helical cavity cross section, including variation in the number of thread starts Z, longest diagonal of the cross section, and eccentricity.
The outer rotor may be formed in such a way that transitions in the cavity cross section extending through the end pieces are neutralized by special inserts flush mounted in the actual end pieces.
The outer rotor may be formed in such a way that the rotor sleeve coincides with a rotor of a motor driving the progressive cavity pump.
A range of alternative rotor inserts adapted to the same rotor sleeve may be stocked at the producer's with a view to adaptation for different customer requirements and applications.
The invention will be particularly advantageous in embodiments in which the rotor sleeve of the pump coincides with the rotor of a motor driving the pump, cf. WO99/22141 mentioned earlier.
In what follows is described an example of a preferred embodiment which is visualized in the accompanying drawings, in which:
In the embodiment of an outer rotor in accordance with
In the section in
The seal seat 105b has a substantially smaller diameter than the longest cross section of the helical cavity portions. The connection between the rotor sleeve 101 and end piece 102 is secured by means of the bolts 107 and sealed with a static seal 108.
In
When the inner and outer rotors have been assembled, it is not possible to slip a helical part 202, see
In
In
In
In
In
Like in the rotor insert of
In a further embodiment of the invention, the outer rotor of a progressive cavity pump is characterized in that several of the inserts have a certain rotation relative to each other, freely adjusted to minor deviations from the ideal ratio between the thread pitches of the inner and outer rotors. In this embodiment, for several of the rotor inserts, it has been omitted to mount precise fixing devices against minor relative rotational movements about the central axis, so that each individual rotor insert finds, as required, its rotational position adjusted to the inner rotor in spite of minor deviations in the pitch of the cavity screw, whether owing to manufacturing deviations or operating conditions with associated geometrical deviations induced chemically, thermally or by pressure.
Thus, according to some embodiments of the present invention, an outer rotor of a progressive cavity pump comprises at least one inner helical rotor with Z external thread starts; and at least one adapted outer rotor with a helical cavity with Z+1 internal thread starts. The at least an outer rotor (1, 3) is assembled from several concentric rotor inserts (109-113, 307-311) following closely one after another axially, with helical cavities and Z+1 internal thread starts. Each rotor insert of the several concentric rotor inserts is tightly surrounded by and concentrically fixed in a common rigid rotor sleeve (101, 301). The rotor sleeve is detachably connected to at least one removable end piece (102, 302, 303) with a principally concentric hollow portion extending axially through the at least one end piece. The through hollow portion of the end piece (102) or end pieces (302, 303) forms a gradual transition (106, 306, 312) between a principally circular cross section (135, 313, 314) furthest out from the rotor inserts and a cross section adapted to the helical cavity in the rotor insert (109, 307, 311) nearest to the at least one end piece.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20083616 | Aug 2008 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO2009/000274 | 8/6/2009 | WO | 00 | 2/17/2011 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2010/021549 | 2/25/2010 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 1892217 | Moineau | Dec 1932 | A |
| 2483370 | Moineau | Sep 1949 | A |
| 2553548 | Canazzi et al. | May 1951 | A |
| 3499389 | Seeberger et al. | Mar 1970 | A |
| 3932072 | Clark | Jan 1976 | A |
| 3938915 | Olofsson | Feb 1976 | A |
| 3999901 | Tschirky | Dec 1976 | A |
| 4080115 | Sims et al. | Mar 1978 | A |
| 4482305 | Nátkai et al. | Nov 1984 | A |
| 4580955 | Karge | Apr 1986 | A |
| 4585401 | Baldenko et al. | Apr 1986 | A |
| 4592427 | Morgan | Jun 1986 | A |
| 4676725 | Eppink | Jun 1987 | A |
| 4711006 | Baldenko et al. | Dec 1987 | A |
| 5017087 | Sneddon | May 1991 | A |
| 5097902 | Clark | Mar 1992 | A |
| 5120204 | Mathewson et al. | Jun 1992 | A |
| 5275238 | Cameron | Jan 1994 | A |
| 5358390 | Jager | Oct 1994 | A |
| 5407337 | Appleby | Apr 1995 | A |
| 5549465 | Varadan | Aug 1996 | A |
| 5553742 | Maruyama et al. | Sep 1996 | A |
| 5588818 | Houmand et al. | Dec 1996 | A |
| 5722820 | Wiki et al. | Mar 1998 | A |
| 5807087 | Brandt et al. | Sep 1998 | A |
| 5820354 | Wild et al. | Oct 1998 | A |
| 5988992 | Tetlaff et al. | Nov 1999 | A |
| 6063001 | Suhling et al. | May 2000 | A |
| 6241494 | Pafitis et al. | Jun 2001 | B1 |
| 6336796 | Cholet et al. | Jan 2002 | B1 |
| 6439866 | Farkas et al. | Aug 2002 | B1 |
| 6457958 | Dunn | Oct 2002 | B1 |
| 6461128 | Wood | Oct 2002 | B1 |
| 7074018 | Chang | Jul 2006 | B2 |
| 7300431 | Dubrovsky | Nov 2007 | B2 |
| 7413416 | Bartu | Aug 2008 | B2 |
| 20010005486 | Wood | Jun 2001 | A1 |
| 20040057846 | Denk et al. | Mar 2004 | A1 |
| 20050169779 | Bratu | Aug 2005 | A1 |
| 20100239446 | Ree | Sep 2010 | A1 |
| 20100329913 | Ree | Dec 2010 | A1 |
| Number | Date | Country |
|---|---|---|
| 3119568 | Feb 1982 | DE |
| 3712270 | Oct 1988 | DE |
| 86 17 489 | Nov 1990 | DE |
| 197 15 278 | Dec 1998 | DE |
| 0255336 | Feb 1988 | EP |
| 1400693 | Mar 2004 | EP |
| 1 418 336 81 | May 2004 | EP |
| 1 559 913 | Aug 2005 | EP |
| 327505 | Jul 2009 | NO |
| WO 9922141 | May 1999 | WO |
| WO 2009035337 | Mar 2009 | WO |
| Entry |
|---|
| U.S. Appl. No. 13/059,427, filed Jan. 17, 2011, Ree. |
| USPTO Notice of Allowance, U.S. Appl. No. 12/678,889, Nov. 8, 2012, 13 pages. |
| USPTO Office Action, U.S. Appl. No. 12/677,280, Sep. 26, 2012, 14 pages. |
| USPTO Office Action, U.S. Appl. No. 12/677,280, Feb. 14, 2013, 12 pages. |
| USPTO Office Action, U.S. Appl. No. 13/059,427, Jan. 15, 2013, 9 pages. |
| USPTO Notice of Allowance, U.S. Appl. No. 13/059,427, Apr. 1, 2013, 8 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20110150689 A1 | Jun 2011 | US |
