Patent Application
20110200474
This invention relates in general to a swash pump; and in particular to a more efficient swash pump adapted for pumping a gas or a mixture of gas with liquid.
A “swash pump” is a form of pump in which nutatory motion of a swash plate against opposing cone plates within a circular pumping chamber causes a fluid to move around the pumping chamber, from an inlet port to an outlet port.
“Nutation” refers to the peculiar orbital movement made by a swash plate inside a swash pump. It resembles the wobbling movement of a coin after being dropped obliquely on to a hard flat surface. Truly effective pumping results from nutation where the swash plate makes simultaneous contact with both cone plates at two moving “sealing lines”; one sealing line being 180 degrees apart from the other sealing line, on the opposite side of the plate. In practice, contact may be achieved on one side at any particular moment, while the other side may almost make contact. Each rotatable sealing line rotates, about the axis of the swash pump during nutation, advancing towards and past a substantially fixed, transverse divider plate, forcing fluid against the divider plate and through an outlet port.
Parts of a generic swash pump include:
“Inner swash sphere” is the visible sphere that supports the firmly attached and rigid swash plate, and which moves with the swash plate within the fixed housing. Motion is centred on the centre of nutation. The swash plate is located between the cone plates and makes contact with them during use at a movable sealing line. The inner swash sphere is concentric within an abbreviated outer swash sphere, incorporated in the pump body, located above the gap between the cone plates. A slidable seal is provided between the outer edge of the swash plate and the inner aspect of the outer swash sphere. The inner swash sphere and swash plate move in a nutating movement during use.
“Cone plate” refers to each of a pair of conic plates having a fixed, radially symmetrical, sloping inner surface facing the swash plate with which it comprises a movable line-shaped seal. The plates may comprise part of the pump housing or be insets.
The swash plate should always maintain a rotatable line-like sealing contact with the or each cone plate by means of pump construction. In the present invention, the drive shaft is slanted at just the right angle (the “slant angle”), as it penetrates the inner swash sphere and is journalled therein.
Each pumping chamber is defined by a cone plate and one side of the swash plate, by the outer swash sphere, and by the inner swash sphere, and material is moved through the pump by the moving sealing line. Both sides of the pumping chamber may be used in parallel for a less pulsatile output, or separately, by suitable porting arrangements.
“Trunnion” refers to a sliding bearing which creates an effective seal between the nutating swash plate and the fixed divider plate that intersects the cone plates and the swash plate.
“Engineering plastics material” as used herein refers to advanced inorganic compounds, alloys and mixtures capable of being formed to close tolerances. They are tough, strong, and suitable for sliding seals, having low friction and low wear. Such plastics are typically alloys comprised of a base plastic (55 to 70% ratio) selected from a range exemplified by polyethyletherketone (PEEK), polyphenylenesulphide (PPS) preferred for the trunnion, or polyphthalamide (PPA) (currently used on the other sliding surfaces) alloyed with polytetrafluorethane (PTFE), carbon, carbon fibres, and sometimes silicon, and are injection mouldable. Commercially available examples include ˜Fortron 7140A4 (Polyplastics, Japan), “UCL-4036 HS” (Sabic, Saudi Arabia) or equivalents as well-known to those skilled in the art.
Swash pumps, engines, or flow meters with nutating disks have been known for more than 50 years. Yet only one commercialised swash pump, (“Genta”™ Fristam; Hamburg, Germany; based on patents by Heng and Thomas) is known. All of the prior art incurs a good deal of sliding friction particularly between the inner swash sphere and the opposing part-spherical sections of the housing, which results in high frictional losses, especially when pumping gases. Gas provides less lubrication than a liquid at the contacting faces of any seals or fluid exposed bearing faces. The frictionally generated heating is added to localised adiabatic heating when pumping a gas which itself detracts from cooling functions. Previous designs of swash pump have relied on precision manufacture to hold parts in close or sliding proximity for improved sealing, but are vulnerable to distortion of parts by thermal expansion and then possible pump seizure. Unlubricated wear also causes short parts life.
In particular, use of a rigid swash plate assembly with a rigid inner sphere, firmly yet slidably held between part spherical cavities, prevents true self-centering of the swash plate from occurring with respect to the opposing cone faces in response to manufacturing tolerances and thermal expansion, even though there may be a resiliently-mediated bias towards contact. The prior art design leads to high inner spherical contact friction and poor swash to cone sealing.
The present invention will be described in relation to a vapour extraction application inside a fuel dispenser, in order to illustrate a pump that is effective when used to pump a fluid. A vapour recovery function is a regulatory requirement imposed in an increasing number of countries. Explosive gas mixtures are required to be removed from the vicinity of the pump nozzle while a vehicle tank is being filled. The volumetric displacement of gas by this pump must by law or regulations be proportional to the volume delivery of liquid fuel. A relatively small tube ending in the nozzle head, within an outer metal tube or a rubber boot surrounding and sealing the vehicle tank opening is run along or inside the hose to the nozzle and is connected to the pump which usually returns the vapour to the vapour space above a fuel storage tank where condensation may occur and any excess air or vapour is exhausted through a carbon filter vent far from the fuelling event. Since the fuel/air mixture being pumped is flammable and explosive, the pump must not comprise a danger or detract from safety in any way. It is desirable that the pump neither causes any flame or explosion nor transmits any flame or explosion from the exterior or nozzle environment into the storage tank or visa versa.
At the present time, vapour recovery pumps use rotary vanes (Healy, USA), impellers, roller vanes (Pignone, Italy) or piston pumps (Durrtechnik, Germany). These pumps are relatively inefficient, some are noisy, and cannot handle slugs of liquid effectively. A “slug” of liquid is the liquid that will arrive at the pump from time to time, such as if the tank is over-filled or the filling pipe becomes full. A swash pump will cope with this circumstance.
For swash pumps, Griswold U.S. Pat. No. 3,019,964 and Cornelius U.S. Pat. No. 2,887,059 teach an integrated electric motor driving a non-rotating inclined shaft, fixed to the nutating plate, through an external bearing assembly. Cornelius, and Heng U.S. Pat. No. 5,454,699 use a flexible bellows element as a seal and to prevent swash plate rotation. Hartley, U.S. Pat. No. 5,242,281 uses either a non-rotating slant stub axle; or a slant sleeve around a straight axle. Yun (WO2008/140138) has a loading spring like that of Heng U.S. Pat. No. 5,435,705 as an alternative way to impose resilience on the swash/cone contact. Hartley places a resilient part between the straight driving shaft and the interior of the spherical base of the swash plate, within the slant shaft and can drive the pumps such that the wobble angle would cause the cone angle to be exceeded except that the difference is taken up in the resilient member.
A coated swash plate is known from Ford U.S. Pat. No. 3,323,466 (“glass fibre” coating), Hartley (one example) and Yun (one example) as a resilient or as an elastic damping component but is not described as a friction reducing component. Despite the reduction of friction being of importance for swash pumps, few if any innovative solutions for friction reduction have been disclosed. Choice of materials and of surface finish is reasonably obvious. Yun teaches use of replaceable wearing parts made of a very hard steel but accepts friction as a cause of wear, rather than seeking to directly reduce friction.
No prior art is known in which the inner swash sphere is held apart from the part-spherical sliding bearings that are part of, or are firmly attached to, the pump housing. In all the known art, the inner swash sphere is rigidly mounted against the pump housing by means of sliding surfaces. No prior art is known in which a swash pump is adapted for use in fuel vapour recovery applications. No prior art is known in which a swash pump employs the cone plate faces as the primary determinants for positioning the inner swash sphere.
To provide a useful swash pump as a functional unit; preserving the inherent advantages of a swash pump such as a steady output flow and low noise while overcoming at least some of the sliding frictional losses that have been regarded as typical of this type of pump.
The object of this invention may be stated as to provide an improved swash pump, as a positive displacement pump for a compressible fluid, or at least to provide the public with a useful choice.
In a first broad aspect, this invention provides a swash pump adapted for pumping a compressible fluid, the pump having a nutatable inner swash sphere having a central axis and joined to a circumferential swash plate; the inner swash sphere having an axial aperture capable of receiving driving means; the swash plate is sealably confined within a dual, circumferential pumping chamber defined outwardly by a fixed part-spherical surface comprising the outer swash sphere, at each side by a fixed, conical or cone plate; inwardly by the inner swash sphere, and at a beginning and an end by a fixed divider plate which sealably transects the swash plate between the or each inlet port and the or each outlet port; the fluid being admitted from an inlet port then caused, when in use, by nutation of the inner swash sphere to be transported around a side of the pumping chamber towards the divider plate by one of two moving lines each providing substantially complete closure of the pumping chamber between a side of the nutating swash plate and an adjacent, substantially parallel contact line of a cone plate until the fluid reaches an adjacent outlet port, each line herein named a “sealing line”; one sealing line always 180 degrees apart from, and on the other side of the swash plate, from the other sealing line; wherein
In a first related aspect, contact at the or each sealing line is made through a non-resilient layer or coating placed between each side of the swash plate and the adjacent cone plate; said layer having a low-friction characteristic, so that during use losses arising from friction acting on the swash plate at the or each sealing line are minimised.
In a second related aspect, the bias causing the swash plate to form the respective sealing line is applied through resilient means at least partially surrounding the slanted portion of the common drive shaft and inside the axial aperture; said resilient means allowing a greater yet more consistent closing force to be applied at each of the sealing lines than in the absence of said resilient means.
Preferably the greater force is set by the exact angle of the slanted shaft in relation to the angle and position of the cone face sealing lines; and is dependent on a specific application for the integrated swash pump.
In a major subsidiary aspect, the swash pump comprises part of an integrated pump intimately joined together with an electric motor; the motor and the pump sharing the straight section of the common drive shaft; wherein the common section is coaxial with a rotor of the electric motor and passes substantially through the motor; the straight section is rotatably supported by a first bearing means secured to the pump housing and by a second bearing means secured to the motor, thereby also supporting the rotor in relation to a stator of the electric motor.
Preferably the bearing means provided for the slanted section and the straight section of the common drive shaft allow axial movement of the shaft through any of the bearing means during use, so that any change of location of the inner swash sphere is capable of causing movement of the slanted portion of the common drive shaft and in turn of causing axial movement of the straight portion of the common drive shaft; said axial movement having an effect of reducing friction arising from axial forces applied to any bearing means during use, and of allowing said one or both sealing lines to substantially determine the position of the inner swash sphere and the axial position of the straight portion of the common drive shaft.
Preferably roller bearing means support the inner swash sphere on the slant shaft within the axial aperture; said roller bearing means being capable of sliding along the shaft during use, so that movement of the slanted section and hence indirectly of the straight section of the shaft arising from a change of position of the inner swash sphere is unobstructed and friction arising during use from misaligned bearings or from a mis-centered inner swash sphere and swash plate with respect to the pumping cavity cone faces is avoided.
In a related aspect, the resilient layer surrounds the slanted portion of the common drive shaft inside the axial aperture of the inner swash sphere and is comprised of a series of ring-shaped resilient members, each placed in a corresponding circumferential groove within an outer roller bearing race, and held within the axial aperture.
In an alternative aspect, the resilient means is located outside the slanted portion of the drive shaft and inside an inner roller bearing race located inside the axial aperture of the inner swash sphere.
In a subsidiary aspect, the slanted portion of the common drive shaft inside the axial aperture within the inner swash sphere includes directional resilience means, said directional means comprises (a) an inner roller bearing race having an axial slotted aperture in a sliding fit over a slanted portion of the common drive shaft bearing diametrically opposed, flattened sliding surfaces; said slotted aperture including two spaces perpendicular to the flattened surfaces each capable of retaining a resilient means in compression against the slanted shaft; the retained resilient means thereby made capable of exerting directional resilience in an axial plane parallel to the plane of the diametrically opposed, flattened surfaces; said directional resilience being superimposed on the bias applied from the slanted drive shaft on to the swash plate.
Preferably the directional resilience is directed by forming the diametrically opposed, flattened surfaces in a plane parallel to a plane shared by the axis of the straight portion of the common drive shaft and the axis of the slant portion of the common drive shaft, so that, when in use, the directional resilience is aligned with, and rotates with, the sealing lines formed between the swash plate and the two cone plates.
In a further related aspect, the divider plate comprises a fixed peripheral section and a movable central section joined together by means of a telescoping joint biased apart by resilient means; the central section extending inward from the peripheral section and pressing against the surface of the inner swash sphere adjacent the position of a trunnion; the central section being provided with a concave bearing surface having substantially the same radius as that of the inner swash sphere so that the central section forms an effective seal between inlet and outlet ends of each side of the pumping chamber yet friction arising from contact between the sphere and the concave face of the divider plate is minimised.
In a subsidiary aspect, the fixed peripheral section of the divider plate is comprised of a first rigid material having a low coefficient of sliding friction against the slot of the trunnion, while the movable central section is comprised of a second rigid material having a low coefficient of sliding friction against the surface of the inner swash sphere.
In a second broad aspect, the invention provides an integrated motor and swash pump, wherein the integrated assembly is adapted for pumping inherently explosive gases; wherein the swash pump and the motor are separately confined within secure housings each equipped with means for confining any flame or explosion occurring within; said means including:
Preferably the outer periphery of the swash plate is also provided with an outer ring seal, so that an effective seal between the outside (sphere) of the chamber and hence both pumping chambers is maintained yet with minimised mechanical friction. Preferably this is done with a pretensioned peripheral sealing ring.
Preferably the number of shaft seals in contact with the rotating common shaft is minimised; there being one running on the first section of the shaft mounted in the inner swash sphere to retain bearing lubricant, and one at the commencement of the second section of the common shaft leading to the motor, so that total friction between the rotating shaft and seals is reduced.
Accordingly the diameters of said shaft seals may be reduced.
The description of the invention to be provided herein is given purely by way of example and is not to be taken in any way as limiting the scope or extent of the invention. The words “comprising” and “including” should not be taken as limiting the scope or range of any description.
a: is a cross-section through another directional resilient coupling.
This swash pump, preferably supplied with an integrated electric motor, is optimised for pumping compressible fluids; gases and foams, although it will pump liquids as expected from time to time in the example application of a vapour removing pump in a fuel dispenser.
The principles of the present invention include that:
Note that the moving sealing lines against the two cone plates also serve as the axial reference position for the entire common shaft, since the slanted part moves the remainder of the common shaft with it, unless one of the bearings 209 or 210 prevents axial movement, as selected for some purposes. During use, the shaft will settle in a position where the sum of all the forces is minimised. This freedom of movement continuously compensates for any dimensional variations of the assembly (including thermal expansion), and comprises a significant friction-reducing aspect of the invention. It is considered by the inventors that this self-aligning function is particularly useful in making a nutating plate pump that not only has low friction but also has good pump cavity sealing characteristics. Unnecessary thrust loading of the common shaft bearings is avoided. The design avoids application of thrust loading from the inner swash sphere on to an inner spherical bearing of the housing, which is generally characteristic of the prior art. Bearing misalignment is avoided since no more than two bearings on the same shaft are held firmly in alignment. Swash pumps used to pump gases, as compared to pumps for liquids, are prone to thermally caused expansion of components caused by adiabatic compression of gases, relative lack of cooling by the pumped fluid, and inevitable mechanical friction. Use of suitable material combinations in this invention for contacting faces such as the swash to cone sealing contact avoids high component wear rates.
We have made frictional drag tests, as described in
The vertical scale of the bar chart indicates the drag or resistance to turning caused by friction, as a torque in Newton/metres. For test purposes specified components were temporarily deleted in turn. Item 1 compares the drags causing by firmly positioning the inner sphere 211 (A04), or not (A05). Item 2 reports the first seal (223) of the A05 version, mounted against the swash 370 inner sphere with light resilience only, and item 3 reports the second, complementary seal. The rolling bearings used inside the sphere are compared as item 4. Item 5 compares the shaft seal 216 placed around the common shaft and item 6 compares the shaft seal 217 placed around the slant shaft. The seal 230 around the periphery of the swash plate is item 7, scuffing or rolling friction of the swash plate against the cone plate is shown as item 8, and the contribution made 375 by the bearings (209, 210) supporting the common shaft are compared as item 9. In relation to item 9, it seems likely that the A04 pump had badly located bearings. We would expect all prior-art swash pumps for gas to resemble the A04 prototype regarding frictional drag.
Absence of a rigid sliding support for sphere 211 is responsible for much of the frictional reduction shown in
Several constraints fix the instantaneous position of the inner swash sphere 211 within the pump. These include the sealing lines between the swash plate and the cone plate faces, the seal at the fixed divider plate 220 (which prevents rotation of the swash plate) and the slanted portion of the common drive shaft, which maintains, and on rotation moves the sealing line contact or contacts. The straight section 207 of the shaft is preferably free to slide axially through bearings 209, 210 in order that movements made by the sphere 211 along shaft 208 result in minimised axial forces along the shaft and, as described in relation to
A circular rotary shaft seal 216 surrounds the straight or central portion close to the origin of the slanted portion, 208, of the common shaft. The slanted portion extends substantially through the central axis of the inner swash sphere 211 and thus supports the inner swash sphere 211 by cylindrical roller type bearings 214 and 215. Those bearings are sealed from the space 405 that is inside the pump but isolated from the pumping chamber 213 by seals 223 and 224, by sliding (rotary) oil seal 217 around the slanted shaft and by a closed cap 218 at the far end. Long-life seals are preferred. If the pump is exposed to hydrocarbons that may attack normal grease, resistant lubrication such as PTFE-based or polyglycol based lubricants may be used. An optional conductive brush may be installed to ensure electrical grounding across the bearings and prevent spark erosion, shown here at the end of the slant shaft. Conductive grease may be used in the bearings 214 and 215 if required.
The circumferential swash plate 212 is preferably manufactured together with the inner swash sphere 211 as a single part. The pumping chamber 213 encloses the swash plate 212 after assembly. The swash plate is transected once at the fixed divider plate, against which it slides to and fro beneath a seal 221 inside the trunnion 802 and under the fixed divider plate 220; see
Several options for the swash plate/cone plate surfaces in frictional contact at the moving sealing lines are under test. Nutation of the swash plate inherently includes some sliding contact with the cone plates, which varies depending on the position of the swash plate in the pumping cycle. Such contact may cause wear over time if certain surface material combinations are used. An engineering plastic such as “Fortron”, PPS or its alloys, or PPA or its alloys, rubbing against metal is usually preferred. As one option a concentric plastics insert 219 shown in
Ideally both sides of the swash plate, 180 degrees apart, would simultaneously make a moving sealing contact at the sealing lines all the time. In use it has been noted, as far as we can determine, that either but not both of the two sealing lines is likely to make contact at any instant during nutation especially with a pumping load present. The other sealing line remains almost in contact. It is believed that the factors preventing simultaneous contact include (a) additional cone to cone clearance (separation distance) in the cavity required to cope with manufacturing tolerances, and (b) differential force caused by the pressure of the contents of the pumping chambers. The swash to cone plate contact tends to occur closest to the outlet port (i.e. the leading pumping chamber contacts) which is due to the floating nature of the swash on the slanted shaft 208 and the very similar pumping pressure on both sides of the swash plate. This is likely to be because the trailing pumping chamber (180 degrees behind) has more swash plate area exposed to the very similar pumping pressure hence it produces more force and tends to push the swash plate onto the cone plate of the leading chamber. To impose extra pressure by making the slanted end of the common drive shaft with a slightly greater inbuilt angle may result in excessive friction and wear if no resilient element (such as one of those described in relation to
As described with reference to
The motor and swash pump share a single common shaft 300 as shown in particular in
The inventors prefer that the common shaft can within limits slide axially through all bearings in this invention, while complete support of radial loads is maintained, in order that the swash plate, by making contact with the cone plates, initially determines the position of the nutating and rotating parts. Therefore, none of the bearings are press fitted on to the common drive shaft although the diameters of the shaft at these bearing locations are closely matched to the bearing internal apertures so each bearing still properly supports the drive shaft radially. The straight section 207 of the drive shaft is allowed to float in an axial direction inside the inner race of both the deep groove ball bearings 210 and 209 in this option. Any inadvertent thrust set up between the bearings is eliminated, and friction is typically reduced by a further 3-5%. In one option the inner ball bearing races have been lightly sprung loaded against each other to prevent internal ball skid within the bearing which would prolong bearing life if required and also assist in the performance of the pump if it was to be mounted vertically with reference to shaft direction rather than the preferred horizontal orientation. Electrically conductive bearing grease may also be preferred to extend bearing life.
A reader skilled in the art will appreciate that the weight of the rotating parts will bias the above loading arrangement if the pump is not operated with the shaft horizontally aligned, which may have a biasing effect on the position taken up by the sphere 211 and the shaft 207/208. The importance, if any, of this effect has not been established. The axial component of magnetic attraction between the motor stator, when energised, and the rotor may also bias 530 the common shaft position if the motor is not assembled in magnetic alignment. In such cases, one of the common shaft bearings (209 or 210 may be fixed during manufacture on to the shaft for a penalty of perhaps 5 percent of the total frictional loading. Alternatively the magnetic attraction effect may be used to at least partially overcome the effect of gravity on the common shaft.
This integrated motor and pump includes an optimised approach to providing bearings for the rotating parts of a swash pump. The preferably paired needle roller bearings 214 and 215 are free to slide lengthways over the slanted portion 208 of the common shaft. Only two ball-roller bearings (209 and 210) are used to support the straight part of the common shaft 207. One (209) may be supplied as part of the motor and one (210) is included in the pump housing.
Use of a resilient element having compliance between the slant section 208 of the common drive shaft and the swash plate assembly permits more force to be consistently imposed on to the sealing lines and hence allows for more consistent closure of both sealing lines 52 and 53 (see
One variant of the invention having non-directional resilience, as shown in
For a preferred, directionally resilient, drive mechanism, the slant shaft and inner bearing race is modified.
In
The directionally oriented resilient property of the swash plate driving means is preferably oriented with the greatest resilience aligned and maintained during rotation in the direction of the sealing lines, providing greatest compliance over the sealing positions, and providing the least compliance at about 90 degree phase difference apart from the positions of the swash sealing lines. It has been established by theory and by measurement that for a swash pump that two thrust vectors representing the integrated pressure on the plate are always 90 degrees (a quarter revolution) apart from the position of the two sealing lines (ignoring the moments when the sealing lines traverse the ports), although the direction of the vectors alternate. Minimum resilience is preferred in line with the position of the pumping load thrust vector. Hence the invention is preferably provided with the flats on shaft 208A formed at an angle parallel to the plane shared by both axes of the common shaft so that the direction of least resilience is at 90 degrees to the line joining the sealing lines. Optionally the invention may be provided with the flats on shaft 208A formed at optimised angles other than parallel to the plane shared by both axes of the common shaft. Use of resilience in either a non-directional or preferably a directional manner allows a more compliant force closing the swash plate to cone plate contact to be applied at both sealing lines. In the absence of resilience, greater precision of manufacture and greater dimensional stability during use is required to achieve an equivalent seal.
The specific type of joint should be a firm fit, once assembled in the pump, since otherwise it may allow leakage of the pumped fluid. The trunnion slot 801 also guides movement of the inner divider seal part. The divider plate is fixedly held, without leaks, in slots in the pump housing which press against the housing sides. The seal; part 221 of the divider plate assembly, includes an inner sealing face having a concave, part-spherical surface 607 with a radius matching the outer surface of the inner swash sphere. Preferred materials include a hardened and polished metal plate such as a stainless steel for the fixed divider plate and an engineering plastics material (as described earlier) for the inner divider seal part and for the trunnion 802; hence alternating between metal for the swash plate, plastic for the trunnion, and metal for the divider plate for instance. This three part divider plate assembly has been found to give consistent pump performance with very little friction.
The preferred brushless DC motor (inside housing 101—see
Because one intended application for this integrated assembly is the pumping of explosive vapour (as in fuel/air mixtures), and because such a mixture could be ignited at the delivery nozzle, within pipes, or within the pump, this pump should be capable of meeting relevant fire and explosion containment safety requirements. Since one vapour recovery pump may serve two separate filling stations in a single dispenser, an explosion must not propagate from one filling station, through the pump to another filling station. Of course explosion proofing is provided here by way of example and may not be required in all applications.
See
The straight portion 207 of the drive shaft inside the motor is confined as shown in
Variations
A skilled reader will appreciate that many of the developments embodied in the swash pump may be put into practice without having an integrated motor as shown in
Inside the inner swash sphere, a pair of needle roller bearings are preferred since these allow axial sliding. This position minimises the torque applied through the bearings hence allows smaller bearings. Use of a fixed stub axle carried into a bearing external to the sphere and mounted eccentrically from the common drive shaft and at a slant is an option that seems unbalanced and is harder to protect with rotary seals.
An example pump for the intended application works against small pressure differentials, typically about 200 mbar, and needs no valves. Valves are not justified at this relatively low pressure differential and would be an obstacle to passage of the non-compressible fluid (in this example; gasoline). This application also needs to handle non-compressible fluids (liquids). Other applications may handle solid particles like suspended sediments and may involve a higher pressure differential. Both pumping cavities—one on each side of the swash plate—may be effectively combined into one, and use a common (strip) port cut across the swash plate both at the inlet and exhaust. Adiabatic efficiencies may be improved for compressible fluids especially at higher compression ratios. One way valves such as reed valves at the exhaust of the pump may be required. Such valves with appropriate independent porting can stop flow swapping across the swash plate and eliminate reflux or backflow into the pump cavities. At the same time, the porting arrangement should support independent ports for each side of the swash plate. Each side of the swash plate then comprises an independent pumping cavity.
Machined metal parts may be replaced by moulded parts, or parts made of moulded or machined plastics, dependent in part on requirements imposed by the intended application. The reduced precision required permits more use of moulded parts.
A conventional induction motor or indeed any source of rotating power may be used to drive the swash pump.
Pumps according to the invention have the effect of substantially reducing frictional losses and render the swash pump very much more feasible as a commercial solution in a variety of applications. More particularly.
Finally, it will be understood that the scope of this invention as described by way of example and/or illustrated herein is not limited to the specified embodiments. Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are included as if individually set forth. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 572220 | Oct 2008 | NZ | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NZ2009/000198 | 9/18/2009 | WO | 00 | 4/25/2011 |
