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Patent Searching and Data


Title:
DRILL MOTOR
Document Type and Number:
WIPO Patent Application WO/2021/170653
Kind Code:
A1
Abstract:
A rotary drive (1) comprises at least one stage, the at least one stage comprising a stator (4) and a rotor (6), the rotor (6) disposed within the stator (4), wherein a cavity (16) is defined between the stator (4) and the rotor (6), and wherein the stator (4) comprises at least one inlet (18) which extends through the stator (4) and is configured for the ingress of a motive fluid into the cavity (16); and at least one outlet (30) which extends through the stator (4) and is configured for the egress of the motive fluid from the cavity (16), wherein movement of the motive fluid between the inlet (18) and the outlet (30) causes the rotor (6) to rotate.

Inventors:
SUSMAN HECTOR (EG)
HARRIS GARY LAWRENCE (US)
Application Number:
PCT/EP2021/054554
Publication Date:
September 02, 2021
Filing Date:
February 24, 2021
Export Citation:
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Assignee:
FAABORG UK LTD (GB)
International Classes:
F01C1/356; E21B4/02; F01C11/00; F04C2/344; F04C2/356; F04C13/00
Domestic Patent References:
WO1990009510A11990-08-23
WO1999020904A11999-04-29
WO2013159153A12013-10-31
Foreign References:
GB2379482A2003-03-12
FR2125644A51972-09-29
US5785509A1998-07-28
US5833444A1998-11-10
US5518379A1996-05-21
Attorney, Agent or Firm:
MARKS & CLERK LLP (GB)
Download PDF:
Claims:
CLAIMS

1 . A rotary drive comprising at least one stage, the at least one stage comprising: a stator and a rotor, the rotor being disposed within the stator, wherein a cavity is defined between the stator and the rotor, and wherein the stator comprises: at least one inlet which extends through the stator and is configured for the ingress of a motive fluid into the cavity; and at least one outlet which extends through the stator and is configured for the egress of the motive fluid from the cavity, wherein movement of the motive fluid between the inlet and the outlet causes the rotor to rotate.

2. The rotary drive of claim 1 , comprising a valve configured to engage the rotor at a position between the inlet and the outlet.

3. The rotary drive of claim 2, wherein in use, the valve forms a fluid seal between the inlet and the outlet in a counter flow direction.

4. The rotary drive of claim 2 or 3, wherein the stator comprises a recess for accommodating the valve and the valve is radially moveable within the recess.

5. The rotary drive of any preceding claim, comprising a valve support configured to maintain movement of a respective valve to a substantially radial direction.

6. The rotary drive of any preceding claim, wherein the rotary drive comprises a plurality of stages, and wherein the plurality of stages are longitudinally spaced relative to each other.

7. The rotary drive of claim 6, wherein at least two adjacent stages comprise or display an angular offset.

8. The rotary drive of any preceding claim, comprising a shaft, wherein the shaft is connected to the rotor, and wherein rotation of the rotor causes rotation of the shaft.

9. The rotary drive of any of claims 1 to 8, wherein the rotor comprises a metal seal configured to provide at least a partial seal with or against the stator.

10. The rotary drive of any of claims 1 to 8, wherein the rotor excludes or is devoid of a seal.

11. A method of operating the rotary drive of claim 1 , the method comprising the steps of: injecting a motive fluid into the inlet; and circulating the motive fluid into a cavity defined between the stator and the rotor, thereby causing rotation of the rotor, wherein, rotation of the rotor causes displacement of the cavity and the motive fluid contained therein around an internal surface or circumference of the stator from the inlet to the outlet.

12. The method of claim 11 , comprising increasing the pressure of the motive fluid in the cavity so as to cause the rotor to rotate.

13. The method of claim 11 or 12, comprising rotating the shaft.

14. The method of claim 11 to 13, wherein the rotary drive comprises a valve configured to restrict the displacement of the cavity around the internal circumference of the stator in a single direction only.

15. A rotary drive comprising a plurality of stages, wherein at least one of the plurality of stages comprises: a stator and a rotor, the rotor disposed within the stator, wherein a cavity is defined between the stator and the rotor, and wherein the stator comprises at least one inlet which extends through the stator and is configured for the ingress of a motive fluid into the cavity; and at least one outlet which extends through the stator and is configured for the egress of the motive fluid from the cavity, wherein movement of the motive fluid between the inlet and the outlet causes the rotor to rotate.

16. The rotary drive of claim 15, wherein each stage of the plurality of stages of the rotary drive comprises a stator and a rotor, the rotor disposed within the stator, wherein a cavity is defined between the stator and the rotor, and wherein the stator comprises at least one inlet which extends through the stator and is configured for the ingress of a motive fluid into the cavity; and at least one outlet which extends through the stator and is configured for the egress of the motive fluid from the cavity,

17. The rotary drive of claim 15, wherein the rotary drive comprises a longitudinal axis, wherein the rotor and stator of each stage are centred on the longitudinal axis.

18. The rotary drive of claim 17, wherein the plurality of stages are longitudinally offset from each other along the longitudinal axis.

19. The rotary drive of claim 17, wherein the plurality of stages are angularly offset from each other relative to the longitudinal axis.

20. The rotary drive of claim 15, wherein the plurality of stages are interconnected.

21 . A drilling apparatus comprising a rotary drive according to any of claims 1 to 10 or 15 to 20.

22. An underwater excavator comprising a rotary drive according to any of claims 1 to 10 or 15 to 20.

Description:
Drill Motor

Field of the Invention

This relates to positive displacement motors for use in, for example, but not limited to, a geological drilling apparatus or an underwater excavation apparatus.

Background

Fluid driven or hydraulic motors of the type wherein a rotor is rotatably mounted within a stator, are commonplace and widely known in the art.

US 5,518,379 (SUSMAN, HARRIS) discloses a drilling motor comprising a hollow tubular stator having at least one rod recess therein and an exhaust port therethrough corresponding to each of the at least one rod recess; a rod movably disposed in each of the at least one rod recess; a tubular rotor movably disposed within the stator for rotation therein, the tubular rotor having a central motive fluid flow channel therethrough and extending along the length of the rotor, the rotor having one or more radial flow channels therethrough for providing a motive fluid flow path from the central motive fluid flow channel to at least one action chamber between the hollow tubular stator and tubular rotor; the tubular rotor having at least one rotor seal; and the at least one action chamber defined by an interior surface of the hollow tubular stator and an exterior surface of the tubular rotor, each of the at least one action chamber sealed at one end by the rod and at another end by one of the at least one rotor seals. The rotor comprises a central motive fluid flow channel and one or more radial flow channels interconnected therewith for fluid to flow to action chambers, e.g. action chambers between the rotor and a stator of a drilling motor.

Motors such as these have been used to power drilling apparatus in oil/gas wells for a number of years. These motors also find use in underwater excavation apparatus.

However, such motors are susceptible to a number of problems, namely, insufficient hydraulic efficiency. This is of particular importance when used in excavation apparatus where the performance requirements of the motor differs significantly from those for drilling apparatus. For example, in a drilling environment the hydraulic efficiency of the motor is not typically of paramount importance as the remaining energy in the drilling fluid can be dissipated in the drill bit and/or used to transport drill cuttings to the surface. In excavation apparatus, however, the efficiency of the motor has a direct bearing on the rating of the pumps used to supply fluid. Hence in order to minimise the size and complexity of the pumps it is desirable to maximise the hydraulic efficiency of the motor.

It is an object of the present invention to obviate and/or mitigate the limitations and/or disadvantages associated with the prior art and/or with conventional systems.

Summary of the Invention

According to a first aspect, there is provided a rotary drive comprising at least one stage, the at least one stage comprising a stator and a rotor, the rotor disposed within the stator, wherein a cavity is defined between the stator and the rotor, and wherein the stator comprises at least one inlet which extends through the stator and is configured for the ingress of a motive fluid into the cavity; and at least one outlet which extends through the stator and is configured for the egress of the motive fluid from the cavity, wherein movement of the motive fluid between the inlet and the outlet causes the rotor to rotate.

The rotary drive may comprise, may be or may form part of a motor.

The rotary drive may comprise, may be or may form part of a pump.

The rotary drive may comprise, may be or may form part of a rotary actuator.

The rotary drive may comprise, may be or may form part of a positive displacement pump and/or a positive displacement motor.

The rotary drive may comprise, may be or may form part of a hydraulic motor and/or a pneumatic motor.

The rotary drive may comprise an outer casing.

The outer casing may be disposed radially outside the stator.

The outer casing may encapsulate and/or encase and/or surround the stator.

The outer casing may be concentric with the stator.

The rotary drive may comprise a plurality of stages.

The plurality of stages may be longitudinally spaced relative to each other, and/or may be positioned in series, i.e. end-to-end. The plurality of stages may be spaced along their longitudinal axis.

The plurality of stages may share a common longitudinal axis and/or may be longitudinally aligned. The respective longitudinal axes of the plurality of stages may be substantially parallel and/or coincident.

Two or more stages may comprise or may display an angular offset, i.e. two or more stages may be offset relative to each other. At least two adjacent longitudinally spaced stages may be offset relative to each other about the central axis of rotation. The term “offset” will be herein understood to mean that a given stage is rotationally clocked relative to another stage. However, the “offset” stages may still be longitudinally aligned with respect to their rotation axis.

Advantageously, each stage may be offset, e.g. rotationally offset, relative to an adjacent stage, for example relative to its adjacent stage(s). A first stage, e.g. the stage at an upper end of the rotary drive, may be offset relative to a second stage and/or relative to its adjacent stage. An intermediate stage, e.g. a stage located between two adjacent stages, may be offset relative to both adjacent stages. An end stage, e.g. the stage at a lower end of the rotary drive, may be offset relative to a preceding stage and/or relative to its adjacent stage.

It will be appreciated that not all stages need to be offset with every other stage. For example, a stage may be rotationally offset relative of another stage, e.g. relative to an adjacent stage, but may be rotationally aligned with one or more other stages.

The stator may be generally annular in cross section, e.g. in a cross-section substantially perpendicular to its longitudinal axis.

The stator may be, or may take the form of a generally annular cylinder.

The stator may comprise or may define an inner, e.g. central, opening or space.

The stator may be encapsulated by, surrounded by and/or disposed within the outer casing.

The outer casing may be concentric and/or coaxial with the stator and/or the rotor, e.g. with the stator and the rotor.

The outer casing may be disposed radially outside of or around the stator.

The stator may have or may define an internal diameter.

The stator may have a central axis.

The rotor may be rotatably connected to the stator.

The rotor may be disposed axially, for example, concentrically and/or coaxially, within the stator.

The rotor may be disposed within the inner opening or space of the annulus of the stator.

The rotor may have a central axis.

The central axis of the rotor may be parallel to or aligned with the central axis of the stator. The rotor may share a common axis with the stator, i.e. the central axis of the rotor may be coincident with the central axis of the stator.

The rotor may have an outer diameter. The rotor may have an outer surface. The rotor may rotate and/or may be configured for rotational movement within the stator.

The rotor may be rotate and/or may be configured to rotate about the central axis of the rotor.

The rotor may be configured to rotate in one direction only, for example, a forward direction. The forward direction may be a clockwise direction or an anti clockwise direction. Alternatively, the rotor may be configured to rotate in a forward and/or reverse direction, e.g. in a clockwise and/or an anti-clockwise direction.

The rotor may comprise an inner, e.g. central, opening.

The inner or central opening of the rotor may be disposed substantially centrally about the axis of rotation and/or the longitudinal axis of the rotor.

The inner or central opening of the rotor may define a void within the rotor, e.g. a void disposed substantially centrally within the rotor. The inner or central opening may be concentric with the rotor. The inner or central opening may be centred on or about the rotational and/or longitudinal axis of the rotor.

The rotor, e.g. a cross-sectional profile and/or an outer surface of the rotor, may be non-circular.

The rotor may comprise at least one lobe.

The rotor may comprise at least one projection and/or protrusion.

The at least one projection may be, or may form or may define the at least one lobe.

The at least one lobe and/or projection and/or protrusion may extend radially outwards from the axis of rotation and/or from the longitudinal axis of the rotor.

The rotor may comprise a plurality of lobes. The plurality of lobes may be offset from each other and/or may be circumferentially spaced relative to each other.

The plurality of lobes may be evenly and/or regularly spaced and/or may equally offset from each other. For example, for a two-lobe configuration, the lobes may be rotationally offset by about 180 degrees and/or may be disposed opposite each other relative to the longitudinal or rotational axis of the rotor. For a three-lobe configuration, the lobes may be rotationally offset by about 120 degrees. For a four- lobe configuration, the lobes may be rotationally offset by about 90 degrees. For a configuration of X lobes, the angular or rotational offset of a lobe relative to an adjacent lobe may be substantially equal to 360 divided by X, such that the lobes may be evenly or regularly spaced around the circumference of the rotor.

In an embodiment, the rotor may comprise two lobes. Each lobe may have or may define an outer diameter, which may be twice the distance from a tip or outermost portion of the lobe to the axis of rotation of the rotor. The rotor may have or may define a regular or smallest outer diameter. The outer diameter at one or more lobes, e.g. at the lobes, may be greater than the regular or smallest outer diameter of the rotor, i.e. at a position on an outer surface of the rotor away from the lobes.

The rotor and/or inner or central opening of the rotor may comprise at least one rotor recess. At least one rotor recess may be generally rectilinear. Alternatively, or additionally, at least one recess may be semi-circular, triangular or any other suitable shape. Typically, the rotor recesses may have the same profile.

The at least one rotor recess may extend in a radial direction.

The rotor may and/or inner or central opening of the rotor may comprise a plurality of rotor recesses. The at least one rotor recess and/or plurality of rotor recesses may be disposed and/or located on an inner surface of the rotor. The plurality of recesses of the rotor may be evenly spaced and/or equally or regularly offset, e.g. rotationally offset, from each other. For example, for a two-recess configuration, the rotor recesses may be offset by about 180 degrees. For a three- recess configuration, the rotor recesses may be offset by about 120 degrees. For a four- recess configuration, the rotor recesses may be offset by about 90 degrees. For a configuration of X rotor recesses, the angular offset between adjacent recesses may be substantially equal to 360 divided by X, such that each of the rotor recesses may be evenly or regularly spaced around the circumference of the rotor.

The rotary drive may comprise a flywheel. The flywheel may be connected to and/or may be disposed on the rotor.

The flywheel may comprise a mass which may be greater than the mass of the rotor. The flywheel may be incorporated to increase a momentum of the rotor during rotation when in use. A person of skill in the art will understand that the inclusion of a large mass will increase the momentum of the system when in motion, thereby acting as a means for storing rotational energy of the rotor while the rotor is rotating when in use.

The rotary drive may comprise a shaft.

The shaft may be connected to the rotor.

The shaft may be generally cylindrical. The shaft may be disposed within the rotor. The shaft may be disposed within the inner or central opening of the rotor. The shaft may be concentric and/or coaxial with the rotor.

The shaft may be disposed axially centrally within the rotor, for example, within the inner or central opening of the rotor.

The shaft may comprise at least one shaft recess. The shaft may comprise a plurality of shaft recesses. The at least one shaft recess and/or plurality of shaft recesses may be disposed on an outer surface of the shaft. The plurality of recesses of the shaft may be evenly or regularly spaced and/or equally offset from each other. For example, for a two-recess configuration, the shaft recesses may be offset by about 180 degrees. For a three- recess configuration, the shaft recesses may be offset by about 120 degrees. For a four- recess configuration, the shaft recesses may be offset by about 90 degrees. For a configuration of X recesses, the angular offset between adjacent recesses may be equal to 360 divided by X, such that the recesses may be evenly or regularly spaced around the circumference of the shaft.

At least one shaft recess may be generally rectilinear. Alternatively, or additionally, at least one shaft recess may be semi-circular, triangular or any other suitable shape. Typically, the shaft recesses may have the same profile

The recesses of the shaft may be positioned and/or configured to be positioned adjacent a respective recess on the rotor. The at least one recess or plurality of recesses of the shaft may align with, and/or may be configured to align with the at least one recess or plurality of recesses on the rotor. The aligned recesses may each form or may each define a channel. A/the channel may be square or rectangular. Alternatively, or additionally, a/the channel may be any suitable shape, for example, circular, triangular, hexagonal or the like. Typically, when a plurality of channels is present, the channels may have the same profile.

The shaft may be connected to the rotor by a keyed arrangement, i.e. a key may form a means of connection between a recess of the shaft and a respective recess of the rotor.

At least one key may be disposed and/or inserted within a channel or one of the channels. They key may mate and/or may fixedly engage the shaft to the rotor. By such provision, rotation of the rotor within the stator may cause rotation of the shaft. Typically, a key may be provided within each of the channels defined by a rotor recess and a respective shaft recess.

A/the channel(s) may be configured for the insertion of a key. The key may be disposed, and/or may be inserted into a/the channel(s).

The key may interlock at least one recess of the rotor with a respective recess of the shaft

The rotation of the shaft may be used for downstream power, for example, to power tools, motors, pumps or the like.

When the rotary drive comprises a plurality of stages, the stages may be longitudinally spaced along the shaft.

The plurality of stages may share a common longitudinal axis and/or may be longitudinally aligned with a longitudinal axis of the shaft.

At least two adjacent longitudinally spaced stages may be offset relative to each other about the shaft.

Advantageously, each stage may be offset, e.g. rotationally offset, relative to an adjacent stage, for example relative to its adjacent stage(s), about the shaft.

Away from the lobes, an outer dimension, e.g. outer diameter, of the rotor may be less than an inner dimension, e.g. inner diameter, of the stator. A void may be formed and/or defined between the stator and the rotor. The void may be or may define, or may be referred to as a cavity. In use, the cavity may contain, or may be configured to contain a/the motive fluid.

The stator may have an inner diameter. The stator may have an inner surface. The inner surface may define the inner diameter of the stator.

The cavity may be defined between the inner surface of the stator and the outer surface of the rotor.

The stator internal diameter may be substantially equal to the outer diameter of the rotor at the lobes. Advantageously, the stator internal diameter may be marginally greater than the greatest outer diameter of the rotor, e.g. than the outer diameter or outermost dimension of the rotor at the lobes.

The distance between the inner diameter of the stator and the outermost dimension or outer diameter of the lobes may be defined as a clearance or gap. The clearance or gap may be sufficiently small such that at least a partial seal is formed between at least one lobe, e.g. the lobes, and the stator. By such provision, efficiency of the rotary drive may be optimised.

The clearance may be less than about 10mm, or less than about 5mm, or less than about 2mm, or less than about 1mm, or less than about 500pm (micrometres), or less than about 200pm, or less than about 100pm, or less than about 50pm. The cavity may be sealed or may be substantially sealed. The cavity may be partially sealed.

The seal of the cavity may be defined by, may be determined by and/or may be dependent on the clearance between the lobes and the stator.

The clearance between at least one lobe, e.g. the lobes, and the stator may be sufficiently small that cavity may be sufficiently sealed such the motive fluid is not able to pass between a/the lobe(s) and the stator.

In an embodiment, the clearance may be such that only a partial seal is formed. In such instance, a portion of the motive fluid may pass between a/the lobe(s) and stator. The amount or portion of the motive fluid to pass between a/the lobe(s) and the stator may be relatively small relative to the total amount of motive fluid, such that the motive fluid still exerts sufficient pressure on the rotor to cause rotation of the rotor.

The rotor may comprise a seal. The seal may be configured to form a seal with or against the stator. The seal may provide a partial seal with or against the stator.

The seal may be a metal seal, for example, a soft metal seal. The soft metal seal may comprise a soft, malleable metal such as aluminium (Al), lead (Pb) or the like.

The seal may be a polymeric seal. In such instance, the seal may be made of a polymer resistant to high temperatures and/or high pressures, preferably an HPHT polymer. The polymer may comprise or may be PEEK (polyetheretherketone). The polymer may be selected to with stable at operating temperatures up to 200°C, e.g. up to 250°C, e.g. up to 280°C.

Alternatively, the rotor may not comprise a seal, i.e. may exclude a seal. In such an embodiment, despite the absence of a seal, the clearance between an outer surface of the rotor and the inner surface of the stator may be sufficiently small that the pressure within the cavity is large enough to cause rotation of the rotor, i.e. reach or exceed the activation pressure.

The rotor may comprise one or more seals provided on one or more lobes thereof. For example, each lobe may comprise one or more seal. Alternatively, one or more lobes may comprise a seal, and one or more lobes may be devoid of a seal.

The seal may be configured to be resistant to elevated temperatures and/or elevated pressures, e.g. the material of the seal may have a melting point greater than a typical atmospheric temperature experienced when in use and/or the material of the seal may have sufficient toughness, strength, rigidity or the like to withstand the atmospheric pressures experienced when in use. The seal may be configured to be resistant to corrosive environments, e.g. acidic, alkaline environment or the like.

As described above, the stator comprises at least one inlet which extends through the stator and is configured for the ingress of a motive fluid into the cavity; and at least one outlet which extends through the stator and is configured for the egress of the motive fluid from the cavity.

The at least one inlet may extend from a radially outer surface of the stator to a radially inner surface.

The at least one inlet may extend radially through the stator. Alternatively or additionally, the inlet may extend at any direction, for example, tangentially, or at an oblique angle or the like. One or more inlets, e.g. the at least one inlet, may extend in a plane perpendicular to a longitudinal axis of the stator. One or more inlets, e.g. the at least one inlet, may extend in a direction tangential, oblique, curved, or the like, relative to a longitudinal axis of the stator.

The at least one inlet may form a flow path from outside the stator to inside the stator.

The flow path may be straight, linear, and/or direct. Alternatively, the flow path may be at least partially convoluted.

The stator may comprise an inlet arrangement.

The inlet arrangement may extend through the stator, e.g. through the wall of the stator.

The inlet arrangement may comprise, be, or form an inlet.

The inlet arrangement may comprise an inlet chamber.

The inlet arrangement may comprise an inlet channel.

The inlet arrangement may comprise a slot.

The inlet arrangement may comprise a valve.

The inlet arrangement may permit the ingress and/or injection of the motive fluid into the cavity.

The inlet arrangement may allow the motive fluid to be injected, directed or transported from the exterior of the stator to the cavity.

The slot may be or may form a recess in the stator.

The recess in the stator may be generally rectilinear.

At least one inlet of a first stage may be rotationally offset relative to at least one inlet of a second stage, e.g. of an adjacent stage.

The rotary drive may comprise a plurality of inlets. One or more stages, e.g., each stage, may comprise a single inlet. One or more stages, e.g., each stage, may comprise a plurality of inlets. Alternatively, the rotary drive may comprise a single inlet only.

The inletjnay occupy or may have a length substantially equal to a length of a respective stage of the rotary drive. Alternatively, the inlet may comprise or may have a length less than a respective stage of the rotary drive. Alternatively, the inlet may occupy a length greater than the length of a stage of the rotary drive, for example, the total length of the rotary drive.

Alternatively, the inlet may be a discrete inlet port, for example, a cylindrical port and/or channel which may not occupy a significant length relative to the axial length of a respective stage and/or of the rotary drive.

It will be understood by a person skilled in the art that the motive fluid inserted and/or injected into the cavity will cause the rotor to rotate. Consequently, the motive fluid will apply a torque on the rotor. It will be understood by a person skilled in the art that the number of inlets of the rotary drive may affect and/or may be proportional to the torque applied to the rotor for a given pressure of the motive fluid. I.e. increasing the number of inlets will increase and/or will multiply the torque applied to the rotor by n, where n is the number of inlets. For example, if the number of inlets is doubled, the applied torque may be doubled, relative to an embodiment comprising a single inlet; and if the number of inlets is tripled, the applied torque may be tripled, relative to an embodiment comprising a single inlet.

One or more of the inlet, inlet channel, inlet arrangement and/or slot of one or more stage of the rotary drive may be in fluid communication with each other, e.g. the inlet of a first stage may be in fluid communication with the inlet of one or more other stage. By such provision, the motive fluid may be inserted, pumped, injected or the like into each stage of the rotary drive simultaneously, for example, via each of the fluidly connected inlets.

The inlet arrangement may comprise a valve support.

The valve support may be integral with the stator, e.g. the valve support may be machined into the stator. Alternatively, the valve support may be a separate component which may be inserted, fitted, bonded, adhered or the like to the rotary drive, e.g. the stator.

The valve support may take the form of one or more spacers, cushions, supports or the like.

The valve support(s) may be, or may take the form of one or more cylinders. The valve support(s) may be, or may take the form of one or more rectilinear profiles, e.g. a cuboid. It will be understood that the valve support may occupy any suitable shape and/or volume.

The valve support(s) may protrude from an edge wall of the slot and/or the inlet.

The valve support(s) may be disposed in, within or adjacent the inlet, inlet channel and/or inlet arrangement.

Advantageously, the valve support may be configured to permit a fluid, e.g. the motive fluid to flow from the inlet to the cavity. For example, when the valve support comprises a plurality of longitudinally spaced supports, the motive fluid may be permitted to flow into the cavity via a gap provided between adjacent supports.

The valve support(s) may be suitable for, and/or configured to support the valve and/or hold the valve in a position in a particular plane, e.g. hold the valve in a lateral position.

The valve support(s) may occupy a space, e.g. may have a diameter, which is substantially equal to, or marginally less than the difference between the width of the inlet and/or slot and the width of the valve. For example, the valve support may be configured, e.g. sized to occupy the gap between the valve and walls of the inlet and/or slot. By such provision, the valve support may prevent the valve from moving laterally and/or circumferentially within the inlet and/or slot. By such provision, movement of the valve may be limited to a radial direction only.

Without the provision of the valve support, the valve may be free to move in a lateral and/or circumferential direction such that in use, the valve may flutter and/or may vibrate within the inlet and/or slot, which may limit or prevent the valve from sealing, which may allow the motive fluid to bypass the rotor, i.e. short circuit the flow path, thereby preventing the rotor from rotating. The valve support may permit the motive fluid to pass the valve without causing the valve to flutter, vibrate or move in a lateral direction.

The stator may comprise one or more valve supports.

Each stage of the rotary drive may comprise one or more valve supports. For example, each stage may comprise three valve supports. The valve supports may be spaced, e.g. may be equally spaced, for example equally spaced along the length of the inlet and/or stage, so as to provide support for the valve along the length of a respective inlet and/or along the length of a respective stage.

Advantageously, the valve support may prevent the valve from blocking the inlet. The at least one outlet may extend from a radially inner surface of the stator to a radially outer surface.

The at least one outlet may extend radially through the stator. Alternatively or additionally, the inlet may extend at any direction, for example, tangentially, or at an oblique angle or the like. One or more outlets, e.g. the at least one outlet, may extend in a plane perpendicular to a longitudinal axis of the stator. One or more outlets, e.g. the at least one outlet, may extend in a direction tangential, oblique, curved, or the like, relative to a longitudinal axis of the stator.

The at least one outlet may form a flow path from inside the stator to outside the stator.

The flow path may be straight, linear and/or direct. Alternatively, the flow path may be at least partially convoluted.

The stator may comprise an outlet arrangement.

The outlet arrangement may extend through the stator, e.g. through the wall of the stator.

The outlet arrangement may comprise an outlet chamber.

The outlet arrangement may comprise an outlet port.

The outlet arrangement may comprise an outlet channel.

The outlet arrangement may permit the egress of the motive fluid out of the cavity.

The outlet arrangement may allow the motive fluid to be directed or transported from the cavity to the exterior of the stator.

The at least one inlet may be configured to allow ingress and/or injection of the motive fluid.

The ingress of the motive fluid may be passively drawn in as a result of a pressure differential, e.g. may be naturally aspirated.

The ingress of the motive fluid may be actively pumped and/or drawn in by a pump, motor, fan, compressor, injector, turbo, supercharger or the like.

The at least one outlet may be configured to allow egress of the motive fluid.

The egress of the motive fluid may be passively expelled as a result of a pressure differential.

The egress of the motive fluid may be actively pumped and/or drawn out by a pump, motor, fan, impeller or the like.

The rotary drive may comprise an inlet manifold.

The inlet manifold may allow fluid communication between one or more inlet. The inlet may be fed via the inlet manifold, e.g. the motive fluid may be directed to the inlet via the manifold.

The inlet manifold may permit insertion and/or ingress of the motive fluid.

The inlet manifold may connect to each inlet in a parallel configuration, i.e. the inlet manifold may connect to each inlet such that motive fluid is fed to/inserted in each inlet simultaneously, e.g. at the same rate.

The inlet manifold may connect directly to each inlet, i.e. with no intervening components or fluid paths between the inlet manifold and each inlet.

The inlet manifold may connect to each inlet in a series configuration, i.e. the outlet of a stage may feed the inlet of an adjacent stage, such that the motive fluid is fed to/inserted in each inlet in turn, for example, one after the other.

The inlet manifold may be, or may form the inlet, inlet arrangement and/or inlet channel.

The rotary drive may comprise an outlet manifold.

The outlet manifold may allow fluid communication between one or more outlet.

The outlet manifold may feed and/or direct motive fluid to the outlet.

The outlet manifold may permit extraction of the motive fluid.

The outlet manifold may connect to each outlet in a parallel configuration, i.e. each outlet may connect to the outlet manifold such that motive fluid is fed from/extracted from each outlet simultaneously, e.g. at the same rate.

Each outlet may connect directly to the each manifold, i.e. with no intervening components or fluid paths between each outlet and the outlet manifold.

The outlet manifold may connect to each outlet in a series configuration, i.e. the outlet of a stage may feed the inlet of an adjacent stage, such that the motive fluid exits each outlet, which in turn feeds the inlet of an adjacent stage, for example, one after the other and the outlet manifold is connected to the ultimate stage of the series. The outlet manifold may connect only to the final stage.

The rotary drive may comprise a single inlet. The rotary drive may comprise a plurality of inlets. The rotary drive may comprise a single outlet. The rotary drive may comprise a plurality of outlets. The rotary drive may comprise any combination of inlets and outlets and/or series and/or parallel configurations, for example, the rotary drive may comprise a single inlet and a single outlet, the rotary drive may comprise a plurality of inlets and a single outlet, or the rotary drive may comprise equal numbers of inlets and outlets, or the rotary drive may comprise dissimilar numbers of inlets and outlets. The outlet manifold may be, or may form the outlet channel.

The motive fluid may comprise a gas.

The motive fluid may be any insert and/or non-flammable gas.

The motive fluid may comprise any suitable gas, for example, one or more of air, compressed air, carbon dioxide, nitrogen, oxygen, helium or the like, or a combination of any of the above and/or any other suitable gas.

The motive fluid may comprise a liquid.

The motive fluid may, e.g. liquid and/or gas be pressurised.

The motive fluid may be any inert and/or non-flammable and/or non-corrosive liquid.

The motive fluid may comprise any suitable liquid, for example, one or more of water, oil, drilling mud or the like, or a combination of any of the above

Advantageously, the motive fluid may comprise a gas. Using a gas may particularly advantageous or well suited in an underbalanced drilling arrangement. The use of a gas as the motive fluid may permit the use of the rotary drive for under balanced drilling. Underbalanced drilling is defined as a process of drilling the well whereby the pressure in the well is lower than the pressure in the formation. By such provision, water, formation gas, oil or the like may flow only in a direction from the formation into the well. Underbalanced drilling may prevent water, formation gas, oil or the like from flowing back into the formation from the well. Should water, formation gas, oil or the like flow into the foundation, it may cause formation plugging, i.e. may clog, plug and/or saturate the formation with the water, formation gas, oil or the like, potentially causing damage to the formation and/or reduce, limit or stop the flow of water, formation gas, oil or the like through the well bore to the well head for extraction.

Underbalanced drilling is well known in the art and provides a number of distinct advantages.

Advantageously, no parts and/or components of the rotary drive, or at least one stage thereof, are made of a perishable material, for example, polymer, rubber, plastic or the like.

The rotary drive may comprise and/or contain no perishable materials, for example, polymer, rubber, plastic or the like.

Advantageously, the rotary drive comprises no perishable materials which may perish or degrade, e.g. melt, corrode, warp, break or the like, for example, when exposed to the extreme temperatures and/or pressures and/or environment of the well, formation, oilfield or the like. The rotary drive may comprise or may be made of metal parts only.

The motive fluid and/or a pressure of the motive fluid may apply a force on the rotor and/or at least one lobe, e.g. the lobe(s).

The rotor may be configured to rotate when a force or pressure, e.g. a specific or predetermined force and/or pressure, is applied to the rotor and/or lobe(s).

The rotor may be configured to rotate at or above an activation pressure. The activation pressure may be the pressure of the motive fluid within the cavity required to cause the rotor to rotate.

At or above the activation pressure, the pressure and/or force applied on the rotor and/or lobe may be sufficient to cause the rotor to rotate and/or to maintain rotation of the rotor.

The rotary drive may comprise a valve.

The valve may be configured to engage the rotor.

The valve may be configured to engage the rotor at a position between the inlet and the outlet.

The valve may form a fluid seal between the inlet and the outlet.

The valve may be radially moveable.

The valve may be disposed and/or housed within a respective slot of the stator.

The respective slot of the stator may be, form or comprise the inlet, inlet arrangement and/or inlet channel. Alternatively, the respective slot may be any other suitable channel disposed in, on and/or through the stator.

The valve may be sized, e.g. have a diameter such that it fits within a respective slot.

The valve may be sized to fit within the inlet, inlet arrangement and/or inlet channel. The outer diameter of the valve may be less than the width of the inlet, inlet arrangement and/or inlet channel.

The valve may be free to move, e.g., linearly, within the slot.

The valve may be free to move in a radial direction to and/or in a place substantially perpendicular to the axis of rotation of the rotor. By such provision, movement of the valve may be limited to a single linear direction.

Lateral movement of the valve may be prevented by the slot.

The valve may be configured to engage with and/or abut the rotor, for example an outer surface of the rotor, upon ingress or injection of the motive fluid, for example during rotation of the rotor. The valve may be configured to or may be free to move in a radial direction as the rotor rotates. By such provision, the valve may engage with and/or abut the outer surface of the rotor, regardless of the diameter of the rotor at a position adjacent the valve, and/or relative position of the lobe. By such provision, the valve may account for and/or accommodate the asymmetric profile of the rotor and/or the lobes.

The valve may continuously engage and/or abut the surface outer surface of the rotor as the rotor rotates.

The valve may be configured to seal the cavity.

The valve may separate the cavity from the outlet.

The valve may have a circular cross section. The valve may be, or may take the form of a cylinder. The valve may be, or may form a roller. The valve may be configured to rotate, roll and/or spin. The valve may be housed and/or supported by the inlet, inlet channel or the like and may be configured to rotate within the inlet, inlet channel or the like. The valve may comprise a central longitudinal axis. The valve may be configured and/or be free to rotate, roll and/or spin about the central longitudinal axis of the valve.

Advantageously, rotation of the valve ensures that any wear, abrasion, damage or the like, for example, caused by friction with any other components, for example, the rotor and/or inlet, inlet channel or the like, is evenly or uniformly distributed around the circumference and/or periphery of the valve, i.e. the valve may wear evenly. By such provision, the ability of the valve to seal against the rotor and/or seal the cavity is not affected by localised damage on or at the surface of the valve. An imperfect or compromised seal may affect the power and/or torque generated by the motor.

Alternatively, the valve may be a spherical valve. By such provision, the risk of damage to an outer surface of the rotor during rotation thereof and contact with the valve, may be reduced or minimised.

The valve may occupy a length substantially equal to the length of a stage of the rotary drive.

Rotation of the rotor may cause displacement of the cavity.

Rotation of the rotor may cause displacement of the motive fluid contained in the cavity.

Displacement of the cavity and/or the motive fluid contained in the cavity may define a flow path.

The direction of the fluid circulation in use may define the flow path. The flow path may be disposed or located around an internal surface or circumference of the stator.

The flow path may be defined in a single direction only, e.g. clockwise or counter-clockwise.

The cavity and/or the motive fluid contained in the cavity may move along or relative to the flow path.

The cavity and/or the motive fluid contained in the cavity may move along or relative the flow path in a single direction only, e.g. clockwise or counter-clockwise.

An/the outlet may correspond to a respective/the inlet, i.e. an inlet may have a corresponding outlet.

The flow path may be defined as the flow path from an inlet to its corresponding outlet.

The direction of the flow path may be defined as a flow direction.

The direction opposite the flow direction may be defined as the counter flow direction.

The flow direction may be defined as downstream. A second position may be defined as downstream of a first position, if the second position is offset in the direction of the flow direction relative to the first position.

The counter flow direction may be defined as upstream. A first position may be defined as upstream of a second position, if the first position is offset in the direction of the counter flow direction (i.e. opposite direction to the flow direction) relative to the second position.

The/a valve may be disposed upstream, i.e. in the counter flow direction, of the/ a respective inlet.

The/a valve may be disposed between an outlet and a respective inlet relative to the flow direction.

In the direction of the flow path, i.e. in the flow direction, the/a valve may be disposed after the/a respective outlet but before the/a respective inlet. By such provision, in use, the fluid is expelled through the outlet in a single direction only.

One or more valves, e.g. the valve(s) may be a one-way valve, i.e. may permit fluid flow in a single direction only.

The valve may permit fluid flow around the rotor in the flow direction only.

The valve may prevent fluid from flowing around the rotor in the counter flow direction. The total distance of the flow path in the flow direction may be longer than the distance of the flow path in the counter flow direction. By such provision, the motive fluid may be forced to circulate or travel around at least a portion of the inner circumference of the stator and outer circumference the rotor, i.e. in the flow direction and not in the counter flow direction. For example, the motive fluid is forced to circumnavigate at least a portion of the rotor in a direction towards a corresponding outlet and not bypass, shortcut, or short circuit.

The region of the flow path in a counter flow direction between the valve and the outlet may be defined as a stripper region. The stripper region may be a dead- space, i.e. with no fluid flow.

As described above, the inlet arrangement may comprise a valve support. The valve support may provide support and/or guidance for/to/on the valve(s), and/or may prevent the valve(s) from abutting, touching, leaning, contacting or the like, a wall of the inlet, inlet channel, slot, or the like. By such provision, a fluid connection may be maintained between the inlet and the cavity on a side of the inlet, e.g. a side on the downstream side of the valve when in use. The valve support may bias the valve towards a wall of the inlet on the upstream side, i.e. the side opposite the downstream side, and/or the valve support may restrict movement of the valve near or adjacent a wall of the inlet on the upstream side. The valve support may bias or may confine the valve to seal the cavity on an upstream side of the inlet.

The rotary drive may comprise a plurality of inlet arrangements.

The rotary drive may comprise a plurality of outlet arrangements.

Advantageously, each inlet arrangement may have a corresponding outlet arrangement.

The plurality of inlet arrangements may be evenly or regularly spaced and/or equally offset from each other. For example, for a two-inlet arrangement configuration, the inlet arrangements may be offset by about 180 degrees. For a three-inlet arrangement configuration, the inlet arrangements may be offset by about 120 degrees. For a four-inlet arrangement configuration, the inlet arrangements may be offset by about 90 degrees. For a configuration of X inlet arrangements, the angular offset of adjacent inlet arrangements may be substantially equal to 360 divided by X, such that the inlet arrangements may be evenly or regularly spaced around the circumference of the stator.

The plurality of outlet arrangements may be evenly or regularly spaced and/or equally offset from each other. For example, for a two-outlet arrangement configuration, the outlet arrangements may be offset by about 180 degrees. For a three-outlet arrangement configuration, the outlet arrangements may be offset by about 120 degrees. For a four-outlet arrangement configuration, the outlet arrangements may be offset by about 90 degrees. For a configuration of X outlet arrangements, the angular offset of adjacent outlet arrangements may be substantially equal to 360 divided by X, such that the outlet arrangements may be evenly or regularly spaced around the circumference of the stator.

Each inlet of the plurality of inlets may have a corresponding outlet. There may be a plurality of flow paths. Each flow path may be defined between an inlet and the corresponding outlet.

In an embodiment comprising a plurality of inlet arrangements and outlet arrangements, the/ a respective valve may be disposed between an outlet and an adjacent inlet relative to the flow direction.

It will be understood that at a point where the/a lobe is exactly aligned with the/an inlet, the inlet may become blocked or closed. At such point, the motive fluid may not be able to enter the cavity and thus may not be able to exert a pressure and/or a force on the/a lobe of the rotor and consequently. Whilst this may cause momentary loss or reduction of rotational force on the rotor and potential reduction in momentum, it will be understood that, in use, the momentum of the rotor may cause the lobe to pass the inlet so that the process may continue in spite of the temporary lack of or reduction in propulsion or force. This momentum may be increased with the inclusion of a flywheel. The flywheel may comprise a mass which is greater than the mass of the rotor, thereby increasing the momentum of the rotor. This potential limitation may be reduced, mitigated or prevented with the use of multiple stages of the rotary drive, in which a first stage may be angled or clocked relative to an adjacent second stage. By such provision, while a/the lobe of the rotor of the first stage may be aligned with the inlet, and thus exerting no or reduced propulsive force, a/the lobe of the rotor of the second stage may be positioned such that the inlet may be fluidly connected to the cavity. Consequently, at any one time, at least one cavity of at least one stage is in fluid communication with the corresponding inlet, i.e. at least one lobe of at least one stage does not block the inlet, i.e. is in an open position. By such provision, at any one time, a propulsive force is always applied to at least one lobe and/or rotor. The motive fluid may exert a rotational moment on the shaft at all times. The plurality of stages may be connected together. By such provision, movement of a single stage may cause movement of the other stage(s). This configuration may allow each stage to be phased relative to other stage(s). The rotary drive may comprise any number of stages, for example, 1 , 2, 3, 4, 5, 6, 7, 8 or more.

Advantageously, the greater the number of stages, the smoother the transmission of power may be.

When two or more stages are rotationally offset, it will be understood that the offset may be provided in a number of ways.

In an embodiment, two adjacent stages may have the same number of inlets, and the inlets be rotationally aligned, but the respective rotor may be offset and/or clocked.

In another embodiment, two adjacent stages may have respective rotors that are rotationally aligned, but may have a different number of inlets, such that the inlets of one stage may be offset and/or clocked relative to the inlets of the adjacent stage.

In another embodiment, two adjacent stages may have respective rotors that are rotationally aligned, and may have the same number of inlets, but the inlets of one stage may be offset and/or clocked relative to the inlets of the adjacent stage.

It will be appreciated that, regardless of the particular configuration, a first and second “offset” or “clocked” stages may have in common that injection of fluid via an inlet in the first stage will exert a rotational force at a (rotational) location different from the (rotational) location where rotational force is exerted when injecting fluid via an inlet in the second stage. Advantageously, this ensures that, in a multistage arrangement, when a first stage is in an inactive position (e.g., in a position when one or more lobes of the rotor is/are aligned with or is/are closing the/an inlet), a different or second stage is in an active position (e.g. in a position when one or more lobes of the rotor is/are not aligned with or is/are not closing the/an inlet).

According to a second aspect, there is provided a method of operating a rotary drive according to the first aspect, the method comprising the steps of: injecting a motive fluid into the inlet; and circulating the motive fluid into a cavity defined between the stator and the rotor, thereby causing rotation of the rotor, wherein, rotation of the rotor causes displacement of the cavity and the motive fluid contained therein around an internal surface or circumference of the stator from the inlet to the outlet.

The method may comprise increasing the pressure of the motive fluid in the cavity so as to cause the rotor to rotate. The method may comprise rotating the shaft.

The rotary drive may comprise a valve. The method may comprise operating the valve so as to restrict the displacement of the cavity around the internal circumference or surface of the stator in a single direction only.

The motive fluid may be injected, pumped or inserted into the inlet arrangement. The motive fluid may pass, flow, be directed or be transported to the cavity, for example through the inlet, inlet arrangement and/or inlet channel.

The motive fluid may enter the cavity at a position downstream, i.e. in the flow direction, of the valve.

The valve may form a seal in the counter flow direction. The valve may prevent the motive fluid from flowing in the counter flow direction.

The valve may be a one-way valve, for example, the valve may permit fluid flow in a single direction only.

The motive fluid may be retained within the cavity downstream of the valve.

As more motive fluid is inserted into the cavity, the pressure of the motive fluid in the cavity may increase. When the pressure of the motive fluid in the cavity reach the activation pressure, the rotor may being to rotate. The rotor may begin to rotate in the direction of the flow direction.

The valve may maintain contact with the surface of the rotor.

The valve may continuously maintain contact with the surface of the rotor.

The valve may maintain the seal.

The valve may be pushed radially inwards towards the rotor by the motive fluid.

As the rotor rotates, the lobes may also rotate.

As the lobes align with the inlet, the lobes may fluidly isolate the cavity from the inlet.

The fluidly isolated cavity may form or may provide a discrete quantum of the motive fluid within the cavity.

As the lobe passes the inlet, a cavity disposed on an opposing side of the rotor may subsequently make fluid contact with the inlet.

As the rotor continues to rotate, the discrete quantum of the motive fluid contained in the first cavity may fluidly contact the outlet port. When the motive fluid makes fluid contact with the outlet port, the motive fluid may escape, exit or leave through the outlet arrangement.

The aforementioned process may continue while the ingress of the motive fluid through the inlet is maintained. The features described above in connection with the first aspect may equally apply to the method according to the second aspect, and are not repeated here merely for brevity.

According to a third aspect, there is provided a rotary drive comprising a plurality of stages, wherein at least one of the plurality of stages comprises a stator and a rotor, the rotor disposed within the stator, wherein a cavity is defined between the stator and the rotor, and wherein the stator comprises at least one inlet which extends through the stator and is configured for the ingress of a motive fluid into the cavity; and at least one outlet which extends through the stator and is configured for the egress of the motive fluid from the cavity, wherein movement of the motive fluid between the inlet and the outlet causes the rotor to rotate.

Each of the plurality of stages of the rotary drive may comprise a stator and a rotor, the rotor disposed within the stator, wherein a cavity is defined between the stator and the rotor, and wherein the stator comprises at least one inlet which extends through the stator and is configured for the ingress of a motive fluid into the cavity; and at least one outlet which extends through the stator and is configured for the egress of the motive fluid from the cavity,

The rotary drive may comprise a longitudinal axis.

Each of the plurality of stages may be centred and/or aligned on the longitudinal axis.

Each rotor of the plurality of stages may be centred and/or aligned on the longitudinal axis.

Each stator of the plurality of stages may be centred and/or aligned on the longitudinal axis.

The plurality of stages may be longitudinally offset from each other, e.g. along the longitudinal axis.

The plurality of stages may be angularly offset, e.g. rotationally clocked, from each other.

The plurality of stages may be interconnected and/or may be arranged on a common shaft.

Advantageously, the use of a rotary drive comprising a plurality of stages may address and/or limit, reduce or mitigate the risks associated with the aforementioned issues related to a lack of propulsive force experienced at the point when the lobes align with and/or cover, block or restrict the inlet. The use of a rotary drive comprising a plurality of stages ensures that at any one time, at least one cavity is in fluid communication with at least one inlet, thereby ensuring that at any one time, the motive fluid is able to apply a pressure on at least one lobe, thereby providing a rotational force on the rotor. By such provision, the motive fluid may continuously provide a rotational force, e.g. torque or moment on the rotor, thereby ensuring continuous rotation of the rotor and shaft, irrespective of an angular position of the rotor and/or lobes.

The features described above in connection with the first aspect may equally apply to the rotary drive according to the third aspect, and are not repeated here merely for brevity.

According to a fourth aspect there is provided a drilling apparatus comprising a rotary drive according to the first aspect or the third aspect.

The drilling apparatus may comprise or may be a geological drilling apparatus or a subterranean drilling apparatus.

According to a fifth aspect there is provided an underwater excavation apparatus comprising a rotary drive according to the first aspect or the third aspect.

It should be understood that the features defined above or described below may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment.

Brief Description of the Drawings

These and other aspects will now be described, by way of example only, with reference to the accompanying drawings, of which:

FIG. 1 shows a sectional view of a rotary drive according to a first aspect of the present invention;

FIG. 2 shows sectional views of a rotary drive according to an embodiment of the present invention comprising multiple stages, at different longitudinal positions along the length of the rotary drive;

FIG. 3 shows sectional views of the rotary drive of FIG. 2 at a later time point to that of FIG. 2, wherein relative rotation of the rotor has occurred;

FIG. 4 shows a sectional view of a rotary drive according to an embodiment, wherein the rotor comprises a seal. FIG. 5 shows a longitudinal view of the rotary drive at (a) a first time and (b) a second, later time when the rotor has rotated through about 90 degrees.

FIG. 6 shows a sectional view of the rotary drive of FIG. 1 showing an enlarged view of the inlet, valve and valve support.

FIG. 7 shows a plan view of the longitudinal length of the rotary drive of FIG. 1 showing the inlet and valve supports.

Detailed Description of the Drawings

Referring first to FIG. 1 of the accompanying drawings, there is shown a rotary drive 1 according to a first aspect of the present invention. The rotary drive 1 takes the form of a fluid driven motor. As shown in FIG. 1 , the rotary drive 1 comprises a stator 4 and a rotor 6. The stator 4 is generally annular in cross section such that it comprises a central opening. The stator 4 has a central axis, and the rotor 6 has a central axis which is coincident and coaxial with the central axis of the stator 4. The rotor 6 is disposed axially, for example, concentrically, within the stator 4, for example within the central opening of the annulus of the stator 4. The stator 4 is encapsulated within an outer casing 2, which is concentric with the stator 4 and rotor 6 and is disposed radially outside of the stator 4. The rotor 6 is rotatably attached to the stator 4 and configured for rotational movement within the stator 4 in a direction denoted by arrow A, which is shown as a clockwise direction in FIG. 1. Arrow A illustrates the flow direction. The direction opposite to arrow A is defined as the counter flow direction.

The rotor 6 comprises two lobes 8, which are disposed radially opposite each other, i.e. offset by 180 degrees. The lobes 8 take the form of a protrusion such that an outer diameter at the lobes 8 is greater than the outer diameter of the rotor 6 at a position away from the lobes 8, for example, 90 degrees to the lobes 8.

However, it will be appreciated that the rotor 6 may comprise a plurality of lobes 8. In an embodiment where the rotor 6 comprises more than two lobes 8, the lobes 8 may be evenly spaced and/or equally offset from each other. For example, for a three- lobe configuration, the lobes may be offset by 120 degrees. For a four-lobe configuration, the lobes may be offset by 90 degrees. For a configuration of X lobes, the angular offset of each lobe may be equal to 360 divided by X, such that each of the lobes may be evenly spaced around the circumference of the rotor.

The stator 4 comprises an internal diameter, which is sized such that it is marginally greater than the outer diameter of the rotor 6 at the lobes 8. The distance between the inner diameter of the stator 4 and the outer diameter of the lobes 8 is defined as a clearance 12. The clearance 12 may be sufficiently small such that at least a partial seal is formed between the lobes 8 and the stator 4. For example, the clearance 12 may be less than 10mm, or less than 5mm, or less than 2mm, or less than 1 mm, or less than 500pm (micrometres), or less than 200pm, or less than 100pm, or less than 50pm.

The rotor 6 comprises a central opening, which is disposed centrally along the axis of rotation of the rotor 6. Disposed axially centrally within the rotor 6, for example, within the central opening of the rotor 6 is a shaft 10. The shaft 10 is generally cylindrical. The shaft 10 comprises two generally rectilinear, e.g. rectangular recesses on its outer surface. The two recesses of the shaft are disposed radially opposite, i.e. offset by 180 degrees from each other. The rotor 6 comprises two generally rectilinear, e.g. rectangular recesses on the inner surface of the central opening of the rotor 6. The two recesses of the rotor are disposed radially opposite, i.e. offset by 180 degrees from each other. The recesses of the shaft 10 are configured to be positioned adjacent a respective recess on the rotor 6 such that the recess on the shaft 10 and the recess on the rotor 6 align to form a rectilinear, e.g. rectangular or square channel. Keys 14 are disposed within the rectilinear e.g. rectangular or square channel, thereby mating and fixedly engaging the shaft 10 to the rotor 6. By such provision, rotation of the rotor 6 within the stator 4 causes rotation of the shaft 10.

Away from the lobes 8, the outer diameter of the rotor 6 is less than the inner diameter of the stator 4, thereby forming a void disposed between the stator 4 and the rotor 6 and bound between the lobes 8. The void is referred to as a cavity and is denoted 16. In use, the cavity 16 is configured to contain a motive fluid. The clearance 12 between the lobes 8 and the stator 4 is sufficiently small that cavity 16 is sufficiently sealed such the motive fluid is not able to pass between the lobe 8 and the stator 4.

The amount or portion of the motive fluid to pass between the lobes 8 and the stator 4 is relatively small relative to the total amount of motive fluid, such that the motive fluid still exerts sufficient pressure on the rotor 6 and/or lobes 8 to cause rotation of the rotor 6.

In an embodiment, the clearance 12 may be such that only a partial seal is formed such that at least a portion of the motive fluid may pass between the lobe 8 and stator 4.

Advantageously, the degree of sealability of the clearance may allow the efficiency of the rotary drive to be varied. Alternatively or additionally, a bypassed portion of the motive fluid may be extract and/or used for alternative uses, for example, for propelling drilling cuttings away from the rotary drive, for example, to a surface of a drill hole or well bore or the like.

The stator 4 further comprises an inlet arrangement which permits the ingress of the motive fluid into the cavity 16. The inlet arrangement extends through the wall of the stator 4. The inlet arrangement comprises an inlet 18, valve support 20, slot 22 and valve 24. The inlet 18 extends through the stator 4 and allows the motive fluid to be directed or transported from outside the stator 4, through the inlet 18, to the cavity 16. Adjacent the inlet 18 is slot 22 which forms a generally rectilinear, e.g. rectangular recess in the stator 4. Disposed within the slot 22 is valve 24 which is sized such that is free to move linearly within the slot 22 in a radial direction to and/or from the axis of rotation of the rotor 6. The valve support 20 is integral with the stator 4, for example, machined into the stator. In an alternative embodiment, the valve support 20 may take the form of a separate insert which is fitted to the stator 4. The valve support 20 extends in a radial direction and is adjacent the side walls of the slot 22 of the inlet 18. The valve support 20 is sized such that the width or diameter of the valve support 20 is marginally less than the distance between the valve 24 and the wall of the slot 22 of the inlet 18, by such provision, the valve 24 is supported in position within the slot such that any lateral movement of the valve 24 within the slot 22 is negligible or prevented entirely, whilst still permitting movement of the valve 24 in a radial direction, i.e. perpendicular to lateral movement. By such provision, movement of the valve 24 is limited to a single linear direction and lateral movement is prevented by the valve support 20 and slot 22.

In the present embodiment, each stage of the rotary drive 1 comprises three valve supports 20 (visible in FIG. 5). The valve supports 20 are evenly distributed along the length of the stage of the rotary drive 1 while the inlet 18 and slot 22 run the full length of the stage. By such provision, the valve 24 is supported in position by the valve support 20 whilst still permitting a fluid pathway from the inlet 18 to the cavity 16 through the regions between the valve supports 20.

The valve 24 is configured to engage with, and abut the outer surface of the rotor 6. Due to the linear, radial freedom of movement of the valve 24, the valve 24 is free to move in a radial direction as the rotor 6 rotates, thereby accounting for the asymmetric profile of the rotor 6 as a result of the lobes 8, meaning that the valve 24 is able to continuously engage and abut the surface outer surface of the rotor 8 as the rotor 8 rotates. In the direction of the flow path, i.e. in the flow direction, the valve 24 is positioned after the outlet but before the inlet.

The valve 24 is configured to separate the cavity into upstream cavity portion 16 and downstream cavity portion 16’ at a location adjacent the inlet 18. The valve 24 forms a seal 26, which prevents the motive fluid in the downstream portion of the cavity 16 from passing in the counter flow direction to the upstream portion of the cavity 16. By such provision, the motive fluid is only permitted to travel in the flow direction A. This applies similarly to a second inlet arrangement, in which like parts are denoted by like numerals, but represented as 16’, 18’, 20’ 22’, 24’, 26’, 28’ and 30’.

For example, the motive fluid which enters the cavity 16’ through inlet 18 will circulate through the cavity 16’, 16 and exit the cavity 16 through outlet port 28 and outlet channel 30.

A motive fluid which enters the cavity 16’ through inlet 18’ will circulate through the cavity 16’, 16 and exit the cavity 16 through outlet port 28’ and outlet channel 30.

In an embodiment, the valve 24 takes the form of a cylinder which occupies the full length of each stage, however, it will be understood that alternative shapes may be used, for example a sphere, cube, rectangular cuboid or the like.

Advantageously, a cylindrical valve 24 minimises or reduces the risk of damage to an outer surface of the rotor 6 during rotation thereof and contact with the valve 24.

Since the clearance 12 forms at least a partial seal between the stator 4 and lobe 8 the cavity 16 forms at least a partially sealed chamber. Consequently, the ingress of the motive fluid into the cavity 16 will increase the pressure within the cavity 16. Since the motive fluid is not able to pass between the lobe 8 and the stator 4, nor to the portion of the cavity 16 upstream of the inlet 18, the increase in pressure applies a force on the lobes 8 of the rotor 6, which causes the rotor 6 to rotate.

It will be understood that FIG. 1 shows the cross section of the rotary drive 1 at a point along the longitudinal axis of the rotary drive 1. It will be understood that the rotary drive 1 may comprise any number of stages, which may be the plurality of stages may be disposed longitudinally offset relative to each other, i.e. they may be connected end-to-end. The plurality of stages may be angularly offset, e.g. may be clocked relative to each other. Such an embodiment is shown in FIG. 2 and FIG. 3 which shows the cross section of the rotary drive 1 , 101 , 201 comprising three stages. FIG. 2(a), FIG. 2(b), and FIG. 2(c) show the cross section of rotary drive 1 , 101 , 201 at three distinct locations along the longitudinal length of the rotary drive 1 , 101 , 201 , such that FIG. 2(a) shows the cross section of a first stage, FIG. 2(b) shows the cross section of a second stage, and FIG. 2(c) shows the cross section of a third stage. The angular offset, e.g. clock angle of each stage can clearly be seen.

The first stage, e.g. the stage at an upper end of the rotary drive 1 , 101 , 201 , is offset relative to the second, adjacent, stage. The third stage, e.g. a stage located at an end of the rotary drive 1 , 101 , 201 distal to the first stage is offset relative to the second, adjacent, stage. It will be appreciated that not all stages need to be offset with every other stage. For example, a stage may be rotationally offset relative of another stage, e.g. relative to an adjacent stage, but may be rotationally aligned with one or more other stages.

Each of the stages are longitudinally spaced along the shaft 10, 110, 210.

It will be understood that the rotary drive may comprise any number of stages.

In reference also to FIG 2 and FIG 3. It can be seen that in use, rotation of the rotor 6 causes displacement of the cavity 16 and the motive fluid contained therein.

The motive fluid is injected, pumped or inserted into the inlet arrangement and passes through the inlet 18 and into the cavity at a position downstream, i.e. in the flow direction, of the valve 24. The presence of the valve 24 and seal 26 prevents the motive fluid from flowing in the counter flow direction, which in FIG. 1 is shown as anticlockwise, i.e. the valve 24 is a one-way valve and permits fluid flow in a single direction only. Consequently, the motive fluid is retained within the cavity 16 downstream of the valve. As more motive fluid is inserted into the cavity 16, the pressure of the motive fluid in the cavity 16 increases. When the pressure of the motive fluid in the cavity 16 reaches the activation pressure, the rotor 16 beings to rotate in the direction of the flow direction, shown by arrow A, which in FIG. 1 is a clockwise direction. The radially moveable valve 24 continuously remains in contact with the surface of the rotor 6, thereby maintaining seal 26. The valve 24 is pushed radially inwards towards the rotor 6 by the continued influx of the motive fluid through the inlet arrangement. As the rotor 6 rotates in direction A, the lobes 8 will also rotate. As the lobes 8 pass the inlet 18, the lobes will fluidly isolate the cavity 16 from the inlet 18, thereby forming a discrete quantum of the motive fluid within the cavity 16. At such point, a cavity disposed on the opposing side of the rotor 6 will simultaneously fluidly contact the inlet 18, and the process will continue. As the rotor 6 continues to rotate, the discrete quantum of the motive fluid contained in the first cavity will fluidly contact the outlet port 28, where the motive fluid will escape through the outlet channel 30 and outlet chamber 32 to the exterior of the stator 4. The aforementioned process will continue while the ingress of the motive fluid through the inlet 18 is maintained. It will be understood that at a point where the lobe 8 is exactly aligned with the inlet 18, the inlet 18 will be blocked. At such point, the motive fluid is not able to enter the cavity 16 and thus cannot exert a pressure and/or force on the lobe 8 of the rotor 6 and consequently, there is a risk that the rotor 6 will stop turning. However, it is likely that during use, the momentum of the rotor 6 will cause the lobe to pass the inlet 18 so that the process can continue in spite of the temporary lack of propulsion. Nevertheless, this risk is prevented with the use of multiple stages of the rotary drive 1 , in which the rotor 6 of a first stage is angled relative to the rotor 6 of an adjacent second stage. By such provision, while a lobe of the rotor 6 of the first stage is aligned with the inlet, and thus exerting no propulsive force, the lobe of the rotor of the second stage is positioned such that the inlet 18 is fluidly connected to the cavity 16, thereby providing the propulsive force (illustrated in FIG. 2 and FIG. 3). As the plurality of stages are connected together, movement of a single stage will cause movement of the other stages. This configuration allows each stage to be phased relative to other stages. It will be understood that the rotary drive 1 may comprise any number of stages. In a similar manner to the number of cylinders in an automotive engine, the greater the number of stages, the more smooth the transmission of power is likely to be.

As described above, the presence of the valve 24 and seal 26 prevents the motive fluid from flowing in the counter flow direction. Consequently, the motive fluid is forced to take a flow path which at least partially circumnavigates the stator 4 and rotor 6.

The total distance of the flow path between the inlet and the outlet in the flow direction is longer than the distance of the flow path in the counter flow direction between the inlet and the outlet. By such provision, the circulation of the motive fluid is forced to travel around at least a portion of the circumference of the stator 4 and the rotor 6, i.e. in the flow direction, and not in the counter flow direction. For example, the motive fluid is forced to circumnavigate at least a portion of the rotor 6 in a direction towards a corresponding outlet channel 30 and not bypass, shortcut, or short circuit, i.e. flow in the counter flow direction to a different outlet.

The region of the flow path in a counter flow direction between the valve 24 and the outlet channel 30 defines as a stripper region.

FIG. 2 is an embodiment in which the rotary drive 1 comprises three stages, each offset by 120 degrees, the cross sectional profiles of which are shown in FIG. 2(a) to FIG. 2(c). The rotary drive 1 is shown at an initial time point, t=0. FIG. 2(a) shows the rotor 6 of a first stage in which the rotor 6 is positioned at 0 degrees, i.e. the lobes are directly in line with the inlet, generally denoted 40.

FIG. 2(b) shows the rotor 106 of a second stage of the rotary drive 101 , in which the rotor 106 is positioned at 120 degrees, i.e. 120 degrees relative to the rotor 6 of FIG. 2(a). The rotary drive 101 is generally similar to the rotary drive 1 of FIG. 1 and FIG. 2, like parts being denoted by like numerals, but incremented by Ί00’.

FIG. 2(c) shows the rotor 206 of a third stage in which the rotor 206 is positioned at 240 degrees, i.e. 240 degrees relative to the rotor 6 of FIG. 2(a). The rotary drive 201 is generally similar to the rotary drive 1 of FIG. 1 and FIG. 2, like parts being denoted by like numerals, but incremented by ‘200’.

FIG. 3 is an embodiment of the rotary drives 1 , 101 and 201 of FIG. 2 at an increased time relative to FIG. 2, for example at a later time point, t=0+n, where n is the time increment, in which the rotor 6, 106, 206 has rotated through 45 degrees. The rotors 6, 106, 206 are shown to have rotated in the flow direction indicated by the arrow. The cross sectional profiles of the rotary drives 1 , 101 , 201 are shown in FIG. 3(a) to FIG. 3(c).

FIG. 3(a) shows the rotor 6 of a first stage of the rotary drive 1 , in which the rotor 6 has repositioned to 45 degrees, i.e. 45 relative to FIG. 2(a).

FIG. 3(b) shows the rotor 106 of a second stage of the rotary drive 101 , in which the rotor 106 has repositioned to 165 degrees, i.e. 165 degrees relative to the rotor FIG. 2(b).

FIG. 3(c) shows the rotor 206 of a third stage of the rotary drive 201 , in which the rotor 206 has repositioned to 285 degrees, i.e. 285 degrees relative to FIG. 2(c).

FIG. 4 shows an embodiment of the present invention in which the lobes 408 of the rotary drive 401 comprise a seal 460.

The rotary drive 401 is generally similar to the rotary drive 1 of FIG. 1 and FIG. 2, like parts being denoted by like numerals, but incremented by ‘400’.

In this embodiment, the clearance 412 between the lobes 408 and stator 404 is reduced by the presence of seal 460. The seal may be a metal seal, for example, a soft metal seal, in which the tip of the lobe 408 comprises a soft metal portion, such as aluminium, lead (Pb), copper alloys or any other suitable soft, malleable metal. The soft metal seal may comprise stainless steel. Alternatively or additionally, the seal may comprise a temperature-resistant polymer, e.g. a thermoplastic polymer , for example, polyether ether ketone (PEEK) or the like. The presence of seal 460 reduces the relative importance of the clearance 412 since any gap, space or void between the lobes 408 and stator 404 is occupied by the seal 460, thereby ensuring that the cavity 416 is fluidly sealed.

As described above, this applies similarly to a second inlet arrangement, in which like parts are denoted by like numerals, but represented as 416’, 418’, 420’ 422’, 424’, 426’, 428’ and 430’.

For example, the motive fluid which enters the cavity 416’ through inlet 418 will circulate through the cavity 416,416’ and exit the cavity 416 through outlet port 428 and outlet channel 430.

A motive fluid which enters the cavity 416’ through inlet 418’ will circulate through the cavity 416’, 416 and exit the cavity 416 through outlet port 428’ and outlet channel 430.

Referring now to FIG. 5 there is shown a longitudinal view of the rotary drive. FIG. 5(a) shows the rotary drive at a first time and FIG. 5(b) shows the rotary drive at a second, later time, where the rotor 6,106,206 has rotated through 90 degrees relative to the position of FIG. 5(a).

The casing 2 is shown as a wire line for improved clarity of the internal components of the rotary drive.

The rotary drive comprises three stages with each rotor 6,106,206 being angularly offset or “clocked” relative to each other. Each stage comprises the same components and has an identical assembly, other than the offset alignment. The valves 24,124,224 of the stages take the form of cylindrical rollers which are fitted within the slot of the inlets 140,240 of each stage (the inlet of the first stage is not visible in FIG. 5). The valves 24,124,224 are supported within the slots by the valve supports 20,120,220 which prevent the valves 24,124,224 from moving in a lateral and/or circumferential direction within the slot of the inlets 140,240. A motive fluid is permitted to flow from inlets 140 to a respective cavity via gaps provided between adjacent supports 20,120,220.

Without the provision of the valve supports 20,120,220, there would be a risk that the valve 24,124,224 may vibrate and/or flutter within the slot and/or inlets 140,240, thereby not forming a fluid seal. Consequently, a poor fluid seal would permit the motive fluid to escape and/or bypass the rotor 6,106,206, i.e. would short circuit the fluid flow path, thereby not applying a force on the lobe 8,108,208, thereby not rotating the rotor 6,106,206. Advantageously, the valve supports 20,120,220 support the valve 24,124,224 in position to ensure an adequate fluid seal is achieved and ingress or injection of the motive fluid causes rotation of the rotor 6,106,206.

In this embodiment the valve supports 20,120,220 take the form of a rectilinear profile which protrudes from the wall of the slots of the inlets 140,240 in a circumferential direction. The faces of the valve supports 20,120,220 adjacent the valves 24,124,224 comprise a smooth surface with negligible friction such that whilst the valves 24,124,224 are supported to prevent or limit movement in a lateral and/or circumferential direction, the valves 24,124,224 are free to move in a radial direction, for example, perpendicular to the lateral and/or circumferential direction. The freedom of movement of the valves 24,124,224 in the radial direction permits the valves 24,124,224 to move and be repositioned by the asymmetric cross-sectional profile of the rotors 6,106,206 and lobes 8,108,208. By such provision, as the rotor 6,106,206 rotates, the lobes 8,108,208 apply a force on the valves 24,124,224, moving them in a radial outwards direction away from the axis of rotation of the rotor. As the rotor 6,106,206 continues to rotate and the lobes 8,106,206 pass the valves 24,124,224, the valves 24,124,224 move in a radial inwards direction towards the axis of rotation. This permits the valves 24,124,224 to remain in continuous contact with the lobes 8,108,208 ensuring a continuous seal to be achieved. It can be seen in FIG. 5(a) that the valve 124 of the second stage is adjacent the lobe 108 and is thus in a position radially farthest from the axis of rotation, whereas in FIG. 5(b), the rotor 106 and lobe 108 have rotated through 90 degrees and the valve 124 is in a position radially closest to the axis of rotation. The same applies to each respective stage of the rotary drive as the rotor 6,106,206 rotates and the lobes 8,108,208 make contact and subsequently break contact with the valves 24,124,224.

Referring now to FIG. 6 and FIG. 7, there is shown an embodiment of the rotary drive showing an enlarged view of the inlet region 40 (FIG. 6) and a plan view of the longitudinal length of the rotary drive (FIG. 7).

As shown in FIG. 6, the inlet 18 passes radially through the stator 4 towards the cavity 16,16’. The valve 24 is disposed within the inlet 18 and takes the form of an elongated cylinder with a circular cross-section which is free to rotate about the central longitudinal axis C of the valve 24. The valve support 20 biases the valve 24 and/or maintains the valve against, adjacent or near an opposite wall (the upstream wall) of the inlet 18 (shown as the left wall in FIG. 6), thereby supporting and/or securing the valve 24 in a lateral position, preventing lateral movement, vibration or fluttering of the valve 24, and preventing the valve from contacting or leaning against the downstream wall of the inlet 18 (shown as the right side wall of inlet 18 in FIG. 6), and thus blocking the connection between the inlet 18 and the downstream cavity 16’.

The diameter of the valve 24 is marginally less than the width of the inlet 18 such that the valve is free to move and/or rotate within the inlet, whilst limiting the range of motion of the valve in a lateral direction and/or circumferential direction, i.e. perpendicular to the radial direction. It will be understood that it is desired for the valve 24 to have a diameter as close to the width of the inlet 18, thereby ensuring as good a seal as possible, whilst also allowing for sufficient tolerances to ensure that the valve 24 is free to rotate and/or move radially within the inlet 18 without becoming blocked or jammed within the inlet and without significant friction between the valve 24 and the inlet 18 and/or valve support 20.

While FIG. 6 shows the cross-sectional profile of the apparatus at a longitudinal midpoint of the valve support 24, it is to be understood that the inlet 18 comprises a plurality of valve supports 20 which are evenly distributed along the longitudinal length of the rotary drive and/or inlet, as shown in FIG. 7. In between adjacent valve supports 20 is a void (not visible in FIG. 6) which defines a fluid flow path between the inlet 18 and cavity 16,16’. Consequently, the valve support 20 may permit the motive fluid to travel along the fluid flow path from the inlet 18 to the downstream cavity 16’ and pass the valve 24 on the downstream side, whilst still sealing the inlet 18 from the upstream cavity 16.

As described above, the ingress of motive fluid into the inlet 18, creates a higher pressure region in the inlet 18 and the downstream cavity 16’, i.e. shown as the upper and right hand sides of the valve in FIG. 6, whereas the upstream cavity 16 (shown as the left hand side of the valve 24 in FIG. 6) is at a lower pressure. The high pressure region on the upstream side of the valve 24 in the region of inlet 18 and the downstream cavity 16’, therefore biases the valve 24 towards the rotor 6 and away from the downstream cavity 16’ (towards the upstream cavity 16), illustrated by resultant force Fff, which in FIG. 6 is shown as pointing towards lower left corner.

This is further enhanced since the centre point C of the valve 24 is offset towards the upstream direction (shown as left in FIG. 6) from the centre point M of the inlet 18. By such provision, a volume of motive fluid on the downstream side of the valve (upper and right side) will always be greater than a volume of motive fluid on the upstream side of the valve, thereby creating an inherent bias for the valve 24 towards the upstream (left) side. By such provision, provided that the ingress of motive fluid is maintained into the inlet 18, the valve 24 will leans against the upstream (left) wall of the inlet 18, and rotor 6, thereby ensuring a seal is maintained between the higher pressure regions in the inlet 18 and the downstream cavity 16’, and the lower pressure region in the upstream cavity 16.

As described above, the ingress and/or injection of the motive fluid into the cavity 16,16’ causes rotation of the rotor 6 in the direction A. Furthermore, the valve 24 is free to rotate about central axis C. Since the valve 24 is in contact with the rotor 6, rotation of the rotor 6 in direction A causes rotation of valve 24 in an opposite direction B. Advantageously, rotation of the valve 24 ensures that any wear, abrasion, damage or the like on the circumference and/or periphery of the valve 24, for example, caused by friction with the rotor 6 and/or inlet 18, inlet channel or the like, is evenly and/or uniformly distributed around the circumference and/or periphery of the valve 24, i.e. the valve 24 may wear evenly. By such provision, the ability of the valve 24 to seal against the rotor 6 and/or seal the cavity 16,16’ is not affected by localised damage on or at the surface of the valve 24. An imperfect seal may affect the power and/or torque generated by the rotary drive 1.

As described above, the asymmetric nature of the rotor 6, i.e. with the provision of the lobes (visible in FIG. 1 to FIG. 4), means that the radial position of valve 24 when in contact with the outer surface of the rotor 6 will vary as the rotor 6 rotates, i.e. as the rotor 6 rotates, and the lobes come into contact with the valve 24, the lobes will apply a radial force onto the valve 24, moving the valve 24 in a radial outwards direction, and as the lobe passes the valve 24, the valve 24 will be biased towards a radial inwards direction by the ingress of the motive fluid (and associated higher pressure regions) until the valve 24 abuts the surface of the rotor 6. The ability of the valve 24 to freely move radially within the inlet 18 (i.e. without significant friction or becoming blocked or jammed), permits the valve 24 to move in response to rotation of the rotor 6 and account for the lobes in this manner.

By way of example, the forces experienced by valve 24 can be calculated as follows. According to Pascal's law the force Fff resulting from the fluid pressure, will divide into two equal forces at points X and Y, of which the scalar sum is equal to Fff.

Thus Fff =1/2 Fff + 1/2 Fff

The valve 24 exerts force FP2 at point X applied perpendicularly against the surface of the stator 4, and force FP1 at point Y applied perpendicularly against the surface of the rotor 6. These forces FP1 and FP2 are equal and act in perpendicular directions to each other. The reaction forces exerted by the stator 4 at point X, and the rotor 6 at point Y, cause deformation in the valve 24 which in turn creates high and unequal contact pressures at points X and Y. This then affects the behaviour of the valve 24 through the different values of friction forces at points X and Y. The contact pressures at locations X and Y can be calculated as follows, where:

FP1 = Perpendicular force at point Y FP2 = Perpendicular force at point X v = Poison’s ratio constant = 0.3 for the materials used.

W = Width of the pressurised area.

L = Length of pressurised area.

E = Modulus of Elasticity of the materials used.

R1 = Radius of valve.

R2 = Radius of the rotor.

Fff = force on the valve as result of fluid pressure.

For valve 24 on curved surface R2 at point Y:

For valve 24 on flat surface at point X:

Where W is the width of the affected local pressure areas.

Simplifying the equations by dividing both formulae under the square root by 32 * (1-v 2 ) and multiplying by p * L * E gives: and

W x = (FP 2 * R2) 0 5

Therefore,

Wy is proportional to: and Wx is proportional to:

W x « FP2 * R2

Therefore, Wy is considerably smaller than Wx, which in turn provides that the area at point Y is smaller than that at point X.

Since pressure is force FP/W * L, a smaller value of W will result in a higher point contact pressure.

Therefore the point contact pressure at Y is higher than that at X for equal forces FP1 and FP2. The effect of this is that the valve 24 will rotate or roll at Y rather than slip against the braking force from FP2 at point X when the rotor rotates in the direction R as indicated.

It will be understood that various modifications may be made to the method and/or apparatus and/or device without departing from the scope of the invention as defined in the claims.