Improvements relating to hydraulic systems for wind turbines

Abstract

A wind turbine comprising a hydraulic system having a hydraulic fluid supply system located in a stationary reference frame, and a hydraulic fluid using system located in a rotary reference frame. A rotary union module is provided for conveying hydraulic fluid between the stationary reference frame and the rotating reference frame. The rotary union module comprises: a rotary union module having a stationary component providing a stationary hydraulic coupling in communication with the hydraulic fluid supply system, and a rotatable component providing a rotatable hydraulic coupling communicating with the hydraulic fluid using system. An adapter is provided which is configured to join to the rotary union module at the rotatable component. The adapter comprises a module-side coupling configured to interface with the rotatable hydraulic coupling of the rotary union module and a pipe-side coupling configured to interface with at least a first hydraulic pipe, wherein the adapter is provided with a first conduit extending between the pipe-side coupling and the module-side coupling, and wherein the adapter further comprises a drain passage that extends from a tapping point at the first conduit. The drain passage may be configured to lead to a low-pressure drain area such as a tank or low-pressure side of a fluid pump.

Description

[0001] IMPROVEMENTS RELATING TO HYDRAULIC SYSTEMS FOR WIND TURBINES

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a hydraulic system for a wind turbine, and a wind turbine including such a hydraulic system.

[0004] BACKGROUND OF THE INVENTION

[0005] A typical Horizontal Axis Wind Turbine (HAWT) comprises a tower, a nacelle on top of the tower, a rotor hub mounted to the nacelle and a set (usually three) of wind turbine rotor blades coupled to the rotor hub. Depending on the direction of the wind, the nacelle and rotor blades are turned and directed into an optimal direction by a yaw system for rotating the nacelle and a pitch system for rotating the blades.

[0006] In wind turbines having hydraulically-driven pitch systems, a known configuration is for a hydraulic supply system to be located within the nacelle in a stationary reference frame, whereas the hydraulic pitch system, being a hydraulic user or ‘consumer’, is located at the rotor hub in a rotary reference frame. As such, it is known to provide a rotary interface between the hydraulic supply system in the nacelle and the pitch system within the rotor hub to transport hydraulic fluid cleanly and safely. The rotary interface may include a rotary union which has a stationary coupling to receive hydraulic fluid from the hydraulic supply system and a rotary coupling to provide a rotating fluid outlet such that hydraulic fluid can be conveyed to the pitch system in the rotary reference frame. A component sometimes referred to in the art as a ‘pitch tube’ may be provided to house one or more hydraulic pipes leading from the rotary coupling of the rotary union to a corresponding coupling at the pitch system.

[0007] Effective sealing of such rotary unions and associated components can be challenging. It is against this background that the invention has been devised.

[0008] SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a wind turbine comprising a hydraulic system having a hydraulic fluid supply system located in a stationary reference frame, and a hydraulic fluid using system located in a rotary reference frame. A rotary union module is provided for conveying hydraulic fluid between the stationary reference frame and the rotating reference frame. The rotary union module comprises: a rotary union module having a stationary component providing a stationary hydraulic coupling in communication with the hydraulic fluid supply system, and a rotatable component providing a rotatable hydraulic coupling communicating with the hydraulic fluid using system. An adapter is provided which is configured to join to the rotary union module at the rotatable component. The adapter comprises a module-side coupling configured to interface with the rotatable hydraulic coupling of the rotary union module and a pipe-side coupling configured to interface with at least a first hydraulic pipe, wherein the adapter is provided with a first conduit extending between the pipe-side coupling and the moduleside coupling, and wherein the adapter further comprises a drain passage that extends from a tapping point at the first conduit. The drain passage may be configured to lead to a low-pressure drain area such as a tank or low-pressure side of a fluid pump.

[0009] A benefit of the invention is that any leaking fluid that leaks from between the first hydraulic pipe and the first conduit is able to drain to low-pressure through the drain passage. This avoids any leaking fluid making its way external to the rotary union module which could be a source of contamination.

[0010] The adapter may accommodate a single hydraulic pipe or more than one pipe. As such the adapter may be provided with a second conduit extending between the pipe-side coupling and the module-side coupling. The two pipes may be a pressurised pipe and a non-pressurised pipe. Therefore, one pipe may carry high pressure fluid to the hydraulic fluid using system wherein the other one of the pipes may carry fluid at a lower pressure back to a low-pressure area, which may be a tank or a low-pressure side of a fluid pump.

[0011] Conveniently, where there are more than two conduits in the adapter, the drain passage may extend between two of the conduits. In this way, therefore, fuel that leaks from a high- pressure area at the first conduit may drain into the relatively low pressure of the second conduit. In an alternative arrangement, the drain passage may be configured to extend to an external surface of the adapter where it can be tapped off by a low-pressure hydraulic connection.

[0012] Other configurations are possible. For example, it is also envisaged that the drain passage may extend directly into the rotating component of the rotary union module without going into the second conduit or being extended to an external surface of the adapter. Suitable passages may therefore be provided inside the rotary component to manage leaking fluid.

[0013] The tapping point may be located adjacent to a seal arrangement within the first conduit. So, any fuel that is able to leak past the seal arrangement can be drained through the tapping point and drain passage. In some examples the tapping point may be located between a first seal and a second seal of the seal arrangement. The seal arrangement may comprise annular seals such as O-rings.

[0014] The hydraulic pipe or pipes may in some examples be housed within a tubular housing. The tubular housing may be a pitch tube. The pitch tube is an elongated component having an axis. The axis may be aligned with the longitudinal direction in which the pipe or pipes extend.

[0015] A particular benefit of the invention is that it serves as a leakage prevention measure where the pipe or pipes are received into the adapter in such a way that they are able to slide axially somewhat (that is, to have some axial play) with respect to the conduits within which they are received.

[0016] In some examples the hydraulic fluid using system is a blade pitch system.

[0017] Further optional and advantageous features are provided in the dependent claims.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will now be described, by way of example only, with reference to the attached drawings, in which:

[0020] Figure 1 is a schematic diagram of a typical wind turbine, which shows the main functional components housed within a wind turbine nacelle; Figure 2 shows a high-level schematic overview of a hydraulic system within the wind turbine of Figure 1 ;

[0021] Figure 3 shows aspects of the hydraulic system in Figure 2 in more detail;

[0022] Figure 4 shows an aspect of the hydraulic system in Figure 3 in more detail.

[0023] DETAILED DESCRIPTION

[0024] Examples of the invention will now be described in which numerous features will be discussed in detail to provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to the skilled person that the examples of the invention may be put into effect without the specific details and that in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

[0025] In order to place the examples of the invention in a suitable context, reference will firstly be made to Figure 1 , which illustrates a typical Horizontal Axis Wind Turbine (HAWT) 1. Although the wind turbine 1 is referred to as ‘horizontal axis’, it will be appreciated by the skilled person that for practical purposes the axis is usually slightly inclined to prevent contact between the rotor blades and the wind turbine tower in the event of strong winds. The examples of the invention are applicable to other types of wind turbines, for example vertical axis machines.

[0026] The wind turbine 1 comprises a tower 2, a nacelle 4 rotatably coupled to the top of the tower 2 by a yaw system 6, a rotor hub 8 mounted to the nacelle 4 and a plurality of wind turbine rotor blades 10 coupled to the rotor hub 8. The nacelle 4 and rotor blades 10 are turned and directed into the wind direction by the yaw system 6.

[0027] The nacelle 4 houses many functional components of the wind turbine, including a gearbox 12, a generator 14 and a power converter system 16 for converting the mechanical energy of the wind into electrical energy for provision to the grid.

[0028] The gearbox 12 is driven by a low-speed main shaft 20 that is coupled to the rotor hub 8 and which extends into the nacelle 4. The main shaft 20 is supported on a suitable bearing (not shown). The main shaft 20 is driven by the rotor hub 8 and provides input drive to the gearbox 12. The gearbox 12 steps up the rotational speed of the low-speed main shaft 20 via internal gears (not shown) and drives a high-speed drive shaft 22. The drive shaft 22 in turn drives the generator 14, which converts the rotation of the drive shaft 22 into electricity. The electricity generated by the generator 14 is then converted by the power converter system 16 as required before being supplied to an appropriate consumer (e.g. an electrical grid), by a suitable conductor 26. In some arrangements the gearbox 12 and generator 14 may be coupled together in an integrated unit.

[0029] The gearbox 12 may be configured in various ways. For example, in some applications epicyclic or ‘planetary’ gearboxes may be used. As the skilled person would know, an epicyclic gearbox comprises a series of planet gears that are arranged about a central sun gear, and which collectively are arranged within an encircling ring gear. The ratio of the number of teeth between the ring gear, the planet gear and the sun gears determines the gear ratio of the gearbox. For clarity, detail of the gearbox will not be described in further detail here as the gearbox is not the principal subject of the invention. Suffice to say that other gearbox configuration could also be used, although it is currently envisaged that an epicyclic gearbox provides an elegant solution suitable for the confines of a wind turbine nacelle.

[0030] The wind turbine also includes a hydraulic system, which is shown generally in Figure 1 and in schematic form in Figure 2. The hydraulic system is indicated generally as ‘30’.

[0031] As will be noted in Figure 1 , the hydraulic system 30 comprises a hydraulic fluid supply system 32 and a blade pitch system 34. The hydraulic fluid supply system 32 is located in the nacelle 4 and the blade pitch system 34 is located in the rotor hub 8.

[0032] The hydraulic fluid supply system 32 communicates with the blade pitch system 34 byway of a hydraulic conduit 36. The hydraulic conduit 36 is shown in Figure 1 in schematic form and extends through the generator 14, drive shaft 22, gearbox 12 and main shaft 20. Notably, the hydraulic conduit 36 extends along the rotational axis of the drive shaft 22, the main shaft 20, the generator 14 and the gearbox 12.

[0033] It should be noted at this point that the blade pitch system 34 is a user or ‘consumer’ of hydraulic fluid and so may be referred to more generally as a hydraulic fluid using system. The hydraulic conduit 36 is configured to house one or more hydraulic pipes for carrying hydraulic fluid from the hydraulic fluid supply system 32 and the blade pitch system 34. The hydraulic conduit 36 may also serve to house electrical power supply and data cables, as would be understood by the skilled person. Although in general it is known to provide electrical connections and cables in such a rotary union, the electrical aspects are not a focus of this application and so will not be discussed in detail so as not to obscure the invention. The skilled person would be aware of the necessary electrical aspects of rotary unions.

[0034] The hydraulic conduit 36 may also be known in the art as a ‘pitch tube’. An example of a pitch tube is disclosed in W02020 / 221403.

[0035] It should be appreciated at this point that the hydraulic fluid supply system 32 is shown schematically in Figure 1 and that its location in the Figure is merely illustrative. In practice, the hydraulic fluid supply system 32 may comprise many components such as hydraulic fluid accumulators, pipes, connectors and pumps that may be distributed about the interior of the nacelle 4.

[0036] In Figure 2, the hydraulic system 30 is shown in more detail. In this Figure, the hydraulic fluid supply system 32 is shown as communicating with a rotary union module 40. As is known in the art, a rotary union is a device for transferring various service functions, such as hydraulic fluid supply and electrical power supply between a stationary frame of reference and a rotating frame of reference. Therefore, it is by means of the rotary union module 40 that the supply of hydraulic fluid may be transferred from the hydraulic fluid supply system 32 located in the stationary reference frame within the nacelle of the wind turbine, to the blade pitch system 34 which is located in the rotor hub 8 in the rotating reference frame.

[0037] The design and structure of rotary unions is generally known in the art and so further discussion on this will not be provided here in order not to obscure detail of the invention. However, it should be noted that the rotary union module 40 comprises a stationary part 42 connected to the hydraulic fluid supply system 32 and a rotary part 44 connected to the hydraulic conduit 36. The rotary part 44 is configured to rotate within the stationary part 42, in this example. Such an arrangement is known for typical rotary unions and so will not be discussed in further detail. At the end of the hydraulic conduit 36 proximate to the rotary union module 40, there is provided a first adapter 50. The first adapter 50 is configured to couple the hydraulic conduit 36 and the pipes contained within it to the rotary part 44 of the rotary union module 40. The first adapter 50 rotates with the rotary part 44.

[0038] At the end of the hydraulic conduit 36 distal from the rotary union module 40, there is provided a second adapter 52. The second adapter 52 is configured to couple the hydraulic conduit 36 and the pipes contained within it to the blade pitch system 34. The second adapter 52 is configured to rotate with the hydraulic conduit 36.

[0039] Reference will now be made to Figure 3 which shows a more detailed view of the rotary union module 40, the hydraulic conduit 36, and the first adapter 50.

[0040] The rotary union module 40 includes a fluid supply line 54 and a fluid return line 56.

[0041] The fluid supply line 54 comprises an annular inlet gallery 58 defined in the stationary part 42. The annular inlet gallery 58 has an inlet port 60 which leads from an outer surface of the stationary part 42 to the annular inlet gallery 58. The inlet port 60 can be connected to a fluid inlet connection as indicated by the arrow 62.

[0042] The fluid return line 56 comprises an annular outlet gallery 64 also defined in the stationary part 42. The annular outlet gallery 64 has an outlet port 66 which leads from the outer surface of the stationary part 42 to the annular outlet gallery 64. The outlet port 66 can be connected to a fluid outlet connection as indicated by the arrow 68. The fluid outlet connection 68 may be connected to a low-pressure part of the system, which may be a low-pressure fluid tank or a low-pressure side of a hydraulic supply pump, for example.

[0043] In the rotary part 44 of the rotary union module 40, the fluid supply line 54 comprises a fluid supply passage 70. The fluid supply passage 70 leads from the annular inlet gallery 58 to a first port 72 provided at the end of the rotary part 44.

[0044] The rotary part 44 is also provided with a fluid return passage 74. The fluid return passage 74 leads from the annular outlet gallery 64 to a second port 76 at the end of the rotary part 44. Together, the first port 72 and the second port 76 provide a module-side coupling to couple the pipe or pipes within the rotary adapter 50 to the rotary part 44 of the rotary union module 40.

[0045] The first rotary adapter 50 is coupled to the rotary part 44 of the rotary union module 40. The coupling may be achieved in various ways but in Figure 3 the coupling is shown by way of a bolted connection illustrated by hidden threaded rods 78.

[0046] The first rotary adapter 50 is also coupled to the hydraulic conduit 36. The coupling between these components may be achieved in various ways. As shown in Figure 3 the coupling is achieved by way of an annular connection collar 80. The connection collar 80 supports a set of radially arranged bolts 82 that complete the coupling between the first rotary adapter 50 and the hydraulic conduit 36. It should be noted that the configuration of the connection collar 80 should not be considered limiting.

[0047] The function of the first rotary adapter 50 is to serve as a connection point to enable the hydraulic conduit 36 to be connected mechanically to the rotary union module 40 but also as a means to couple hydraulic pipework within the hydraulic conduit 36 to the rotary union module 40 fluidically.

[0048] As can be seen in Figure 3, the hydraulic conduit 36 is in the form of a generally hollow tube and houses two hydraulic pipes in its interior. A first one 84 of the hydraulic pipes is fluidically coupled to the fluid supply line 54. The second one 86 of the hydraulic pipes is coupled to the fluid return line 56.

[0049] The fluidic coupling of the hydraulic pipes 84, 86 is provided by way of a pair of transfer passages provided in the first adapter 50.

[0050] A first transfer passage or conduit 88 connects between the fluid supply line 54 in the rotary part 44 of the rotary union module 40 and provides a first receiving port or socket 90 for receiving an end of the first hydraulic pipe 84. Since the first hydraulic pipe 84 is connected to the fluid supply line 54 the first hydraulic pipe 84 will now be referred to as the hydraulic supply pipe 84. The direction of fluid flow within the hydraulic supply pipe 84 is illustrated by the fuel flow arrow marked ‘A’. A second transfer passage or conduit 92 connects between the fluid return line 56 in the rotary part 44 of the rotary union module 40 and provides a second receiving port or socket 94 for receiving an end of the second hydraulic pipe 86. Since the second hydraulic pipe 86 is connected to the fluid return line 56, the second hydraulic pipe 86 will now be referred to as the hydraulic return pipe 86. The direction of fluid flow within the hydraulic return pipe 86 is illustrated by the fuel flow arrow marked ‘B’.

[0051] Together, the sockets 92,94 provide a pipe-side coupling for coupling the adapter 50 to the pipes 84,86 of the hydraulic coupling 36.

[0052] It will be observed in the illustrated example that the hydraulic supply pipe 84 and the hydraulic return pipe 86 within the hydraulic conduit 36 are not connected to the first rotary adapter 50 by a rigid hydraulic coupling. Instead, the pipe 84,86 are received into the respective passages 88,92 in a ’floating’ arrangement. This permits an amount of relative axial movement to occur between the pipes 84,86 and the passages 88,92 which is useful for compensating for mechanical tolerance in the system which may otherwise put stress on the pipes and connections. Therefore, in practice the pipes 84,86 may slide back and forth slightly within their respective passages 88,92 during rotation of the hydraulic conduit 36.

[0053] In more detail, it will be noted that the hydraulic supply pipe 84 is not rigidly connected to the respective first transfer passage 88 but is sealed in the passage 88 by a first sealing arrangement 96.

[0054] Similarly, the hydraulic return pipe 86 is not rigidly connected to the second transfer passage 92 but is sealed in the passage 92 by a second sealing arrangement 98.

[0055] The sealing arrangements 96,98 are shown in more detail in Figure 4.

[0056] In this example, the first sealing arrangement 96 comprises a pair of annular sealing rings 100a, 100b that are spaced axially along the first transfer passage 88. The annular sealing rings 100a, 100b may be any type of annular seal sufficient to seal between a pipe and a bore.

[0057] The second sealing arrangement 98 also comprises a pair on annular sealing rings 102a, 102b which are spaced apart along the second transfer passage 92. The sealing rings 102a, 102b may be any type of annular seal sufficient to seal between a pipe and a bore.

[0058] As shown in Figure 4, the sealing rings 100a, 100b, 102a, 102b are shown as captive in the first rotary adapter 50 and seal against the respective pipes 84,86. However, this is just exemplary and other configurations are acceptable. For example, the sealing rings 100a, 100b, 102a, 102b may be captive on their respective pipes 84,86 and seal against the respective transfer passages 88,92.

[0059] As has been discussed above, it is expected that during use the rotational movement of the pitch system 34 and the hydraulic conduit 36 may cause some axial movement back and forth of the hydraulic supply pipe 84 and the hydraulic return pipe 86. In most circumstances, it is expected that the sealing arrangements 96,98 will be sufficient to prevent any leakage of hydraulic fluid. However, there is a risk that over time the relative movement of the pipes 84,86 against the sealing arrangements 96,98 may reduce the effectiveness of those seals. This issue may be particularly of concern in respect of the hydraulic supply pipe 84 since it carries hydraulic fluid at a much higher pressure compared to the hydraulic return pipe 86. For example, the pressure within the hydraulic supply pipe 84 and passages connected to it is expected to be between 2500 psi and 3000psi.

[0060] To guard against leakages of hydraulic fluid from the first adapter 50, there is provided a leakage drain passage 104. The function of the leakage drain passage 104 is to convey any high-pressure hydraulic fluid that compromises the first seal arrangement 96 to a lower pressure area of the system.

[0061] In the illustrated example, the leakage drain passage 104 is fluidly connected to a tapping point 106 at the first seal arrangement 96. More specifically, the tapping point 106 is located between the first sealing ring 100a and the second sealing ring 100b. Therefore, if high pressure fluid manages to leak past the second sealing ring 100b and into a chamber 108 between the first and second sealing rings 100a, 100b, any leakage fluid in the chamber 108 can drain off into the leakage drain passage 104. Here, the tapping point 106 is shown as an opening providing fluid communication between the leakage drain passage 104 and the chamber 108. It is currently preferred for there to be provided two sealing rings, such that the second sealing ring 100b is the primary seal against high pressure fluid in the transfer passage 88 which the first seal 100a is a backup seal to capture any fuel that is able to compromise the second seal 100b. The drain passage 104 is therefore operable to evacuate fuel from the low-pressure side of the seal arrangement 96.

[0062] In the illustrated example, the leakage drain passage 104 connected from the tapping point 106 at the first transfer passage 88 to a tapping point or outlet 110 at the second transfer passage 92. Notably, the tapping point 110 is positioned downstream from the second sealing arrangement 98, considered the direction of fluid flow B.

[0063] The provision of the outlet 110 at the second transfer passage 92 therefore provides a means for leaked hydraulic fluid to drain from a high-pressure area of the system to a low- pressure area of the system. Since fluid flow in the second transfer passage 92 is flowing towards the fluid return line 56 in the rotary union module 40, the leaked hydraulic fluid is able to flow back to a low-pressure part of the system, which may be to a low-pressure tank, or to a low-pressure supply for a hydraulic pump, for example.

[0064] The leakage drain passage 104 is shown in this illustrated example as an internal passageway such as a drilling within the first adapter 50. This may be a convenient way to provide such a passage which may minimise the length of the passage. However, other examples are possible within the inventive concept.

[0065] A second example of leakage drain passage 105 is shown in Figure 3 and 4. Here, the second leakage drain passage 105 is shown as extending from a second tapping point 112 at the chamber 108 and extends radially from the second tapping point 112 to an opening 113 in an external surface 114 of the first adapter 50, as can be seen by reference to Figure 3. The second leakage drain passage 105 is shown in dashed lines in Figures 3 and 4.

[0066] Since the second leakage drain passage 105 extends to the external surface 114 of the first rotary adapter 50, a suitable route to a low-pressure area should be provided. One way in which this may be achieved is a leak capture collar 120 (see Figure 3) that is configured to extend about the first adapter 50 to capture leaked fluid draining through the opening 113. A suitable drainage pipe 122 can be provided to allow the leaked fluid to drain to a low-pressure tank 124. The drainage pipe 122 may be in the stationary reference frame, as may be the collar 120. As a further alternative, a connection line 126 may be provided from the drainage pipe 122 to the stationary part 42 of the rotary union module 40 where it may connect to the outlet port 66.

[0067] Further alternative low pressure drainage routes may also be apparent to the skilled person.

[0068] The skilled person would appreciate that various adaptations may be made to the examples described above without departing from the inventive concept as defined in the claims.

Claims

CLAIMS1. A wind turbine (1) comprising a hydraulic system (30) having a hydraulic fluid supply system (32) located in a stationary reference frame, and a hydraulic fluid using system (34) located in a rotary reference frame, and a rotary union module (40) for conveying hydraulic fluid between a stationary reference frame and a rotating reference frame, wherein the rotary union module comprises a stationary component (42) providing a stationary hydraulic coupling in communication with the hydraulic fluid supply system, and a rotatable component (44) providing a rotatable hydraulic coupling communicating with the hydraulic fluid using system, an adapter (50) configured to join to the rotary union module (40) at the rotatable component (44), the adapter (50) comprising a module-side coupling (78) configured to interface with the rotatable hydraulic coupling of the rotary union module and a pipe-side coupling (80) configured to couple to at least a first hydraulic pipe, wherein the adapter (50) is provided with a first conduit (88) extending between the pipeside coupling and the module-side coupling, and wherein the adapter (50) further comprises a drain passage (104,105) that extends from a tapping point (106,112) at the first conduit (88).

2. The wind turbine of Claim 1 , wherein: the adapter (50) is provided with a second conduit (92) extending between the pipe-side coupling and the module-side coupling.

3. The wind turbine of Claim 2, wherein: the drain passage (104,105) extends from the tapping point (106,112) of the first conduit (88) to the second conduit (92).

4. The wind turbine of Claim 1 or Claim 2, wherein the drain passage (104,105) extends from the tapping point (106,112) at the first conduit (88) to an outlet port (113) at an external surface (114) of the adapter (50).

5. The wind turbine any one of the preceding claims, wherein the tapping point (106,112) is located adjacent to a seal arrangement (96) within the first conduit (88).

6. The wind turbine of Claim 5, wherein the seal arrangement (96) within the first conduit (88) comprises first and second sealing members (100a, 100b) spaced along the first conduit (88), and where the tapping point (106,112) is located between the first and second sealing members.

7. The wind turbine of any one of the preceding claims, wherein the adapter (50) is configured for connection to a tubular housing (36).

8. The wind turbine of any one of the preceding claims, wherein the tubular housing (36) extends along an axis which is aligned with the direction along which the first conduit extends.

9. The wind turbine of any one of the preceding claims, wherein the pipe-side coupling of the adapter (50) is configured such that the first hydraulic pipe (84) is received within the first conduit (88) with axial play.

10. The wind turbine of any one of the preceding claims, wherein the hydraulic fluid using system is a wind turbine blade pitch system.

11. The hydraulic system of Claim 10, when dependent on Claim 7, wherein the tubular housing is a pitch tube.

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