A hydraulic actuator and a method

Abstract

A hydraulic actuator for moving a gangway, comprising a cylinder and a cylindrical shaft protruding into a cylinder interior. The cylindrical shaft has an annular shaped partitioning element defining a hydraulically controlled primary and secondary chamber for moving said cylindrical shaft. The cylindrical shaft further protrudes into a hydraulically controlled tertiary chamber such that upon pressurizing the tertiary chamber the cylindrical shaft tends to move.

Description

[0001] Title: A hydraulic actuator and a method

[0002] The invention relates to a hydraulic actuator for moving a gangway, comprising a cylinder and a cylindrical shaft that moves in the interior of the cylinder along a cylinder axis upon hydraulically pressurizing the cylinder interior.

[0003] Such hydraulic actuators are widely known for moving portions of structures. A known hydraulic actuator comprises a cylinder having a cylindrical wall surrounding an interior of the cylinder and extending along a cylinder axis between a first cylinder end and a second cylinder end; a first sealing element mounted to the cylindrical wall near the first cylinder end; a second sealing element mounted in the cylinder interior to the cylindrical wall at a position axially offset from the first cylinder end; a cylindrical shaft extending from an actuator end to a protruding end, the protruding end of the cylindrical shaft protruding, through the first sealing element, into the cylinder interior, wherein the cylindrical shaft is provided with an annular shaped partitioning element, also referred to as piston, fixedly surrounding the shaft and slidingly received in the cylinder interior between the first sealing element and the second sealing element, defining a primary chamber axially extending along the cylinder axis between the first sealing element and the partitioning element, and a secondary chamber axially extending along the cylinder axis between the partitioning element and the second sealing element, wherein the cylindrical wall is provided with a first port for hydraulic communication between the primary chamber and a first hydraulic pressure line, and with a second port for hydraulic communication between the secondary chamber and a second hydraulic pressure line, such that upon pressurizing the primary chamber the partitioning element and the cylindrical shaft tend to move along the cylinder axis towards the second sealing element, while upon pressurizing the secondary chamber the partitioning element and the cylindrical shaft tend to move along the cylinder axis towards the first sealing element.

[0004] The first and second sealing elements define a permanent axial wall of the primary and the secondary chamber, respectively, while the annular shaped partitioning element fixedly surrounding the shaft defines an intermediate wall between the primary and secondary chamber. By selectively pressurizing the primary chamber or the secondary chamber, the partitioning element, and thus also the cylindrical shaft, may be axially moved along the cylindrical axis.

[0005] Gangways are generally known, e.g. as a motion compensated gangway, for transferring a load / person from a vessel to an object such as an offshore construction, or vice versa.

[0006] The structure of the gangway may be heavy consuming a lot of energy upon moving.

[0007] It is an object of the invention to counteract at least one of the disadvantages mentioned above. It is also an object of the invention to provide a hydraulic actuator for moving a gangway that is less energy consuming.

[0008] Thereto, according to an aspect of the invention, a hydraulic actuator according to claim 1 is provided. The hydraulic actuator is provided for moving a gangway, comprising a cylinder having a cylindrical wall surrounding an interior of the cylinder and extending along a cylinder axis between a first cylinder end and a second cylinder end; a first sealing element mounted to the cylindrical wall near the first cylinder end; a second sealing element mounted in the cylinder interior to the cylindrical wall at a position axially offset from the first cylinder end; a cylindrical shaft extending from an actuator end to a protruding end, the cylindrical shaft traversing the first sealing element and the second sealing element, into the cylinder interior, wherein the cylindrical shaft is provided with an annular shaped partitioning element fixedly surrounding the shaft and slidingly received in the cylinder interior between the first sealing element and the second sealing element, defining a primary chamber axially extending along the cylinder axis between the first sealing element and the partitioning element, and a secondary chamber axially extending along the cylinder axis between the partitioning element and the second sealing element, wherein the cylindrical wall is provided with a first port for hydraulic communication between the primary chamber and a first hydraulic pressure line, and with a second port for hydraulic communication between the secondary chamber and a second hydraulic pressure line, such that upon pressurizing the primary chamber the partitioning element and the cylindrical shaft tend to move along the cylinder axis towards the second sealing element, while upon pressurizing the secondary chamber the partitioning element and the cylindrical shaft tend to move along the cylinder axis towards the first sealing element, wherein the second cylinder end is sealingly closed defining a tertiary chamber axially extending along the cylinder axis between the second sealing element and the second cylinder end, wherein the protruding end of the cylindrical shaft further protrudes, through the second sealing element, into the tertiary chamber, and wherein the cylindrical wall is provided with a third port for hydraulic communication between the tertiary chamber and a third hydraulic pressure line such that upon pressurizing the tertiary chamber the cylindrical shaft protruding end tends to move along the cylinder axis towards the second sealing element.

[0009] By configuring a tertiary hydraulically pressurizable chamber receiving the protruding end of the cylindrical shaft an additional force can be exerted on the cylindrical shaft, separately from the forces exerted by the pressures in the primary and secondary chambers, respectively, while maintaining a compact overall design of the actuator.

[0010] The invention is at least partly based on the insight that axial forces can not only be applied via the annular shaped partitioning element or piston fixed on the shaft but also via a tip area of the cylindrical shaft protruding end.

[0011] By delivering an additional force, energy needed for operating the actuator can be distributed in an efficient way. As an example, a static force can be exerted by the tertiary chamber, while a dynamic force can be exerted by the primary and secondary chambers. In principle, the static force can be maintained with a minimum amount of energy, e.g. using a gas spring providing a mainly passive balance force, thereby significantly reducing energy required for performing dynamic operations or the actuator performance in terms of speed can be approved. Then, also the total required energy for the hydraulic actuator reduces significantly. Further, the delivered static force can be functionally realized independent from the delivered dynamic force, thereby obtaining an inherent safe system wherein the static force may be maintained even in the case of power failure counteracting that a load may move in an uncontrollable manner.

[0012] Further, dimensions of the actuator geometry can be optimized for delivering static and dynamic forces, based on the insight that the force exerted by the pressure in the tertiary chamber depends on other geometry dimensions than the force exerted by the pressure in the primary and secondary chambers. Specifically, the tertiary chamber force depends on the tip area of the cylindrical shaft while the primary and secondary chamber force depends on the annular area of the partitioning element.

[0013] A hydraulic fluid pump with an electric motor is used for controlling a hydraulic pressure in the pressure chambers, enabling operation in a power regenerating mode. As an example, a four quadrants pump may be applied, driven by an electric motor such as an electric servomotor. Advantageously, a single hydraulic fluid pump can be used for controlling the hydraulic pressure in both the primary chamber and the secondary chamber, and optionally also for controlling the hydraulic pressure in the tertiary chamber, supplying pressure and flow in combination.

[0014] The invention additionally relates to a method of moving a gangway.

[0015] The invention will be further elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention. In the drawings:

[0016] Fig. 1 shows a first schematic cross-sectional view of a hydraulic actuator according to the invention;

[0017] Fig. 2 shows a second schematic cross-sectional view of the hydraulic actuator shown in Fig. 1;

[0018] Fig. 3 shows a schematic partial side view of a gangway provided with the hydraulic actuator shown in Fig. 1, and

[0019] Fig. 4 shows a flow chart of a method according to the invention.

[0020] In the figures identical or corresponding parts are represented with the same reference numerals. The drawings are only schematic representations of embodiments of the invention, which are given by manner of non-limited examples.

[0021] Fig. 1 shows a first schematic cross-sectional view of a hydraulic actuator 1 according to the invention. The hydraulic actuator 1 can be used for moving a gangway, in particular a gangway mounted to a vessel or an offshore structure such as a windmill or oil platform. Typically, the gangway facilitates a transfer of persons and / or goods between a vessel and an offshore structure. The hydraulic actuator 1 shown in Fig. 1 can be used for positioning the gangway, or a part thereof, e.g. for luffing an elongate boom unit of a gangway.

[0022] The hydraulic actuator 1 comprises a cylinder 2 having a cylindrical wall 3 surrounding an interior 4 of the cylinder 2. The cylindrical wall 3 extends along a cylinder axis A between a first cylinder end 2a and a second cylinder end 2b. The actuator 1 further comprises a first sealing element 5 mounted to the cylindrical wall 3 near the first cylinder end 2a, as well as a second sealing element 6 mounted in the cylinder interior 4 to the cylindrical wall 3 at a position axially offset, at an offset distance D from the first cylinder end 2a.

[0023] Further, the hydraulic actuator 1 comprises a cylindrical shaft 10 extending from an actuator end 10a to a protruding end 10b. Said cylindrical shaft 10 traverses the first sealing element 5 and the second sealing element 6, into the cylinder interior 4, in particular into a tertiary chamber C3 of the cylinder interior 4 as discussed below, typically aligned with the cylinder 2, parallel to the cylinder axis A. The cylindrical shaft 10 is provided with an annular shaped partitioning element, also referred to as piston 11 fixedly surrounding the shaft 10 and slidingly received in the cylinder interior 4 between the first sealing element 5 and the second sealing element 6. The partitioning element 11 is fixedly mounted to the cylindrical shaft 10 such that the partitioning element is locked against axial movement relative to the cylindrical shaft 10. The partitioning element 11 defines a primary chamber C 1 axially extending along the cylinder axis A between the first sealing element 5 and the partitioning element 11, and a secondary chamber C2 axially extending along the cylinder axis A between the partitioning element 11 and the second sealing element 6.

[0024] Upon moving the shaft 10 with the partitioning element 11 along the cylinder axis, the volume of the primary chamber Cl and the secondary chamber C2 changes accordingly. Generally, when the volume of the primary chamber Cl increases with a volume portion, the volume of the secondary chamber C2 decreases with the same volume portion, and vice versa, such that a sum of the primary chamber volume and the secondary chamber volume remains mainly constant. The second cylinder end 2b is sealingly closed defining a tertiary chamber C3 axially extending along the cylinder axis A between the second sealing element 6 and the second cylinder end 2b.

[0025] The protruding end 10b of the cylindrical shaft 10 further protrudes, through the second sealing element 6, into the tertiary chamber C3. Then, the cylindrical shaft 10 is continuous running through the first sealing element 5 and the second sealing element 6, traversing both the primary chamber Cl and the secondary chamber C2, and extending into the tertiary chamber C3.

[0026] Then, the interior 4 of the cylinder 2 includes the primary, secondary and tertiary chambers Cl, C2, C3 such that the partitioning element 11 separates the primary chamber Cl from the secondary chamber C2, and that the second sealing element 6 separates the secondary chamber C2 from the tertiary chamber C3.

[0027] The primary, secondary and tertiary chambers Cl, C2, C3 are filled with a hydraulic fluid, during operation of the actuator 1.

[0028] The cylindrical wall 3 is provided with a first port 12 for hydraulic communication between the primary chamber Cl and a first hydraulic pressure line 13, shown in Fig. 2. The cylindrical wall 3 is also provided with a second port 14 for hydraulic communication between the secondary chamber C2 and a second hydraulic pressure line 15, shown in Fig. 2.

[0029] In operation, the primary chamber Cl can be pressurized such that the partitioning element or piston 11 together with the cylindrical shaft 10 tend to move along the cylinder axis A towards the second sealing element 6. Similarly, upon pressurizing the secondary chamber C2 the partitioning element 11 together with the cylindrical shaft 10 tend to move along the cylinder axis A towards the first sealing element 5. For reasons of accurate control, the pressure in the primary chamber C 1 and the secondary chamber C2 are controlled as an ensemble, in concert, minimizing an amount of energy needed to move the cylindrical shaft 10 a desired distance along the cylinder axis A, thereby also realizing a safe and efficient operation of the hydraulic actuator.

[0030] The cylindrical wall 3 is further provided with a third port 16 for hydraulic communication between the tertiary chamber C3 and a third hydraulic pressure line 17 such that upon pressurizing the tertiary chamber C3 the cylindrical shaft protruding end 10b tends to move along the cylinder axis A towards the second sealing element 6.

[0031] In operation, the pressure in the tertiary chamber C3 can be controlled independently from the pressures in the primary chamber Cl and the secondary chamber C2. As an example, the pressure in the tertiary chamber C3 can be controlled in a static process so as to set a static or stationary axial position of the cylindrical shaft 10, while the pressures in the primary chamber C 1 and the secondary chamber C2 can be controlled in a dynamic process so as to dynamically control an axial position of the cylindrical shaft 10, e.g. for the purpose of motion compensating wherein a location of a specific portion of the gangway, e.g. its tip, is controlled to compensate for movements such as movements of a ship rolling on sea waves. In principle, the pressures in the primary, secondary and tertiary chamber Cl, C2, C3 can be controlled in another manner, e.g. such that the pressures in all chambers Cl, C2, C3 are controlled in a dynamic process. Generally, in accordance with an applied pressure control operation, the first, second and third hydraulic pressure lines 13, 15 and 17 are arranged for dynamic and / or static hydraulic communication, respectively.

[0032] In operation, a pressure in the tertiary chamber C3 exerts a force on the shaft 10 oriented towards the first end 2a of the cylinder 2, i.e. away from the second end 2b of the cylinder 2. The exerted force equals the pressure in the tertiary chamber C3 multiplied by the tip area TA of the cylindrical shaft protruding end 10b facing towards the second end 2a of the cylinder 2. On the other hand, a pressure in the primary and secondary chambers Cl, C2 may also exert a force on the partitioning element 11 on the shaft 10 along the cylinder axis A. The exerted force induced by the primary chamber Cl equals the pressure in the primary chamber Cl multiplied by the area AA1 of the annular shaped partitioning element 11 facing towards the primary chamber Cl. Similarly, the exerted force induced by the secondary chamber C2 equals the pressure in the secondary chamber C2 multiplied by the area AA2 of the annular shaped partitioning element 11 facing towards the secondary chamber C2.

[0033] The total force exerted by the pressures in the primary and secondary chambers Cl, C2 on the partitioning element 11 is the vector summation of the individual forces exerted by the pressure in the primary and secondary chambers Cl, C2, respectively.

[0034] Further, the net force exerted on the shaft 10 is the vector sum of the total force exerted by the pressures in the primary and secondary chambers Cl, C2, and the force exerted by the pressure in the tertiary chamber C3 described above.

[0035] As indicated above, the total force exerted by the pressures in the primary and secondary chambers Cl, C2 depends on the annular shaped area AA1, AA2 of the partitioning element 11, i.e. the cross sectional area of the cylinder interior 4 minus the cross sectional area of the shaft 10 at the axial position where the partitioning element 11 is mounted to the shaft 10.

[0036] A ratio of the total force exerted by the pressures in the primary and secondary chambers Cl, C2 versus the force exerted by the pressure in the tertiary chamber C3 can not only be set by controlling values of the pressures in the respective chambers, but also by selecting diameters of the shaft 10 and the cylinder 2, respectively. As an example, by varying the diameter of the cylinder 2 the annular shaped areas AA1, AA2 of the partitioning element 11 increase or decrease accordingly, while the tip area TA remains constant. As another example, by varying the diameter of the shaft 10 the tip area TA may increase while the annular shaped areas AA1, AA2 of the partitioning element 11 may decrease, or vice versa. In principle, the diameter of the cylinder 2 and the diameter of the shaft 10 can be dimensioned to arrive at a desired force ratio. In a product design, the diameter of the cylinder 2 can be kept constant while the diameter of the shaft 10 can be selected to meet pre-specified design values, thus obtaining a modular design offering flexibility in a range of force ratios range while using same or similar exterior dimensions, e.g. regarding the cylinder 2 dimensions. By dimensioning the shaft parameters, the force exerted by the pressure in the first and second chambers Cl, C2 can thus be scaled or tuned independently from the force exerted by the pressure in the tertiary chamber C3.

[0037] In the embodiment shown in Fig. 1 the actuator end 10a of the cylindrical shaft 10 and the second cylinder end 2b are provided with a corresponding mounting structure 18, 19 for moving a gangway. Additionally or alternatively, a mounting structure may be provided at another portion of the hydraulic actuator 1, e.g. at an intermediate position relative to the cylinder axis A, on the cylinder wall 3.

[0038] The annular shaped partitioning element 11 is fixedly mounted to the shaft 10, preferably in a sealing manner, such that an axial movement of the partitioning element 11 also entails a similar movement of the shaft 10, and vice versa. Further, the annular shaped partitioning element 11 is slidingly, preferably, in a sealing manner, received in the cylinder interior 4 between the first sealing element 5 and the second sealing element 6. Then, the partitioning element 11 sealingly separates the primary chamber Cl from the secondary chamber C2. Here, the first sealing element 5 and second sealing element 6 are sealingly mounted to the cylindrical wall 3, while also sealingly receiving the continuous shaft 10 so as to counteract or minimize any undesired hydraulic leakage from the primary, secondary and / or tertiary chamber Cl, C2, C3, such as along the shaft 10. In the embodiment shown in Fig. 1, the hydraulic actuator 1 further comprises a third pressure controlled container 20 hydraulically communicating, via the third pressure line 17, with the tertiary chamber C3. The third pressure controlled container 20 is accommodated in a so- called gas spring 23 comprising a gas pressurizable container 21 interfacing with the third pressure controlled container 20 via a movable membrane 24 so as to generate a static pressure in the tertiary chamber C3 for generating a passive support. The gas spring 23 further contains a gas container 22 filled with a gas, e.g. nitrogen, for pressurizing the gas pressurizable container 21 to a desired pressure level. Preferably, the gas pressurizable container has a volume sufficiently large to provide a mainly constant pressure during dynamic movements of the shaft 10 during operation of the hydraulic actuator 1. As shown in more detail in Fig. 2, the hydraulic actuator 1 also has corresponding pressure controlled containers 33, 35 connected to the first pressure line 13 and the second pressure line 15, respectively. As an alternative to the gas spring 23, another pressurizing structure can be applied such as a mechanical spring for setting and controlling a static counterpressure to the hydraulic pressure in the tertiary chamber C3.

[0039] Figure 2 shows a second schematic cross-sectional view of the hydraulic actuator 1 shown in Fig. 1. As shown, the first pressure line 13 is connected, at a first end 13a, with the first port 12, and, at a second end 13b, to a first pressure controlled container formed as a first conduit 33. Similarly, the second pressure line 15 is connected, at a first end 15a, with the second port 14, and, at a second end 15b, to a second pressure controlled container formed as a second conduit 35. Also, the third pressure line 17 is connected, at a first end 17a, with the third port 16, and at a second end 17b, to the third pressure controlled container 20 described above. In the shown embodiment, the first and second pressure lines 13, 15 contain an optional valve unit V for controlling purposes. The hydraulic actuator 1 further comprises a hydrauhc fluid pump

[0040] 36 with an electric motor 37 controlling a pressure in both the first and second pressure controlled containers 33, 35 connected to the second end 13b, 15b of the first and second pressure lines 13, 15, respectively. In the shown embodiment, a single hydraulic fluid pump 36 is applied, saving hardware components. As an example, a four quadrant pump is applied enabling pressure and fluid flow supply in two directions. The electric motor

[0041] 37 of the hydraulic fluid pump 36 can be used in a power regenerating mode, for temporarily converting hydraulic energy into electrical power. In another configuration, multiple hydraulic fluid pumps can be applied, e.g. a first electrically driven hydraulic fluid pump controlling the first pressure controlled container 33, and a second electrically driven hydraulic fluid pump controlling the second pressure controlled container 35. Further, in principle, a hydraulic fluid pump driven in another way can be applied such as a hydrauhc fluid pump driven by a combustion motor.

[0042] Generally, any pressurizing structure, including a hydrauhc fluid pump with electric or combustion type motor or a gas spring, may be provided with an electronic controlling module provided with hardware and controlling lines for controlling operation of the pressurizing structure.

[0043] In the embodiment shown in Fig. 2, the second end 15b of the second pressure line 15 is interconnected with the second end 17b of the third pressure line 17, via an intermediate conduit 41 containing a valve unit 42 in order to enable the pump 36 to pressurize the gas spring 23. Further, the shown embodiment includes a pre-loading conduit structure 43 provided with a check valve 43’ for pre-loading the first conduit 33 and the second conduit 35 mentioned above. Also, a drain conduit 44 is provided flowing hydraulic fluid from the pump 36 towards a tank for depressurizing.

[0044] Figure 3 shows a schematic partial side view of a gangway 50 provided with the hydrauhc actuator 1 shown in Fig. 1. The gangway 50 has a transfer deck 51 that can be mounted to a vessel or an offshore construction, as well as an elongate boom unit 52, such as a telescopable boom unit, movably mounted to the transfer deck 51. As described in more detail above, the hydraulic actuator 1 has a cylinder 2 and a shaft 10 movably received in said cylinder 2. Further, the shaft 10 is provided, at its actuator end, with a first mounting structure 18 that is pivotably attached to the elongate boom unit 52. Similarly, the second cylinder end 2b of the cylinder 2 is provided with a second mounting structure 19 pivotably attached to the transfer deck 51. In the shown embodiment, the actuator 1 is used for luffing the elongate boom unit 52 of the gangway 50. It is noted that the described hydraulic actuator 1 may, alternatively, be used for driving another movement of the elongate boom unit 52, e.g. a telescoping movement. Further, the described hydraulic actuator 1 may be used for moving another portion of the gangway 50, e.g. a movement of the transfer deck 51 relative to the vessel or offshore structure.

[0045] Figure 4 shows a flow chart of a method 100 according to the invention. The method 100 includes a step of using 110 a hydraulic actuator 1 described above for moving a gangway 50.

[0046] Various variations are possible. It will be clear to the skilled person that the invention is not limited to the exemplary embodiment represented here. Many variations are possible.

[0047] It is noted that the described hydraulic actuator can not merely be applied for moving a gangway, but also for moving other structures, such as the boom of a crane.

[0048] Such variations shall be clear to the skilled person and are considered to fall within the scope of the invention as defined in the appended claims.

Claims

Claims1. A hydraulic actuator for moving a gangway, comprising: a cylinder having a cylindrical wall surrounding an interior of the cylinder and extending along a cylinder axis between a first cylinder end and a second cylinder end; a first sealing element mounted to the cylindrical wall near the first cylinder end; a second sealing element mounted in the cylinder interior to the cylindrical wall at a position axially offset from the first cylinder end; a cylindrical shaft extending from an actuator end to a protruding end, the cylindrical shaft traversing the first sealing element and the second sealing element, into the cylinder interior, wherein the cylindrical shaft is provided with an annular shaped partitioning element fixedly surrounding the shaft and slidingly received in the cylinder interior between the first sealing element and the second sealing element, defining a primary chamber axially extending along the cylinder axis between the first sealing element and the partitioning element, and a secondary chamber axially extending along the cylinder axis between the partitioning element and the second sealing element, wherein the cylindrical wall is provided with a first port for hydraulic communication between the primary chamber and a first hydraulic pressure line, and with a second port for hydraulic communication between the secondary chamber and a second hydraulic pressure line, such that upon pressurizing the primary chamber the partitioning element and the cylindrical shaft tend to move along the cylinder axis towards the second sealing element, while upon pressurizing the secondary chamber the partitioning element and the cylindrical shaft tend to move along the cylinder axis towards the first sealing element,wherein the second cylinder end is sealingly closed defining a tertiary chamber axially extending along the cylinder axis between the second sealing element and the second cylinder end, wherein the protruding end of the cylindrical shaft further protrudes, through the second sealing element, into the tertiary chamber, and wherein the cylindrical wall is provided with a third port for hydraulic communication between the tertiary chamber and a third hydraulic pressure line such that upon pressurizing the tertiary chamber the cylindrical shaft protruding end tends to move along the cylinder axis towards the second sealing element, wherein the first, second and third pressure lines are connected, with their first respective end, to a corresponding port in the cylindrical wall, and with a second respective end to a corresponding pressure controlled container, the hydraulic actuator further comprising a hydraulic fluid pump with an electric motor controlling a pressure in a pressure controlled container connected to the second end of the first or second pressure line, respectively, wherein the actuator end of the cylindrical shaft and / or the second cylinder end is provided with a mounting structure for moving a gangway, and wherein the hydraulic fluid pump is operable in a power regenerating mode.

2. A hydraulic actuator according to claim 1, wherein the annular shaped partitioning element sealingly separates the primary chamber from the secondary chamber.

3. A hydraulic actuator according to claim 1 or 2, wherein the first hydraulic pressure line and the second hydraulic pressure line are arranged for dynamic hydraulic communication.

4. A hydraulic actuator according to any of the preceding claims, wherein the third hydraulic pressure line is arranged for static hydraulic communication.

5. A hydraulic actuator according to any of the preceding claims, wherein the pressure controlled container connected to the second end of the third pressure line includes a gas pressurized container.

6. A hydraulic actuator according to claim 5, further comprising a single hydraulic fluid pump controlling a pressure in both pressure controlled containers connected to the second end of the first and second pressure lines, respectively.

7. A method for moving a gangway using a hydraulic actuator according to any of the preceding claims 1-6, including a step of controlling a pressure in the primary and / or secondary and / or tertiary chamber of the cylinder.

8. A method according to claim 7, wherein a static position of the gangway is set by controlling a pressure in the tertiary chamber of the cylinder.

9. A method according to claim 7 or 8, wherein a dynamic position of the gangway is set by controlling a pressure in the primary and / or secondary chamber of the cylinder.

10. A method according to any of the preceding claims 7-9, wherein the hydraulic actuator is used for luffing an elongate boom unit of a gangway.

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