TECHNICAL FIELD

The invention relates to a pressure compensator and a system for use in a pressurized atmosphere or medium comprising such a pressure compensator.

BACKGROUND ART

Patent document GB2078878A discloses pressure control tank arrangements for compensating ambient pressure acting on shaft-sealing parts of an apparatus which snugly receives a rotating shaft. In one of the embodiments, the pressure control tank comprises a protective sleeve with an expandable diaphragm body. On an enclosed side of the diaphragm body, a tank chamber is defined, having a variable volume which is filled with a pressurized medium like oil. A fluid discharge outlet provided in the control tank connects this tank chamber with a shaft chamber comprising a pressurized medium that surrounds the rotating shaft inside the apparatus. This shaft chamber is sealed by the shaft-sealing parts, which experience the ambient pressure exerted on the apparatus during use. A pressure differential between the ambient pressure acting on an outside of the expandable diaphragm body and the pressurized medium in the tank chamber causes the diaphragm body to deform. Consequently, the volume of the tank chamber will be changed until the pressurized medium inside the shaft chamber compensates for the ambient pressure acting on the shaft sealing parts.

GB2078878A shows a number of different pressure control tank arrangements, such as arrangements using bellows or reciprocable pistons.

GB2078878A provides a solution for equalizing the pressure on both sides of a seal. However, such a solution can not be used in situations where seals are used to seal different spaces which are to be kept at different pressures.

SUMMARY OF INVENTION

It would be desirable to provide a pressure compensation system which can provide two or more compensation pressures at the same time.

Therefore, according to a first aspect, according to an embodiment there is provided a system for use in a pressurized atmosphere or medium, comprising:

- a shaft housing, - a shaft which is rotatably accommodated within the shaft housing, wherein the shaft and shaft housing jointly define a shaft compartment, wherein at least three bearing seals are provided between the shaft and the shaft housing positioned at different axial positions along the shaft, the bearing seals shielding the shaft compartment with respect to an environment having an ambient pressure, creating a first space between a first and second bearing seals and creating a second space between the second and third bearing seals, the second space being closer to the shaft compartment than the first space,

wherein the system further comprises a pressure compensator for transferring a first compensation pressure via a pressure fluid to the first space, wherein the pressure compensator comprises a reservoir with a reservoir volume which is arranged to contain the pressure fluid, the internal volume of the reservoir being variable under the influence of an ambient pressure, the pressure compensator comprising a first supply pipe, the first supply pipe being in fluid communication with the reservoir and the first supply pipe being connectable to the first space,

wherein the pressure compensator comprises a second supply pipe being in fluid communication with the reservoir and the second supply pipe being connectable to the second space for transferring a second compensation pressure to the second space, wherein the second supply pipe comprises a pressure resistance or pressure regulating device positioned in the second supply pipe,

wherein the first supply pipe is in fluid communication with the first space and the second supply pipe is in fluid communication with the second space.

The bearing seals may be any suitable seal type, including lip-seals, mechanical seals such as dual cone seals or O-rings.

With such a pressure compensator, two different pressures can be applied to different spaces.

The pressure resistance or pressure regulating device causes a pressure drop and is thus used to refer to a device which causes a pressure drop. The term pressure resistance or pressure regulating device is thus used to refer to a pressure let down device.

The first compensation pressure PI may be equal to the ambient pressure P0, but may also be smaller than the ambient pressure P0. The second compensation pressure is smaller than the first compensation pressure PI . The pressure compensator may advantageous be used in systems which have an internal pressure different from an ambient pressure and in which two or more spaces are provided as barrier to bridge the pressure difference between the interior of the system (for instance being at atmospheric pressure) and the ambient pressure (for instance being 10 bar). First and second spaces are provided to bridge this pressure difference. The first space may be kept at a first pressure, the first pressure being equal to the ambient pressure (e.g. 10 bar) or may be lower than the ambient pressure (e.g. 8 bar). The second space may be kept at a second pressure lower than the first pressure (e.g. 5 bar), and may for instance be equal to or close to the internal pressure.

It will be understood that the pressure compensator may comprise any suitable number of additional supply pipes comprising additional different pressure resistance or pressure regulating devices positioned in the different additional supply pipes, with the first supply pipe optionally comprising a first pressure resistance or pressure regulating device. The pressure compensator may comprise a third supply pipe being in fluid communication with the reservoir and the third supply pipe being connectable to a third space for transferring a third compensation pressure to a third space, wherein the third supply pipe comprises a pressure resistance or pressure regulating device positioned in the third supply pipe. Optionally a fourth, fifth, sixth etc. supply pipe may be provided with respective pressure resistances or pressure regulating devices. The pressure resistances or pressure regulating devices preferably all have different characteristics to generate different compensation pressures.

Thus, according to an embodiment, the second compensation pressure is smaller than the first compensation pressure. In general the following relation will apply:

P0>Pl>P2>P _int .

According to an embodiment the first supply pipe comprises a pressure resistance or pressure regulating device.

The first supply pipe and the second supply pipe may be parallel pipes both independently being in fluid communication with the reservoir (as will be explained in more detail below with reference to Fig. lb), wherein the first and second supply pipe both comprise a respective first and second pressure resistance or pressure regulating device, or alternatively, only the second supply pipe may comprise a pressure resistance or pressure regulating device. According to an embodiment the second supply pipe branches off from the first supply pipe (as will be explained in more detail below with reference to Fig.'s la, lc, Id).

According to an embodiment the first supply pipe comprises a pressure resistance or pressure regulating device upstream with respect to the branching off of the second supply pipe.

The term upstream is used to indicate that the pressure resistance or pressure regulating device is positioned in between the branching off of the secondary supply pipe and the reservoir. This embodiment will be described in more detail below with reference to Fig. Id.

According to an embodiment the first supply pipe comprises a pressure resistance or pressure regulating device downstream with respect to the branching off of the second supply pipe.

The term downstream is used to indicate that the pressure resistance or pressure regulating device is positioned in between the branching off of the secondary supply pipe and the space. This embodiment will be described in more detail below with reference to Fig. la.

According to an embodiment the first supply pipe comprises a pressure resistance or pressure regulating device upstream with respect to the branching off of the second supply pipe and comprises a further pressure resistance or pressure regulating device downstream with respect to the branching off of the second supply pipe.

According to an embodiment the pressure resistance or pressure regulating device of the first supply pipe is arranged to cause a first pressure drop and wherein the pressure resistance or pressure regulating device of the second supply pipe is arranged to cause a second pressure drop, the second pressure drop being greater than the first pressure drop.

This way, the first pressure is greater than the second pressure.

According to an embodiment the first supply pipe and the second supply pipe both are in fluid communication with the reservoir via a shared discharge opening or via respective discharge openings.

This embodiment allows to use a pressure compensator with a reservoir having one discharge opening, resulting in a simple design of the reservoir. In case the first and second supply pipes are connected to the reservoir via different discharge openings, the pressure compensator is made more robust, as failure of one supply pipe or discharge opening will not cause a complete failure of the pressure compensation.

According to an embodiment the pressure compensator comprises a container defining the reservoir, the container comprises

- a container wall provided with a container opening , wherein the container wall is at least partially made of a flexible material that deforms if subjected to the ambient pressure, such that the reservoir volume changes,

- a cover for closing the container opening in a leakproof manner, the cover further comprising one or more discharge openings, the discharge openings being arranged to be connected to the first and second supply pipes for discharging the pressure fluid from the reservoir volume in case of a decrease of the reservoir volume thereto.

According to an embodiment the pressure fluid comprises an incompressible lubricating fluid, wherein the reservoir is arranged for retaining the incompressible lubricating fluid.

According to an embodiment at least one of the pressure resistance or pressure regulating devices is adjustable. This provides a flexible pressure compensator which can be adjusted to control the compensation pressure(s) generated by it. For instance, in case of a spring loaded check valve, the spring force may be adjusted to control the pressure drop.

According to an embodiment at least the second bearing seal in between the first and second space is a lip-seal.

According to an embodiment, the first, second and third bearing seals are lip- seals. BRIEF DESCRIPTION OF DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Fig. la schematically shows a side view of an embodiment of a bearing system comprising a pressure compensator according to an embodiment,

Fig. lb - Id schematically depict alternative embodiments of the pressure compensator, Fig. 2 presents a side view of a bearing system with a more detailed view of a pressure compensator.

The figures are meant for illustrative purposes only, and do not serve as restriction of the scope or the protection as laid down by the claims.

DESCRIPTION OF EMBODIMENTS

Fig. la schematically shows a bearing system for underwater use, comprising a bearing arrangement 50 and a pressure compensator 2 for transferring a compensation pressure via a pressure fluid 6 to spaces 41, 42 provided as barrier spaces between an internal space or sealed shaft compartment 58 located within the bearing arrangement 50. The bearing arrangement 50 has a shaft housing 56 wherein a driving shaft 54 is rotatably accommodated. The shaft 54 and the shaft housing 56 enclose the shaft compartment 58.

A plurality of lip seals 531, 532, 533 is provided between the shaft 54 and the shaft housing 56, arranged concentrically with respect to a central axis of the shaft 54, and for shielding the shaft compartment 58 with respect to the environment. The pressure fluid 6 is an incompressible lubricating fluid, here grease, for lubricating the lip-seals 531, 532, 533. The lip seals 531, 532, 533 create the first and second spaces 41, 42 in between adjacent lip seals.

The pressure compensator 2 is shown in more detail in Fig. 2 and comprises a flexible container wall 8, in this case provided by a rubber pouch 8. The container wall 8 defines a container opening 9, which is closed by a cover 12, thereby forming a container 4, which defines a reservoir 5.

The flexible container wall 8 and the cover 12 form a reservoir filled with a lubricating fluid, in this case grease 6. The reservoir has a reservoir volume Vr.

The flexible container wall 8 has a flexibility that allows the flexible container wall 8 to deform under influence of the ambient pressure P0.

The pressure compensator 2 is via a first supply pipe 32 connected to the first space 41. The first supply pipe 32 is by means of a bolt 23 connected to a discharge opening 22 provided in the cover 12.

The first space 41 and the reservoir 5 are in fluid connection, and an ambient pressure P0 exerted on an outside of the flexible container wall 8 transfers by means of the pressure fluid 6 via the first supply pipe 32 a compensation pressure PI to the first space 41.

In the embodiment shown in Fig. la and 2, a pressure resistance or pressure regulating device 34 is present in the first supply pipe 32. The term pressure resistance or pressure regulating device is used in this text to refer to a device which lets down pressure, i.e. a pressure let down device.

In this embodiment the pressure resistance or pressure regulating device 34 is provided by a spring loaded check valve 34, which generates a pressure reduction thereby providing a compensation pressure PI to the first space 41 which is lower than the ambient pressure PO. The pressure resistance or pressure regulating device 34 may also be provided by a valve.

Hence, the pressure inside the first space 41 will be lower than the compensation pressure inside the pressure compensator 8, which (approximately) equals the ambient pressure PO.

The pressure compensator 2 is via a second supply pipe 36 connected to the second space 42. The second supply pipe 36 is connected to a discharge opening 22 provided in the cover 12, which may be the same (as shown in Fig. la and 2) or a separate discharge opening 22 the first supply pipe 32 is connected to (schematically shown in Fig. lb).

The second space 42 and the reservoir 5 are in fluid connection, and an ambient pressure PO exerted on an outside of the flexible container wall 8 transfers by means of the pressure fluid 6 via the second supply pipe 36 a compensation pressure P2 to the second space 41.

In the embodiment shown in Fig. la and 2, a pressure resistance or pressure regulating device 38 is present in the second supply pipe 36. In this embodiment the pressure resistance or pressure regulating device is provided by a spring loaded check valve 38, which generates a pressure reduction thereby providing a compensation pressure P2 to the second space 42 which is lower than the ambient pressure PO. The pressure resistance or pressure regulating device 34 may also be provided by a valve.

The pressure resistance or pressure regulating device 38 present in the second supply pipe 36 creates a pressure drop which is larger than the pressure drop generated by the pressure resistance or pressure regulating device 34 present in the first supply pipe 32, thereby creating a pressure in the second space 42 which is lower than the pressure in the first space.

Hence, the pressure inside the second space 42 will be lower than the

compensation pressure inside the pressure compensator 8, which (approximately) equals the ambient pressure PO and also lower than the compensation pressure PI inside the first space 41.

This provides the advantage that two different compensation pressures can be provided using a single pressure compensator 2.

Fig. la and 2 show an embodiment wherein the second supply pipe 36 branches off from the first supply pipe 32 and both the first and second supply pipes 32, 36 comprise a pressure resistance or pressure regulating device downstream of the branching off.

Fig. lb shows another embodiment, wherein the first and second supply pipes 32, 36 are parallel and independently connected to the reservoir 5. Both the first and second supply pipes 32, 36 comprise a pressure resistance or pressure regulating device, although the pressure resistance or pressure regulating device 34 may be omitted.

Fig. lc shows an embodiment wherein the second supply pipe 36 branches off from the first supply pipe 32 and only the second supply pipe 36 comprise a pressure resistance or pressure regulating device downstream of the branching off.

Fig. Id shows an embodiment wherein the second supply pipe 36 branches off from the first supply pipe 32 and the second supply pipe 36 comprise a pressure resistance or pressure regulating device downstream of the branching off and the first supply pipe 32 comprises a pressure resistance or pressure regulating device upstream of the branching off.

Next, an embodiment of the pressure compensator 2 will be explained in more detail by reference to Fig. 2. However, it will be understood that other types of pressure compensators 2 can be used.

Cover 12 further comprises a supply opening 26 for filling and refilling the pressure fluid 6. The supply opening 26 is connected to a supply pipe by means of a bolt 24.

Cover 12 further comprises a ventilation discharge opening 30. The ventilation discharge opening 30 is used to allow trapped air/gas to escape from the reservoir 5. As can be seen in Fig. 2, the pressure compensator 2 further comprises a frame, to which the container 4, formed by the flexible container wall 8 and the cover 12, is mounted. The frame is as a protective housing and comprises means for clamping the container wall 8 to the cover 12 to provide a substantially leak proof connection.

The container wall is flexible, and will be reduced and pushed inward as a result of overpressure acting on the outside of the container wall. An inner side or closing side of the cover body is directed toward the inside of the container, and defines in a "closed state" (wherein the cover body covers the container opening) a wall or interface of the fluid reservoir. The cover is shaped such that the flexible container subject to compression is pushed against the inner side of the cover. The cover may for example be formed as a rigid plate.

The container wall 8 may be formed by a pouch or bellows made of the flexible deformable material. The container wall may for instance be made of rubber, e.g. be formed as a rubber pouch.

A pouch or bellows of flexible deformable material, e.g. rubber, is easy to manufacture or to obtain as a commercial product. This availability reduces the maintenance costs for the pressure compensator.

According to an embodiment, the pressure fluid 6 is an incompressible lubricating fluid, wherein the container is arranged for retaining the incompressible lubricating fluid.

The ability to substantially empty the reservoir is very useful for systems with movable parts and sealed intermediate compartments, wherein the sealing means can only endure slight pressure differentials with respect to the ambient pressure.

Exemplary systems may comprise a sealed bearing of a hinge or a rotation shaft that operates in a pressurized atmosphere or medium such as water, with the ambient pressure acting on the sealed bearing. The sealed compartment may be connected to the abovementioned pressure compensator, in order to provide a desired compensation pressure. The pressure fluid may simultaneously function as a lubricant for the movable parts (a so-called "pressurized lubricating fluid") to reduce friction between these parts. Any system with such a pressure compensator, wherein the pressurized lubricating fluid is also permitted to leak away a little to the environment, will require refilling. The incompressible lubricating fluid may for example comprise grease, oil or water. The container wall 8 may be provided with a container edge 10 along a periphery of the container opening 9, wherein the pressure compensator is provided with closing means 14, 16 for leak proof attachment of the container edge 10 to the cover 12.

The container edge is shaped so as to contribute to the leak proof sealing of the container by the cover. The container edge may project outwardly along the periphery of the container opening.

The container edge may also be made of the flexible material, like rubber, allowing the container edge to be firmly clamped by the closing means along the entire container opening. In this manner, the leak proof closing is efficiently obtained.

The closing means may be formed by any suitable closing means. Preferably, the closing means comprise clamping means to clamp the container edge to the cover.

According to a further embodiment the container edge 10 projects outward and spans an edge plane, wherein the closing means 14, 16 comprise:

- a clamping flange 14, arranged for clamping the container edge 10 between the clamping flange 14 and the cover, and

- flange connectors 16 for fixating the clamping flange 14 on the cover 16.

A container wall with an outward projecting container edge in a common plane around the container opening (e.g. a flat ring shape) is easily clamped between the inner or closing side of the cover and the clamping flange. The flange connectors may for example be formed by screws or nut passing through holes in the cover and in the clamping flange, which may be secured by bolts or the like. The flange connectors may possibly also pass through holes in the container edge.

According to a further embodiment, the container edge 10 has a shape which allows to secure the container edge to the clamping means in a form-fitted way. The container edge may comprise a thickening towards its outer perimeter, for instance around the perimeter of the container edge forming a peripheral ridge 11, which bulges or projects out of the edge plane. Such a thickening may be clampingly accommodated in at least one complementary shaped gutter provided in the cover and/or the clamping flange. This improves the sturdiness and reliability of the leak proof sealing.

The descriptions above are intended to be illustrative, not limiting. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice, without departing from the scope of the claims set out below.