TECHNICAL FIELD

The invention relates to a pressure compensator for transferring a compensation pressure via a pressure fluid and with respect to an ambient pressure. The invention further relates to a system comprising such a pressure compensator. The system may be a bearing or a sealing system.

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. Another similar system is disclosed in US Pat. No. 3,740,057, using a pressure applying device consisting of a pressure chamber surrounding a buffer fluid reservoir with a flexible diaphragm to maintain pressures surrounding a driveshaft.

This control tank arrangement with an expandable variable volume diaphragm disclosed in GB 2078878 A has the disadvantage that temporary (irregular) pressure differentials or non-uniform flexibility of the diaphragm may cause the diaphragm to block the discharge outlet, thereby preventing further discharge of the fluid from the chamber. In arrangements wherein leaking out of the pressurized fluid via the shaft sealing parts is expected, the probability of discharge outlet blockade increases due to depletion of the pressure fluid in the chamber. Steady operation of such arrangement using the known pressure compensator demands for frequent refilling.

SUMMARY OF INVENTION

It would be desirable to provide a pressure compensator, which enables more reliable drainage of the pressure fluid. Therefore, according to a first aspect, there is provided a pressure compensator for transferring a compensation pressure via a pressure fluid and with respect to an ambient pressure, wherein the pressure

compensator is provided with a container defining a reservoir with a reservoir volume which is arranged to contain the pressure fluid, wherein 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, the cover further comprising a discharge opening, the discharge opening being arranged for discharging the pressure fluid from the reservoir volume in case of a decrease of the reservoir volume,

characterized in that the cover is provided with grooves facing the reservoir volume, wherein at least a portion of the grooves open into the discharge opening.

The grooves are in fluid communication with the discharge opening, even when the flexible container wall is fully collapsed.

The grooves together may form a pattern or network of interconnected grooves, which are in fluid communication with the discharge opening via the portion of grooves that open into the discharge opening.

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 cover closes the container opening in a leakproof manner. In general, the grooves on the inside of the cover define transversal channels or gutters along the surface of the cover, having groove openings directed toward the fluid reservoir, wherein the grooves along the closing side are in fluid connection with the fluid discharge opening. The grooves may have typical depths (D, transversal to the closing side of the cover) and widths (along the closing side) of several millimeters, depending on the expected viscosity of the pressure fluid.

The container wall may for instance be made of rubber, e.g. be formed as a rubber pouch.

In general, when the reservoir volume decreases, the fluid in the reservoir will fill the grooves and will subsequently be conveyed through the grooves along the inner side of the cover towards the discharge opening, and will finally be discharged out of the fluid reservoir through the discharge opening.

By means of these grooves, the fluid reservoir remains connected to the discharge opening, even if a compressed portion of the flexible container wall blocks the discharge opening or is pressed against part of the inner side of the cover. The grooves and the flexible container wall are dimensioned such that the flexible container wall cannot enter the grooves. Thus, no additional structures or measures, such as a screen or web near the discharge opening are required to ensure that the fluid reservoir remains connected to the discharge opening.

The presence of the grooves allows the container wall to be completely compressed and the container to be substantially entirely emptied. The grooves reliably maximize the pressure compensation capacity. Such a pressure compensator is particularly useful in underwater applications, in which the container wall is subject to substantial water pressures.

Such a pressure compensator is arranged for generating a compensation pressure substantially equal to the ambient pressure.

According to an alternative embodiment, the pressure compensator is provided with a pressure resistance or with pressure regulating device, for generating a compensation pressure that is adjustable to a value lower than the ambient pressure.

Such a pressure resistance or pressure regulating device may be provided downstream of the discharge opening and may for instance be formed by a valve or a spring loaded check valve. 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.

According to an embodiment, the pressure fluid comprises 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 seal 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 less refilling, leading to mean time between maintenance of several years, for instance 5 years. The incompressible lubricating fluid may for example comprise grease, oil or water.

According to an embodiment the grooves form an interconnected network of grooves. At least a portion of the grooves forming the network open into the discharge opening. Of course, more than one interconnected network may be formed. Each network may be formed by one or more grooves.

The grooves may form any suitable network pattern.

According to an embodiment the portion of the grooves that open into the discharge opening are formed as linear grooves. Possibly all grooves that open into the discharge opening are linear grooves. The linear grooves may extend radially with respect to the discharge opening.

The linear grooves on the inner or closing side of the cover or plate are easy to form, for example via gouging or milling. The linear grooves may be radially orientated with respect to the discharge opening. According to an embodiment, a plurality of radial linear grooves are provided, which open into the discharge opening.

In a further embodiment, several linear grooves are provided in the cover in a mutually intersecting configuration, with the discharge opening situated in a common point of intersection.

Such a groove configuration is easily manufactured, and improves the depletion effect.

According to a further embodiment the pressure compensator comprises one or more further grooves formed as circling grooves. The one or more circling grooves do not open into the discharge opening, but are connected to grooves that do open into the discharge opening.

The term "circling groove" refers herein to a groove or channel forming a closed path enclosing an inner area. The shape of a circling groove is not limited to a circle.

The circling groove intersects the several linear grooves creating a network of grooves in fluid connection with the discharge opening.

By providing such circling grooves, any or all of the linear grooves in the cover may become interconnected, in order to improve the discharge capacity.

According to yet a further embodiment, the circling grooves are provided concentrically around the discharge opening.

The circling grooves may indeed have a circular shape. Such circular symmetric grooves are easily formed via e.g. a gouging or milling while rotating the cover.

According to an embodiment the cover is provided with a ventilation discharge opening, wherein at least one of the grooves flows out into the ventilation discharge opening.

The at least one groove flowing out into the ventilation discharge opening may be a linear or a circular groove. The discharge opening may also be located at in intersection of a linear or circular groove.

The grooves together may form a network of interconnected grooves, which are in fluid communication with the ventilation discharge opening. In case more than one network of interconnected grooves are provided, each network may be provided with its own ventilation discharge opening. During filling or operation, undesired air or other compressible gas may accumulate inside the container filled with the pressure fluid, which disrupts the compensating function. A distinct ventilation discharge opening allows removal of this compressible gas from the filled container.

In an embodiment wherein the cover has linear grooves, circling grooves, as well as a ventilation opening, both the ventilation opening and the fluid discharge opening are in fluid communication with the plurality of grooves located on the cover side, in order to optimize the gas ventilation effect as well as the fluid depletion effect.

In a further embodiment, the grooves have a groove depth that increases towards the ventilation discharge opening.

For gas having a lower mass density than the pressure fluid, the pressure compensator may be held with the cover substantially horizontally oriented during ventilation. The accumulated gas inside the container will, subject to buoyancy, be forced along the deepening grooves toward the ventilation opening, and can subsequently be removed from the container.

According to an embodiment, the container wall is formed by a pouch or bellows made of the flexible deformable material.

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 container wall is provided with a container edge along a periphery of the container opening, wherein the pressure compensator is provided with a closing arrangement for leakproof attachment of the container edge to the cover.

The container edge is shaped so as to contribute to the leakproof sealing of the container by the cover. The container edge may be 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 arrangement along the entire container opening. In this manner, the leakproof closing is efficiently obtained.

The closing arrangement may be formed by any suitable closing arrangement. Preferably, the closing arrangement comprises a clamp to clamp the container edge to the cover. According to a further embodiment the container edge projects outward and spans an edge plane, wherein the closing arrangement comprises:

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

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

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 has a shape which allows to secure the container edge to the clamping flange 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, 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 leakproof sealing.

According to a further aspect, and in accordance with the advantages and effects described herein above, 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 for holding a pressure fluid at a compensation pressure, wherein a bearing seal is provided between the shaft and the shaft housing shielding the shaft compartment with respect to an environment having an ambient pressure,

wherein the system further comprises a pressure compensator according to the above, wherein the shaft compartment is in fluid communication with the discharge opening of the pressure compensator and wherein the container wall is subject to the ambient pressure.

The system may be also be referred to as a bearing system or a sealing system. According to an embodiment the shaft compartment is in fluid communication with the discharge opening by means of a supply pipe and the system comprises a pressure resistance or pressure regulating device positioned in the supply pipe.

The pressure resistance or pressure regulating device is provided for reducing the compensation pressure supplied to the shaft compartment with respect to the ambient pressure.

According to an embodiment the bearing seal comprises at least one lip-seal, wherein the pressure fluid inside the shaft compartment and the reservoir is an incompressible lubricating fluid for lubricating the lip-seal. The lip-seal may be in a concentric configuration with respect to the shaft.

According to an embodiment the at least one lip-seal comprises multiple lip-seals, which are arranged in a concentric configuration with respect to the shaft.

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. 1 schematically shows a side view of an embodiment of a bearing system;

Fig. 2 presents a side view of a pressure compensator according to an

embodiment;

Figs. 3a and 3b show a bottom view and a cross-sectional view of a cover of a pressure compensator according to an embodiment;

Figs. 4a and 4b show a top view and a cross-sectional view of a clamping flange of a pressure compensator according to an embodiment.

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. l schematically shows a bearing system 48 for underwater use, comprising a bearing arrangement 50 and a pressure compensator 2 for transferring a compensation pressure PI via a pressure fluid 6 to a 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 holding the pressure fluid 6. A plurality of lip seals 53 is provided between the shaft 54 and the shaft housing 56, arranged concentrically with respect 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 53.

The pressure compensator 2 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 when subjected to pressure differentials between the ambient pressure

P2 and the compensation pressure PI .

The pressure compensator 2 is via a supply pipe 32 connected to the shaft compartment 58. The supply pipe 32 is connected to a discharge opening 22 provided in the cover 12.

The shaft compartment 58 and the reservoir are in fluid connection, and an ambient pressure P2 exerted on an outside of the flexible container wall 8 transfers by means of the pressure fluid 6 via the supply pipe 32 a compensation pressure PI to the shaft compartment 58.

In the embodiment shown in Fig.1, a spring loaded check valve 34 is provided in the supply pipe 32, which generates a pressure reduction over the lip seals 53. Hence, the pressure inside the sealed shaft compartment 58 will be lower than the

compensation pressure PI inside the pressure compensator 8, which (approximately) equals the water pressure P2 outside the system 48. In another embodiment (not shown), the supply pipe 32 could also be connected to a compartment between two lip seals 53.

Fig.2 presents a side view a further embodiment of a pressure compensator 2. Again, the pressure compensator 2 comprises a flexible container wall 8, defining a container opening 9, which is closed by a cover 12. The cover comprises a discharge opening 22. The flexible container wall 8 and the cover 12 form a container 4 defining a reservoir 5. Also present is the supply pipe 32 which is connected to the discharge opening 22 by means of a bolt 23. The bearing arrangement 50, the lip-seals 53 and the shaft compartment 58 are shown schematically.

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 and can be closed by a cap 28.

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 a clamp for clamping the container wall 8 to the cover 12 to provide a substantially leakproof connection. Both embodiments of Fig. 1 and Fig. 2 may comprise a cover 12 provided with grooves on the side of the cover facing the reservoir. The grooves together form a network of pattern of grooves, whereby the grooves open into the discharge opening 22. Some grooves may open into the discharge opening directly, other grooves may open into the discharge opening via other grooves.

Fig. 3a shows an embodiment of a cover 12, having a discharge opening 22 in the middle and comprising linear grooves 18, in this case four linear grooves 18 radially directed with respect to the discharge opening 22. The linear grooves 18 open into the discharge opening 18. This means that the grooves are in direct fluid communication with the discharge opening 22, even when the flexible container wall 8 is compressed and (partially) lies against the cover 12.

The cover 12 may further comprise a plurality of circling grooves 19. The embodiment shown in Fig. 3a shows one circling groove 19, which in Fig. 3a is a round groove, positioned concentrically with respect to the discharge opening and intersects all linear grooves 18.

Also shown in Fig. 3a are the supply opening 26 and the ventilation discharge opening 30. The supply opening 26 and or the ventilation discharge opening 30 may also be provided on one of the grooves 18, 19. In particular, the ventilation discharge opening 30 may be positioned such that the grooves open into the ventilation discharge opening 30 to ensure that gas/air trapped in the reservoir can escape.

Fig. 3b shows a cross sectional view of Fig. 3a, in which it is shown that the grooves have a groove depth D (distance from bottom of groove to surface of cover 12, wherein the groove depth D increases towards the ventilation discharge opening 30, to facilitate ventilation.

Fig. 4a show a cross sectional top view of a clamping flange 14, which is part of a closing arrangement 14, 16 used to attach the container wall 8 to the cover 12. Fig. 4b shows a cross sectional view (as indicated in Fig. 4a), of the clamping flange 14, together with part of the container wall 8

As can be seen in Fig. 4b, the container wall 8 is provided with a container edge 10 along a periphery of the container opening 9. The container edge 10 projects outward and spans an edge plane, whereby the container edge 10 comprises a thickening 11 towards the outer peripheral edge.

The closing arrangement 14, 16 comprise a clamping flange 14. The clamping flange 14 comprise a groove 15 formed to receive the thickening 1 lof the container edge 10. The thickening 11 and the groove 15 are shaped to be form- fitted.

The clamping flange can be clamped to the cover 12 by suitable flange connectors, thereby clamping the flexible container wall 8 to the cover 12.

Both the clamping flange 14, the cover 12 comprise holes 17 through which a screw or nut can be passed which can be secured by one or more bolts 16.

The screws or nuts may be part of the frame.

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.