AU2015318725A1

AU2015318725A1 - A retrievable subsea apparatus with a pressure and volume compensating system

Info

Publication number: AU2015318725A1
Application number: AU2015318725A
Authority: AU
Inventors: Orjan Lag; David Muir MCCAREY; Roald Pedersen; Devraj SONAVANE; Einar WINTHER-LARSSEN
Original assignee: Aker Solutions AS
Current assignee: Aker Solutions AS
Priority date: 2014-09-19
Filing date: 2015-09-17
Publication date: 2017-03-23
Anticipated expiration: 2035-09-17
Also published as: GB2544688B; BR112017003994A2; NO20141138A1; WO2016043600A1; US20170306715A1; AU2015318725B2; NO338854B1; GB201703364D0; BR112017003994B1; GB2544688A

Abstract

A retrievable subsea apparatus (1) with a pressure and volume compensating system, the apparatus comprising: a housing (1') having in its interior a control system (9) located in a first section (3) thereof and an operating unit (6) located in a second section (4) thereof. The apparatus further comprises a penetrator (2) which constitutes an interface between the first section (3) and the second section (4), wherein the first section (3) has a substantially constant first pressure. An external pressure compensator (5, 5') is associated with the second section (4) having a second pressure. The operating unit (6) comprises at least a first sub-unit (6') and at least a second sub-unit (6"). The second section (4) is subdivided into at least a first sub-section (4') and at least a second sub-section (4") which is sealed off from the first section (4') and being associated with respective sub-unit (6', 6").

Description

PCT/N02015/050164 WO 2016/043600 1

A RETRIEVABLE SUBSEA APPARATUS WITH A PRESSURE AND VOLUME COMPENSATING SYSTEM

Background of the invention 5

The present invention relates to a retrievable subsea apparatus with a pressure and volume compensating system, the apparatus comprising a housing having in its interior a control system located in a first section thereof and an operating unit located in a second section thereof, as defined in the preamble of attached 10 claim 1.

The invention is also related to a usage of the various embodiments of the subsea apparatus, as defined in claim 31. 15 Currently, compensating may be grouped in several categories. They all work on the principle of providing a “displaceable” or flexible barrier between one environment and a second environment. The barrier may have attributes so that the pressures of the environments are within a certain ratio compared to each other. This is achieved by having different pressure areas on each side of the 20 barrier, or by having a barrier movement that is also controlled by a parallel force, such as through the stiffness of the barrier or by a separate spring.

The three most common pressure and volume compensating devices are related to: a displacement piston in a cylinder, a flexible “bellow” of e.g. a 25 polymeric material or metal, and a flexible membrane, e.g. exhibiting a rubber diaphragm.

The displacement piston relies on dynamic seals, and may leak or get stuck, and the rubber of the flexible membrane may deteriorate such as by oxidation 30 or cracking of the material, which may in the end lead to leakage.

In a subsea operating system which compensates for pressure and/or volume as regards more than one chamber in the system, then typically each chamber PCT/N02015/050164 WO 2016/043600 2 has a compensator device which has an interface to the external environment. This will inherently add to the external bulk of the subsea apparatus, such as e.g. an actuator which is to operate on subsea installations, and doubles the risk of leakage of seawater through the compensators and into the oil filled 5 chambers of the apparatus. Also, this makes it more difficult to realize an optimal, pre-defined pressure ratio between the oil filled chambers due to these chambers being controlled independently.

Such a prior art system may have compensators in “series”. The compensators 10 may be physically “stacked” onto each other. This will yield only one interface to the external environment, and the ratio between the chambers may easily be controlled. However, such a prior art arrangement again adds external bulk to the subsea apparatus. It also makes the monitoring of the position of the barrier which interfaces with the seawater, through a sensor, very difficult. This is due 15 to the second compensator in the series masking access to the first compensator as regards the sensor.

Object of the invention 20 The present invention has an object to provide an improved retrievable subsea apparatus which remedies the disadvantages of prior art systems and devices, in order to yield an apparatus which is technically simpler, has reduced weight and volume, can be made more compact and durable, facilitates easier monitoring, and presents a reduced cost of the apparatus compared to the prior 25 art.

Summary of the invention

According to the invention, the retrievable subsea apparatus comprises the 30 features of: - that a penetrator constitutes an interface between the first section and the second section, wherein the first section has a substantially constant first pressure, PCT/N02015/050164 WO 2016/043600 3 - that an external pressure compensator is associated with the second section having a second pressure, - that at least a first sub-unit and at least a second sub-unit constitute the operating unit, 5 - that at least a first sub-section and at least a second sub-section constitute the second section , - that a first liquid is located in the first sub-section, and a second liquid is located in the second sub-section, - that the second sub-section is sealed off from the first sub-.section, 10 - that the external compensator is in communication with the first sub section, - that the first sub-unit is at least partly associated with the first subsection and the second sub-unit is associated with the second subsection, and 15 - that an internal pressure compensator is configured to adjust for any pressure differences between said first and second sub-sections and is in contact with the first liquid in the first sub-section and with the second liquid in the second sub-section. 20 Further embodiments of the inventive retrievable subsea apparatus appear from the attached sub-claims 2 - 30.

The usage of the apparatus, as defined in claim 31, is in a non-limiting embodiment related to operate or adjust the state of a subsea installation by 25 letting a movable connector at a downstream region of the second sub-unit engage a moveable mating connector on the installation.

The invention is related to a novel pressure and volume compensating apparatus, and in particular, but not necessarily an apparatus commonly known 30 as a rotary subsea actuator or a subsea drive module apparatus for subsea related oil and gas industry. PCT/N02015/050164 WO 2016/043600 4

It is the intention with the present inventive apparatus to maintain the internal pressures of at least two isolated, oil-filled compartments in the apparatus to be at pre-defined ratios compared to the pressure of the outside environment.

Such environment is usually, however not always, seawater at different water 5 depths of down to 4,000 meters or even more. In other words, the external pressure outside the apparatus may vary from atmospheric pressure to more than 400 bars.

In addition to this, the ambient temperature about the actuator may vary. 10 Typically, the temperature may lie between zero and plus 50 degrees

Centigrade. Furthermore, the internal temperature of the oils used inside the apparatus may fluctuate independently from the ambient temperature. Also, compounding this, the temperatures of the oils in the at least two oil-filled subsections of the second section, may mutually fluctuate. The reason for such 15 internal fluctuation is that the apparatus has internal devices such as e.g. a motor, a control system and a transmission system, e.g. a gear assembly.

During operation of the apparatus, these devices produce different heat energies and associated therewith there may be a rise in the temperature of the 20 oil in the respective sub-section or chamber. Further, the different oil filled chambers have different devices therein, and they obviously contain different volumes of oil. This may then lead not only to different temperatures in the chambers, but also to different changes of the oil volumes caused by temperature changes. 25

In a non-limiting embodiment of the invention, the oils in the sub-sections or chambers are typically also different, implying that one sub-section may contain e.g. a dielectric silicone oil, whereas the other may contain e.g. a mineral oil or a synthetic or semi-synthetic lubrication oil. Different types of oils may have 30 different physical properties which can influence how their volumes change according to pressure or temperature changes. This property is the so-called “bulk modulus” of the oil. PCT/N02015/050164 WO 2016/043600 5

Typically, the pressure compensating means of the apparatus works by “allowing” that the oil volumes of inside the sub-section of the apparatus vary according to circumstances described above, at the same time as pre-defined pressure ratios are maintained. 5

When, due to the shortcomings of the prior art the series arrangement of compensators, the internal compensator is placed internally of the apparatus between the oil chambers, the internal bulk of the apparatus is increased. This is disadvantageous as regards the axial length or height of the apparatus. When 10 the height of the apparatus increases, so does the weight of the apparatus as well. The apparatus is typically to be of a retrievable type. This means that it may be positioned on a subsea installation as well as being retrieved therefrom e.g. by pulling action, to be replaced, and wherein such operation is to be carried out by a ROV (Remotely Operated Vehicle). However, there is a limit to 15 what weight load such a ROV may be able to operate. In many cases, it is difficult to be able to engineer the apparatus to have a low enough weight load for the ROV operation. This implies that having an internal compensator in series in a prior art configuration is a prohibitive approach. The present invention therefore aims at providing a simplified solution to the well known 20 problems and challenges.

Thus, it will be appreciated that the present invention enables a provision of an internal compensator in a “series” system that does not add to the height and weight of the actuator. This greatly increases the likelihood of achieving a 25 weight load that a ROV may handle.

Further, the present invention enables monitoring by a sensor of the position of the external compensator of the apparatus. If there occurs a leakage of oil out from the second sub-section or oil-filled chamber, this will be registered as a change of position of the external compensator. When the internal 30 compensator “compensates” for such a leak, the compensation is in turn compensated by the external compensator. Thus, the internal compensator adapts to a reduced oil volume in the second sub-section caused by the leakage. In effect, the total oil volume present in the first and second sub- PCT/N02015/050164 WO 2016/043600 6 section is reduced by the volume of leakage, and movement of the external compensator compensates such reduction when the internal compensator moves to ensure that the second sub-section will still be fully filled with oil. The oil volume in the first sub-section which contacts one face of the internal 5 compensator will thus remain unchanged due simultaneous movements of both the external compensator and the internal compensator. The internal compensator does not have to be monitored by sensors, as it will be sufficient and more easy to only monitor movement of the external compensator. 10 Brief description of the drawings

Fig. 1 shows a first embodiment of the retrievable subsea apparatus of the present invention.

Fig. 2 shows a second embodiment of the retrievable subsea apparatus of the 15 present invention.

Fig. 3 shows a third embodiment of the retrievable subsea apparatus of the present invention.

Fig. 4 shows a fourth embodiment of the retrievable subsea apparatus of the present invention. 20 Fig. 5 shows a fifth embodiment of the retrievable subsea apparatus of the present invention.

Detailed description of the invention 25 The five embodiments, which are illustrated, are non-limiting examples of the invention. The embodiment of Fig. 5 is currently the preferred mode of the invention.

In the description to follow, in a series arrangement, the compensator which 30 interfaces the external environment, and controls the first oil-filled sub-section or chamber, is named the “external compensator” 5. PCT/N02015/050164 WO 2016/043600 7

Further, in a series arrangement, in this description, we deal with two oil filled sub-sections or chambers. This does not however limit the scope of this invention to the use of only two sub-sections or chambers. In the description to follow, the compensator which controls this second oil filled sub-section or 5 chamber is named the “internal compensator”.

It will be appreciated that “at least one first sub-section” and “at least one second sub-section” should be interpreted as implying that more than one of the first and/or second sub-sections could be provided. 10

Further, the terms “at least one first sub-unit” and “at least one second sub-unit” constituted by the operating unit should be interpreted to imply that more than one of the first and/or second sub-units could be present. 15 A loss of oil in the first or second sub-section or chamber may be caused by leakages through static or dynamic seals into the environment, or internally between the different sub-sections. The invention enables through the use of the compensators of the apparatus to compensate for such leakages to a certain extent. If the leakages are excessive, the apparatus may require 20 replacement. If the oil volume in a sub-section becomes so low that the operation of the compensator will no longer be sufficient for compensation of leakage. Flowever, the embodiment of Fig. 4 and more so the embodiment of Fig. 5 is able to compensate for a larger loss of oil in the second sub-section than the other embodiments. 25

In the shown embodiments of the retrievable subsea apparatus 1 they all have a housing T and a penetrator 2, which constitutes an interface between a first section 3 and a second section 4. The first section 3 is sealed off by the penetrator 2 and has a substantially constant first pressure, suitably 30 atmospheric pressure, e.g. sea surface level atmospheric pressure. The first section 2 is a dry chamber filled with air or gas. PCT/N02015/050164 WO 2016/043600 8

The external pressure compensator 5 is associated with the second section 4, which has a second pressure. The second pressure may be equal to or suitably be above subsea pressure surrounding the apparatus housing. Suitably, the external compensator 5 can be pre-tensioned to one side thereof to cause such 5 over-pressure in the second section 4.

The external pressure compensator 5 is of a type configured to be able to compensate for a volumetric displacement of a first liquid 7 in a sub-section 4’ of the second section 4 to yield a corresponding volumetric change in a second 10 sub-section 4” of the second section 4 via the action by an internal pressure compensator which is in contact with said first liquid 7 and a second liquid 8 in the second sub-section A”. Thereby, any pressure difference temporarily arising between the pressures in sub-section 4’ and sub-section 4” will be automatically adjusted in order to retain a pressure balance between these two 15 sub-sections.

Specific preferred embodiments of the internal pressure compensator will be explained in more detail below with reference to the drawing figures 1-5, respectively. 20

The external pressure compensator 5 is configured with one side thereof to be in contact with seawater and with the other side thereof to be in contact with or surrounded by the first liquid 7. The external pressure compensator 5 should be of a material or a composition of materials, which will not deteriorate in contact 25 with seawater and in contact with a selected type of the first liquid 7. Such material is selectable suitably from a metal, a metal alloy, a rubber-type material and a plastics material, and any combination of two or more of these materials could constitute said composition. In a preferred, although non-limiting embodiment of the apparatus, the external pressure compensator 5 is a first 30 bellow open at one end and closed at the other end.

Other types of materials than those mentioned and having similar properties may be used as technical alternatives. PCT/N02015/050164 WO 2016/043600 9

Although the use of a bellow 5 is contemplated in the currently preferred embodiment of the external pressure compensator, other types of pressure compensators with capability of volumetric liquid displacement could be used. 5

The inside of the first bellow 5 is in communication with seawater via a perforated wall member 14. The outside and closed end of the first bellow 5 is surrounded by the first liquid 7. The closed end 5’ of the first bellow is linked to or communicates with a bellow movement sensor 15. The sensor 15 is suitably 10 a linear movement sensor, which may be of inductive, capacitive or resistive type.

The control system 9 communicates with the first sub-unit 6’, e.g. an electric motor, via lines 16, and the movement sensor 15 of the external pressure 15 compensator 5, i.e. the first bellow, via lines 17.

At least one first sub-unit 6’ and at least one second sub-unit 6” constitute an operating unit 6. In a specific embodiment, the first sub-unit 6’ comprises an electric motor, and the second sub-unit 6” comprises a gear assembly. The 20 second section 4 is subdivided into at least one first sub-section 4’ and at least one second sub-section 4” which is sealed off from the first section 4’. As seen from the drawings, the first bellow 5 is associated with the first sub-section 4’, the first sub-unit 6’ is at least partly associated with the first sub-section 4’, and the second sub-unit 6” is associated with the second sub-section 4”. As seen 25 from Figs. 1 -5, the first sub-unit 6’ could also at least partly extend with its housing into the second sub-section 4” to be at least partly surrounded a second liquid 8 which is located in the second sub-section 4”.

The first liquid 7, which is located in the first sub-section 4’, has a first set of 30 properties and a second liquid 8, which is located in the second sub-section 4”, has a second set of properties. The first properties are compatible with a structure and operation of the first sub-unit 6’ and the second properties are compatible with a structure and operation of the second sub-unit 6”. The first PCT/N02015/050164 WO 2016/043600 10 and second properties are suitably at least one of viscosity, dielectric property, lubrication and materials compatibility. In a currently preferred, although not limiting embodiment, the first liquid 7 has low viscosity and high dielectric properties and could be, as indicated above, e.g. a silicone oil, and the second 5 liquid 8 has suitably a high viscosity and lubrication properties and could e.g. be a mineral oil or a synthetic or semi-synthetic oil.

The first section 3 contains a control system 9 in communication with external power and communication equipment 10 via said penetrator 2 and cable 11 10 through the first sub-section 4’ and a watertight connector 12.

The internal pressure compensator mentioned above is configured to adjust for any pressure differences between said first sub-section 4’ and the second subsection 4”. The internal pressure compensator is located in or associated with a 15 wall 18 or structural component, which divides or makes an interface wall between the first sub-section 4’ and the second sub-section A”. The wall 18 is suitably integral with or is in a sealed engagement with a housing of the first sub-unit 6’. 20 The exemplifying various embodiments of the internal pressure compensator are now to be explained in further detail.

The embodiment of Fig. 1 shows an internal pressure compensator 19, which is a piston movable in a cylindrical hole in the wall 18. It is seen that a first end 25 face of the piston 19 contacts the first liquid 7, and a second end face of the piston 19 contacts the second fluid 8.

The embodiment of Fig. 2 shows an internal pressure compensator 20 which is a diaphragm membrane located transversely of a hole 21 in the wall 18. A first 30 face of the membrane 20 contacts the first liquid 7, and a second face of the membrane 20 contacts the second fluid 8. It is noted that the membrane 20 is located at one axial end of the hole 21. Optionally, a perforated member 22 may be located at the other axial end of the hole and being integral with the wall 18. PCT/N02015/050164 WO 2016/043600 11

The embodiment of Fig. 3 shows that the wall 18 has a circular opening 23 radially inwards of its circumference and extending axially through the wall 18. The internal pressure compensator 24 is a diaphragm membrane located 5 transversely of the opening 23 at one axial end thereof. Optionally, a perforated circle-shaped member 25 may be located at the other axial end of the opening 24 integrally with the wall 18. A first face of the membrane 24 contacts the first liquid 7, and a second face of the membrane 24 contacts the second fluid 8. 10 The embodiment of Fig. 4 shows an internal pressure compensator 26, which is a bladder or a second bellow of rubber material being. It is noted that the compensator 26 is substantially located in the first sub-section 4’ and has an outlet 26’ which communicates with an axially extending hole 27 through the wall 18. An interior of the bladder or second bellow 26 is in communication with 15 the second liquid 8 present in the second sub-section 4”. In any case, compared with the embodiments of Figs. 1 - 3, the compensator 26 which has liquid 8 inside provides for extra supply of oil 8 to the sub-section 4” in case of oil leakage from the sub-section 4” or via the sub-unit 6” by virtue of the bladder or bellows 26 being compressed due to volumetric displacement of the liquid 7 in 20 the sub-section 4’ caused by the bladder 5. Thereby a pressure drop in section 4” is effectively compensated to yield a substantially same pressure in both sub-section 4’, 4”.

Oil leakage of oil 7 from the first sub-section 4’ could be via a first dynamic seal 25 28, which is present between the first sub-unit 6’ and the second sub-unit 6”.

Further, oil leakage of oil 8 could be via a second dynamic seal 29 being present at a downstream region of the second sub-unit 6”.

The embodiment of Fig. 5 shows an internal pressure compensator 30 which is 30 a circular continuous hose of rubber material being substantially located in the first sub-section 4’. The hose 30 has at least one branched-off outlet 31 which engages a hole 32 through the wall 18. An interior of said outlet 31 and hose 30 is in communication with the second liquid 8 present in the second sub-section PCT/N02015/050164 WO 2016/043600 12 4”. The volume of the hose 30 implies that there is an extra supply of oil 8 available in case of excessive oil leakage of oil 8 to the outside of the apparatus 1. However, it will be appreciated that the oil which can be pressed out of the hose is very much dependent on the volume of oil 7 which the bellow 5 is able 5 to cause a corresponding volume compression onto the hose 30 to yield a corresponding volume of oil 8 to leave the inside of the hose 30 and into the second sub-section, thereby providing for the required pressure compensation. Suitably, the hose 30 resides with a part of its body in a recess of a face of the wall 18 in the first sub-section 4’. 10

As indicated above, an exemplifying use of the inventive apparatus 1 could be to operate or adjust the state of a subsea installation 33 by letting a movable connector 34 at a downstream region of the second sub-unit 6” engage a moveable mating connector 35 on the subsea installation, see Fig. 1. 15

Although the first and second sub-units 6’; 6” could be an electric motor and a gear assembly, respectively, such a choice should not be considered to limit the present invention, as other choices could be made.

Claims

Patent claims 1. A retrievable subsea apparatus (1) with a pressure and volume compensating system, the apparatus comprising: - a housing (1’) having in its interior a control system (9) located in a first section (3) thereof and an operating unit (6) located in a second section (4) thereof, characterized in that - a penetrator (2) constitutes an interface between the first section (3) and the second section (4), wherein the first section (3) has a substantially constant first pressure, - that an external pressure compensator (5, 5’) is associated with the second section (4) having a second pressure, - that at least a first sub-unit (6’) and at least a second sub-unit (6”) constitute the operating unit (6), - that at least a first sub-section (4’) and at least a second sub-section (4”) constitute the second section (4), - that a first liquid (7) is located in the first sub-section (4’), and a second liquid (8) is located in the second sub-section (4”), - that the second sub-section (4”) is sealed off from the first subjection (4’), - that the external compensator (5, 5’) is in communication with the first sub-section (4’), - that the first sub-unit (6’) is at least partly associated with the first subsection (4’) and the second sub-unit (6”) is associated with the second sub-section (4”), and - that an internal pressure compensator (19; 20; 24; 26, 27; 30, 31) is configured to adjust for any pressure differences between said first and second sub-sections (4’; 4”) and is in contact with the first liquid (7) in the first sub-section (4’) and with the second liquid in the second sub-section (4”).
2. The apparatus of claim 1, characterized in that the first liquid (7) has a first set of properties, and wherein the second liquid (8) has a second set of properties.
3. The apparatus of claim 2, characterized in that the first and second properties are at least one of viscosity, dielectric property, lubrication and materials compatibility.
4. The apparatus of claim 1,2 or 3, characterized in that the first sub-unit (6’) comprises an electric motor, and wherein the second sub-unit (6”) comprises a gear assembly.
5. The apparatus of any one of claims 1 - 4, characterized in that the first pressure in the first section (3) is substantially at sea surface level atmospheric pressure.
6. The apparatus of any one claims 1 - 5, characterized in that the second pressure is equal to or above subsea pressure surrounding the apparatus housing (T).
7. The apparatus of any one of claims 1 - 5, characterized in that the external pressure compensator is pre-tensioned to one side to yield a pressure in the second section (4) above an external pressure, e.g. a subsea pressure.
8. The apparatus of any one of claims 1 - 7, characterized in that the external compensator (5) is linked to or communicates with a compensator movement sensor (15).
9. The apparatus of claim 8, characterized in that the external pressure compensator (5) is configured to effect a volumetric displacement of the first liquid (7) in said first sub-section (4’) to cause the internal pressure compensator (19; 20; 24; 26, 27; 30, 31) to yield a corresponding volumetric change in the second sub-section (4”).
10. The apparatus of any one of claims 1 - 9, characterized in that the external pressure compensator (5) is a first bellow open at one end and closed at the other end, the inside of the first bellow (5) to be in communication with sea water, and wherein the outside and closed end of the first bellow (5) being surrounded by the first liquid (7).
11. The apparatus of any one of claims 1-10, characterized in that the external pressure compensator (5) is made from at least one of or a composition of at least two of: a metal, a metal alloy, a rubber-type material and a plastics material.
12. The apparatus of any one of claims 1 - 11, characterized in that the external pressure compensator (5) is linked to or communicates with a movement sensor (15).
13. The apparatus of claim 10, characterized in that the closed end (5’) of the first bellow (5) is linked to or communicates with a bellow movement sensor (15).
14. The apparatus of claim 12 or 13, characterized in that the sensor (15) is a linear movement sensor of inductive, capacitive or resistive type.
15. The apparatus of any one of claims 1-14, characterized in that the control system (9) communicates (11, 12) with external power and communication equipment (10) via said penetrator (2) and the first sub-section (4’).
16. The apparatus of any one of claims 1-15, characterized in that the control system (9) communicates with the first sub-unit (6’), e.g. a motor, and a movement sensor (15) of the external pressure compensator (5).
17. The apparatus of any one of claims 1-16, characterized in that the internal pressure compensator (19; 20; 24; 26, 27; 30, 31) is located in or associated with a wall (18) or component which divides the first sub-section (4’) and the second sub-section (4”).
18. The apparatus of claim 17, characterized in that the wall (18) between said first and second sub-sections (4’, 4”) is integral with or is in a sealed engagement with a housing of the first sub-unit (6’).
19. The apparatus of any one of claims 1-18, characterized in that the internal pressure compensator (19) is a piston movable in a cylindrical hole in the wall (18), and wherein a first end face of the piston (19) contacts the first liquid (7), and a second end face of the piston (19) contacts the second fluid (8).
20. The apparatus of any one of claims 1-19, characterized in that the internal pressure compensator (20) is a diaphragm membrane (20) located transversely of a hole (21) in the wall (18), and wherein a first face of the membrane (20) contacts the first liquid (7), and a second end face of the membrane (20) contacts the second fluid (8).
21. The apparatus of claim 20, characterized in that the membrane (20) is located at one axial end of the hole (21).
22. The apparatus of claim 20 or 21, characterized in that a perforated member (22) is located at the other axial end of the hole (21) and being integral with the wall (18).
23. The apparatus of any one of claims 1-19, characterized in that the wall (18) has a circle shaped opening (23) radially inwards of its circumference and extending axially through the wall (18), wherein the internal pressure compensator (24) is a diaphragm membrane which is located transversely of the opening (23) at one axial end thereof, wherein a first face of the membrane (24) contacts the first liquid (7), and wherein a second face of the membrane (24) contacts the second fluid (8).
24. The apparatus of claims 23, characterized in that a perforated member (25) is located at the other axial end of the opening (23) integrally with the wall (18).
25. The apparatus of any one of claims 1-19, characterized in that the internal pressure compensator (26, 26’) is a bladder or a second bellow of rubber material being substantially located in the first sub-section (4’) and having an outlet (26’) which communicates with an axially extending hole (27) through the wall (18), an interior of said bladder or second bellow (26) being in communication with the second liquid (8) present in the second sub-section (4”).
26. The apparatus of any one of claims 1-19, characterized in that the internal pressure compensator (30, 31) is a circular continuous hose (30) of rubber material being substantially located in the first sub-section (4’), wherein the hose (30) has at least one branched-off outlet (31) which engages a hole (32) through the wall (18), an interior of said outlet (31) and hose (30) being in communication with the second liquid (8) present in the second sub-section (4”).
27. The apparatus of claim 26, characterized in that the hose (30) resides with a part of its body in a recess of a face of the wall (18) in the first sub-section (4’).
28. The apparatus of any one of claims 1 - 27, characterized in that at least one of the first and second liquids (7, 8) is a mineral oil, a synthetic or semi-synthetic oil or a silicone oil.
29. The apparatus of any one of claims 1 - 28, characterized in that the first section (3) is a dry chamber filled with air or gas.
30. The apparatus of any one of claims 1 - 29, characterized in that a first dynamic seal (28) is present between the first sub-unit (6’) and the second subunit (6”), and wherein a second dynamic seal (29) is present at a downstream region of the second sub-unit (6”).
31. Usage of an apparatus according to any one of claims 1 - 30 to operate or adjust the state of a subsea installation (33) by letting a movable connector (34) at a downstream region of the second sub-unit (6”) engage a moveable mating connector (35) on the installation (33).