A liquid detection indicator and an apparatus comprising a liquid detection indicator

Abstract

The present invention relates to a liquid detection indicator, configured to provide a visual and / or tangible indication if liquid such as water leaks into a cavity / space. The liquid soluble element can be made to withstand oil, but dissolve completely or partly in water, thereby allowing the liquid detection indicator to be installed either in a dry void, or in a void filled completely or partly with oil such as lubrication / gear oil, this so that if water enters said dry void, or if an amount of water ingress to said oil filled void exceeds a certain value, the liquid soluble element will dissolve partly or complete to release a mechanism allowing for a visual and / or tangible signal, e.g. release plunger.

Description

[0001] A LIQUID DETECTION INDICATOR AND AN APPARATUS COMPRISING A LIQUID

[0002] DETECTION INDICATOR

[0003] The present invention relates to a liquid detection indicator configured to provide an indication of liquid leakage into a cavity for housing a liquid soluble element provided in a housing. The liquid detection indicator preferably comprises a plunger and a potential energy storage. The liquid soluble element is preferably arranged at least partly within said cavity. A trigger element is provided which when the liquid soluble element is exposed to liquid the trigger element releases potential energy from the storage to plunger so that at least a part of the plunger moves and directly or in-directly provides one from an exterior visible and / or tangible indication. The present invention also relates to an apparatus comprising a liquid detection indicator.

[0004] BACKGROUND OF THE INVENTION

[0005] Leaking seals, particularly leaking dynamic seals, have always been a challenge. The relative movement is causing wear on both seal and mating surface. Dynamic seals have limited life. Expected lifetime depends on parameters such as; Number of cycles per minute, accumulated cycles, operating environment, pressure, heat, type of fluid / liquid, seal-material, etc..

[0006] Premature failure of dynamic seals is also a known problem. Reasons for this includes installation error, material defects, marine growth, operating error, lack of cooling, and so on.

[0007] The most basic way of confirming seal performance, is monitoring the expected consequence of this leaking seal. This can be parameters such as visual oil loss to sea, low / high oil levels, increased water content in oil, and similar. These parameters prove to some extent how well the seal is working, but "water content in oil" falls short in cases where oil is stagnant, and inaccessible.

[0008] To increase seal robustness, seals have evolved in many ways, such as multiple sealing surfaces used instead of single contact surface seal. By this, the following benefits may be achieved: A) Outer seal protects the inner seal from harsh environment (silt, sand, marine growth, etc..).

[0009] B) Leak across two seals will not occur until both seals are leaking.

[0010] However, case B) above, comes with a drawback. Unless leak detection monitor the cavity between the two seals, one can not know if both barriers are intact. This is specially true if say outer seal experience more wear than inner seal.

[0011] Some solutions to this problem have been suggested. One commonly used method for leak detection is having a channel connected to the cavity between two seals. This channel allows leakage / spill flowing to a designated location where it is easily detected. A further benefit is that one typically can collect and store limited amounts of leaks, thereby continue operating whilst planning for repairs. The drawback is the cost of implementing such leak detection channel(s). For equipment having multiple degrees of freedom, leak detection channels become impractical. This as hydraulic rotary swivel joints are needed to extend leak detection channel onto a suitable location. Leak detection channel, if at all possible to implement due to space restrictions, often becomes costly, and non- robust. Hydraulic rotary swivel joints represent complexity, space requirement, cost and additional risk for leaks.

[0012] An example of leak detection device embodied as a liquid activated electric switch is disclosed in JPA 1976006781. This disclosed liquid activated electric switch, will upon detecting liquid, provide possibility for instant leak alarm. However, the use of electric signal require cabling, and where rotation is involved, the use of slip rings, which affects requirements for serviceability, space, and robustness, and adds complexity and cost.

[0013] An example of detection liquid is disclosed in EP1425527B1. This document discloses a water soluble pill for insertion into assembly of an automatic inflator. Whilst the trigger mechanisms disclosed in EP1425527B1 is triggered by contact with water, the result of triggering is inflation of a life jacket and it does not function as a leak detection device. The present invention aims to provide a reliable early warning showing that one of the two seals such as one part of a Y-shaped seal has started leaking.

[0014] OBJECT OF THE INVENTION

[0015] It is an object of the invention to provide an easy detection and indication of a leaking seal. It is a further object of the present invention to provide an alternative to the prior art.

[0016] SUMMARY OF THE INVENTION

[0017] Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a liquid detection indicator configured to provide an indication if liquid leakage into a cavity for housing a liquid soluble element provided in a housing of said indicator, said liquid detection indicator preferably comprises:

[0018] • a plunger,

[0019] • a potential energy storage, preferably a spring,

[0020] • said liquid soluble element is arranged at least partly within said cavity,

[0021] • a trigger element which when said liquid soluble element is exposed to liquid which dissolves the element, provides said trigger element to release potential energy from said storage to said plunger either directly, or via a separate actuator member so that at least a part of the plunger moves and directly or in-directly provides one from an exterior of the liquid detection indicator visible and / or tangible indication, preferably being this exposing a protruding surface, or change of orientation and / or dis-location of a cover or a member to which the plunger cause a movement; wherein

[0022] • said liquid detection indicator preferably comprises a seal configured to protecting said cavity against said exterior prior to said movement of plunger.

[0023] In preferred embodiments, the seal, e.g. comprising a number of individual seals, may be configured to protection said cavity against said exterior during and after said movement of the plunger.

[0024] A tangible indication refers in preferred embodiment to an indication which can be felt by a human hand. In preferred embodiment, the movement of the plunger when the liquid detection indicator is being triggered is used to mechanically trigger other mechanism, such a flicking an electrical switch, pulling a rope, hammer on a bell or the like. The mechanical triggering of other mechanism may be assisted by a rotating propeller shaft.

[0025] In preferred embodiments, the liquid detection indicator may be configured in an air filled or oil filled cavity to provide an indication of ingress of polar liquid such as water.

[0026] In many preferred embodiments, the liquid soluble element is soluble by water, such as sea water and non-soluble by oil. By this, the liquid detection indicator will not be triggered by oil e.g. present in the cavity of the liquid detection indicator. In preferred embodiment, such oil is displaced and / or diluted by water, such as sea water leaking past a seal whereby the liquid soluble element will dissolve at least to an extend triggering the liquid detection indicator.

[0027] By arranging the liquid soluble element at least partly within the cavity, liquid may be provided easy access to the liquid soluble element. In preferred embodiments, liquid access to the liquid soluble element is provide in a manner where flow obstacles generating flow resistance are reduced. Reduction of flow obstacles may be provided by shaping flow path(s) leading to the liquid soluble element meandering-less and / or dimensioning the flow path(s) to limit or even prevent flow being influence by air pockets, such as air bubbles being trapped in the flow path(s). In some embodiment, trapping of air may be caused by an "inverted U- shape" which may be provided due to design considerations. Air trapping can be increased by the combination of fluid surface tension, adhesion, and / or fluid cohesion.

[0028] In such cases a capillary effect, e.g. provided by a capillary cord as disclosed herein such as in Fig 6B, may be used to draw liquid into contact with the liquid soluble elements. Having two channels when these channels are narrow such as less than 06 allows for air escaping OUT one of them, whilst allowing liquid IN the other. Meandering-less typically refers to that the bends and / or kinks in a flow path may be present to the extends needed to provide the flow path in a device in which the liquid detection indicator arranged.

[0029] A liquid detection indicator according to the first aspect has, inter alia, the advantages of being purely mechanical without the need for electrical components for detection that a liquid, such as a polar liquid (e.g. water), has entered into the cavity preferably entered the cavity with as little flow obstruction as practical possible. In addition, when being triggered, the liquid detection indicator can easily be brought back to a detection state by replacing the liquid soluble element and loading the potential energy storage with potential energy (e.g. compress the spring). The liquid soluble element may be designed to withstand oil, whilst being soluble by water, thereby allowing the cavity to initially be oil filled. As water leaks into the cavity in such embodiments, the water dilution and washout-effects and the fact that non emulsifying oil has less density than water, cause the original oil to be replaced with water, resulting in triggering of liquid detection indicator's plunger.

[0030] A double acting seal as used herein typically refers to a seal providing a seal between a first region and a second region, wherein the double acting seal prevents liquid from flowing from the first region and to the second region and at the same time prevents liquid from flowing from the second region to the first region.

[0031] A double acting seal may be a single seal or provided in combination with another double acting seal. For instance, the Y-profile blade seal illustrated in the accompanying figures to seal between the propeller hub and propeller blades has two lips, where each of these lips is a double acting seal. Another example is the X-profile seal illustrated in the accompanying figures at the upper end of the plunger. In this use, the X-profile has four lips and is arranged to act as single double acting seal. Accordingly, a double acting seal as used herein may refer to a part of seal element, such as a lip of a Y-profile blade seal, or as a single or multiple seals, such as X-profiled seal. The invention relates in a second aspect to an apparatus comprising a first part and a second part, said first part is arranged on or at said second part and said apparatus preferably comprises a double acting outer seal and a double acting inner seal between said first part and said second part, forming a void, wherein said apparatus preferably comprises

[0032] • a liquid detection indicator according to the first aspect of the invention wherein a housing of said indicator is arranged, preferably in a counterbored hole of said apparatus, so that said visible and / or tangible indication preferably is / are recognizable from said exterior;

[0033] • at least one channel fluidicly connecting a void located in-between said double acting inner seal and said double acting outer seal with said cavity.

[0034] An apparatus according to the second aspect has, inter alia, the advantage that failure of a seal may be detected and indicated in a principally mechanical manner.

[0035] An apparatus according to the second aspect has, inter alia, the advantage that the liquid detection indicator can be retro-fitted to an existing apparatus or included in the apparatus during a design process.

[0036] The first and the second aspect may be used for detection as dissolvement of the liquid soluble element allows for release of plunger, which is transferred mechanically to become an indicator that can be visually and / or mechanical.

[0037] In preferred embodiments, the present invention relates to a liquid detection indicator, configured to provide a visual and / or tangible indication if liquid such as water leaks into a cavity / space. The liquid soluble element can be made to withstand oil, but dissolve completely or partly in water, thereby allowing the liquid detection indicator to be installed either in a dry void, or in a void filled completely or partly with oil such as lubrication / gear oil, this so that if water enters said dry void, or if an amount of water ingress to said oil filled void exceeds a certain value, the liquid soluble element will dissolve partly or complete to release a mechanism allowing for a visual and / or tangible signal, e.g. release plunger. The first and second aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0038] "Water" herein preferably refers to seawater, freshwater or brackish water.

[0039] BRIEF DESCRIPTION OF THE FIGURES

[0040] The present invention and in particular preferred embodiments thereof will now be described in more details with regard to the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0041] Fig. 1 schematically illustrates a first embodiment of a liquid detection indicator. The figure in the left hand side of Fig. 1 illustrates a thruster in which the liquid detection indicator has been arranged and the figure in the right hand side is a close-up and cross sectional view of the liquid detection indicator positioned to monitor the propeller blade seal.

[0042] Fig. 2 is a cross sectional and exploded view of a first embodiment of a liquid detection indicator.

[0043] Fig. 3 is a cross sectional and exploded view of second embodiment of a liquid detection indicator.

[0044] Fig. 4A shows in a cross sectional view the first embodiment of the liquid detection indicator prior to being activated by seawater leaking past an outer double acting seal of the thruster illustrated in Fig. 1. Fig 4B shows the first embodiment after water has leaked past the outer double acting seal and entered a void between and the inner and outer double acting seal and thereafter entered the channel and the cavity, and having at least partly dissolved the liquid soluble element whereby the plunger is released, and the spring forces it outwards to become visible / tangible. In Fig. 4B air in channel 6 and-void 33 is replaced with water as seal 17 has started leaking. Fig. 5A shows in a cross sectional view the second embodiment of the liquid detection indicator prior to being activated by seawater leaking past an outer double acting seal of the thruster illustrated in Fig. 1. Fig 5B shows the second embodiment after water has leaked past the outer double acting seal and entered a void between and the inner and outer double acting seal and thereafter entered the channel and the cavity, and having at least partly dissolved the liquid soluble element whereby the plunger is released, and the spring forces it outwards to become visible / tangible.

[0045] Fig. 6A shows in a cross sectional view the first embodiment of the liquid detection indicator prior to being activated by seawater leaking past an outer double acting seal of the thruster illustrated in Fig. 1. Fig. 6B is a cross sectional view along plane "A-A" indicated in Fig. 6A. The cross sectional view of Fig. 6B discloses inter alia, a further optional channel and optional capillary or, optionally, a liquid repellent, preferably water repellent cord material extending between the void between the inner and outer double acting seals and the liquid detection indicator.

[0046] Fig. 7 is a photograph depicting a preferred embodiment of a liquid activation release device and a preferred embodiment of plunger.

[0047] Fig. 8A shows in a cross sectional view the third embodiment of the liquid detection indicator prior to being activated by seawater leaking past an outer double acting seal of the thruster illustrated in Fig. 1. Fig 8B shows the third embodiment after water has leaked past the outer double acting seal and entered a void between and the inner and outer double acting seal and thereafter entered the channel and the cavity, and having at least partly dissolved the liquid soluble element whereby the plunger is released, and the spring forces it outwards to become visible / tangible and pop-off a cover.

[0048] Figs. 9A, 9B and 9C schematically illustrates triggering of an embodiment where the cavity and channels and void are pre-filled with an oil. Fig. 10 illustrates a thruster propeller shaft seal box having a liquid detection indicator. Upper part of Fig. 10 is a cross sectional view showing the propeller shaft and rope guard, and lower part of Fig. 10 is a close-up focusing on propeller shaft seal box.

[0049] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0050] The following description of preferred embodiments has been focused towards seawater. However, the embodiments are equally useable in relation to fresh and brackish water, or other liquid which can at least partly dissolve the liquid soluble element 3.

[0051] Reference is made to the accompanying figures and in particular to Fig. 2 illustrating in a cross sectional and exploded view a first embodiment of a liquid detection indicator. As will become apparent from the following description, preferred embodiments of a liquid detection indicator 10 are configured to provide an indication if liquid, preferably polar liquid such as water, leaks into a cavity 14. This cavity 14 is typically provided in a housing 8 and the cavity 14 is designed for housing a liquid soluble element 3. The liquid soluble element is an element which is at least partly dissolved when in contact with water, or other liquids that can dissolve the liquid soluble element 3.

[0052] The material of the liquid soluble element 3 is selected in accordance with the liquid to be detected, in the sense that the liquid to be detected must be able at least partially dissolve the liquid soluble element 3 to trigger the liquid detection indicator 10. In preferred embodiments, the liquid soluble element 3 is designed to dissolve in a polar liquid, such as water, and typically designed not dissolve in a non-polar liquid, such as an oil.

[0053] As illustrated in Fig. 2, the liquid detection indicator 10 comprises a plunger 1 which can be disclosed as an elongate element, typically being rotationally symmetric along a longitudinal axis of the plunger. The plunger 1 is typically a unitary member.

[0054] The liquid detection indicator also has a potential energy storage, which in the embodiment disclosed in the figures is a spring 29. An upper end of the spring is configured to abut a lower end, such as an actuator part 23, of the plunger 1, so that when the spring 29 releases its potential energy and expands, a spring force is exerted by the spring on the actuator part 23 which moves the plunger in the direction the spring expands. The spring 29 - or in general the potential energy storage - is in a loaded configuration prior to triggering of the liquid detection indicator. As an example, prior to being triggered, the spring 29 is compressed and when the liquid detection indicator is triggered, the spring 29 expands.

[0055] The liquid soluble element 3 is arranged at least partly within said cavity 14.

[0056] A trigger element 25, 26 is provided partly on the plunger 1 and partly on a receptable 31. The parts 25 and 26 of the trigger element are typically designed to engage with each other and prevent movement of the plunger, that is in with reference to the illustrated embodiments, the spring is prevented from expanding. However, when the liquid soluble element 3 is exposed to pre-determined type of liquid, this will allow the trigger element 25, 26 to disengage so that release potential energy from storage 29 is initiated.

[0057] In the illustrated embodiment, the liquid soluble elements 3 retains the part of the trigger element 25 (shown as a ledge) radially inward and when the liquid soluble element is at least partly dissolved, the trigger element 25 can move radially outward and give way for the trigger element 26 of the plunger to pass by. Thus, when the liquid soluble element 3 is at least partly dissolved, the energy storage 29 releases its potential energy to said plunger 1 either directly, or via a separate actuator member 23 whereby at least a part of the plunger 1 moves.

[0058] The movement of the plunger 1 provides either directly or in-directly one from an exterior 4 of the liquid detection indicator 10 visible and / or tangible indication.

[0059] The indication may be an exposure of a surface protruding above an upper end of the housing 8, or change of shape or orientation and / or location of a cover 24.

[0060] A change of shape of e.g. a cover 24 (see Fig. 8A) may be that the cover is made from an elastic material so that movement of the plunger 1 provides a deformation of the cover 24, such as a provides an outwardly protruding dent in the cover 24. Such embodiments might allow for providing a sealing by cover 24. The liquid detection indicator 10 is designed to detect liquid finding its way into the cavity 14 from a lower position (lower refers to the orientation of Fig. 2), and it has been found advantageous to prevent liquid from entering into the cavity 14 from an upper position, that is with reference to Fig. 2 to prevent liquid to enter into the cavity through the through going opening 36. To prevent such an inflow, the liquid detection indicator 10 may have a seal 5 configured to protecting said cavity 14 against the exterior 4 prior to the movement of plunger 1. As illustrated in Fig. 2, an end 28 of the plunger 1 is provided with two seals 5 which when the liquid indicator device is assembled seal against the sealing surface 9.

[0061] As can be realized from Fig. 2, the two seals of the seal 5 will be position outside the housing 18 when the liquid indicator device has been triggered. This is also disclosed Fig. 4B. By this cavity 14 is no longer effectively sealed at the troughgoing opening 36. This may result in that liquid contained in the cavity 14 may leak out along the through-going opening 36 to the exterior 4.

[0062] If it is preferred to maintain an effective seal at the through going opening 36 after triggering of the liquid detection indicator, the embodiment illustrated in Fig. 3 can be used. As illustrated, the embodiment of Fig. 3 has an addition seal of the seal 5, whereby the seal 5 protecting the cavity 14 forms a double acting seal 5 protecting the cavity 14 against the exterior 4 and prevent an interior liquid from leaking to the exterior prior to, during and at an end of the movement of the plunger 1. This is illustrated in Fig. 5B, which shows that an inner most of the three seals 5 are located interior of the through-going opening 36 after the liquid detection device has been triggered.

[0063] In some preferred embodiments, the cavity 14 of the liquid detection indicator is pre-filled with an oil, such as a lubrication oil. Pre-filled herein typically refers to that the cavity is filled with oil prior to leaks causing water or other fluid entering into the cavity. The channel(s) 6 may also be prefilled with an oil or other nonpolar liquids. In such embodiments, the liquid soluble element 3 is essentially non-soluble by said oil. By filling the cavity with an oil, this oil may, in case of leaking seal 17 at least promote another liquid such as water to at least partly replace the oil contained in the cavity 14 as there may be essentially no air to be displaced. Air could otherwise form non-displaceable air pocket(s). Water (being a polar liquid) will upon at least partly replacing oil in cavity 14 cause the liquid soluble element 3 to at least partly dissolve, thereby cause the release of plunger 1. One such embodiment is disclosed in Figs. 9A, 9B and 9C.

[0064] In preferred embodiments of a liquid detection indicator, the liquid detection indicator is configured to provide the visible indication as a change in shape and / or a change in colour, and tangible indication as a change of shape

[0065] Figs. 4A, 4B, 5A and 5B, 9C illustrates an example of such visible indication where a part of the plunger 1 extends above an outer surface of the housing 8 after the liquid detection indicator has been triggered. In such, and other embodiments, the housing 8 has an upper surface facing towards the exterior 4 and is provided with a through-going 36 opening extending from the exterior 4 and into the cavity 14. An end 28 of said plunger 1 protrudes into the through-going opening 36 and when the liquid detection indicator 1 has been triggered at least part of the end 28 extends above the upper surface.

[0066] As indicated above, preferred embodiments comprise that at least a section of the plunger 1 extends through said through-going opening 36. This through-going opening 36 is provided with a sealing surface 9 and the plunger 1 typically has one or more double acting seals 5 co-operating with the sealing surface 9 to provide exterior protection of the cavity 14 against the exterior 4. Such one or more double acting seals 5 also prevent oil loss the exterior, such as seawater, in embodiments where the cavity 14, void 33 and / or channel(s) 6 are is / are oil filled.

[0067] As an alternative to or in combination with double acting seals 5 provided on the plunger 1, such seals 5 may be provided in the housing, typically at the through- going opening 36. In such embodiments, the part of the plunger 1 extending through the through-going opening 36 is provided with a sealing surface 9.

[0068] In the preferred embodiments shown in Figs. 4A, 4B, 5A, 5B, 6A, 6B, 9A, 9B and 9C an upper surface of the plunger 1 is flush with the outer surface of the 8 prior to movement of the plunger 1. However, the invention is not limited to this, as in preferred embodiments, the liquid detection indicator is configured to position at least a section of the end 28:

[0069] • above the upper surface of the housing 8,

[0070] • flush with the upper surface of the housing 8, or

[0071] • recessed relatively to the upper surface of the housing prior to said movement of the plunger 1. The positioning of the plunger in either of these three position can be achieved inter alia by the selecting the length of the plunger 1 above the second part of the trigger element 26 to provide the desired positioning. As the plunger 1 moves upon triggering of the liquid detection indicator, at least a section of the end 28 will change position which can in many instances be at least visually perceived and / or tangible perceived.

[0072] In preferred embodiments, where the plunger is a unitary body, this unitary body will change position.

[0073] In preferred embodiments as those illustrated in Figs. 4A, 4B, 5A, 5B, 6A, 6B, 9A, 9B and 9C, the liquid detection indicator is configured for providing the visible indication as a change in a position of plunger 1 to a position wherein at least a section of the end 28 is above the upper surface of the housing 8, after the liquid detection indicator has been triggered.

[0074] Reference is made to Fig. 8A and 8B schematically illustrating a preferred embodiment of liquid detection indicator 10 comprising a cover 24. As illustrated, the cover 24 is arranged to cover an outer opening of through-going opening 36 prior to the movement of the plunger 1. The cover 24 may be press-fitted onto a part of the housing 8 in a manner preventing the cover 24 from incidentally come off. It is noted, that if the cover 24 makes a liquid tight fit with e.g. the housing 8, the seal 5 may be redundant and omitted. The plunger 1 is configured to act upon the cover 24 from an underside thereof during the movement of the plunger 1 to change a shape of the cover, to change position of the cover 24, e.g. by the cover 24 being hinged to the housing 8 or propeller blade 39, or as illustrated in Fig. 8B to make the cover 24 come off. Thus, in the illustrated embodiment of Figs. 8A and 8B, triggering of the liquid detection indicator makes the plunger 1 to push on the underside of the cover 24 and eventually make the cover 24 to come off. In other embodiments, the cover 24 is hingedly connected, so that when the plunger 1 push on the underside of the cover 24, the cover 24 will swing outwardly although still being connected to e.g. the liquid detection indicator or to a part in which the liquid detection indicator is arranged, e.g. propeller blade 39.

[0075] In preferred embodiments, the seal 5 protecting the cavity 14 comprises one or more of the seal types of an X-ring-seal, or O-ring-seal, or U-shaped seal, or V- shaped seal, trapetzodial or square seals or combinations thereof. In embodiment comprising two or three of the seal 5, the seals may be of different types or of the same type.

[0076] Reference is made in particular to Fig. 2, Fig. 3 and Fig. 7, the latter illustrating on the left hand side a preferred embodiment of a liquid activated release device 16. The right hand side of Fig. 7 illustrates the liquid activated release device 16 without the liquid soluble elements 3 and with an end of the plunger 1 extending into the liquid activated release device 16. The liquid activated release device 16 comprises a receptacle 31 made from a non-soluble material, such as plastic, in which liquid soluble element 3 is housed. The receptacle 31 has a tubular passage 32 defined by an interior flexible wall 30 from which the first part 25 of trigger element extends radially inward.

[0077] A longitudinal section of the plunger 1 extends into the tubular passage 32, and the plunger 1 has a second part 26 of trigger element extending radially outward (see e.g. Figs. 2 and 3). The first 25 and second part 26 of the trigger element are configured to engage, as disclosed above, with each other to prevent movement of the plunger 1, thereby prevent release of stored potential energy 29 when the soluble element 3 is not at least partly dissolved.

[0078] In the embodiment illustrated in Fig. 7, the interior flexible wall 30 is configured to flex upon the liquid soluble element 3 being at least partly dissolved to provide a disengagement between the first 25 and the second part 26 of the trigger element 25, 26 to allow the movement of the plunger 1 further into the tubular passage 32. When the liquid soluble element 3 is dissolved to a certain extend, it can no longer withstand / support the forces acting on the trigger element 25 from the trigger element 26 and the flexible wall 30 will flex radially outwardly. The force acting on the trigger element 25 due to the potential energy storage, such as the spring 29, pushes onto the lower end of the plunger 1.

[0079] As illustrated in Fig. 7, the interior flexible wall 30 may have longitudinal extending slits 37 to allow the interior wall to flex.

[0080] The material of the liquid soluble element 3 may be selected according to which liquid to be detected. The material of the liquid soluble element 3 may be selected to be soluble only by a certain type of liquid, such as a polar liquid, such as water. In preferred embodiments, the liquid detection indicator is used for detection a polar liquid, such as water, such as seawater and in such, and other use cases, the liquid soluble element 3 can be made from cellulose, sugar, sodium chloride, calcium, or combinations thereof.

[0081] As perhaps most clearly visible in Fig. 2 and Fig. 3, the plunger 1 may have an actuator part 23 to which the potential energy is released. In the disclosed embodiments, the actuator part 23 comprises a section protruding radially from the plunger at a lower end thereof and being abutted by the spring 29.

[0082] As detailed herein, the potential energy storage may be a coiled spring 29. However, in other embodiments other types of potential energy storages such as other types of springs, or an airbag-like cushion containing compressed air, are used.

[0083] As presented herein, the liquid to at least partly dissolve the liquid soluble element 3 may seawater, freshwater or brackish water. However, the liquid may be other liquids such as a coolant liquid, brake fluid, oil, or any polar liquid may also be used.

[0084] The invention also relates to an apparatus in which one or more preferred embodiments of liquid detection indicator is / are arranged. The liquid detection indicator(s) can be arranged in e.g. a stand still apparatus, a moveable / rotatable apparatus such a thruster, e.g. as a swing-up thruster where the blades are rotating (pitching) in a 4thaxis of rotation. The liquid detection indicator(s) may be arranged essentially on any part of any apparatus, as long as liquid detection indicator is fluidly connected to a void between seals, into which void a liquid may leak due to malfunction of the seals. In this regards, the liquid detection indicator may be viewed as to detecting liquid leaking into said void as the liquid eventually will / may end up in the cavity of the liquid detection indicator 10. In preferred embodiment, which will be further detailed below, the seals are positioned between moving / rotating parts (dynamic seals), such as in a propeller hub.

[0085] In preferred embodiments of an apparatus, the apparatus has a first part and a second part, where the first part is arranged on or at the second part. With reference to Fig. 1, the first part is the propeller hub 38 in which propeller blades 39 are pitchable mounted. Accordingly, the second part comprising the propeller blade 39 which are controllable pitch propeller blade. One or more liquid detection indicators are arranged in a base of the propeller blade(s) 39 as indicated inter alia in Fig. 1 illustrating a single liquid detection indicator. As illustrated in Fig. 1 in a cross sectional view, the apparatus comprising a double acting outer seal 17 and a double acting inner seal 7. The invention is not limited to double seals as the inner and / or outer seal may be a single acting seal, or a seal in general. These seals 7 and 17, seal between the first part (the hub) and the second part (the propeller blade). The outer double acting seal 17 is for preventing leak of water such as seawater into void 33 and oil loss to sea from the void. The double acting inner seal 7 is for preventing hub internal oil to leak out to void 33 formed between seal 7 and 17, and in case of failed seal 17, prevent the water, such as seawater, freshwater or brackish water, now entering void 33, to further seep into propeller hub. The fact that seal 7 and 17 are double acting, enables seal 7 to by its own, act as a barrier between oil and water such as seawater. Ditto for seal 17. Double acting seals 7 and 17 allows for separate oil to be filled in void 33, where this oil is separated from water such as seawater, and from oil inside propeller hub.

[0086] As illustrated, the apparatus comprises a liquid detection indicator 10. In the embodiment of Fig. 1, the liquid detection indicator 10 is the second embodiment of the liquid detection indicator. However, as will become apparent from e.g. Fig. 4A and B (showing implementation of the first embodiment of the liquid detection indicator), an apparatus is not limited to the second embodiment. Before water enters into the channel 6 and the cavity 14, the channel 6 and cavity 14 may be occupied by air or a non-polar liquid such as oil. Depending on the dimensioning and / or shape of the channel 16, there might be risk that air is trapped inside the cavity 14 preventing water to contact the liquid soluble element 3. Such a risk may arise due to the shape of combined liquid flow path, liquid adhesion, liquid cohesion and / or space restriction(s) and in such and other embodiments, such risk(s) may be alleviated by arranging the liquid soluble element 3 directly exposed to the cavity 14. Directly exposed typically a surface of the liquid soluble element faces and is in direct contact with the cavity 14. In the embodiments illustrated in Figs. 1,4A, 4B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B, and 9C, and other embodiments, the liquid detection element 3 is arranged directly exposed to the cavity 14 by the liquid soluble element 3 being directly accessible for liquid contained in the cavity 14.

[0087] As presented herein, some embodiments comprise a further channel and / or a capillary cord which may assist the flow of liquid thereby assist removing air potentially trapped inside the cavity. Example of trapped air, is air in an inverted U-shaped hose which is placed under water.

[0088] The housing 8 is arranged in a counterbored hole 34 of the apparatus. However, such a counterbored hole 34 is optional and is used to prevent that the housing 8 protrudes and creates a drag, when the propeller rotates.

[0089] The housing 8 is arranged so that the visible and / or tangible indication is / are recognizable from said exterior upon triggering of the liquid detection indicator 10.

[0090] To allow for the liquid entering into the void 33 to flow to the liquid detection indicator and into the cavity 14, at least one channel 6 is provided which fluidicly connects the void 33 located in-between the double acting inner seal 7 and the double acting outer seal 17 with the cavity 14.

[0091] The inventor has realized that when a relative thin channel(s) 6, typically having a diameter less than 6mm, liquid properties like cohesion and adhesion may come into action and possible affecting the flow of liquid in the channel(s). In such thin channel(s) air can get "trapped" thereby preventing liquid from reaching the cavity 14. A second channel 6 will assist in that such air "escapes" via this second channel 6, thereby allowing liquid to flow in the first channel. Such an air escape may be amplified by (when the part rotates) rotation of the propeller whereby liquid is "hurled into" the one of the channels.

[0092] The inventor has realised that for a thruster (or similar apparatus) as disclosed in Fig. 1, the outer double acting seal 17 fails earlier than the inner double acting seal 7. The outer double acting seal 17 seals against seawater and the inner double acting seal 7 seals against oil in propeller hub which may be fluidically connected to thruster lubrication oil. Thus, as the outer double acting seal 17 is the one which fails before the inner double acting seal 7, triggering of the liquid detection indicator based on leaking of water such as seawater can advantageously be used to schedule maintenance, such as replacement of both the inner and outer double acting seals 7, 17 prior to failure of the inner double acting seal 7, thereby preventing leakage of oil into water such as seawater, and / or water ingress to propeller-hub / thruster.

[0093] In order to allow for a less restricted flow of liquid from the void 33 to the liquid detection indicator 10, the apparatus may have two or three, or even more, channels 6 fluidicly connecting void 33 with cavity 14. By having more than one channel 6, e.g. air contained in the channels 6 may be transported by the liquid flow in one of the channels toward the cavity 14, whereby air here is allowed to evacuate in the opposite direction via the other channel.

[0094] In preferred embodiments, the double acting outer seal 17 and / or the double acting inner seal 7 each comprises a number of X-ring-seal(s), O-ring-seal(s), U- shaped seal(s), V-shaped seal(s), Y-profile seal(s), or combinations thereof, or as illustrated in the accompanying figures, being part of a double lip seal having Y- profile. The seals 7 and 17 can be referred to as two single V-lip seal, combined into a Y-profile.

[0095] One or more, such as all the channels 6 may have been provided with a hydrophilic coating. Such a hydrophilic coating may reduce the risk of capillary surface tension effects occurring in the channel(s) which could reduce the air escape thereby affecting flow of liquid in the other channel(s).

[0096] Reference is made to the embodiment illustrated in Fig. 6A and B. In this embodiment, two channels 6 are provided. This embodiment has a capillary material 35b, such as a cord made from cotton forming a capillary cord, arranged in one of the channels 6 and extending between the void 33 and the cavity 14. The capillary material extends towards or in is contact with liquid soluble element 3. The latter is illustrated in Fig. 6B. The capillary material 35b is used for drawing / transporting liquid, such as water or oil from the void 33 to the liquid detection device 10. By use of such a capillary material 35b, the capillary effects e.g. arising from the dimensioning of the channel(s) 6 which could prevent air escape is overcome by the fact that a capillary cord has a stronger pull on water, thereby strongly pulling water into cavity 14, thereby forcing air out the bore without the capillary cord.

[0097] Hence, in preferred embodiments, at least two channels 6 as illustrated in Figs. 6A and 6B are provided. Such two channels 6 reduces the risk that air or other gases is trapped inside the combination of cavity and channels. This-as one of the two channels function as air escape and the other functions allows liquid such as water into the cavity 14. This effect may be increase by arranging a capillary material in one of the at least two channels 6.

[0098] Preferred embodiments of an apparatus may comprise a liquid repellent, such as water repellent material 35a, such as a cord made from impregnated material, preferably cotton arranged in one of said channels and extending between the void 33 and the cavity 14, thereby allowing air escape by preventing liquid entering this bore. The liquid repellent, such as water repellent material may be a cord impregnated with a material to make it liquid repellent, such as water repellent.

[0099] To make the apparatus even more robust in the sense of being able to detect water (on in general a liquid, such as a polar liquid) entering void 33, two or more channel 6 are preferred when diameter of channel 6 is 6mm or less. Also, one or more chords may be installed in one or more of the channels to allow for the following benefits:

[0100] A) a water repellent chord, such as the water repellent material 35a, in one of the channels 6 will allow air escape as water is prevented from entering this channel

[0101] B) a water absorbing chord, such as the capillary material 35b, will use capillary effect to transport water towards the cavity 14, thereby forcing air out the other channel 6.

[0102] In embodiments comprising two or more channels 6, the capillary material 35b may be installed in one of the channels and a water repellent material 35a may be installed another of the channels 6.

[0103] The channel(s) 6 may be given essentially any cross sectional size allowed by the apparatus' material thickness in which the channel(s) is(are) formed. In preferred embodiments, one or more, such as all the channels each have a hydraulic diameter being less than 6.0 mm and larger than 1.0 mm. The cross section of the channel(s) 6 may be circular, square, elliptic or other shapes.

[0104] In Figs. 1, 4A, 4B, 5A, 5B, 6A, 6B, 7, 8, 9A, 9B, 9C, the liquid detection indicator 10 is arranged on a rotating part of the thruster, in particular in the base of a propeller blade s. The-location of the liquid detection indicator-relatively to the orientation of a centrifugal force arising during rotation is selected so that the centrifugal force will be acting on water, such as sea water, which after leakage is present in the channel(s) 6 and water will be "forced" into the cavity 14. As can be realized e.g. from Fig. 1, the liquid detection indicator is arranged so that an outward facing opening 45 into the cavity 14 faces in opposite direction than the centrifugal force and with a longitudinal orientation of the plunger 1 is aligned with the centrifugal force. With reference to the above listed figures, the outward facing opening 45 faces downwardly and the centrifugal force acting upwardly. The longitudinal orientation of the channel(s) 6 is aligned with the centrifugal force.

[0105] Hence in preferred embodiments, wherein the liquid detection indicator 10 is arranged in a rotating element, it may be advantageously to arranged the liquid detection indicator in a manner where the outward facing opening 45 of the cavity 14 faces in direction where a normal to the plane spanned by the outward facing opening 45 forms an acute angle, preferably lower than 90 degrees, with the direction of the centrifugal force or is aligned with the direction of the centrifugal force.

[0106] In preferred embodiments, the channel(s) 6 may also advantageously be arranged so that a longitudinal orientation, such as a dominant longitudinal orientation, of the channels forms an acute angle, preferably lower than 90degrees, with the direction of the centrifugal force or is aligned with the direction of the centrifugal force. A dominant longitudinal orientation typically refers to the orientation between an inlet and an outlet at the cavity 14 of the channel in question.

[0107] Accordingly, the location of a liquid detection indicator in combination of flow path from seal to cavity 14 may be selected so that that centrifugal force and / or gravity force will promote leaking liquid at least partly into the cavity 14 thereby liquid coming at least partly in contact with water soluble element.

[0108] While the apparatus in preferred embodiment disclosed in the accompanying figures is a propulsion device for a vessel, such as a thruster, an apparatus according to the invention is not limited to such a propulsion device, or may be used on other seals on a propulsion or sub-surface device, such a stabilator fin, or a steering column for thruster or rudder.

[0109] A liquid detection indicator may be used in essentially any sub sea device to detect leakage involving one or more seals.

[0110] Reference is made to Fig. 10 illustrating a thruster having a liquid detection indicator 10. Upper part of Fig. 10 is a cross sectional view, and lower part of Fig. 10 is a close-up of a part of the upper part of Fig. 10. In Fig. 10, the blades of the thruster is left out. Such blades would otherwise be arranged on the propeller blade root shown. The liquid detection indicator is positioned in a chamber formed between two seals, on one side seals 42-1 and 42-2, and on the other side seals 42-3 and 42-4. This chamber may be dry (air filled), or filled with oil. If water enters chamber due to leak past one or more seals, oil will become diluted. With sufficient amount of water in chamber, the liquid detection indicator 10 will be triggered thus provide a tangible and / or visual indication proving this fact.

[0111] In the embodiment of Fig. 10, the liquid detection indicator 10 is arranged in a propeller shaft seal box behind what ordinary is referred to as a rope guard 41. Lip seals typically defined as single acting seals, which in the illustrated embodiment are numbered as 42-1, 42-2, 42-3, and 42-4. Chamber 46 is in this example filled with and pressurised by oil. This can be mineral or EAL-type oil.

[0112] Seal box preferably refers to an assembly of parts which interfaces a stationary body, and a rotating body, thereby allowing for movement / rotation of one body with relation to the other body, whilst preventing leaks between the bodies. As an example, a propeller shaft seal box separates sea water from the propeller shaft lubrication oil.

[0113] Seal 42-1 and 42-2 are arranged to prevent water ingress to the void 33.

[0114] The void 33 may be oil filled, or dry, typically meaning that there is no liquid, such as oil or water in the void 33 although oil typically occupies the void 33. In embodiments, the void 33 is oil filled, the liquid soluble element is non-soluble by the oil, but soluble by water, such as sea water. Hence, in such embodiments, the liquid detection indicator 10 will be triggered only when the oil originally occupying the void 33 has been adequately diluted with water or replaced with water, such as seawater, thereby indicating leaking seal 42-1 and 42-2. Such a leak will typically negatively affect the lubrication of both seal 42-2 and 42-3, where 42-3 is a critical seal for preventing oil loss to sea. Dotted line in Fig 10 illustrates flow path for water ingress into void (33) and further into channel 6.

[0115] Fig 10 is mainly for illustration purposes, as any number of seals and seal orientation can be used. Point being that LDI 10 can be installed in any chamber either dry or oil filled. Using a liquid detection indicator 10 in a seal box may allow for detection of water ingress to a chamber equipped with liquid detection indicator. This also includes seal boxes for vertical shafts. Locating a liquid detection indicator 10 in the lower part of the Chamber, allows water to "fall down" and at least partly come in contact with Liquid soluble element 3 thereby trigger LDI 10. This as water have higher specific gravity than oil.

[0116] To provide for triggering of the liquid detection indicator by water, the liquid soluble element 3 is in the embodiment of Fig. 10 a water soluble element. In case of failure or malfunction of any combination of outer seal(s) (e.g. the two seals 42-1 and 42-2 in Fig. 10), a flow passage 44 is generated allowing water such as sea water to enter into the void 33 as illustrated in Fig. 10 by the dotted line labelled 44. Once water enters into the void 33, the water enters through the channel 6 and begin to dissolve the water soluble element 3, resulting in a triggering of the liquid detection indicator 10. Although the seals illustrated in Fig. 10 are illustrated as single acting seals, one or more such as all of the illustrated seals may be double acting seals.

[0117] As indicated in Fig. 10, the seals 42 extend the full circumference of the wear liner 43 (being a cylindrical element) and the liquid detection indicator 10 may be placed typically at lower position in the seal housing by arranging the liquid detection indicator with the opening of the cavity 14 facing upward as in Fig. 10, gravity which acts downwardly in Fig. 10 assist in water such as sea water to "fall" into the cavity 14 and at least partly into contact with the liquid soluble element 3. Such a gravity assisted flow may mitigate or even eliminate the risk of air pocket(s) being trapped inside the channel 6 and in the cavity 14.

[0118] Thus, in preferred embodiments in which an apparatus comprising an element having multiple degrees of freedom such as rotating (e.g. steerable thruster, and / or liftable (retractable thruster) or a swing up thruster) during use of the apparatus, the liquid detection indicator 10 may advantageously be arranged in the rotating (steerable, liftable, or swing up-capable) element in an orientation which allows a liquid affected by gravity to come in contact with water soluble element with an outward facing opening 45 of said cavity 14 facing in direction in which a normal to a plane spanned by outward facing opening 45 forms an acute angle, preferably lower than 90 degrees, with a direction of centrifugal force arising due to rotating of the rotating element or is aligned with the direction of the centrifugal force. In preferred embodiments, the channel(s) is arranged with a longitudinal orientation, such as a dominant longitudinal orientation, of the at least one channel 6 forming an acute angle, preferably lower than 90 degrees, with a direction of the centrifugal force arising due to rotating of a rotating element in which the channel(s) is provided or is aligned with said direction of the centrifugal force. A dominant longitudinal orientation typically refers to the orientation of a straight line connecting an opening of the channel facing into the void 33 and an opening of the channel facing into the cavity 14. Inspection of whether or not the liquid detection indicator has been triggered can be made e.g. by removing the rope guard or by providing an inspection hatch in the rope guard, or even feel using finger inside a designated inspection bore.

[0119] Although the embodiment of Fig. 10 has a single channel 6, multiple channel 6 including water repellent and / or capillary material such as a capillary cord (as disclosed herein) may be applied to the embodiment of Fig. 10.

[0120] LIST OF REFERENCE SYMBOLS USED:

[0121] 1 Plunger

[0122] 3 Liquid soluble element

[0123] 4 Exterior

[0124] 5 Double acting seal(s)

[0125] 6 Channel

[0126] 7 Double acting inner seal

[0127] 8 Housing

[0128] 9 Sealing surface for seal 5

[0129] 10 Liquid detection indicator

[0130] 11 Lead in edge for seal 5

[0131] 12 Sealing surface for seal 15

[0132] 13 Thread

[0133] 14 Cavity

[0134] 15 Seal (typically being a static seal)

[0135] 16 LARD (Liquid Activated Release Device)

[0136] 17 Double-acting outer seal

[0137] 21 Associated apparatus

[0138] 23 Actuator part

[0139] 24 Cover

[0140] 25 First (1st) part of trigger element

[0141] 26 Second (2nd) part of trigger element

[0142] 27 Groove for seal 5

[0143] 28 End (which may protrudes to generate a visual signal) of plunger

[0144] 29 Energy storage, such as a spring

[0145] 30 Interior flexible wall

[0146] 31 Receptacle

[0147] 32 Tubular passage

[0148] 33 Void (between seals)

[0149] 34 Counterbored hole

[0150] 35a Water repellent material, cord impregnated with a material to make it liquid preferably water repellent

[0151] 35b Capillary material, such as a capillary cord (a wick)

[0152] 36 Through-going opening

[0153] 37 Slits 38 Propeller hub

[0154] 39 Controllable pitch propeller blade

[0155] 40 Water filled space (under rope guard)

[0156] 41 Rope guard 42-n Single acting seal, n refers to 1st, 2nd, 3rd, or 4th

[0157] 43 Wear liner; rotates with the propeller

[0158] 44 Water passage

[0159] 45 Outward facing opening of cavity

[0160] 46 Chamber 47 Chamber

[0161] 48 Members of the Seal housing

Claims

CLAIMS1. A liquid detection indicator (10) configured, preferably in an air filled cavity, to provide an indication if liquid leakage into a cavity (14) housing a liquid soluble element (3) provided in a housing (8) of said indicator, said liquid detection indicator (10) comprises:• a plunger (1),• a potential energy storage, preferably a spring (29),• said liquid soluble element (3) is arranged at least partly within said cavity (14),• a trigger element (25, 26) which when said liquid soluble element (3) is exposed to liquid which dissolves the element, provides said trigger element (25, 26) to release potential energy from said storage (29) to said plunger (1) either directly, or via a separate actuator member (23) so that at least a part of the plunger (1) moves and directly or in-directly provides one from an exterior (4) of the liquid detection indicator (10) visible and / or tangible indication, preferably being this exposing a protruding surface, or change of shape or orientation and / or dis-location of a cover (24); wherein• said liquid detection indicator (10) comprising a seal (5) configured to protecting said cavity (14) against said exterior (4) prior to said movement of plunger (1).

2. A liquid detection indicator (10) according to claim 1, wherein said seal (5) protecting said cavity (14) is a double acting seal (5) protecting said cavity (14) against said exterior (4) and prevent an interior liquid from leaking to said exterior preferably prior to, preferably during and preferably at an end of said movement of said plunger (1).

3. A liquid detection indicator (10) according to claim 1 or 2, wherein said cavity (14) is pre-filled with an oil, such as a lubrication oil, and wherein said liquid soluble element is essentially non-soluble by said oil.

4. A liquid detection indicator according to any one of the preceding claims, wherein said liquid detection indicator is configured to provide said visible indication as a change in shape and / or a change in colour.

5. A liquid detection indicator according to any one of the preceding claims, wherein said housing (8) having an upper surface facing towards said exterior (4) and comprising a through-going (36) opening extending from said exterior (4) and into said cavity (14), and wherein an end (28) of said plunger (1) protrudes into said through-going opening (36).

6. A liquid detection indicator according to claim 5, wherein• at least a section of said plunger (1) extends through said through-going opening (36), and• said through-going opening (36) comprising a sealing surface (9) and said plunger (1) comprising one or more, seals such as double acting seals (5) cooperating with said sealing surface (9) to provide said protection of said cavity (14) against said exterior (4), preferably prior to, preferably during and preferably at an end of said movement of said plunger (1).

7. A liquid detection indicator according to any one of the preceding claims, wherein one or more seals, such as double acting seals (5), are provided in said housing (8), preferably at said through-going opening (36), preferably, a part of the plunger (1) which extends through said through-going opening (36) is provided with a sealing surface (9).

8. A liquid detection indicator according to any one of claims 5-7, wherein said liquid detection indicator is configured to position at least a section of said end (28):• above said upper surface,• flush with said upper surface, or• recessed relatively to said upper surface prior to said movement of the plunger (1).

9. A liquid detection indicator according to any one of the preceding claims 5-8, wherein said liquid detection indicator is configured for providing said visible indication as a change in a position of plunger (1) to a position wherein at least a section of said end (28) is above said upper surface.

10. A liquid detection indicator according to any one of the preceding claims 5-9, comprising a cover (24) covering an outer opening of said through-going opening prior to said movement and wherein plunger is configured to act upon said cover (24) during said movement to change a shape of said cover, or to make said cover (24) to change position or come off.

11. A liquid detection indicator according to any one of the preceding claims, wherein said seal (5) protecting said cavity (14) comprising one or more of an X- ring-seal, or O-ring-seal, or U-shaped seal, or V-shaped seal or trapetzodial shaped seal or square shaped seal or combinations thereof.

12. A liquid detection indicator according to any one of the preceding claims, comprising• a receptacle (31) made from a non-soluble material, such as plastic, in which said liquid soluble element (3) is housed, and comprising a tubular passage (32) defined by an interior flexible wall (30) from which a first part (25) of said trigger element (25, 26) extends radially inward, wherein• a longitudinal section of said plunger (1) extends in said tubular passage (32) and having a second part (26) of said trigger element (25, 26) extending radially outward,• said first and second parts of said trigger element (25, 26) are configured to engage with each other to prevent said movement of said plunger (1) thereby prevent the release of stored energy (29) when said soluble element (3) is not at least partly dissolved,• said interior flexible wall (30) is configured to flex upon the liquid soluble element (3) being at least partly dissolved to provide a disengagement between said first and the second parts of said trigger element (25, 26) to allow said movement of said plunger (1).

13. A liquid detection indicator according to claim 12, wherein said interior flexible wall (30) comprising longitudinal extending slits (37).

14. A liquid detection indicator according to any one of the preceding claims, wherein the liquid soluble element (3) is made from cellulose, sugar, sodium chloride, calcium, or combinations thereof.

15. A liquid detection indicator according to any one of the preceding claims, wherein said plunger (1) comprising an actuator part (23) to which said potential energy is released.

16. A liquid detection indicator according to any one of the preceding claims, wherein said liquid soluble element (3) is positioned directly exposed said cavity (14).

17. A liquid detection indicator according to any one of the preceding claims, wherein said potential energy storage comprising a spring (29).

18. A liquid detection indicator according to any one of the preceding claims, wherein said liquid is seawater, freshwater or brackish water.

19. A liquid detection indicator according to any one of the preceding claims 1-17, wherein said liquid is coolant or any polar liquid.

20. A liquid detection indicator according to any one of the preceding claims, wherein said liquid soluble element (3) is water soluble.

21. An apparatus comprising a first part and a second part, said first part is arranged on or at said second part and said apparatus comprising an outer seal, such as an single acting seal or a double acting seal (17) and an inner seal, such as a single acting seal or a double acting seal (7) between said first part and said second part, forming a void, wherein said apparatus comprises• a liquid detection indicator (10) according to any one of the preceding claims, wherein said housing (8) is arranged, preferably in a counterbored hole (34) of said apparatus, preferably so that said visible and / or tangible indication is / are recognizable from said exterior;at least one channel (6) fluidicly connecting a void (33) located in-between said double acting inner seal (7) and said double acting outer seal (17) with said cavity (14).

22. An apparatus according to claim 21, comprising one or more, such as two or three channels (6) fluidicly connecting said void (33) with said cavity (14).

23. A apparatus according to claim 21 or 22, wherein said double acting outer seal (17) and / or said double acting inner seal (7) each comprising one or more of X- ring-seal(s), O-ring-seal(s), U-shaped seal(s), V-shaped seal(s), Y-profile seal(s), trapetzodial shaped, square shaped, or any shape, or combinations thereof.

24. An apparatus according to any one of the preceding claims 21-23, wherein one or more, such as all said channels (6) has / have been provided with a hydrophilic coating.

25. An apparatus according to any one of the preceding claims 21-24, comprising a capillary material (35b), such as a cord made from cotton arranged in one of said channels and extending between said void (33) and said cavity (14), preferably towards or in contact with said liquid soluble element (3).

26. An apparatus according to any one of the preceding claims 21-25, comprising a liquid repellent, preferably water repellent material (35a), such as a cord made from impregnated cotton arranged in one of said channels and extending between said void (33) and said cavity (14), thereby allowing air escape via this bore by preventing liquid entering this bore.

27. An apparatus according to any one of the preceding claims 21-26, wherein one or more, such as all said channels each have a hydraulic diameter being less than 6.0 mm and larger than 1.0 mm.

28. An apparatus according to any one of claim 21-27, wherein• said apparatus comprising an element rotating during use of the apparatus, and• the liquid detection indicator (10) is arranged in said rotating element with an outward facing opening (45) of said cavity (14) facing in direction in which a normal to a plane spanned by said outward facing opening (45) forms an acute angle, preferably lower than 90 degrees, with a direction of centrifugal force arising due to rotating of said rotating element or is aligned with said direction of the centrifugal force.

29. An apparatus according to any one of the preceding claims 21-28, wherein said at least one channel is in an element rotating during use of the apparatus and is arranged with a longitudinal orientation, such as a dominant longitudinal orientation, of the at least one channel (6) forms an acute angle, preferably lower than 90 degrees, with a direction of a centrifugal force arising due to rotating of said rotating element or is aligned with said direction of the centrifugal force.

30. An apparatus according to any one of the preceding claims 21-29, wherein the first part is a propeller hub (38) and the second part is a pitchable propeller blade (39).

31. An apparatus according to any one of the preceding claims 21-30, wherein said apparatus comprises a propulsion device for a vessel or comprises components of a tidal turbine.

32. An apparatus according to any one of claims 21-31, wherein said cavity (14) is pre-filled with an oil, such as a lubrication oil, and wherein said liquid soluble element is essentially non-soluble by said oil.

33. An apparatus according to any one of the preceding claims 21-32, wherein said liquid detection indicator is arranged in a seal box of said apparatus, wherein• said seal box comprises one or more seals configured to seal an oil containing interior of said apparatus from an exterior of said apparatus, and• said apparatus is submerged in water, such as sea water, during use of the apparatus, at least to an extend where said seal box is submerged• said liquid soluble element is soluble by water, such as seawater.

34. An apparatus according to any one of the preceding claims 21-33, wherein said liquid detection indicator (10) is arranged in said apparatus in an orientation with an outward facing opening (45) of said cavity (14) facing in direction in which a normal to a plane spanned by outward facing opening (45) forms an acute angle, preferably lower than 90 degrees, with a downward direction of gravity or is aligned with said downward direction of gravity during use of the apparatus.

35. An apparatus according to any one of the preceding claims 21-34, wherein said channel(s) (6) is arranged with a longitudinal orientation, such as a dominant longitudinal orientation, said channel(s) (6) forming an acute angle, preferably lower than 90 degrees, with a downward direction of gravity or is aligned with said downward direction of gravity during use of the apparatus.

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