TECHNICAL FIELD

Pressure sensing device, comprising a diaphragm having a first pressure chamber on one side and a second pressure chamber on a second side, wherein said first and second pressure chambers are connected to a system pressure by means of flow passages having different cross sectional passage area arranged to facilitate detection of a pressure change.

BACKGROUND ART

In many applications it is desired to be able to sense a pressure and/or a change in pressure, e.g. a pressure drop. One such application area is diving equipment provided with means for sensing breathing, e.g. to enable activation of safety measures in conjunction with too long breathing paus.

In skin diving with dive tanks, so called SCUBA diving (Self Contained Underwater Breathing Apparatus), the diver is provided with air from pressure tanks that he carries with him during the dive. For obvious reasons it is extremely important that the diving takes place in an appropriate way in order for accidents not to occur. Most persons that plan to dive choose to participate in training before starting to dive for real. Throughout the years, many appliances have been developed in order to prevent accidents in connection with diving. One example is the inflatable diving jacket carried by the diver, which helps him to control buoyancy and which is used in combination with weights in order to help the diver to descend. Examples of other appliances are tables and portable dive computers that help the divers to plan diving in order not to risk the bends or having to surface quickly because air is running out e.g. The diving equipment itself has also developed and has been provided with devices that aim to prevent accidents. Most of these devices have the object of sensing any problems arising or to facilitate for the diver during a dive.

Numerous safety devices in connection with diving equipment are previously known, which intend to give improvement in respect of the shortcomings described above, e.g. FR 2741853 EP 034569, US 4,176,418, US 5,746,543 and US 5,560,738 which all present some disadvantage/s. Rather recently there has been presented a concept that provides an elegant conceptual solution, disclosed in WO2008143581 and WO2007058615, and further developed as disclosed in WO2011108985. However also in relation to these disclosures there is room for improvement that may increase safety even more and/or improve other aspects.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a pressure sensing device, to be used in connection e.g. in connection with the diving equipment, that provides high reliability and is compact, which is achieved by means of pressure sensing device in accordance with claim 1.

Thanks to the invention there is provided a pressure sensing device that may provide more accurate sensing and having a design that may provide extra compact that will allow for scalable production and maintaining high reliability.

According to one aspect of the invention the breathing sensing device comprises multiple interconnected diaphragms having a first pressure chamber on one side and a second pressure chamber on a second side, wherein said first and second pressure chambers are connected to a system pressure by means of flow passages having different cross sectional passage areas arranged to facilitate detection of a pressure drop.

Said cross sectional passage areas of said flow passages are preferably arranged to be constant through a pressure change in said system pressure LI . The relation of cross sectional passage area between the cross sectional passage area providing a restricted flow passages to and/or from second pressure chamber may be in the range of 1/2 - 1/1000 in relation to the cross sectional passage area providing a flow passage to and/or from the first pressure chamber. Thanks to the design according to the invention there is acquired a momentary pressure difference between said first and second pressure chambers as a consequence of a pressure change in said system pressure.

According to a further aspect of the invention it is provided that between said second pressure chamber and the system pressure, there is a arranged a further, sealed through passage, having a seal arranged to open said passage above a pressure drop that exceeds a pressure drop that may caused by breathing within said system pressure, wherein preferably Apopen> 3 bar, more preferred 4 - 9 bar, which provides the advantage that the breathing sensing device will not be exposed to undesired forces in relation to sudden pressure increases within the system, e.g. when connecting a new pressure vessel to a diving system.

According to further aspect it is provided that also the height of said pressure chambers is limited to provide compactness, and that a sufficient volume in communication with the second pressure chamber is achieved by arranging at least one additional distributed chamber in connection with said second pressure chamber which provides the advantage that the balancing volume needed for reliable sensitivity of the breathing device is maintained also if the system pressure changes, e.g. in connection with moving up and down in water of a diver, and at the same time provide a compactness of the actuator device itself, due to the fact that the relatively large volume is needed to achieve desired reliability. Hence if all of that volume needed is placed within the balancing pressure chamber itself, it will lead to a bulky unit. According to further aspect of the invention it is provided that at least one of said passages is adjustably arranged, which provides the advantages that the sensitivity of the breathing sensing device may be adjusted in accordance with different desires. According to further aspect of the invention it is provided that pistons are fixedly connected to said diaphragms, at least one of said pistons being fixedly connected to a valve body interacting with a seal, which provides the advantage that the diaphragm with the piston unit may be used to operate devices within the unit using the breathing sensing device.

According to further aspects of the invention it is provided that at least said end portion of said piston is arranged to provide a balanced configuration in relation to the surrounding pressure influence, which provides the advantage that the breathing sensing device will not be affected by pressure differences acting on a piston connected to the diaphragm. According to further aspect of the invention it is provided that said piston is arranged to provide an area difference exposing a larger area of the diaphragm in the first pressure chamber than the area exposed in the second pressure chamber, which provides the advantage that a continuous force will be applied across the diaphragm in a closing direction also when the pressure in both pressure chambers are equal. BRIEF DESCRIPTION OF THE FIGURES

In the following the invention will be described with reference to the appended drawings, wherein: presents a cross sectional view of a prior art actuator housing of a breathing sensing arrangement, schematically showing the different aspects of the arrangement,

presents a diagram schematically presenting pressure development over time in the pressure chambers around a diaphragm and in the timer volume chamber within the prior art breathing sensor arrangement of fig 1,

shows a corresponding diagram as in Fig. 2, showing a different scenario compared to the one presented in Fig. 2, and

presents the principles of the cross sectional design of an actuator according to the invention,

shows a perspective view of a vertical cross sectioned of one embodiment of possible design aspects of an actuator according to the invention, presents a table confirming the good effect of an actuator according to the invention,

presents a diagram schematically presenting pressure development over a time in the pressure chambers and in the timer volume chamber within a breathing sensor arrangement being equipped with an actuator according to the invention, and,

shows schematically the principles for an alternative embodiment according to the invention for activation of a valve by means of a diaphragm.

DETAILED DESCRIPTION

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings. Further, the description, and the examples contained therein, are provided for the purpose of describing and illustrating certain embodiments of the invention only and are not intended to limit the scope of the invention in any way.

In Fig. 1 there is shown, in cross section, a schematic view of a prior art actuator 8. Within the housing 8 there are arranged channels LI connected to the supply pressure of oxygen from the first stage (not shown) and channels 7 connected to ambient pressure. These channels LI, 7 are interconnect via a number of mechanical valves arranged in the body 8 to fulfill the functionality in accordance with the invention, as will be described in detail below.

Adjacent a first end of the actuator body 8 there is arranged a diaphragm 200 of an ON/OFF valve OV. This valve OV may be affected by water pressure to be activated into the "on mode". This is achieved by means of the water pressure acting on an outer side of the diaphragm 200. The other side of the diaphragm 200 is balanced by air chamber 201 that is calibrated to allow the diaphragm to move into active state at the desired calibrated pressure. Before applying system pressure (i.e. by connecting the actuator 8 to a first stage of a diving regulator) air chamber 201 is open towards the atmosphere via a valve 202 and channel 7 hereby being in connection with ambient pressure. Once system pressure is applied (air tank is opened), air will flow through channel LI and said valve 202 is affected to move into a closed position, thereby closing the interface between the environment and the chamber 201 underneath the diaphragm 200. The air chamber 201 is thus hermetically closed, and calibrated to the environmental pressure at the surface. Accordingly, when the water pressure acting on the diaphragm 200 exceeds a certain pressure, a piston 208 fixedly attached to the diaphragm will move downwards into contact with a seal 220 and thereby open up connection to the hollow channel 230 within the piston 208 to a restriction passage 212 leading to a timer volume 213, which is achieved by means of grooves (not shown) on the inner wall of the piston 208, above the inactive position of the seal of sealing body 240 within the hollow channel 230. Hence, when inactive (neutral diaphragm 200) the body 240 seals, but when active (diaphragm 200 and piston 208 move downwards) air will pass by the body 240. The timer volume 213 will hereby slowly be filled in order to gradually build up the pressure therein. The restriction passage 212 is preferably extremely small to allow the actuator body to be very compact. In other words, a very little flow of air through the restriction 212 should be allowed, to provide sufficient time for the small volume 213 to achieve the function of the timer volume 213, i.e. opening up the release valve 25 when no breathing has occurred for a predetermined amount of time. The timer volume 213 is positioned next to the on/off valve OV. The release valve 25 is positioned adjacent the opposite end of the actuator body compared to the ON/OFF valve OV. Between the release valve, RV, and the timer volume, TV, there is arranged the activity sensor valve, AV. This valve AV also comprises a diaphragm 100 having a piston 103 fixedly attached thereto. The piston 103 has a seal, for example an upper lip seal, arranged to seal against flow towards the timer volume TV. Also the piston valve of the AV is hollow, i.e. provides a central passage 111. On one side of the diaphragm 100 there is a pressure chamber 120 in contact with the system pressure line LI . Below, on the other side of the diaphragm 100, there is a pressure chamber 121 providing a balancing pressure. The flow connection opening 153 between the upper chamber 120 and the system pressure LI is rather large, e.g. to about 2 mm/diameter to allow unrestricted flow there between. The balancing pressure in the lower chamber 121 is achieved by providing a flow restriction arrangement 130 with a restricted passage 143 between the system pressure LI and the lower pressure chamber 121. In one aspect the restriction passage 143 is combined with a kind of check valve functionality that is obtained by means of e.g. a lip seal 144. The skilled person understands that it is also possible to use other types of flow restriction arrangements 130.

Thanks to this design the AV will empty the timer volume 213 in connection with sensing of a breathing. The pressure development inside the pressure chambers 120, 121 around the diaphragm 100 as well as within the TV chamber 213 will now be described with reference to the details of Fig. 1 and the diagrams presented in Figs. 2 and 3.

In Figs. 2 and 3 graph A is the pressure inside upper pressure chamber 120 (direct pressure) over time and graph B shows the pressure inside lower pressure chamber 121 (delay pressure) over time. Graph C in Figs. 2 and 3 represents the pressure inside timer volume chamber 213 over time.

In brief, when a breathing occurs (see time point a) in Fig. 2) the system pressure LI will suddenly drop and thereby simultaneously provide a pressure drop in the upper chamber 120 (see graph A in Figs. 2 and 3). However, the lower chamber 121 (see graph B in Figs. 2 and 3) will maintain a higher pressure for a while thanks to the restriction passage 143. As a consequence, a force AF will act on the diaphragm 100 and move it and thereby the piston 103 will move up from the seat 107, to interconnect the timer volume 213 with ambient pressure 7 (see time point b) in Fig. 2). When the system pressure slowly again increases, the opposite phenomena will occur, i.e. that the for a while lower pressure will occur 121 in the lower chamber 121 thereby

safeguarding closing of the piston 103 against the seat 107 (see time point c) in Fig. 2). Consequently, again the timer volume 213 will be closed and sealed to successively fill up pressure via flow through the restriction 212. Looking at the diagram in Fig. 3, here is seen a scenario where breathing has stopped (time point a), and pressure inside pressure chamber 213 is increasing (graph C) until the release valve RV is opened leading to that pressure in volume chamber 213 is nullified (time point b).

In order to further safeguard the sealing of the piston 103 against the seat 107 the upper portion 103 A of the piston 103 preferably has a smaller outer diameter and through passage than the lower portion 103B. Further, the piston 103 is so positioned in relation to the diaphragm 100 that part of the undermost area of the diaphragm 100 is covered by the corresponding lower portion of the piston 103B leading to a reduced pressure area compared to the opposite upper side of the diaphragm 100. Thus, at balanced pressure (i.e. when the pressures inside upper 120 and lower 121 chambers respectively are equal), the difference in pressure area leads to that the diaphragm 100 is biased downwards pushing the piston 103 against the seat 107.

There is preferably a lip seal 144 around the AV restriction 130, which lip seal 144 will open up when there is major (and sudden) increase of the system pressure LI, e.g. in connection with change of pressure vessel. Accordingly, the lip seal 144 always seals in the direction from the lower pressure chamber 121 to the system pressure LI, but may open in the other direction if the pressure difference between the supply line LI and the lower chamber 121 exceed a certain level, e.g. 2 bars. Thanks to this arrangement the diaphragm 100 will not be exposed to any major pressure differences, at the same time as the chosen pressure level of opening of the lip seal 144 is chosen such that it may not occur due to the pressure drop provided during breathing.

In order to obtain a desired functionality by means of the membranes 100 A, B there is a need for very quick response in relation to the airflow in conjunction with breathing of the diver. It is the pressure drop that occurs during breathing that need to be identified. This pressure drop may be about 0.5 bars, normally within 0.2-1.5 bars and need to be sensed independent on which pressure that exists in the supply line Lib. This is a necessity for instance because a diver will move between different depths leading to different pressure levels, etc. By means of the new valve arrangement it is feasible to quickly identify that breathing is initiated. In order to establish a sufficient difference in pressure between the chambers 120 A, 121 A and 120B, 12 IB respectively the reduction of through passage area A _r in connection with the slow pressure chamber 121 A, B may preferably be in the magnitude of about 1/20-1/50 in relation to the area Af of the flow passage 153 to the upper chamber 120. At least there is a need of a relation between 1/2, but it may possibly be as large as 1/1000. In the used embodiment the through hole 122 for allowing free passage of air to the upper chamber has a diameter about two millimeters, and accordingly the diameter of the restricted passage preferably corresponds to about 0,04-0,1 mm.

It is evident for the skilled person that the functionality that has been described above in relation to the restriction arrangement 130 may easily be achieved in various manners without as many details as has been described above. In an extreme embodiment all of it may be included in one single unit just presenting a desired fixed restriction passage 143 in combination with the kind of check valve functionality that is obtained by means of the lip seal 144. Accordingly, many variations may be made to the exact design of this arrangement 130.

In Fig. 4 there is shown a schematic side view of a valve arrangement AV in accordance with the invention. The basic working principal of this valve arrangement AV is the same as for the corresponding valve AV according to what is described and presented in Figs. 1, 2 and 3 above.

A major difference in a relation to the prior art, is that there are two diaphragms 100A, 100B. These two diaphragms 100 A, 100B are interactively connected to each other by means of a piston member 300, extending between the two diaphragms that are coaxially positioned, and wherein the rod member 300 extends centrally along the common axis C. The two diaphragms may preferably have the same diameter Dl . The first diaphragm 100 A is positioned between a first delay pressure chamber 121 A on a first side thereof, and a first direct pressure chamber 120 A on the other side of the diaphragm 100 A. The first delay pressure chamber 121 A is connected to the system pressure line LI via a first flow line 143 A having a throttling member 143B providing restricted flow area Ar. The first direct pressure chamber 120 A is in connection with the system pressure line LI via an unrestricted flow line 153 A having an unrestricted flow line with a larger (smallest) cross-sectional area Af.

The first direct pressure chamber 120 A is positioned on a side of the diaphragm 100 A that faces in direction against the second diaphragm 100B. On this side of the diaphragm 100 A there is centrally fixedly attached a first slim piston portion 306 of the piston member 300. A corresponding slim piston portion 301 is fixedly attached with its remote end centrally to the second diaphragm 100B. Accordingly these slim rod portions 301, 306 will be pointing against each other. The diameters dl of the slim piston portions 301, 306 are preferably the same and also preferably presents the smallest diameter dl of the piston member 300.

Fixedly connected to the end of the second slim piston portion 301 there is valve body 302. This valve body 302 is interacting with a valve seat 303, in such a manner that when the diaphragms 100A, 100B are in a balanced state, the valve body 302 will sealingly be in contact with the valve seat 303. Accordingly, when the second diaphragm 100B moves in a direction away from the valve seat 303, it will also move the valve body 302 away from the valve seat 303 and thereby open a passage that is arranged at the center of the valve seat 303.

Also the upper diaphragm 100 A may act on the valve body 302. This is achieved by having the first slim rod portion 306 connected to an intermediate piston portion 304, which in turn is connected to a central rod portion 305 that is in contact with the valve body 302. The rod portions 301 - 306 may be integrated, to form one single integrated rod unit, or may also be divided in different parts, wherein the first slim piston portion 306 may form a first separate part and/or having the intermediate and central portions forming a separate part. However, it is a necessity to have the second slim piston portion 301 fixedly connected to the valve body 302. The reason for this is that the second slim piston portion 301 will act with a pulling force on the valve body 302, whereas the other rod portions 304, 305, 306 will act by means of pushing onto the valve body, i.e. from the opposite direction compared to the pulling force of the second slim piston portion 301.

As shown the intermediate rod portion 304 preferably is arranged with a relatively large diameter D2, due to the fact that there is a need of a sealing 320 to interact with the cylindrical surface of the intermediate portion 304. Preferably an O-ring is used for this purpose. As is well-known O-rings of too small diameter may not be very reliable and therefor it is an advantage to have the intermediate portion 304 to present a relatively large diameter D2, e.g. in a range of 2-30 mm preferably at least 4 mm. Also against the valve body 302 there is a need of a sealing 321. Therefor also the valve body 302 preferably presents a diameter D4 that is relatively large, e.g. in a range of 20-30 mm, preferably at least 4 mm. The two seals 320, 321 seal an upper chamber 312 and a lower chamber 313 on opposite parts of the valve seat 303. The valve seat 303 has an opening D3 that is smaller than the diameter D4 of the valve body, such that the valve body 302 may safely seal against the seat 303. The upper chamber 312 is in communication with environment, e.g. the water pressure depending on the deep. The lower chamber 313 is connected to the timer volume chamber TV. Further, the diameter D4 of the valve body 302 is preferably larger than the diameter D2 of the intermediate piston portion 304, in order to present a larger surface area A2 pushing against the valve seat 303 than the surface area Al pushing in the other direction, which is a result if, as is preferred, the slim portions 301, 306 having the same diameter d.

The second diaphragm 100B is arranged in a corresponding manner as the first diaphragm 100A, i.e. with a second delay pressure chamber 121B on a first side of the diaphragm and second direct pressure chamber 120B on the second side of the diaphragm 100B. The second delay pressure chamber 12 IB may be connected to a restricted flow either coming from the first low pressure chamber 120 A, or directly as a branch 143B from the supply line 143 A, and having similarly acting throttling devices HOB, 1 10B' to provide a desired restricted cross-sectional area Ar for the flow to the second delay pressure chamber 12 IB. Also if supply is arranged via the first delay pressure chamber 121 A there is a need of a further throttling member HOB' in the supply line 143B'. In a similar manner the supply to the second- high pressure chamber 120B may be arranged either directly, e.g. as a branch line 153B of the first line 153A, or via a line 143B' leading a supply from the first direct pressure chamber 120A.

In Fig. 5 there is shown a perspective schematic view of a valve arrangement as presented in connection with Fig. 4. It is shown how, in accordance with one

embodiment, the different members described in connection with Fig. 4 may be positioned and arranged physically, as is well understood by the skilled person from the description presented in connection with Fig. 4 and therefore merely some specific features will be mentioned in the following. It is seen that the piston member 300 is one integral unit and has an intermediate portion 304 with a diameter that preferably is just slightly smaller than the diameter of the valve body 303, sufficiently to achieve the desired sealing force, as described above. However, thanks to the resiliency of the diaphragm it may often be sufficient do use that force to reposition the valve body 302 in its sealing position, without any need of diameter difference, i.e. a kind of slide valve, as indicated in Fig. 5. Also it is shown that the piston member 300 is enclosed by a valve housing 330 having a first radial bore 312 for connection to ambient pressure and a second radial bore 313 for connection to the timer volume TV. The seals 320, 321 are here arranged in grooves in the cylindrical surface of the intermediate portion 304 and the valve body 303 respectively. The central portion 305 is arranged by having ring shaped space 314 between the intermediate portion 304 and the valve body 303. The slim portions 301, 306 are connected to plate like devices 301 A, 306 A that are integrated to the center of each respective diaphragm 100A, 100B. Limit stop members 301B, 306B may preferably be arranged.

The functioning of the valve arrangement according to the invention as exemplified in Fig. 4 and 5, is similar to that described in connection the prior art, i.e. when a diver breathes there will be a pressure drop, which pressure drop will act onto the diaphragms 100 A, 100B. Due to the restricted flow to the delay pressure chambers 121 A, 121B a pressure drop will be achieved quicker in the direct pressure chambers 120A, 120B, resulting in a movement of the diaphragms (downwardly in Figs. 4 and 5) that will move the valve body 302 out of contact with the valve seat 303 and thereby open up a passage between the ambient pressure and the time volume chamber, thereby cause a resetting. According to the embodiment shown in fig. 5 this will be achieved by having the ring shaped space 314 moving downwardly in communication with the radial bore 313 for connection to the timer volume TV. Thanks to the arrangement according to the invention there are several advantages that are gained. Firstly, the diameter Dlof the diaphragms 100A, 100B may be drastically reduced in comparison with prior art devices, which will provide for the possibility of making a much more compact valve arrangement. Secondly the piston member arrangement 300 that may be provided thanks to the inventive arrangement allows for use of appropriate sealing members 320, 321 to achieve very high reliability.

In Fig. 6 there is shown a table presenting beneficial sensitivity results, (with figures provided in Newton) i.e. large AF, when using a double diaphragm arrangement according to the invention despite using a diaphragm diameter Dl being as small as 25 mm. When using a prior art arrangement, it would be necessary to have a significantly larger diameter of the diaphragm, e.g. 80 mm, i.e. at least 2,5 times the diameter as that of the invention, to achieve the same level of sensitivity.

In Fig. 7 there are shown graphs that compare the ability of improving sensitivity by the use of valve arrangement in accordance with the invention. In brief, when a breathing occurs (see time point a) in Fig. 7) the system pressure LI will suddenly drop and thereby simultaneously provide a pressure drop in the direct pressure chambers 120A, 120B, (see graph A in Fig. 7). However, the delay pressure chambers 121A, 121B (see graphs B and B' in Figs. 7) will maintain a higher pressure for a while thanks to the restricted passages 110A, 11 OB or 110A, 11 OB'. As a consequence, the diaphragms 100 A, 100B will exert a force 5F that in turn will move the piston and valve body 302 away from the seat 303, to interconnect the timer volume 213 with ambient pressure 7 (see time point b) in Fig. 7). As can be noted the serially connected delay chambers may provide extra delay (see graph B') and thereby a larger time slot when AF is above a resetting level compared to parallel connected chambers 121 A, 12 IB (as indicated by the dotted C-line). When the system pressure LI slowly again increases, the force AF will decrease thereby safeguarding closing of the piston 103 against the seat 107 (see time point c) in Fig. 7). Consequently, again the timer volume 213 will be closed and sealed to successively fill up pressure (see graph C after time point c) via flow through the timer restriction 212, where after the procedure will be repeated.

As can be noted a drastically more sensitive system may be achieved, thanks to having two diaphragms and two serially or parallel connected delay pressure chambers 121 A, 121B.

The function during normal use is such that when the diver breathes the above described small pressure drops will occur in the inlet line Lib. This pressure drop will

immediately be communicated to the upper pressure chamber 120. However, the lower pressure chamber 121 will not instantly be provided the same pressure due to the restricted passage 143 that connects inlet line Lib with said pressure chamber 121. Accordingly, there will for a moment, (about 20-50 ms) be created a pressure difference over the membrane 100, which in turn will affect the membrane 100 to flex in the direction where the lowest pressure resides. Hence the membrane 100 will move upwardly into the upper chamber 120 and thereby move the piston 103. Thereby the timer release activation will be obtained as described above and the actuator reset.

In Fig. 8 there is shown the principles of alternative solution to use a diaphragm 100 to obtain sensing of breathing and activation of a valve device 302, 303 in accordance therewith. There is shown that there is a lever 400 connected to the diaphragm 100. A first endpoint 401 of a first lever arm 402 is fixedly attached to the center of the diaphragm 100. The first lever arm 402 extends substantially in parallel with the diaphragm. A second lever arm 407 extends perpendicularly to the first lever arm 402 from a second end 409 of the first lever arm 402. The second lever arm 407 passes through an opening 403 in the delay pressure chamber 121. In this passage 403 there is arranged a sealing member 405 that pivotally keeps the lever 400 in place. In the shown embodiment this is achieved by means of an O-ring 405 that interacts with a

corresponding groove 406 in the lever. On the other side of the pivot point 405 the second lever arm 407 continues. The second lever arm 407 comprises an upper portion 407 A, and a lower portion 407B. The pivoting length L of the first lever arm 102 is larger than the pivoting length 1 of the second lever arm 407. In the shown embodiment the relationship is 2: 1, implying that twice the force will be achieved at the second end 408 of the lever 400 compared to that at the first end 401. At the end of the second lever arm there is attached the valve body 302. Thanks to the larger force supplied by the lever 400 it will be able to counteract the force from the pressure acting on the valve body 302 and therefore be able to lift the valve body 302 from the seat 303 to arrange for an open passage to supply resetting flow to the timer volume TV. It is evident that this solution for achieving the latter functionality is not restricted to the use of using two diaphragms, but may also be applied in applications using merely one diaphragm, since the solution eliminates loss of active area of diaphragm as is the situation if a centrally positioned piston rod is used and therefore a higher sensitivity may be achieved which in turn leads to the possibility of a very compact pressure sensing unit.

The invention is not limited by the embodiments presented above, but may be varied within a plurality of aspects without departing from the basic principles of the invention. Further, it is foreseen that the alternative embodiment shown in Fig 8 may be the subject for its own protection by one or more divisional applications, as may also be the case regarding other aspect/details described above and/or identified as dependent claims in the set of claims. Further the design shown in fig. 8 may of course also function having the valve/seat situated sideways in relation to the diaphragm, e.g. implying the use of a straight lever 407, but then with inversed arrangement of valve/seat or pressure chambers.