A CLOSED BREATHING SYSTEM FOR DIVERS

Abstract: A closed breathing system for divers, comprising a circulation circuit having a supply line (1) and a return line (2) for circulation of breathing gas through the helmet (3) of diver, a pump means (4) for pumping of the breathing gas in the circuit, a gas recovery means (9) arranged in the circuit, and a regulating valve (8) for controlling the breathing gas respectively to and from the diver's helmet (3). The pump (4) is a pneumatic pump which is constructed so that, at any time, it maintains a given relatively small pressure difference between the supply line (1) and the return line (2). In the supply line (1) there is connected a buffer volume (10) maintaining a positive supply pressure, the volume being provided with a means, such as a pneumatic cylinder (11), creating a counter-pressure on the gas in the buffer volume (10), and the regulating valve (8) is arranged to be operated under the influence of very small pressure variations in the helmet (3).

Description: A closed breathing system for divers The invention relates to a closed breathing system for divers, comprising a circulation circuit having a supply line and a return line for circulation of breathing gas through the helmet of a diver, a pump means for pumping of the breathing gas in the circuit, a gas recovery means arranged in the circuit, and a regulating valve for controlling the breathing gas respectively to and from the diver's helmet. In the later years it has become increasingly more necessary to be able to carry out operational diving at great depths. It has turned out that substantial problems are connected with such activity, and the problems are strongly increasing with the depth. Economic circumstances make it necessary to base oneself on systems which are able to recover and recirculate the breathing gas. The recovery normally takes place at the surface, and with traditional valve technology the recirculation requires a considerable energy consumption. Further, it has turned out to be problematic to procure a breathing system which is ergonomic, which is sufficiently easy to breathe with at large depths, and which in addition ensures sufficient escape time for the diver in case of interruptions in the gas supply etc. It has also turned out to be problematic to achieve a satisfactory communica- tion, since noise in gas regulating valves etc. increases strongly with the depth. Generally, there are two types of closed breathing systems for diving. One type is based on the demand principle, which is characterized in that the diver breathes through an oral-nasal mask, and breathing valves control the supply and return of breathing gas in accurate correspondence with the diver's demand. The use of an oral-nasal mask gives poorer ergonomics, but is necessary in order to avoid a high C0 2 level in the breathing gas. The other type of closed breathing system is based on free flow of the breathing gas. Here the diver breathes directly from the helmet, the resilient neck seal of the helmet being used as a buffer volume (breathing bag). In such breathing systems the C0 2 content is maintained at an acceptable level in that fresh gas continuously flows through the helmet. A general disadvantage of free flow is a high noise level and communication problems at great depths. Moreover, a considerable energy quantity is required in order to recirculate the conti¬ nuous gas flow. Some producers have tried to reduce the energy s demand by moving the electrical pump system downwards to a diving bell or a habitat forming part of the system. However, the divers have not been very positive to the fact that high-voltage current is then sent down to the region wherein they are to operate. The above problems have entailed that free flow systems today are o only used in commercial diving at shallow or intermediate depths. The object of the invention is to provide a breathing system which has a moderate energy demand and a good ergonomics, and which satisfies all existing demands and directions down to depths of at least 500 meters. s The above-mentioned object is achieved with a breathing system of the introductorily stated type which, according to the invention, is characterized in that the pump is so arranged as to maintain at any time a given relatively small pressure difference between the supply line and the return line, that, in 0 the supply line, there is connected a buffer volume which maintains a positive supply pressure, said volume being provided with a means creating a counter-pressure on the gas in the buffer volume, and that the regulating valve is arranged to be operated under the influence of very small pressure variations in the helmet. An advantageous embodiment of the breathing system is characterized in that the pump is a pneumatic pump which is arranged to be driven by compressed gas from a compressor or the like at the surface, said given pressure difference being maintained automatically in that the drive pressure of the pump is adjusted to the correct value from the compressor or the like. Thereby one achieves a pump having a quick response and which at any time maintains the given pressure difference, in contra¬ distinction to an electrical pump which works with a greater inertia . The breathing system according to the invention is not very energy-demanding and is very easy to breathe with, also with high ventilation at great depths. The system normally is based on habitat or bell-based recovery of the breathing gas. The system may be used as a pure demand system, or as a free flo system. The buffer volume, which preferably is placed on the diver's back, provides for the gas supply during the inhalatio phase of the diver. During this phase the gas supply therefore 5 is based on the buffer volume having a continuous over-pressure in relation to the helmet pressure, and this is achieved by means of said counter-pressure-creating means. A sufficient flow capacity is obtained with an overpressure of ca. 0,1 bar in relation to the ambient pressure provided that the buffer volume o is placed on the diver's back and that the circulation circuit is suitably dimensioned. The counter-pressure-creating means, for example a pneumatic cylinder, preferably may utilize the pressure in a separate supply line which is used to blow breathing gas directly into the helmet if a failure occurs in the pump system. s Normally, the buffer volume is included in a closed emergency breathing system which may begin functioning if the primary supply fails. With said pneumatic cylinder one may remove the overpressure in a simple manner and utilize the buffer volume as a breathing bag when the emergency breathing system is connected. o A condition is then that the buffer volume orms part of a diver- borne system including an emergency gas reservoir, a C0 2 absorber, a dosing mechanism for 0 2 , etc. The objective concerning a good ergonomics has been achieved by simplifying/reducing that part of the breathing 5 system which the diver has to carry along. The energy consumption of the system is reduced to a minimum in that the gas flow respectively to and from the diver is controlled by the sensitive regulating valve which, when fully opened, gives a minimal restriction for the gas flow, and which maintains a stable 0 pressure in the diver's helmet. The invention will be further described below in connection with exemplary embodiments with reference to the drawings, wherein Fig. 1 shows a schematic view of an embodiment of the 5 breathing system according to the invention; Figs. 2 and 3 show sectional views of the pneumatic pump in the system, in two different operational conditions; and Fig. 4 shows a sectional view of an embodiment of the regulating valve of the system. As shown in Fig. 1, the system comprises a closed circulation circuit having a supply line 1 and a return line 2 for circulation of breathing gas through the helmet 3 of a diver by means of a pneumatic pump means 4. The pump 4 is mounted on a diving bell (possibly a habitat) 5 and is arranged to maintain a predetermined pressure difference between the supply line 1 and the return line 2, as further described below. The breathing gas is supplied to the diver's helmet 3 through an inlet conduit 6 and is discharged through an exhaust or outlet conduit 7, controlled by a regulator or regulating valve 8. Exhaled gas from the diver is "fetched" by the pump 4 and directed through a gas recovery means 9, and is conducted further therefrom to a buffer volume means 10 which is connected to the supply line 1. The buffer volume 10 is spring-loaded in a suitable manner, to provide for a continuous overpressure in the stored gas, to supply the diver with fresh breathing gas during the inhalation phase. To this end the buffer volume is provided with a pneumatic cylinder 11 providing for a counter pressure on the gas in the buffer volume. The pneumatic cylinder is connected to a separate supply line 11 for a secondary system for gas supply. This secondary system may be constituted by the diver's emergency breathing system. In Fig. 1, the supply line 12 is shown to be connected to a feed line 13 for driving gas from the surface to the pneumatic pump means 4. The supply line is connected to the diver's helmet 3 through an emergency cock 15. The regulating valve 8 and the buffer volume means 10 with associated pneumatic cylinder 11 may, as suggested in Fig. 1, be arranged in a backpack 16 carried by the diver. In order to maintain an approximately constant gas volume in the circuit, the buffer volume 10 in practice will be provided with a valve means (not shown) for the supply of make-up gas or dumping of excess gas as required. More specifically, this valve means comprises an admission valve injecting gas into the circuit if the buffer volume is emptied during the diver's inhalation, and a dump valve seeing that gas is withdrawn from the circuit if the buffer volume is filled before the diver has exhaled. The admission valve and the dump valve are based on traditional technology, and are therefore not shown or further described. The recovery means 9 is also based on traditional technology. Normally, it comprises a lime mixture absorbing C0 2 . Further, it comprises equipment for gas analysis with respect to 0 2 and C0 2 level, together with a mechanism compensating for s consumed 0 2 . An embodiment of the pneumatic pump 4 will now be further described with reference to Figs. 2 and 3. The pump is driven by compressed gas which is pre¬ ferably supplied from the surface, and thus has an inlet 20 which o is connected to the feed line 13 shown in Fig. 1. The outlet 21 of the pump is connected to a return line 14. The embodiment in question is based on the fact that the exhaust gas is returned to the surface with a pressure corresponding to the ambient pressure of the diving bell 5, in order to be subsequently s compressed up 15 bars and recirculated. This implies that the system may be driven by traditional compressor plants for surface-based gas recovery. With an appropriate dimensioning of the circulation circuit (Fig. 1), a pressure difference of 2 bars between the o supply line 1 and the return line 2 gives a sufficient flow capacity. If, as an example, one presupposes that 30 litres of gas per minute is sufficient in the circuit, the pump may be dimensioned so that by supplying 4 litres of gas (with an overpressure of 15 bars) one is able to circulate 30 litres of 5 gas in the circuit. In a traditional surface-based recovery system, the breathing valves (for inhalation and exhalation) are dependent on that the pressure difference between supplied gas and return gas is approximately 15 bars. Thus, compared to such a system, the present system us able to manage with ca. 13% of 0 the energy consumption according to the prior art. The pump 4 according to Figs. 2 and 3 comprises a piston housing 22 wherein there are arranged a first and a second piston unit 23 and 24, respectively, which are operatively connected through an operating rod 25. The first piston unit 23 5 comprises a double piston having a first piston 26 which is slidable in a first cylinder 27 and divides the cylinder into a pair of chambers I and II which are supplied with driving gas in a controlled manner, as described below, and a second piston 28 which is slidable in a second cylinder 29 and divides the cylinder into a pair of chambers III and IV. These chambers communicate with the supply line 1 and the return line 2 of the circuit through a valve arrangement comprising four one-way valves 30, 31, 32, 33 which see to it that the breathing gas is pumped in the same direction in the circuit irrespective of the movement direction of the piston 28, as can be seen when looking at Figs. 2 and 3. The piston 28 has a substantially greater pressure surface than the piston 26, in order to circulate a gas volume in the circuit which is correspondingly larger than the volume of the driving gas supplied to the pump, and then under maintenance of the predetermined pressure difference of about 2 bars between the supply and return lines. The second piston unit 24 comprises a piston 34 which is slidable in a cylinder 35 which, at one side of the piston 34, communicates with the chamber I, and at the other side of the piston communicates with the outlet 21 of the pump. At the latter side the piston 34 is connected to one end of a tube element 36 of which the other end is arranged to influence a spring-loaded valve disk 37 in a valve arranged between an inlet chamber 38 and a channel 39 which, with open valve, connects the inlet chamber 38 with the chamber I. The end of the tube element 36 which is fastened to the piston 34, is provided with holes as shown at 40, so that the interior of the tube communicates with the pump outlet 21. The inlet chamber 38 communicates with the chamber II through a conduit 41. The operating rod 25 is connected with one end to the piston 34 and is carried through a hole in a screw body 42 which is threaded into the piston 26, and the other end of the rod is formed with a disk body 43 which is slidable in a cylindrical guide 44 in the piston unit 23. At each side of the disk body 43 there is arranged a spring 45 and 46, respectively, for abutment against the screw body 42 and the bottom, respectively, of the cylindrical guide 44 when the piston unit 23 is in its respective extreme positions. The pump 4 is also provided with a cylinder/piston unit comprising a piston 47 which is slidable in a cylinder 48 and divides the cylinder in a pair of chambers V and VI which are connected in the supply line 1 and the return line 2, respec¬ tively, as shown in Figs. 2 and 3. The piston is provided with a stem 49 which is slidable in a guiding cylinder at one end of which there is formed a chamber 50 communicating with the inlet chamber 38 of the pump through a conduit 51. Thus, the piston 47 is permanently under the influence of the driving gas pressure. 5 By means of this arrangement the pressure conditions in the circuit are maintained when the movement direction of the piston unit 23 is reversed. A movement cycle of the pump 4 will be described below. In the situation shown in Fig. 2, the chamber I o communicates with the inlet chamber 38, the valve disk 37 being raised from its seat. The chamber II is in permanent communica¬ tion with the inlet chamber, but the pressure surface of the piston 26 towards this chamber is only half of its effective pressure surface towards the chamber I, so that the piston 26 is s pressed downwards. The pump is maintained in this mode in that the pressure in the chamber I presses the piston 34 upwards so that the tube element 36 presses the valve disk 37 upwards from its seat. The piston unit 23 will seek to maintain a pressure difference of 2 bars between the chambers IV and III and will, 0 when gas circulates in the circuit, be able to move very rapidly downwards. When the piston 28 approaches the bottom position, the screw body 42 is brought into contact with the spring 45, and the operating rod 25 consequently pulls the piston 34 downwards. The spring-actuated valve disk 37 follows and comes to rest against 5 the valve seat, and thereby closes the connection between the inlet chamber 8 and the chamber I. The tube element 36 instead establishes an open connection between the channel 39 and the outlet 21 of the pump, so that the chamber I is vented via the return line 14 to the surface, and the piston 26 immediately is o pressed in the opposite direction. This mode is shown in Fig. 3. When the piston 26 approaches its upper position, the bottom of the cylinder guide 44 hits the spring 46, and the operating rod 25 and the tube element 36 then are moved upwards. This firstly results in that the connection between the chamber I and the 5 outlet 21 is shut off. Thereafter the tube element 36 again presses the valve disk 37 up from its seat, so that the connec¬ tion between the inlet chamber 38 and the chamber I is opened. Accordingly, the piston unit 23 is again pressed downwards. An embodiment of the regulating valve 8 is shown in Fig. 4. The regulating valve is arranged in connection with the diver's helmet 3, the inlet and outlet conduits 6 and 7, in a manner not further shown, being brought respectively into and out of the helmet. The regulating valve comprises a sensing diaphragm 60 which senses the pressure in the diver's helmet 3 and via a schematically shown transfer mechanism 61 is coupled to an inlet valve 62 and an outlet valve 63 to precision-control the gas flow respectively to and from the diver's helmet, so that the respiration of the diver only causes insignificant pressure variations in the helmet. In Fig. 4, the sensing diaphragm 60 is located in the plane of the drawing, one side thereof facing the surrounding water, whereas its other side faces a chamber 64 which is in open connection with the outlet conduit 7 of the helmet through a channel 65 (only shown as an opening in the conduit wall). The regulating valve sees to it that the pressure in the helmet 3, or more accurately in the outlet conduit 7, just balances the ambient pressure. Advantageously, the regulating valve may be "removed" from the diver's helmet. It may be physiologically favourable to place the valve so that the sensing diaphragm 60 is located adjacent to the neck pit of the diver. It will also be possible to place the valve, for example, at the back of the diver. In that case one should, in a mechanical manner, arrange for influencing the sensing diaphragm so that this "sees" a pressure which is approximately identical with the hydrostatic pressure outside the neck pit. The inlet valve 62 comprises a valve housing 66 having a valve body in the form of a piston 67 which is slidable in a cylinder guide 68. The piston cooperates with a seat 69, and the cylinder guide is provided with ports 70 for through-flow of gas when the piston is raised from the seat. The piston 67 has an axial passage 71 balancing the pressure forces, so that the piston is able to be moved with a very small force. As shown, the piston is spring-loaded towards the closed position by means of a suitable spring 72. Even if the piston 67 rests against the seat 69, there will be a small gas leakage between the piston and the cylinder guide 68. This leakage is, however, of no operatio¬ nal importance. The piston is coupled to the transfer mechanism 61 by way of an operating rod 73 of which one end is coupled to a rocker arm 74 forming part of the transfer mechanism. Between th sensing diaphragm 60 and the rocker arm 74 there is arranged linkage of which there is only suggested a link arm 75. The outlet valve 63 is constructed in a manner corre 5 sponding to the inlet valve 62 and thus comprises a valve housin 76, a valve body in the form of a piston 77 which is slidable i a cylinder guide 78, a seat 79, ports 80 in the cylinder guide, an axial passage 81 in the piston for balancing of the pressur forces, and a spring 82 for actuation of the piston 77 toward o the closed position. The piston is coupled to the transfe mechanism 61 by way of an operating rod 83 which is coupled t a rocker arm 84 which is actuated by said linkage. As appears from Fig. 4, the outlet valve 63 is oriente opposite to the inlet valve 62, the operating rods 73 and 8 s being moved in opposite directions in opening and closing, respectively, of the valves. If the pressure in the outlet conduit 7 of the helme is reduced, the sensing diaphragm 60 is pressed inwards toward the chamber 64 under the influence of the surrounding wate o pressure. This results in that the link arm 75 is lifted and th piston 67 of the inlet valve 62 is pressed downwards, and ga flows into the helmet from the supply line 1. Correspondingly, an increase of the pressure in the outlet conduit of the helme will result in that the piston 77 of the outlet valve 63 i 5 pulled upwards and opens for exhausted gas through the retur line 2. By means of this regulator structure large gas quan¬ tities may be precision-controlled with a very small force. Thus, the regulator has a very good capacity and provides for ver 0 stable pressure conditions in the helmet during all relevan conditions. In other respects it is remarked that, for securit reasons, safety valves have to be incorporated in the circulatio circuit to eliminate the possibility that dangerous pressur variations may occur in case of failure in the system. 5 The fundamental mode of operation of the breathin system will be described in the following. Firstly, it is take as a starting point that the system is to be used as a pur demand system. Further, it is supposed that the diver is jus about to start inhalation. The buffer volume 10 then will b approximately filled, and there is no circulation of breathing gas in the circuit. During the inhalation the pressure in the helmet 3 (and consequently in the outlet conduit) falls immedia¬ tely, and the regulating valve 8 then opens for supply from the buffer volume. In this phase the pump 4 is inoperative, since no gas is discharged via the return line 2. When the diver termina¬ tes the inhalation, the buffer volume is partly emptied, and the regulating valve closes for additional supply. In the succeeding exhalation, the pressure in the helmet 3 rises immediately, and the regulating valve 8 opens for withdrawal of exhausted gas via the return line 2. The suction pressure in the return line is immediately reduced, and the pump 4 begins functioning. The exhaled gas is absorbed and directed through the gas recovery means 9, and therefrom is conducted to the buffer volume 10 which is filled again. The pressure changes occurring in the helmet during the breathing of the diver, reflect the properties of the breathing system. The sensitive regulating valve 8 sees to it that the pressure changes are very small, corresponding to a low breathing work. if one wants to avoid the use of an oral-nasal mask in the helmet, one is dependent upon increasing the through-flow of gas in the helmet. In the preferred free flow embodiment of the breathing system according to the invention one has chosen to let the recirculation of breathing gas function approximately according to the demand principle. This implies that the helmet, i.e. the neck seal thereof, does not function as a buffer volume like in a traditional free flow system. An embodiment of interest is to provide for a permanent "leakage" between the outlet conduit 7 from the helmet and the return line 2. This will result in. that the gas quantity which has to be supplied to the helmet during the inhalation phase, at any time will be equal to the sum of the "leakage" and the diver's inhalation. During the exhala¬ tion, the gas quantity passing the outlet conduit 7 will never be smaller than the "leakage" but otherwise be equal to the diver's exhalation. One achieves an efficient ventilation of C0 2 from the helmet even if the "leakage" is substantially smaller than the through-flow which is normally required for free flow systems. It is presupposed, however, that the gas channels in the helmet are arranged so that supplied gas is directed towards the mouth of the diver, and that exhaled gas is directed so that it is effectively catched by the outlet conduit of the helmet. The solution gives a favourable energy consumption and substantially better conditions for communication than the solutions according to the prior art.

Claims: Patent Claims 1. A closed breathing system for divers, comprising a circulation circuit having a supply line (1) and a return line 5 (2) for circulation of breathing gas through the helmet (3) of a diver, a pump means (4) for pumping of the breathing gas in the circuit, a gas recovery means (9) arranged in the circuit, and a regulating valve (8) for controlling the breathing gas respectively to and from the diver's helmet (3), CHARACTERIZED o IN that the pump (4) is so arranged as to maintain at any time a given relatively small pressure difference between the supply line (1) and the return line (2), that, in the supply line (1), there is connected a buffer volume (10) which maintains a positive supply pressure, said volume being provided with a means s (11) creating a counter-pressure on the gas in the buffer volume (10), and that the regulating valve (8) is arranged to be operated under the influence of very small pressure variations in the helmet (3). 2. A breathing system according to claim 1, CHARACTERIZED 0 IN that the pump (4) is a pneumatic pump which is arranged to be driven with compressed gas from a compressor or the like at the surface, said given pressure difference being maintained automatically in that the driving pressure of the pump (4) is adjusted to the correct value from the compressor or the like. 5 3. A breathing system according to claim 2, CHARACTERIZED IN that the pump (4) comprises a piston housing (22) in which there are arranged a first (23) and a second (24) piston unit which are operatively interconnected, the first piston unit (23) being arranged to be reciprocated under the influence of the o pressure gas from the compressor or the like and under control by the second piston unit (24), and further to recirculate the gas in the circuit during maintenance of said pressure difference between the supply and return lines (1 resp. 2). 4. A breathing system according to claim 3, CHARACTERIZED 5 IN that the first piston unit (23) comprises a double piston having a first piston (26) which is slidable in a first cylinder (27) and is driven by the pressure gas, and a second piston (28) which is slidable in a second cylinder (29) and has a substan¬ tially greater pressure surface than the first piston (26), to circulate a gas volume which is correspondingly larger than the volume of the driving gas supplied to the pump (4). 5. A breathing system according to claim 3 or 4, CHARAC¬ TERIZED IN that the pump (4) comprises a cylinder-piston means (47, 48) having cylinder chambers (V, VI) which are connected to the supply and the return line (1 resp. 2), respectively, and which contain a piston (47) which is under the influence of the driving gas pressure, for maintaining the pressure conditions in the circuit when the movement direction of the first piston unit (23) is reversed. 6. A breathing system according to any of the preceding claims, CHARACTERIZED IN that the counter-pressure-creating means (11) of the buffer volume (10) is a pneumatic means which is coupled to a secondary system (12) for the supply of driving gas. 7. A breathing system according to any of the preceding claims, CHARACTERIZED IN that the buffer volume (10) has an overpressure of ca.0,1 bar relative to the surrounding pressure. 8. A breathing system according to claim 6 or 7, CHARAC¬ TERIZED IN that the buffer volume (10) comprises a valve means providing for the supply of make-up gas or dumping of excess gas from the buffer volume as required. 9. A breathing system according to any of the preceding claims, CHARACTERIZED IN that the regulating valve (8) comprises a sensing diaphragm (60) which senses the pressure in the diver's helmet (3) and is operatively connected to an inlet and an outlet valve (62 resp. 63) controlling the gas flow respectively to and from the helmet (3), each valve (62 resp. 63) comprising a valve body (67 resp. 77) which is pressure-balanced so that the valve (62 resp. 63) is opened or closed under the influence of a very small operating force on the valve body (67 resp. 77).

Inventors: OTTESTAD NILS TERJE, OTTESTAD, NILS, TERJE
Applicants: OTTESTAD BREATHING SYST AS, OTTESTAD NILS T, OTTESTAD BREATHING SYSTEMS AS, OTTESTAD, NILS, TERJE
Application year: 1993
Main classification: B63C11
IPC codes: B63C11