US3700000A

US3700000A - Valve arrangement,especially for use in anaesthetic gas supply systems

Info

Publication number: US3700000A
Application number: US804741A
Authority: US
Inventors: Holger Hesse
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-03-04
Filing date: 1969-03-03
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: BE729311A; AT290004B; CH496447A; FR2003192A1; IL31730A0; IL31730A; SU419006A3; BR6906836D0; DE1910979A1; DK122712B; GB1258071A; LU58141A1; SE350699B; NL6903307A

Abstract

A blow-off valve which vents excess gas to the atmosphere when the pressure in a gas circulation system, such as an anaesthetic supply system, exceeds a certain value, as occurs when the patient breathes out, is improved by providing a system to close the valve when the pressure exceeds a still higher value, as occurs when gas is forced into the patient''s lungs. A movable member is exposed to the gas pressure in the system. A force transfer means connects the movable member in the valve and closes the valve when this higher pressure is reached.

Description

United States Patent Hesse, deceased et al.

[ 51 Oct. 24, 1972 [54] VALVE ARRANGEMENT, ESPECIALLY FOR USE IN ANAESTHETIC GAS SUPPLY SYSTEMS {72] Inventors: Holger Hesse, deceased, late of Skovtoftebakken l9, Virum, Copenhagen, Denmark by Ruth Lea Hesse, heiress and executrix', Henning M. Ruben, Skodsborg Strandveg 260, Copenhagen, Denmark [22] Filed: March 3, 1969 [21] App]. N0.: 804,741

[30] Foreign Application Priority Data March 4, 1968 Great Britain ..10,419/68 [52] US. Cl. ..l37/494, 128/1456, 251/65,

[51] Int. Cl. ..A62b 7/00, A61m 17/00 [58] Field of Search..137/494, 63 R; 128/1457, 202,

[56] References Cited UNITED STATES PATENTS 2,222,710 11/1940 Goldschmidt ..251/23l X 3,200,818 8/1965 Johannisson 128/202 3,351,092 11/1967 lngerfield et al. ..251/65 X 3,400,908 9/1968 Bauer ..251/61 X 3,473,529 10/1969 Wallace ..128/145.7 3,503,393 3/1970 Manley 128/1456 Primary Examiner-M. Cary Nelson Assistant Examiner-Robert J. Miller AttorneySpencer & Kaye 7] ABSTRACT A blow-ofi valve which vents excess gas to the atmosphere when the pressure in a gas circulation system, such as an anaesthetic supply system, exceeds a certain value, as occurs when the patient breathes out, is improved by providing a system to close the valve when the pressure exceeds a still higher value, as occurs when gas is forced into the patient's lungs. A movable member is exposed to the gas pressure in the system. A force transfer means connects the movable member in the valve and closes the valve when this higher pressure is reached.

30 Claims, 8 Drawing Figures PATENTEUnm 24 1912 SNEEI 2 IF 7 PATENTED 3.700 000 saw u or 7 PATENTED B I 3 700 000 SHEET 5 BF 7 FIQA PATENTED 24 I97? 3, 700 O00 sum 5 BF 7 VALVE ARRANGEMENT, ESPECIALLY FOR USE IN ANAESTHETIC GAS SUPPLY SYSTEMS The present invention relates to valve arrangements adapted for use in connection with such gas circulation systems as, for example, anaesthetic gas supply systems i.e. systems in which anaesthetic gas and/or oxygen are introduced into the lungs of a person to be treated. More specifically, bot not exclusively the invention refers to valve arrangements for intermittently opening and closing a connection between a so-called semiclosed anaesthetic gas supply system and the atmosphere.

During narcosis it is in many cases a factor of greatest importance to support natural breathing or to administer artificial respiration, which can be performed with the aid of an anaesthetic gas supply system of the type shown in FIG. 1 of the accompanying drawings. Such a system comprises a semi-closed circuit 1 continuously supplied with gas from a gas source 2. The system also comprises an expandable bag or bladder 3 which is filled with gas from the source 2 due to the fact that the gas pressure in the system is slightly higher than atmospheric pressure. Moreover the system is commonly provided with a connection 4 leading to the respiratory system of the patient, with directional valves such as S, 6 forcing the gas the flow through the system in the correct direction, and an absorber 7 removing pollutions such as carbon dioxide from the system. The gas is forced into the lungs of the patient by compression of the bag or bladder 3 causing a state of overpressure to be developed in the system. When the bag is subsequently released and the pressure again drops to substantially atmospheric pressure or below the positive pressure then prevailing in the lungs will force the gas back into the anaesthetic gas supply system. As during the complete process oxygen and/or anaesthetic gas will be continuously supplied and as the amount of air expired is substantially of the same order of magnitude as the amount inhaled it will obviously be necessary to provide a valve connection between the gas'system l and the atmosphere, thereby enabling exccss of gas to be discharged from the system.

The valve arrangements in conventional semi-closed rebreathing systems of the above type usually operate in such a way that the valve disk ofa blow-off valve 8 is lifted from its seat whenever the positive pressure in the system exceeds a predetermined value of, for example, about 0.5 cm H due to spontaneous exhalation or excess supply of gas whereby such excess gas is discharged from the system. When the pressure prevailing in the system has a value lower than that mentioned above the valve disk due to its normal bias, for example by means of a spring or the action of gravity, will rest against its seat whereby the communication between the re-breathing system and the atmosphere will be interrupted.

The so-called controlled ventilation of the patient, i.e. the measure of forcefully introducing gas into the patients lungs by compression of the bladder or bag, requires that a considerably higher positive pressure be built up in the system, the order of magnitude of this pressure being, for example 30 cm 11,0. In many prior art devices the positive pressure necessary for ensuring an adequate controlled ventilation is obtained by making the gas discharge capacity of the blow-off valve, on the one hand sufficiently low to allow said positive pressure to build up in the system during compression of the bag and, on the other hand, sufficiently large to allow the excess gases and/or the exhalation gases to blow-off" to the atmosphere without causing an unduly high pressure to appear in the system.

A considerable drawback of such valve arrangements may be ascribed to the fact that no direct conclusions can be drawn from the degree of compression of the bag or bladder concerning the amount of gas actually introduced into the lungs. Accordingly, it is common practice to evaluate this factor by considering the expansion of the thorax during the inhalation phase, such evaluation however being of a qualitative rather than quantitative character.

Another drawback of said value arrangements is that a considerable volume of gas is lost during each compression of the bag this drawback being particularly pronounced when the system is continuously supplied with an expensive anaesthetic gas.

It has been proposed to solve this problem by increasing the resistance against opening of the blow-off valve, i.e. the closing bias of the valve disk, by manual operations. However, this involves the serious drawback that due to an increase of the pre-loading of the valve disk the blow-off valve will open during the expiratory phase only at an unduly high overpressure. Hereby the blood circulation of the patient may be adversely influenced because the generally excessive pressure prevailing in the lungs caused thereby will oppose the inflow of blood to the heart. These conditions will be aggravated in proportion to the amount of gas supplied to the narcosis system.

As breathing and blood circulation are vital functions which when changed during acute situations may involve danger of life for the patient it is an advantage or even a necessity so to operate an anaesthetic gas supply system that the expiratory phase may take place during normal pressure conditions while still enabling the system to be operated in such a way that any compression of the bag causes an amount of gas substantially corresponding to the amount expelled from the bag to be introduced into the lungs.

It is a purpose of the invention to solve the above problems referring to opening and closing the commu nication between the rebreathing system and the atmosphere in such a way that this communication is held open for discharging excess gas and expiration air, the communication being closed when the bag or bladder is compressed i.e. when the gas is to be forced into the lungs of the patient, the communication being opened again when the compression of the bag is discontinued. Under these conditions the pressure in the anaesthetic gas supply system during the expiration phase is limited to a minimum value corresponding to the value required in order to guarantee the expansion of the bag or bladder due to the continuous supply of gas whereby the bags character as a gas supply reservoir will be maintained.

In accordance with the invention this problem is solved by using, on the one hand, a blow-off valve such as a disk, poppet or membrane valve of a conventional type keeping the communication between the rebreathing system and the atmosphere closed up to a relatively low pressure but adapted to open this communication when there is an excess amount of gas present and when expiration takes place and, on the other hand, a device responsive to the pressure prevailing in the system and adapted to act upon the valve disk of the blow-off valve to close this valve again upon compression of the bag or bladder, i.e. under conditions of an overpressure in the system substantially greater than that at which the biasing force acting on the valve disk is overcome. This result is obtained according to the invention by causing at some place in the system the pressure prevailing therein to act on a movable member which in turn develops a pressure-dependent force which is transferred to the valve disk of the blow-off valve and acts to close the valve when the bag is compressed. It is then necessary, in order that the valve shall be closed upon compression of the bag, that the pressure force applied to the valve disk from the movable member during the compression is greater than the difference between the pressure force acting on the valve disk due to the pressure prevailing in the system and tending to open the valve and the biasing force holding the valve closed during low overpressures in the system. If no particular arrangements are made substantially the same pressure will act on both the movable member and the valve disk, and in this case the above presupposition means that either the pressure within the system will have to be caused to act on the movable member over greater area than the area of the valve disk or that a suitable transfer ratio must be applied in the force transfer from the movable member to the valve disk. Of course these two means for obtaining an overwhelming closing force acting on the blowoff valve upon compression of the bag may be combined.

A further condition for the proper functioning of the valve arrangement according to the invention is that the force developed by the movable member must not be transferred fully to the valve disk at low overpressures prevailing in the system because this would mean that the blow off valve would not open for discharging excess gas after filling of the bag or during the expiration phase. The system would in this case operate as a completely closed system. The desirable way of operation is obtained in accordance with the invention either by providing means exerting a certain, preferably constant and pressure independent force opposing the closing force developed by the movable member, or by providing means making said closing force act upon the valve disk of the blow-off valve only when this force has attained a certain value, ie when the pressure in the system has reached a certain value higher than that at which the biasing force of the blow-off valve is overcome.

Thus, the primary object of the invention is to provide a valve arrangement for use in such gas circulation systems as anaesthetic gas supply systems, in which a connection between the system and the atmosphere is to be opened or closed depending on the pressure prevailing in the system, this arrangement comprising a blow-off valve interconnecting the system and the atmosphere and provided with biasing means tending to hold the valve closed at small overpressures in the system but permitting the valve to be open at slightly higher overpressures caused by supply of excess gas and during expiration, and a movable member connected to the system and adapted to be acted-upon by the pressure prevailing in the system, said movable member developing a force generated by this pressure and transferred via a force transfer system to the valve disk to close the blow-off valve when the bag is compressed and again to open or permit opening of the valve when the compression is discontinued.

This and other objects of the invention will appear from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which:

FIG. 1, which has already been described illustrates a conventional semi-closed re-breathing system;

FIG. 2a and 2b illustrate a preferred embodiment of the valve arrangement according to the invention during different pressure conditions;

FIG. 3 shows another embodiment of the movable member;

FIG. 4 shows another embodiment of the force transfer system;

FIG. 5 and 6 illustrate another embodiment of the force transfer system; and

FIG. 7 shows still another embodiment of the valve arrangement according to the invention.

FIGS. 2a and 2!: represent a preferred embodiment of the valve arrangement according to the invention, FIG. 2a illustrating the insufflation phase with compression of the bladder and FIG. 2b illustrating the exhalation phase with release of the bladder. According to this embodiment the valve arrangement according to the invention is made very compact and comprises a housing 15 provided with an inlet connection 16, an outlet connection 17, and a bladder connection 18. A gas conduit 19 which interconnects the inlet connection 16 and the outlet connection 17 is continuously supplied with oxygen and/or anaesthetic gas from a gas source 2. Said conduit 19 is also provided with a branch conduit leading to the patient and an absorber 7 eliminating pollutions such as charbon dioxide from the gas circulating in the conduit 19. Said conduit also contains one-way valves such as 5 forcing the gas to flow only in the correct direction in the gas conduit 19.

The housing 15 is provided with a blow-off valve 8 putting the interior of the housing in communication with the atmosphere, said valve preferably being made up of a valve disk 14 and a corresponding valve seat 20. The valve disk 14 is subjected to a biasing force obtained by, for example, a spring pressing the valve disk against its seat and/or by the gravity force acting on the valve disk. Said biasing force is adjusted such that the blow-off valve opens as soon as the positive pressure in the system attains a relatively low value of, for example, 0.5 cm H 0, i.e. the pressure required for filling the bladder with gas after compression.

According to the invention the housing 15 is also provided with a connection to a movable member 9 which is shaped as a bellows in the embodiment shown in FIGS. 20 and 2b. The bellows 9 expands and contracts depending on the pressure variations in the system. The pressure dependent force developed by the bellows upon expansion thereof is transferred to the valve disk 14 via a force transfer system in order to exert a closing force on the blow-off valve 8. The force transfer system may be designed in many different ways, a preferred embodiment being shown in FIGS. 2a and 2b. According to this embodiment the bellows 9 is caused to act upon the end of a lever 13, the other end of which is adapted to come into contact with the valve disk 14 in a direction to close the valve.

The lever 13 is double-armed and rotatably fixed to a support structure 26 which is secured to the valve housing 15. In order to obtain a good force transfer from the bellows 9 to the force arm 25 of the lever, the end of said arm is preferably formed as a thin plate, the surface of which corresponds to the upper surface of the bellows 9. When utilizing this embodiment of the force transfer system it is possible mutually to adapt the surface of the movable member 9 exposed to the pressure prevailing in the system, the corresponding surface of the valve disk 14 and the length ratio between the force arm 15 an the load arm 24 of the lever in such a way that the pressure dependent force transferred from the bellows 9 and acting to close the blow-off valve will be greater than the pressure dependent force acting on the valve disk 14 and tending to open the blow-off valve.

The valve arrangement shown in FIGS. 2a and 2b also illustrates a preferable solution of the problem to prevent blocking of the blow-off valve during the expiration phase, i.e. when relatively low overpressure exists in the system. According to this solution there is provided a magnet 21 adapted to attract an iron part 22 comprised by the force transfer system. This iron part 22 is positioned in such a way in relation to the magnet 21 that the force of attraction of the magnet 21 counteracts the closing force produced by the movable member 9 such that the load arm 24 does not close the blow-off valve 8 until the attraction force of the magnet has been overcome. As the force of attraction between the magnet and the iron part decreases rapidly with the distance therebetween there will be a very rapid and effective locking action as soon as the closing force from the movable member overcomes the said attraction force. The value of the force of attraction can be controlled by means enabling the magnet 21 to be shifted in relation to the iron part 22 belonging to the force transfer system. In the embodiment shown in FIGS. 2a and 2b the magnet 21 is disposed above the load arm 24 of the lever 13 comprising the iron part 22, but it is, of course, also possible to dispose the magnet below the force arm 25, which is in this case provided with the iron part. A simple way of varying the attraction force between the iron part 22 and the magnet 21, which is preferably supported by a carrier means 27 secured to the housing 15, is to provide the magnet with a screw thread for engagement with a corresponding nut thread in the carrier means 27, the attraction force then being varied by screwing the magnet more or less into the nut thread of the carrier means, which may also be provided with a scale cooperating with a mark on the magnet and indicating for each setting position, for example, the flow velocity or overpressure at which the blow-off will be blocked.

Another manner of preventing blocking of the blowoff valve at relatively small overpressures or flow velocities is to design the force transfer system such that it will not come into action until the pressure in the system has reached a certain value. Such an arrangement involves the advantage that the valve will not be acted-upon by a successively increasing closing force but rather by a closing force which upon activation of the force transfer system suddenly rises from zero to a relatively high value. Thus, the valve closing action will become more effective. If a bellows is used as the movable member the arrangement may, for example, be suchthat the bellows actuates the force transfer system only when a certain degree of extension of the bellows has been reached. In the construction involving a piston movable in a cylinder a corresponding arrangement may consist in causing the piston to release the force transfer system only after a certain movement of the piston in the cylinder.

The closing action of the valve arrangement according to the invention can be made more effective by providing a check valve such as a disk or flap valve in the system between the position at which the blow-off valve is provided and the position at which the movable member is attached to the system. In this way the gas stream in the system may be suitably controlled to obtain, on the one hand, a more effective closing of the blow-off valve and, on the other hand, a delayed closing action in response to pressure variations during the expiration phase.

As shown in FIGS. 20 and 2b the check valve 28 is preferably placed in the proximity of the movable member 9 or the branch conduit leading to the movable member, and the check valve 28 is directed so as to prevent the gas flow generated by compression of the bag from following the shortest way in the circuit towards the blow-off valve 8. If the movable member 9 is positioned close to the bag 3 and the blow-off valve 8 closely adjacent to the movable member while at the same time causing the check valve 28 to prevent gas from flowing the shortest way between the movable member 9 and the blow-off valve 8, the pressure surge due to compression of the bag 3 will actuate the movable member 9 practically without delay whereas the valve disk 14 of the blow-off valve 8 will be acted-upon only after propagation of the pressure surge through practically the whole system.

In this manner the pressure increase caused by compression of the bag will immediately act on the movable member 9 developing a pressure-dependent closing force, but said pressure increase will not reach the valve disk of the blow-off valve but after a certain period of time. Consequently, the pressure acting on the movable member 9 will during the compression of the bag 3 be higher than the pressure acting on the valve disk 14 and tending to open the blow-off valve 8.

On the other hand, pressure increases due to exhalation or excess supply of oxygene or anaesthetic gas will first act on the valve disk 14 and only thereafter on the movable member 9. On such occations when it is not desired that the blow-off valve be closed the pressure acting on the movable member 9 will be equal to or rather somewhat lower than the pressure acting on the valve disk 14, thereby counteracting blocking of the blow-off valve.

The propagation of the pressure increase caused by compression of the bag can be further delayed by introducing a throttling means in the system. A very simple and efiicient embodiment of such throttling means is shown in FIG. 2a. According to this embodiment the throttling means consists of a disk 29 having a central opening 30 of reduced cross-section. The disk 29 shown i FIG. 2a is disposed between the inlet end of the housing 15 and the blow-off valve 8, but it is also possible to insert the throttling means at some other place in the system downstream of the bladder and upstream of the blow-off valve. Any other conventional throttling means such as different types of jets or nozzles can be utilized in place of the disk 29 in order to reduce the opening force acting on the valve disk of the blow-off valve during compression of the bag and during exhalation.

Another suitable embodiment of the movable member is shown in FIG. 3. In this case the movable member has the shape of a piston which is slidable in a cylinder 1 l which is in communication with the main conduit of the semi-closed re-breathing system, the displacement of the piston 10 being dependent on the pressure in said system, which acts on one surface of the piston 10. The piston may be exposed to the action of a spring 12 counteracting the force for which the piston is exposed due to overpressure in the system and thus permitting transfer of the latter force to the valve disk only when the force has become greater than the spring force, i.e. upon the precence of a relatively high overpressure in the system caused by compression of the bag or bladder 3. The piston 12 may be mechanically connected to one end of a lever 13, the other end of which is adapted to come into contact with the valve disk 14 of the blow-off valve or to actuate said disk via suitable transmission members as has already been described with reference to FIGS. 2a and 2b. The spring 12 can also be replaced by the magnet arrangement described above.

In another embodiment of the invention which is illustrated in FIG. 4 the force transfer system 23 is provided with an adjustable counterweight 31 which is so arranged that the force transferred to the valve disk 14 via the force transfer system 23 will not become large enough to close the blow-off valve 8 until the overpressure in the system has reached a certain value at which the pressure force exerted on the movable member, for example the bellows 9 or the piston 10, is greater than the force exerted by the counterweight 31 and acting in the opposite direction. In this case the force transfer system 23 can be constructed as a lever 13 on or along which the counterweight is adapted to be shifted. The force exerted by the counterweight 31 and counteracting the force exerted by the movable member 9 is in this case depending on the position of the counterweight in relation to the momentum point of the lever 13. Also in this case there may be provided a scale indicating different flow velocities and/or overpressures for different positions of the counterweight on the lever.

As shown in FIGS. 5 and 6 the force transfer system may also be designed as a direct connection between the valve disk 14 and the movable member 9, in which case the forces depending on the pressure prevailing in the narcosis system and acting on respectively the valve disk and the movable member are directed in opposite directions substantially along a common axis. This connection may comprise rigid force transfer members 32 as shown in FIG. 5, or pliable members 33 as shown in FIG. 6, the latter type of connection being exemplified by cords, belts, chains or resilient straps. Care should be taken in this connection to prevent such shifting of the movable member as will appear upon small overpressures in the system (excess gas supply, expiration) from exerting any closing action on the valve disk, there being a degree of lost motion causing such force to act on the valve disk 14 only at higher pressures prevailing in the system (compression of the bag). When rigid connecting member are used some kind of a telescope connection 34 or other connections comprising lost motion should be used to absorb any shifting movement of the movable member 9 due to small overpressures in the system and to permit opening of the blow-off valve 8 to discharge continuous excess gas supply and expiration air without actuation of the valve disk by the movable member in a closing direction.

As shown in FIG. 7 the force transfer may also be performed in such a way that the movable member is caused to act directly against the valve disk 14 of the blow-off valve 8 or a contact surface thereon. According to FIG. 7 a bellows or movable piston or some other expandible member 9 is connected to a first connection of a T-piece 35 which is stationary with respect to the blow-off valve 8. The bag 3 is secured to the second connection of the T-piece 35, the third connection of which communicates with the system via a branch conduit 36. By expansion of the bellows or shifting movement of the piston due to compression of the bag 3 the said member 9 will come into direct contact with the valve disk 14 to close the blow-off valve 8. Care should be taken to prevent such contact from taking place at low overpressures in the system, for example by utilizing one or more magnets 21 attracting an iron part 22 of the expandable member 9. As in the above described embodiments it is advantageous to make use of a oneway valve 28 disposed between the blow-off valve 8 and the branch conduit 36 and a throttling means 29, 30 upstream of the blow-off valve.

By providing the valve device according to the invention with a manually operated deblocator 37 (FIGS. 2a and 2):) such as a push-button which can be locked in two positions it is possible to obtain a de-blocking of the blow-off valve in case a state of blocking has accidentally developed due to faulty operation or adjustment. In the first position, which is indicated in continuous lines in FIGS. 20 and 2b, the push-button 37 does not interfere with the force transfer system, but in the second position, indicated by the dotted lines in FIG. 2b, the push-button interferes with the force transfer system so as to prevent the force developed by the movable member from being transferred to the blow-off valve. The valve arrangement may also comprise means making it possible manually to cause blocking or lock out of the blow-off valve which can be desired during certain types of narcosis, in particular when small amounts of gas are supplied not requiring any communication between the system and the surrounding atmosphere.

With the valve construction as described above it is thus possible to eliminate the draw-backs of previously known valve constructions, especially those utilized in so-called semi-closed re-breathing systems. When utilizing the valve arrangement according to the invention there is obtained an anaesthetic gas supply system which on the one hand, is in communication with the atmosphere at relatively small overpressures (high enough to overcome the biasing force of the blow-off valve) in the system, thus enabling expiration and discharge of excess gas under favorable conditions and,

on the other hand, is shut off from communication with the atmosphere at higher overpressures created in the system by compression of the breathing bag whereby control of the amount of gas thus introduced into the respiratory ducts of the patient is facilitated and the loss of gas is minimized. By adjustment of the various adjustable pre-loading devices used in connection with the invention, such as a shiftable counterweight or a magnet, the narcosis system in a convenient way may be adjusted for use under varying conditions of continuous gas supply to the system so that the valve always will open at a suitable selected pressure, for example of an order of magnitude of 0.5 1.0 cm H 0.

By suitable dimensioning the movable member, suitably selecting the force transfer system and the preloading thereof it is possible to ensure that when compressing the bag the amount of gas which is discharged from the system before the valve disk closes the valve due to the action from the movable member will be substantially zero or amount to an arbitrary value.

Although the invention has been described with reference to a re-breathing system for supporting natural breathing or administrating artificial respiration the valve arrangement according to the invention can be utilized in connection with all types or pressure controlled gas circulation systems in which it is desired to open or close a connection to the atmosphere or to another system depending on the overpressure prevailing in the system.

The valve arrangement can be modified in many way without departing from the scope of the invention. For example, the force transfer from the movable member to the blow-off valve must not be obtained by the above examplified arrangements, but any conventional mechanical, hydraulic, pneumatic or electrical force transfer system can be utlilized in place thereof. Although it has been preferred to arrange the movable member and the blow-off valve adjacent to each other in one compact unit, the invention is not limited to such an arrangement, but the valve arrangement according to the invention is capable of producing a sufficient closing action irrespective of the location of the movable member with respect to the blow-off valve and of the succession of said members in relation to the gas flow direction.

What is claimed is:

l. A blow-off valve arrangement for use in a gas circulation system venting to its environment in dependence on the internal pressure prevailing in the system, comprising a valve housing provided with a valve seat, a valve closing member, disposed on said seat from the side of the environment and arranged to be biased in a closing position against said seat so long as said internal pressure is lower than a first predetermined overpressure value and to pass into an open position under the influence of said internal pressure when said internal pressure exceeds said first predetermined value; a movable member exposed to said internal pressure and force transfer means disposed between said movable member and said valve closing member and arranged to mechanically act to close said valve closing member when said internal pressure exceeds a second predetermined overpressure value which is higher than said first predetermined overpressure, whereby said gas circulation system vents to its environment for releasing surplus gas only when its internal pressure equals such an overpressure whose value lies between said two predetermined values.

2. A blow-off valve arrangement according to claim 1, wherein said force transfer means includes means exerting a force opposing the closing of said valve closing member, said opposing force being greater than said first predetermined value, but smaller than said second predetermined value.

3. A blow-off valve arrangement according to claim 9 wherein said force transfer means includes a magnet which is adapted to attract an armature disposed on said lever of said force transfer means.

4. A. blow-off valve arrangement according to claim 3, wherein the magnet is disposed on the opposite side of the load arm of the lever, and wherein the armature is provided on the load arm.

5. A blow-off valve arrangement according to claim 4, wherein the magnet is disposed on the same side of the force arm of the lever as the movable member, and wherein the armature is provided on the force arm.

6. A blow-off valve arrangement according to claim 3 wherein the distance between said magnet and said armature is adjustable.

7. A blow-off valve arrangement according to claim 9 wherein said force transfer means includes a counterweight provided on said load arm of said double armed lever.

8. A blow-off valve arrangement according to claim 7, wherein said counterweight is slidable on the load arm of the lever.

9. A blow-off valve arrangement according to claim 29 wherein said force transfer means includes a doublearmed lever, the force arm of which is adapted to be acted upon by said movable member and the load arm of which is adapted to act upon said valve closing member.

10. A blow-off valve arrangement according to claim 1 wherein the force transfer means comprises a pliable member such as a cord, belt, chain or a resilient strap interconnecting the movable member and the valve closing element, the length of said pliable member exceeding the shortest distance between its fixing points to such an extent that displacement of said movable member has effect on said valve closing member only after said internal pressure has reached said second predetermined value.

1 l. A blow-off valve arrangement according to claim 1 wherein the force transfer means comprises a rigid force transfer member interconnecting the movable member and the valve closing element, said rigid member having means for producing lost motion to such an extent, that displacement of said movable member has effect on said valve closing element only after said internal pressure has reached said second predetermined value.

12. A blow-off valve arrangement according to claim 11, said lost motion is caused by a telescope connection means.

13. A blow-off valve arrangement according to claim 1 wherein the movable member is a bellows capable of expansion and contraction.

14. A blow-off valve arrangement according to claim 1, wherein the movable member is a piston which is slidable in a cylinder communicating with the gas system.

15. A blow-off valve arrangement for use in a rebreathing system for supplying treating gas to a patient, which system includes a re-circulation conduit having a first connection leading to the patient, a second connection for continuously supplying treating gas to the system, a third connection for a compressible bladder, and a one-way valve forcing the gas to flow in a predetermined direction in said conduit, said arrangement comprising a valve housing adapted to be placed directly in the circuit of said re-breathing system and comprising: a valve seat in said valve housing, a cooperating valve closing member disposed on said seat from the side of the environment and arranged to be biased in a closing position against said seat so long as the internal pressure prevailing in the system is lower than a first predetermined overpressure value and to pass into an open position under the influence of said internal pressure when said internal pressure exceeds said first predetermined value; a movable member exposed to said internal pressure; and force transfer means disposed between said movable member and said valve closing member and arranged to mechanically act to close said valve closing member when said internal pressure exceeds a second predetermined overpressure value which is higher than said first predetermined overpressure, whereby said gas circulation system vents to its environment for releasing surplus gas only when its internal pressure equals such an overpressure whose value lies between said two predetermined values.

16. A blow-off valve arrangement as defined in claim 15, wherein the movable member is disposed opposite said valve seat.

17. A blow-off valve arrangement as defined in claim 16, wherein the bladder is connected to the recirculation conduit at a location opposite said valve seat.

l8v A blow-off valve arrangement as defined in claim 17, wherein said one-way valve is provided in the recir culation conduit at a location between said valve seat and said bladder, said one-way valve being adapted to prevent the gas-expelled from the bladder from flowing the shortest way to the valve closing element.

19. A blow-off valve arrangement as defined in claim 18, wherein the bladder and the movable member are disposed near the valve closing element, thereby causing the gas expelled from the bladder upon compression thereof to flow through almost the entire recirculation conduit before reaching the valve closing element.

20. A blow-off valve arrangement as defined in claim 18 further comprising a throttling means provided in the recirculation conduit between the patient connection and the valve closing element, said throttling means serving to delay the transfer from the bladder to the valve closing element of the pressure surge caused by compression of the bladder.

21. A blow-off valve arrangement as defined in claim 20, wherein said throttling means comprises a disk provided with a central opening having reduced cross-section.

22. A blow-off valve arrangement as defined in claim 20, wherein said throttling means comprises a jet or nozzle.

23. A valve unit for use in a re-breathing system for supplying treating gas to a patient, said unit comprising: a valve housing having an inlet connection; an outlet connection; a ladder co nection; a blow-off valve comprising a v ve seat an a cooperating valve closing element arranged to keep the blow-off valve closed whenever the pressure acting on the closing element from the interior of the valve housing is lower than a first overpressure value; a connection to a movable member which is capable of expansion and contraction in response to pressure variations within the valve housing; a double armed lever including a force arm and a load arm the force arm of which is adapted to be acted-upon by the force produced by expansion of the movable member and the load arm of which is adapted to act on said closing element to close the blow-off valve only when the pressure in the valve housing exceeds a second pressure value higher than said first value; a one-way valve dividing the valve housing into two separate chambers for allowing gas to flow only from a first of said chambers, with which the blow-off valve communicates, to the second chamber, into which the bladder connection and the connection to the movable member opens.

24. A valve unit according to claim 30, wherein the load arm of said lever is provided with an iron part adapted to be attracted by a magnet disposed on the opposite side of the load arm with respect to the blowoff valve, the attraction force between the magnet and the iron part being such that the load arm does not act upon the closing until the overpressure in the valve housing is higher than said second value.

25. A valve unit according to claim 30, further comprising a throttling means disposed in the valve housing between the inlet connection and the blow-off valve.

26. A valve unit according to claim 25, wherein said throttling means is a partition having opening of reduced cross-section.

27. A blow-off valve arrangement as defined in claim 1 further comprising means disposed in said valve housing between said valve seat and said movable member for preventing any appreciable flow of gas in a direction from said member toward said valve seat within said valve housing.

28. A blow-off valve arrangement as defined in claim 1 wherein said force transfer means are constituted by a portion of said movable member and is disposed adjacent said valve closing member so that as the pressure in the gas circulation system increases the force transfer means directly applies the force acting on said surface to said valve closing member.

29. A blow-off valve arrangement according to claim 1, wherein said movable member is disposed on said housing at the side of said valve seat and connected with said valve closing member through force transfer means in the form of a lever.

30. A blow-off valve arrangement according to claim 15, further comprising an absorber for removing pollutions such as carbon dioxide.

Claims

1. A blow-off valve arrangement for use in a gas circulation system venting to its environment in dependence on the internal pressure prevailing in the system, comprising a valve housing provided with a valve seat, a valve closing member, disposed on said seat from the side of the environment and arranged to be biased in a closing position against said seat so long as said internal pressure is lower than a first predetermined overpressure value and to pass into an open position under the influence of said internal pressure when said internal pressure exceeds said first predetermined value; a movable member exposed to said internal pressure and force transfer means disposed between said movable member and said valve closing member and arranged to mechanically act to close said valve closing member when said internal pressure exceeds a second predetermined overpressure value which is higher than said first predetermined overpressure, whereby said gas circulation system vents to its environment for releasing surplus gas only when its internal pressure equals such an overpressuRe whose value lies between said two predetermined values.

4. A blow-off valve arrangement according to claim 3, wherein the magnet is disposed on the opposite side of the load arm of the lever, and wherein the armature is provided on the load arm.

9. A blow-off valve arrangement according to claim 29 wherein said force transfer means includes a double-armed lever, the force arm of which is adapted to be acted upon by said movable member and the load arm of which is adapted to act upon said valve closing member.

11. A blow-off valve arrangement according to claim 1 wherein the force transfer means comprises a rigid force transfer member interconnecting the movable member and the valve closing element, said rigid member having means for producing lost motion to such an extent, that displacement of said movable member has effect on said valve closing element only after said internal pressure has reached said second predetermined value.

15. A blow-off valve arrangement for use in a re-breathing system for supplying treating gas to a patient, which system includes a re-circulation conduit having a first connection leading to the patient, a second connection for continuously supplying treating gas to the system, a third connection for a compressible bladder, and a one-way valve forcing the gas to flow in a predetermined direction in said conduit, said arrangement comprising a valve housing adapted to be placed directly in the circuit of said re-breathing system and comprising: a valve seat in said valve housing, a cooperating valve closing member disposed on said seat from the side of the environment and arranged to be biased in a closing position against said seat so long as the internal pressure prevailing in the system is lower than a first predetermined overpressure value and to pass into an open position under the influence of said internal pressure when said internal pressure exceeds said first predetermined value; a movable meMber exposed to said internal pressure; and force transfer means disposed between said movable member and said valve closing member and arranged to mechanically act to close said valve closing member when said internal pressure exceeds a second predetermined overpressure value which is higher than said first predetermined overpressure, whereby said gas circulation system vents to its environment for releasing surplus gas only when its internal pressure equals such an overpressure whose value lies between said two predetermined values.

18. A blow-off valve arrangement as defined in claim 17, wherein said one-way valve is provided in the recirculation conduit at a location between said valve seat and said bladder, said one-way valve being adapted to prevent the gas-expelled from the bladder from flowing the shortest way to the valve closing element.

23. A valve unit for use in a re-breathing system for supplying treating gas to a patient, said unit comprising: a valve housing having an inlet connection; an outlet connection; a bladder connection; a blow-off valve comprising a valve seat and a cooperating valve closing element arranged to keep the blow-off valve closed whenever the pressure acting on the closing element from the interior of the valve housing is lower than a first overpressure value; a connection to a movable member which is capable of expansion and contraction in response to pressure variations within the valve housing; a double armed lever including a force arm and a load arm the force arm of which is adapted to be acted-upon by the force produced by expansion of the movable member and the load arm of which is adapted to act on said closing element to close the blow-off valve only when the pressure in the valve housing exceeds a second pressure value higher than said first value; a one-way valve dividing the valve housing into two separate chambers for allowing gas to flow only from a first of said chambers, with which the blow-off valve communicates, to the second chamber, into which the bladder connection and the connection to the movable member opens.

24. A valve unit according to claim 30, wherein the load arm of said lever is provided with an iron part adapted to be attracted by a magnet disposed on the opposite side of the load arm with respect to the blow-off valve, the attraction force between the magnet and the iron part being such that the load arm does not act upon the closing until the overpressure in the valve housing is higher than said second value.