Abstract:
A device for passive pressure relief and for reducing the volume flow for an electromechanically driven medical gas delivery means ( 50 ) in a medical device for respirating a patient ( 60 ) with a pressure relief unit ( 1 ) with a first and second gas port ( 2, 3 ), with a relief valve ( 4 ), with a pressure relief outlet ( 8 ) with an equalization space ( 9 ) and with a nonreturn valve ( 11 ) and a valve disk ( 5 ), which is arranged in the relief valve ( 4 ) and is maintained in a position relative to a valve seat ( 7 ) via a bellows ( 60 . The surfaces ( 51, 52 ) facing the first and second gas ports ( 2, 3 ) have different areas, so that the relief valve ( 4 ) opens as soon as an operating pressure ( 23 ) at the first gas port ( 2 ) exceeds a prevailing (stored) pressure level ( 24 ) in the equalization space ( 9 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2010 004 424.5 filed Jan. 13, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a device for pressure equalization and for the controlled reduction of a volume flow of an electromechanically driven medical gas delivery means to a medical device for respirating (also known as ventilating) a patient, especially a respirator or an anesthesia apparatus. 
       BACKGROUND OF THE INVENTION 
       [0003]    Valves for pressure reduction are known as pressure reducers from the state of the art and are used for monitoring. 
         [0004]    A respiration drive is designed in GB 2324122 B2 in the form of a radial flow compressor rotating at a high rpm. The respiration drive acts as a pressure source, which makes available a pressure rising with increasing rpm. Thus, the variation of the rpm is a manipulated variable for adapting the respiration pressure to the respiration situation, which means that the rpm must be cyclically increased and decreased again synchronously with the breathing cycle by varying the respiration pressure in such a way that the variation is resolved for individual breaths. 
         [0005]    U.S. Pat. No. 6,877,511 BB describes a variation of the respiration pressure for the inspiration and expiration phases of a compressor, which variation is brought about by acceleration and deceleration of a rotary compressor. 
         [0006]    In a medical gas delivery means driven electromechanically with variable air delivery capacity according to the state of the art, the particular pressure being currently delivered is brought about by varying the rpm as a function of an external actuating signal, for example, the signal of a respirator. 
         [0007]    A medical gas delivery means driven electromechanically with variable air delivery capacity comprises in the sense of the present invention a gas delivery means, gas delivery device or gas delivery unit in an embodiment with an electromechanical blower drive, radial flow compressor, rotary compressor, or side channel compressor. 
         [0008]    These variations of the rpm lead to accelerations and deceleration operations. The accelerations and decelerations of radial flow compressors and/or rotary compressors, which occur in a cumulative manner during the life of the product, impose very high requirements on temperature and media resistance, reliability and low wear for the components present in the device, such as shafts, bearings and seals, based on the intended use for supplying patients with clean breathing air. These requirements cannot be guaranteed in each application over the entire life of the product, so that some components must undergo maintenance or be replaced at certain time intervals. 
         [0009]    If the electromechanically driven medical gas delivery means is not operated variably but without being affected by an external actuating signal, the electromechanically driven medical gas delivery means must be operated permanently at the maximum necessary pressure level, even in the case in which the medical device being supplied does not continuously call for this pressure level for respirating a patient or the outlet of the electromechanically driven medical gas delivery means is blocked from time to time by closed valves in the respirator. 
         [0010]    Reliable self-cooling by the air stream being delivered is thus no longer available. The self-cooling by the air stream is essential especially if the radial flow compressor or rotary compressor is encapsulated in a housing part to achieve reduced noise generation. The temperature rise resulting herefrom leads to a thermal load for the components such as shafts, bearings and seals. Operation of the electromechanically driven medical gas delivery means without self-cooling is therefore disadvantageous with respect to the service life both for operation with and without variation of the rpm. An essential percentage of the wear is due to thermal load and to dynamic accelerations and deceleration operations brought about by the respiration control. 
       SUMMARY OF THE INVENTION 
       [0011]    It is therefore advantageous to avoid dynamic accelerations and deceleration operations as much as possible. Increases in the respiration pressure to be applied can, of course, be brought about only by increasing the rpm of a radial flow compressor, but the respiration pressure can also be reduced by pneumatically relieving the pressure into the environment. However, the pressure relief must not counteract an increase in the respiration pressure intended by the user and is imposed on the medical device for respirating a patient and should take place independently from an actuation by an external actuating signal and without actively actuated components as parts of the electromechanically driven medical gas delivery means. 
         [0012]    The object of the present invention is to provide an overload protection for pressure equalization between an electromechanically driven medical gas delivery means and a medical device for respirating a patient. 
         [0013]    According to the invention, a device is provided for pressure equalization for an electromechanically driven medical gas delivery means in a medical device for respirating a patient. The device has a pressure relief unit comprising a first gas port and a second gas port comprising a relief valve with a valve disk and a valve crater. The device has a pressure relief outlet, an equalization space and a nonreturn valve. The valve disk of the relief valve is in pneumatic connection with the electromechanically driven medical gas delivery means via a front-side area and via a rear-surface area. The front-side area is made larger than the rear-side area. A front-side force acts on the valve disk via the front-side area and a rear-side force acts via the rear-side area at an operating pressure and a pressure level in the equalization space. A distance between the valve disk and the valve crater is determined by the operating pressure and the pressure in the equalization space and by the ratio of the front-side surface having the area to the rear-side surface having the area and by the ratio of the front-side force to the rear-side force, so that a partial volume flow of a volume flow, which is adapted to the operating state of the medical device for respirating a patient and to the operating state of the electromechanically driven medical gas delivery means, flows off into the environment via a bypass stream branch, via the relief valve and the pressure relief outlet. 
         [0014]    The device according to the present invention is arranged as a pressure relief unit in parallel arrangement in a bypass stream branch of a main stream branch carrying an air flow. The air flow is carried to a pressure sink through the main stream branch by an electromechanically driven medical gas delivery means, designed as a rotary compressor, side channel compressor or radial flow compressor. The pressure sink is a medical device for respirating a patient, especially a respirator or anesthesia apparatus. The medical device for respirating a patient takes a pressure from the electromechanically driven medical gas delivery means, which pressure varies cyclically with the respiration control, and this variation may also result in complete blockage of the main stream branch, besides in an unhindered, free flow from the medical device to the patient without an appreciable flow resistance or pressure drop up to the patient. The pressure relief unit comprises a relief valve, with a valve sealing element designed as a valve disk, with a flexible bellows and with a valve crater, a first gas port, a second gas port, a pressure relief outlet, an equalization space, as well as a nonreturn valve with a nonreturn valve sealing element and with a nonreturn valve crater (valve seat). 
         [0015]    The valve disk is connected with the flexible bellows in such a way that the valve disk is arranged such that it is movable in the direction of the first gas port towards the valve seat. The compressed air pressure relief unit seals, with the relief valve, the amount of removed air into the bypass stream branch on the inlet side against the amount of air being delivered by the electromechanically driven medical gas delivery means in the main stream branch if the pressure sink calls for an amount of air from the electromechanically driven medical gas delivery means. The electromechanically driven medical gas delivery means, designed as a rotary compressor, side channel compressor or radial flow compressor, is cooled in this case by the flowing air stream, and the amount of heat generated in the interior of the housing of the gas delivery means is effectively removed by this self-cooling to the outside. The relief valve closes the pressure relief outlet in this case based on the prestress of the flexible bellows with the front side of the valve disk against the valve seat, so that no amount of air can escape into the environment via the pressure relief outlet. The front side of the valve disk seals off the amount of air in the first gas port via a front-side surface A 1 . The bellows arranged on the rear side of the valve disk is in pneumatic connection on the rear side with the amount of air in the second gas port of the pressure relief unit via a rear-side surface A 2 . The rear-side surface A 2  opposing the amount of air present on the rear side is made smaller than the front-side surface A 1  opposing the amount of air located on the front side. 
         [0016]    The nonreturn valve with the nonreturn valve sealing element and with the nonreturn valve seat is arranged between the rear-side surface A 2  of the valve disk with the bellows and the second gas port of the pressure relief unit. The nonreturn valve seat is arranged towards the second gas port of the pressure relief unit, so that the nonreturn valve element seals against this nonreturn valve seat in such a manner that no air flow is possible from the first gas port into the buffer volume in the direction of the second gas port of the pressure relief unit, but an amount of air and pressure levels corresponding to this amount of air can reach the buffer volume and hence the rear-side surface A 2  of the valve disk from the second gas port. 
         [0017]    If the pressure sink does not receive any volume flow from the electromechanically driven medical gas delivery means, i.e., the main stream branch is fully blocked on the outlet side, for example, by a closed dispensing valve in the medical device for respirating a patient, the relief valve is opened, so that air can reach the pressure relief outlet from the first gas port and can flow off into the environment. Without a gas flow through the pressure relief outlet, the amount of heat generated in the interior of the housing would not be able to be removed to the outside. Gas-delivering states are thus obtained for the electromechanically driven medical gas delivery means, in which the amount of air being delivered cools the electromechanically driven medical gas delivery means, both when the main stream branch is blocked by the dispensing valve of the medical device for respirating a patient via the pressure relief outlet and when the main stream branch is unblocked through the main stream branch itself. 
         [0018]    The mode of operation of the pressure relief unit and of the individual components will be explained in more detail below based on this state as a first working point of an outlet-side blockage of the main stream branch with the main stream branch blocked and on a first operating pressure p w,1  in the main stream branch. 
         [0019]    A first front-side pressure p F,1  corresponding to the first working operating pressure p w,1  acts on the front-side surface A 1  of the valve disk from the side of the first gas port. 
         [0020]    A first rear-side pressure p B,1  corresponding to the first operating pressure p w,1  acts on the system comprising the valve disk and the bellows from the side of the second gas port on the rear-side surface A 2 . 
         [0021]    A couple of forces acting in the opposite direction with F F,1  on the front side of the valve disk and F B,1  on the rear side of the valve disk is obtained via the surfaces A 1  and A 2  of the valve disk from the front-side pressure p F,1  and the rear-side pressure p B,1 . Since the surface A 1  of the valve disk acting on the front side is larger than surface A 2  of the valve disk acting on the rear side, the valve disk is moved away from the sealing crater in the direction of the second gas port. The relief valve is thus open. 
         [0022]    This means that when the main stream branch is closed, an amount of air corresponding to the amount of air being delivered from the pressurized gas source enters the environment via the pressure relief outlet through the bypass stream branch and the sealing crater (seat) from the electromechanically driven medical gas delivery means. The nonreturn valve is closed in this first working point, so that air can flow from the main stream branch via the second gas port into the buffer volume between the bellows and the valve disk and the nonreturn valve on the rear side of the valve disk, so that the first operating pressure p w,1  is present in the buffer volume. 
         [0023]    The conditions for triggering an opening operation of the relief valve can be summarily described in the general form as follows. 
         [0024]    Starting from any desired operating pressure p w,x , the amount of air removed by the pressure sink, i.e., a volume flow flowing through the main stream branch must drop to such an extent, or stop, that the operating pressure rises to a pressure p w,y  in such a way that a force F F,y , which is greater than the force F B,x  acting on the rear side of the pressure disk and being due to a prevailing (stored) pressure value p V,x  and the surface A 2  acting on the rear side, is obtained via the surface A 1  of the front side of the valve disk, which said surface acts on the front side, so that the relief valve partially or fully opens. 
         [0025]    If an amount of air is taken from the medical device for respirating a patient, preferably a respirator or anesthesia apparatus, at a second working point, with the main stream branch not blocked, a second operating pressure p w,2 , which is a lower operating pressure than the first operating pressure p w,1 , becomes established in the main stream branch. A rear-side force F F,2  acting on the valve disk of the relief valve results from the operating pressure p w,2  and the surface A 1  of the valve disk of the relief valve, which said surface acts on the front side. The pressure drop resulting in the main stream branch from the elimination of the blockage of the main stream branch causes a pressure difference at the nonreturn valve, so that the nonreturn valve sealing element of the nonreturn valve, which said element is preferably designed as a diaphragm, is pressed against the nonreturn valve seat and no pressure equalization to the main stream branch can take place via the second gas port of the pressure relief unit. The first operating pressure p w,1  is thus maintained in the equalization space and it is stored in the equalization space as a pressure value p V,1  almost without a time delay. 
         [0026]    This stored (prevailing) pressure value p V,1  continues to act unchanged on the rear side on the valve disk of the relief valve with the surface A 2  of the relief valve such that there is a force F B,1  on the valve disk acting on the rear side. The force ratios at the valve disk of the relief valve change due to the pressure change p w,2 . 
         [0027]    The force F B,1  acting on the rear side of the valve disk of the relief valve is now greater than the front-side force F F,2 , which results from the operating pressure p w,2 . This brings about closure of the relief valve. 
         [0028]    After completion of the closing operation of the relief valve, the pressure p V,1  in the equalization space is released by the relative motion of the bellows, which motion is coupled with the motion of the valve disk, to a pressure value p V,1 , which is slightly lower than the pressure level p V,1  that was previously present. 
         [0029]    The conditions for triggering a closing operation of the pressure relief valve can be summarily described in the general form as follows. 
         [0030]    Starting from any desired operating pressure p w,x , the amount of air removed by the pressure sink, i.e., a volume flow flowing through the main stream branch, must be so large that the operating pressure will drop to a pressure which results over the effective surface A 1  of the front side of the valve disk in a force F F,z  that is weaker than the force F B,x  resulting from a prevailing (stored) pressure value p V,x  and the surface A 2  acting on the rear side on the rear side of the valve disk, so that the relief valve partly or completely closes. 
         [0031]    The opening and closing characteristic of the relief valve is set by dimensioning surface A 1  of the valve disk, which surface acts on the front side and surface A 2  of the valve disk, which latter surface acts on the rear side and by the area ratio QA=A 1 /A 2  resulting therefrom. Ratio QA is preferably selected in a range of 1.1 to 2.0 and especially preferably in a range of about 1.5 to 1.6. The front-side surface A 1  preferably has a front-side surface A 1  with an effective surface area of 60 mm 2  to 80 mm 2 , and the front-side surface A 1  is especially preferably designed with an effective surface area of 70 mm 2 . The rear-side surface A 2  preferably has an effective surface area of 35 mm 2  to 55 mm 2 , and the rear-side surface A 2  is especially preferably designed with an effective surface area of 45 mm 2 . The opening and closing characteristic is adapted to the working pressure ratios arising from the combination of an electromechanically driven medical gas delivery means preferably designed as a radial flow compressor or rotary compressor and a pressure sink preferably designed as a medical device for respirating a patient and especially preferably as a respirator or anesthesia apparatus. A typical operating pressure for an electromechanically driven medical gas delivery means designed as a radial flow compressor for operating a respirator is in a range of 30 mbar to 60 mbar. A typical value at which the relief valve releases the pressure relief outlet and air streams from the main stream branch via the bypass stream branch into the environment is in the range of 70 mbar to 100 mbar. 
         [0032]    The advantage of the relief valve according to the present invention over a solution with a pressure relief valve in which the pressure relief valve is opened beginning from a defined pressure (pressure limit) is the variability of the operating pressure. The relief valve functions at any desired working point of the electromechanically driven medical gas delivery means as long as the difference between the pressure levels p w,1  and p w,2  is great enough. 
         [0033]    In a special embodiment, a dispensing element is present in the equalization space. This dispensing element guarantees that during changes in the operating pressure p w,1 , the corresponding prevailing (stored) pressure value p V,1  in the equalization space can adapt itself to these changes. The adaptation takes place due to a pressure equalization towards the environment. The nonreturn valve would remain closed without a dispensing element in case of a decreasing operating pressure at a prevailing (stored) pressure value p V,1  in the equalization space, which pressure value is higher than the operating pressure p w,1 . The force F B,1  acting on the rear side of the valve disk of the relief valve would now be lastingly stronger than the front-side force F F,2  that results from the operating pressure p w,2 , so that the relief valve would no longer open. 
         [0034]    A dispensing element is necessary especially if the electromechanically driven medical gas delivery means shall not be operated statically at a working point with an operating pressure but at different working points with an operating pressure set continuously or in a stepwise variable manner. 
         [0035]    The dispensing element is designed such that the pressure equalization time via the dispensing element is in the range of about 5 minutes in the case of the application in which the pressure sink is a medical device for respirating a patient, preferably a respirator, especially an intensive respirator. The dispensing element represents a pneumatic resistance R (resistance). 
         [0036]    The following possibilities of technical solutions, for example, a dispensing diaphragm, an air-permeable membrane filter, a sintered filter or even combinations of sintered elements, membranes and diaphragm elements, may be considered for a practice-oriented implementation of the dispensing element. These possible solutions make it possible to generate a pneumatic resistance. A dispensing diaphragm is preferably used, and a dispensing diaphragm with round dispensing opening is especially preferred. The dispensing opening may be preferably prepared by machining by milling or by means of laser machining. Holes with a diameter in the range of a few μm can thus be prepared in a reproducible manner. 
         [0037]    The duration is set by selecting a predetermined width of opening of the dispensing element combined with the volume contained in the equalization space. 
         [0038]    The volume or its special pneumatic property, the compliance C, cooperates with the pneumatic resistance R as a pneumatic time constant τ. 
         [0000]      τ=R·C
 
         [0000]    The compliance is determined here both by the volume contained in a space element or container and by the properties of the outer wall of a dispensing element predetermined in the space element or container. The compliance values needed for the application can be embodied by correspondingly selecting the material, for example, by using either an essentially flexible elastic material or a predominantly solid nonelastic material for the outer wall of the container in conjunction with the material thickness of the outer wall of the container. For the application of the pressure relief unit in a medical device for respirating a patient, the equalization process over time between the equalization space and the environment via the dispensing element shall have concluded completely with a duration of about 3 minutes to 5 minutes. Under the physically generally valid precondition that an equalization process is concluded at a rate of 95% with five times the duration of a time constant τ, a value of one minute is obtained for τ from an equalization time of 5 minutes. 
         [0039]    With a pneumatic compliance C of 
         [0000]    
       
         
           
             C 
             = 
             
               0.22 
                
               
                 mL 
                 
                   m 
                    
                   
                       
                   
                    
                   bar 
                 
               
             
           
         
       
     
         [0000]    which is predetermined by the dimensions and the material selected for the equalization space, a necessary pneumatic resistance R is obtained as 
         [0000]    
       
         
           
             R 
             = 
             
               4545 
                
               
                 
                   m 
                    
                   
                       
                   
                    
                   
                     bar 
                     · 
                     min 
                   
                 
                 L 
               
             
           
         
       
     
         [0000]    as the basis for dimensioning the dispensing element. 
         [0040]    For an embodiment with a dispensing diaphragm, the width of opening of the opening in the dispensing diaphragm is preferably selected in the range of 0.002 μm 2  to 0.008 μm 2  for an equalization space of 0.2 L to 0.3 L resulting from the compliance indicated, which corresponds to a diameter of about 50 μm to 100 μm and results in a duration of about 5 minutes in case of a round dispensing opening. 
         [0041]    In another embodiment, the dispensing element is not connected pneumatically with the environment, but the dispensing element is in connection via an equalization line with an air stream branch guiding the air flow from the gas delivery means to the medical device for respirating a patient. In an arrangement of the pressure relief unit in the bypass stream branch, the dispensing element is preferably in connection with the main stream branch or with the bypass stream branch via an equalization line. It is also preferable to connect the equalization line from the dispensing element pneumatically with the bypass stream branch in the direction of the medical device for respirating a patient, and it is also preferable to connect it with the second gas port of the pressure relief unit. Due to the pressure in the main stream branch and in the bypass stream branch being increased by approximately 30 mbar to 60 mbar relative to the environment and to a pressure level in a range of 70 mbar to 100 mbar being present in the equalization space before opening the relief valve and discharge via the pressure relief outlet, the pressure gradient between the equalization space and the pressure in the main stream branch or bypass stream branch is made lower by about 40% to 70% than the pressure difference between the pressure level in the equalization space and the environment. The consequence of this lower pressure gradient is that the equalization process takes place substantially more slowly in the main stream branch or bypass stream branch than a pressure equalization against the environment with equal dimensioning of the equalization space and dispensing element. In an inversion of the argument, the volume of the equalization space can thus be reduced at equal predetermined duration of the equalization process equaling 3 minutes to 6 minutes. The volume of the equalization space can thus be selected in a range below 0.1 L when dimensioning the time constant τ. 
         [0042]    In another embodiment, the elastic bellows is designed such that it is free from prestress. Thus, the bellows does not act complement or counteract the forces F F , F B  acting on the front side and on the rear side, which forces result from the pressure values p w,1 , p w,2  and the area ratio QA. 
         [0043]    In a special embodiment, the elastic bellows is provided with a prestress. Thus, the bellows acts with or against the forces F F , F B  acting on the front side and on the rear side, which forces result from the pressure values p w,1 , p w,2  and the area ratio QA. It is possible as a result to adapt the areas A 1 , A 2  to the design needs; in particular, it is thus possible to reduce the rear-side area A 2 , because a part of the force F B  acting on the rear side is applied by a prestress of the bellows, which is designed, for example, as a spring. 
         [0044]    However, the prestress can also be set in a preferred embodiment by selecting the elasticity of the material and/or the thickness of the material of the bellows. In another preferred embodiment, it is possible to apply a nonlinear force component to the valve disk by means of the prestress of the bellows, besides the area ratio QA, which linearly applies a continuous force to the valve disk independently from the path of the bellows and the state, the force applied to the valve disk increasing with increasing path of the bellows, i.e., being designed as a force acting progressively. 
         [0045]    The present invention will be explained in more detail with reference to the drawings attached, where identical reference numbers designate identical features. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    In the drawings: 
           [0047]      FIG. 1  is a schematic view showing the basic structure of a pressure relief unit according to the invention; 
           [0048]      FIG. 2   a  is a schematic view showing the pressure relief unit according to  FIG. 1  in a first view with an electromechanically driven medical gas delivery means with a respirator. 
           [0049]      FIG. 2   b  is a schematic view showing the pressure relief unit according to  FIG. 1  in the first view with the electromechanically driven medical gas delivery means with the respirator; 
           [0050]      FIG. 3   a  is a schematic view showing the pressure relief unit according to  FIG. 1  in a second view of the electromechanically driven medical gas delivery means and with the respirator; 
           [0051]      FIG. 3   b  is a schematic view showing the pressure relief unit according to  FIG. 1  in the second view of the electromechanically driven medical gas delivery means and with the respirator; 
           [0052]      FIG. 4  is a schematic view showing a variant of the pressure relief unit according to  FIG. 1  with an electromechanically driven medical gas delivery means and with a respirator; and 
           [0053]      FIG. 5  is a perspective exploded view and aa cross sectional exploded view showing another view of the pressure relief unit according to  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0054]    Referring to the drawings in particular,  FIG. 1  shows a pressure relief unit  1  according to the present invention with a first gas port  2 , with a second gas port  3 , with a relief valve  4 , comprising a valve disk  5 , a flexible bellows  6  and a valve seat  7 , with a pressure relief outlet  8  to an environment  33 , with an equalization space  9 , with a dispensing element  10 , with a nonreturn valve  11 , comprising a nonreturn valve sealing element  12  and a nonreturn valve seat  13 . The pressure relief unit  1  is designed as follows. 
         [0055]    Valve disk  5  is connected with the flexible bellows  6  in such a way that the valve disk  5  is arranged movably and is prestressed preferably in the direction of the valve seat  7 , so that the valve disk  5  lies or almost lies on the valve seat  7  in a pressureless and flow-free state and the pressure relief outlet  8  is largely closed in the direction of the environment  33  in the pressureless and flow-free state. Valve disk  5  is in connection with the front-side surface  51  of valve disk  5 , which said surface  51  has an area A 1 , via the first gas port  2 . Valve disk  5  is in connection with the internal diameter of bellows  6  via the equalization space  9  and the nonreturn valve  11  is in connection with the rear-surface surface  52  of valve disk  5 , which said surface  52  has an area A 2 . Pressure equalization continuously takes place between the equalization space  9  and the environment  33  via the dispensing element  10 . The ratio of the front-side area A 1   51  of valve disk  5  to the rear-side area A 2   52  of the valve disk  5  is designed for a value in the range of 1.1 to 2.0. The front-side surface  51  with the area A 1  of the valve disk  5  preferably has an effective surface of 60 mm 2  to 80 mm 2 , and the rear-side surface  52  with the area A 2  of the valve disk  5  preferably has an effective surface of 35 mm 2  to 55 mm 2 . 
         [0056]    In  FIGS. 2   a  and  3   b , the pressure relief unit  1  according to  FIG. 1  is arranged in parallel in a bypass stream branch  30  of a main stream branch  20  carrying an air flow  40  in a combination with a medical device for respirating a patient with pneumatic connection with a patient. The medical device for respirating a patient is shown in these  FIGS. 2   a  and  2   b  in a schematic view as an example as a respirator  60 .  FIG. 2   a  shows the design features in a schematic view and shows the pressure relief unit  1  according to  FIG. 1  in a first operating state.  FIG. 2   b  additionally shows pressure ratios and force ratios, wherein the design features are identical to the features shown in  FIG. 2   a . Not all the design features shown in  FIG. 2   b  are provided with reference numbers. The air flow  40  enters the pressure relief unit  1  to the relief valve  4  via the first gas port  2 . Equalization space  9  is connected with the main stream branch  20  via the second gas port  3  and the nonreturn valve  11 . A pressure equalization continuously takes place via the dispensing valve  10  between the equalization space  9  and the environment  33  ( FIG. 1 ). 
         [0057]    Identical elements in  FIGS. 2   a  and  2   b  are designated by the same reference numbers as in  FIG. 1 . 
         [0058]    A volume flow  40  is carried by the main stream branch  20  from an electromechanically driven medical gas delivery means  50  to a respirator  60 . The respirator  60  removes a volume flow  40  from the electromechanically driven medical gas delivery means  50  and represents a pressure sink. Respirator  60  removes a volume flow  40  varying cyclically with the respiration of a patient  70  and/or the control of the respirator  60  from the electromechanically driven medical gas delivery means  50 . The air is carried from the respirator to the patient  70  via feed lines  67 . As a result, the pressure level p w  in the main stream branch  20  and the bypass stream branch  30  varies cyclically with the respiration of the patient  70  and/or the control of the respirator  60 . A typical operating pressure in the main stream branch  20  is in the range of 50 mbar to 80 mbar. 
         [0059]    In this arrangement according to  FIGS. 2   a  and  2   b , the respirator  60  is in the first operating state, in which the respirator  60  does not take over any volume flow  40  from the electromechanically driven medical gas delivery means  50 , during one time interval of the respiration cycle. The respirator  60  blocks the main stream branch  20  by closing means  66  present in the respirator  60 . The operating pressure in the main stream branch  20  then rises to a value p w,1    21  of 70 mbar to 100 mbar. 
         [0060]    Nonreturn valve  11  is open towards the second gas port  3  during this time interval of the respiration cycle, and a pressure equilibrium is obtained in this first operating state on the front side and the rear side of the valve disk  5 . The current operating pressure p w,1    21  is present on the front side as a front-side pressure p F,1    25 , and the current operating pressure p w,1    21  is present on the rear side of the valve disk  5  as a rear-side pressure p B,1    26 , so that the pressure ratios in the relief valve  4  are equalized and the current operating pressure p w,1  is also present as an identical pressure level p V,1    22  in the equalization space  9 . The pressure level in the equalization space  9  becomes equalized with the pressure in the environment  33  with a time delay over several respiration cycles via the dispensing element  10  ( FIG. 1 ). 
         [0061]    The duration of this equalization process is selected in a range of about five minutes in an intensive respirator. This duration is set as a time constant τ via a predetermined pneumatic resistance R, for example, by a predetermined width of opening of dispensing element  10  and by the pneumatic compliance C of equalization space  9 . 
         [0062]    The pressure level p V,1  in the equalization space  9 , identical to the current operating pressure p w,1    21 , is present as a rear-side pressure p B,1  on the rear side at the valve disk  5 . 
         [0063]    A force F F,1    43  is obtained at the relief valve  4  via the surfaces  51 ,  52  of valve disk  5  with the areas A 1 , A 2  and via the front-side pressure p F,1  at the valve disk  5  on the front side of the valve disk  5 , and a force F B,1    44  is obtained on the rear side of the valve disk with the rear-side pressure p B,1 . The front-side force F F,1    43  is greater than the rear-side force F B,1    44  at the pressure equilibrium existing in the first operating state between the front-side and rear-side pressures p w,1    21 , p B,1    26  due to the fact that the front-side surface  51  of the valve disk  5 , which said surface has the area A 1 , is larger than the rear-side surface  52  of valve disk  5 , which said surface  52  has the area A 2 . When adding the forces F F,1    43  and F B,1    44  acting in opposite directions, a front-side force acting on the valve disk  5  is obtained in this constellation of forces as a resulting force, so that the valve disk  5  is moved away from the valve seat  7  and the pressure relief outlet  8  is released. A volume flow component  41  of the volume flow  40  thus flows via the opened relief valve  4  from the main stream branch  20  into the environment  33  via the bypass stream branch  30  through the pressure relief outlet  8 . 
         [0064]    In  FIGS. 3   a  and  3   b , the pressure relief unit  1  according to  FIG. 1  is arranged in parallel in a bypass stream branch  30  of a main stream branch  20  carrying an air flow  40  in a combination with a medical device for respirating a patient with pneumatic connection with a patient. The medical device for respirating a patient is shown in these  FIGS. 3   a  and  3   b  as an example as a respirator  60  in a schematic view.  FIG. 3   a  shows in a schematic view the design features and shows the pressure relief unit  1  according to  FIG. 1  in a second operating state.  FIG. 3   b  additionally shows pressure ratios and force ratios, wherein the design features are identical to the features shown in  FIG. 3   a . Not all the design features shown in  FIG. 3   b  are provided with reference numbers. The air flow  40  enters via the first gas port  2  and the pressure relief unit  1  to the relief valve  5 . The equalization space  9  is connected with the main stream branch  20  via the second gas port  3  and the nonreturn valve  11 . Pressure equalization continuously takes place between equalization space  9  and the environment  33  via the dispensing element  10 . 
         [0065]    Identical elements in  FIGS. 3   a  and  3   b  are provided with the same reference numbers as in  FIG. 1 . 
         [0066]    A volume flow  40  is sent through the main stream branch  20  from an electromechanically driven medical gas delivery means  50  to a respirator  60 . The respirator  60  removes a volume flow  40  from the electromechanically driven medical gas delivery means  50  and represents a pressure sink. The respirator  60  removes a volume flow  40  varying cyclically with the respiration of a patient  70  and/or the control of the respirator  60  from the electromechanically driven medical gas delivery means  50 . The air is sent from the respirator to the patient  70  via feed lines  67 . As a result, the pressure level p w  in the main stream branch  20  and the bypass stream branch  30  varies cyclically with the respiration of the patient  70  and/or the control of the respirator  60 . 
         [0067]    In this arrangement according to  FIGS. 3   a  and  3   b , the respirator  60  is in the second operating state during a time interval of the respiration cycle, in which operating state the respirator  60  removes a volume flow  40  from the electromechanically driven medical gas delivery means  50 . 
         [0068]    Respirator  60  sends the volume flow  40  from the main stream branch  20  via feed lines  67  to the patient  70 . Closing means  66  present in the respirator  60  does not bring about any blockages of the main stream branch  20  during the current time interval of the respiration cycle. A typical operating pressure p w  in the main stream branch  20  is in the range of 50 mbar to 80 mbar. 
         [0069]    Due to the fact that the equalization space  9  has been placed under the pressure level p V,1  via the second gas port  3  in a state such as the state described in connection with  FIGS. 2   a  and  2   b , due to the respiration cycle, recurring in time immediately before this current time interval, the pressure level p V,1    21  still continues to be present in the equalization space  9  even during this current time interval of the respiration cycle and acts as a rear-side pressure p B,2    28 . This pressure level p V,1    21  or the rear-side pressure p B,2    28  is higher than the current operating pressure p w,2    23  currently present now in the main stream branch  20  and the bypass stream branch  30 . The nonreturn valve  11  thus closes with the nonreturn valve sealing element  12  against the nonreturn valve seat  13  and the connection between the equalization space  9  and the second gas port  3  is interrupted and the pressure level p V,1 , continues to prevail (be stored) in the equalization space  9 . 
         [0070]    The pressure level p V,1  that has hitherto been present in the equalization space  9  becomes equalized with the pressure in the environment  33  ( FIG. 1 ) with a time delay over several breathing cycles via the dispensing element  10  until a pressure level p V,2    24  is reached in the equalization space  9 . 
         [0071]    The duration of this equalization process is selected in a range of about 5 minutes in an intensive respirator. This duration is set via a predetermined resistance R, for example, by a predetermined width of opening of the dispensing valve  10  and by the pneumatic compliance C of the equalization space  9 . 
         [0072]    The operating pressure p w,2    23  currently present now acts as a front-side pressure p F,2    27  on the front side on the valve disk  5 . Due to the fact that the pressure level p V,1    21  prevailing (being stored) as a rear-side pressure P B,2    28  is higher than the current operating pressure p w,2    23  currently present in the main stream branch  20  and the bypass stream branch  30 , different force ratios are obtained at the relief valve  4 . A force F F,2    45  acts on the front side of the valve disk  5  and the rear-side force F B,2    46  acts on the rear side of the valve disk via the surfaces  51 ,  52  with the areas A 1 , A 2  and the pressure ratio from the pressure level p V,1    21  in the equalization space  9  as the rear-side pressure p B,2    28  and the current operating pressure p w,2    23 . The rear-side force F B,2  acting now is unchanged in this second operating state compared to the rear-side force F B,1    44  acting in the first operating state, because the pressure level p V,1    21  has been stored due to the closing of the nonreturn valve  11  in the equalization space  9  and continues to be present as a rear-side pressure p B,2   28  on the rear side of the valve disk  5 . The front-side force F F,2    45  is lower in this second operating state than the rear-side force F B,2    46  acting in the first operating state due to the reduction of the operating pressure from p w,1    21  to a pressure level p w,2    23  with the front-side pressure p F,2    27  resulting therefrom. When adding the opposite forces F F,2    45  and F B,2    46 , a front-side force acting on the valve disk  5  is obtained in the constellation of forces as a resulting force, so that the valve disk  5  is moved with the elastic bellows  6  in the direction of the valve seat  7 . 
         [0073]    This results in closing of the relief valve  4 , and the pressure relief outlet  8  is largely closed against the environment  33 , so that the volume flow  40  flows nearly completely from the electromechanically driven medical gas delivery means  50  through the main stream branch  20  to the respirator  60  and no volume flow component  41  ( FIGS. 2   a  and  2   b ) of the volume flow  40  is sent into the environment  33 . 
         [0074]    A special variant of the pressure relief unit  1  according to  FIG. 1  is shown in  FIG. 4  arranged in parallel in a bypass stream branch  30  of a main stream branch  20  carrying an air flow  40  in a combination with a medical device for respirating a patient with pneumatic connection with a patient. 
         [0075]    In a schematic view,  FIG. 4  shows the design features and the designation of the pressure relief unit  1  according to  FIG. 1  in the first operating state, wherein the medical device for respirating a patient is shown in a schematic view as an example as a respirator  60 . 
         [0076]    Identical elements in  FIG. 4  are designated by the same reference numbers as in  FIG. 1 . 
         [0077]    The air flow  40  enters the pressure relief unit  1  and reaches the relief valve  4  via the first gas port  2 . The equalization space  9  is connected with the main stream branch  20  via the second gas port  3  and the nonreturn valve  11 . 
         [0078]    A volume flow  40  is sent through the main stream branch  20  from an electromechanically driven medical gas delivery means  50  to a respirator  60 . The respirator  60  removes a volume flow  40  from the electromechanically driven medical gas delivery means  50  and represents a pressure sink. The respirator  60  removes a volume flow  40  varying cyclically with the respiration of a patient  70  and/or the control of the respirator  60  from the electromechanically driven medical gas delivery means  50 . The air is sent via feed lines  67  to the patient  70  from the respirator. 
         [0079]    Pressure equalization continuously takes place between the equalization space  9  and the second gas port  3  via the dispensing element  10  by means of an equalization line  100 . 
         [0080]    In this arrangement according to  FIG. 4 , the respirator  60  is in an identical operating state as in the arrangement according to  FIGS. 2   a  and  2   b . The pressure relief unit  1  is shown in a first operating state in a time interval of the respiration cycle, in which the respirator  60  does not take over any volume flow  40  from the electromechanically driven medical gas delivery means  40 . The respirator  60  blocks the main stream branch  20  by closing means  66  located in the respirator  60 . 
         [0081]    The nonreturn valve  11  is opened towards the second gas port  3  during this time interval of the respiration cycle, and a pressure equilibrium is obtained in this first operating state on the front side and the rear side of the valve disk  5 , so that the pressure ratios are equalized in this relief valve  4  and the current operating pressure is also present as an identical pressure level in the equalization space  9 . The equalization space  9  is in pneumatic connection with the rear side of the nonreturn valve  12  via the equalization line  100  and thus with the second gas port  3 . An equalization volume flow  110  thus flows from the equalization space  9  in the direction of the second gas port  3  as soon as the pressure level in the equalization space  9  is higher than the pressure level in the second gas port  3 . The pneumatic connection with the second gas port  3  by means of the equalization line  100  of the dispensing element  10  makes it possible for the volume of the equalization space  9  to be able to be selected to be smaller than in the solutions according to  FIGS. 1 ,  2   a ,  2   b ,  3   a ,  3   b , in which the dispensing element  10  is in pneumatic connection with the environment  33  ( FIG. 1 ). 
         [0082]      FIG. 5  shows a pressure relief unit  1  according to the present invention according to  FIG. 1  in a combination of a three-dimensional view and a longitudinal section. 
         [0083]    Identical elements in  FIG. 5  are designated by the same reference numbers as in  FIG. 1 . 
         [0084]    The pressure relief unit  1  comprises a first gas port  2 , a second gas port  3  to an environment  33 , a relief valve  4 , a pressure relief outlet  8 , an equalization space  9 , a dispensing element  10 , and a nonreturn valve  11 . The relief valve  4  comprises a valve disk  5  with a valve seat  7 . The valve disk  5  is connected with a space  9  via a flexible bellows  6  in a gas-tight manner. An equalization space  9  is used as a pressure storage means and is closed on the side of the second gas outlet  3  by the nonreturn valve  11 . Space  0 . 9  has an opening into the environment  33  via a dispensing element  10 . The valve disk  5  is pressed by a horizontal motion against the sealing crater  7  in case of a correspondingly great difference between the operating pressure p w  and the pressure p V  in space  9  and thus closes the pressure relief outlet  8  between the first gas port and the environment  33 . 
         [0085]    While specific embodiments of the invention have been described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.