Abstract:
A device for mixing anesthetic vapor with anesthetic gas has a pressure limitation feature achieved in a simple manner. The device has a valve device ( 11 ), with which the evaporator is switched on and off. The valve device ( 11 ) is equipped with an overpressure release device ( 22 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of German Applications DE 10 2004 046 645.9 of Sep. 25, 2004 and DE 10 2004 054 416.6 filed Nov. 11, 2005, the entire contents of each of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to a device for mixing anesthetic vapor with anesthetic gas. 
     BACKGROUND OF THE INVENTION 
     A device of this type has become known from U.S. Pat. No. 3,420,232. Saturated anesthetic vapor from an evaporator chamber is mixed with the anesthetic gas via a dispensing means in the anesthetic vaporizer operating according to the bypass principle in order to set a predetermined concentration of anesthetic in the anesthetic gas. The anesthetic vaporizer is provided with a shut-off valve, which is designed to shut off the gas flow from the evaporator chamber in a first switching position, so that the anesthetic gas reaches a gas outlet from a gas inlet via a bypass line. In a second switching position, the gas flow is released via the evaporator chamber and anesthetic vapor can be mixed with the anesthetic gas with the dispensing device. The shut-off valve comprises a lower part provided with gas ducts, which is part of the evaporator housing, and a rotatably movable upper part, which is fastened thereto in a rotatingly movable manner and has kidney-shaped gas ducts. Depending on the angular position of the upper part, the kidney-shaped gas ducts of the upper part connect corresponding gas ducts in the lower part, so that a gas flow is released via the shut-off valve or the gas ducts in the lower part are closed. The upper part has a carrier pin, which is connected with the setting member for the anesthetic concentration. The shut-off valve is closed in the zero position of the setting member and the anesthetic gas flows via the bypass line directly from the gas inlet to the gas outlet. If the setting member is set to a certain anesthetic concentration starting from the zero position, the shut-off valve opens above the carrier pin and the gas flow from the evaporator chamber is released. 
     An anesthetic vaporizer, in which it is possible to switch over between a transport position, a zero position and a dispensing position by means of individual valves, which are actuated by the setting member, is known from DE 196 13 754 C1 (corresponding to U.S. Pat. No. 5,671,729). The evaporator chamber is completely closed in the transport position of the setting member, so that neither liquid nor gaseous anesthetic can escape. A ventilating valve, with which the pressure in the evaporator chamber of the anesthetic vaporizer can be released, is opened during the transition from the transport position into the zero position. The ventilating valve is again closed during the transition of the setting member into the dispensing position, so that the anesthetic can be dispensed at the pressure level prevailing during operation. 
     A certain system pressure must be maintained within the anesthetic tank in case of anesthetics with a low boiling pint in order to prevent the anesthetic from boiling. A pressure control circuit with a differential pressure sensor as well as a dispensing valve is usually used for the dispensing branch in such evaporators. The differential pressure sensor is especially sensitive to high pressure amplitudes and pressure shocks even if these reach the differential pressure diaphragm with an offset in time. 
     However, an increase in pressure within the anesthetic vaporizer may also be due to external causes, for example, a kinked supply tube for anesthetic gas, which is to be enriched with anesthetic vapor. Such pressure shocks may occur with the anesthetic vaporizer switched on and with the anesthetic vaporizer switched off. 
     In addition, a pressure build-up, which may damage delicate measuring systems, may occur due to minor leaks at dispensing components within the dispensing device when the anesthetic vaporizer is switched off when the anesthetic gas is sent past the dispensing device directly into the anesthesia apparatus. Even though it would be possible to protect these measuring systems with a separate pressure limiting valve, additional components are necessary for this. 
     SUMMARY OF THE INVENTION 
     The basic object of the present invention is to improve a device of the type such that pressure limitation is achieved in a simple manner. 
     According to the invention, a device is provided with a dispensing device for mixing anesthetic vapor with anesthetic gas and with a valve device. The valve device sends anesthetic gas past the dispensing device from a gas inlet to a gas outlet in a first switching position and establishes a path for the gas via the dispensing device in a second switching position. A lower part of the valve device is provided with gas ducts and an upper part is arranged adjustably above the lower part and is provided with gas ducts wherein gas ducts are provided extending from the lower part via the upper part and back into the lower part in such a way that the first switching position and the second switching position can be established depending on the position of the upper part in relation to the lower part. A clamping device fixes the upper part in relation to the lower part in the form of a pressure limiting means for limiting the pressure in the gas ducts. 
     The advantage of the present invention is essentially that an overpressure limiting means is integrated within a valve device, with which the dispensing device for anesthetics is either bridged over or released. Provisions are made for this purpose for the upper part of the valve device, with which the switchover function is performed, to be fixed by means of the clamping device in relation to the lower part. The clamping device is dimensioned such that the upper part lifts off from the lower part when a predetermined pressure is exceeded within the gas ducts that extend between the lower part and the upper part. The valve device, with which the dispensing device for anesthetics is either bridged over or released, is usually present at an anesthetic vaporizer. Due to the integration of the clamping device, which fixes the two components of the valve, namely, the upper part and the lower part, in relation to one another, the valve device is provided with an overpressure limiting means. Due to the fact that the valve device is actuated each time the anesthetic vaporizer is switched on and off, the upper part and the lower part are moved in relation to one another during each switching operation, so that the components of the valve are prevented from sticking. By contrast, there is a risk in case of an overpressure limiting valve arranged separately that sticking of the valve body in relation to the valve seat will occur due to aging or anesthetic vapors, so that the overpressure limiting valve may open at an excessively high pressure only. Another advantage of the valve device according to the present invention can be considered to be the fact that not only the dispensing device but also the gas ducts of the anesthetic vaporizer that carry the anesthetic gas are protected from overpressure. An excessively high pressure may develop, for example, due to a kinked gas line, which is arranged downstream of the anesthetic vaporizer. 
     The valve device can be advantageously designed as a rotary switch or slide switch. 
     The clamping device is advantageously designed as a clamping device that closes again automatically or remains open. An automatically closing clamping device is preferably a leaf spring or a coil spring or a weight, with which the upper part is pressed against the lower part. A clamping device that remains open may be designed as a stop notch jumping over in case of a limiting force or as a predetermined breaking point in a clamping element. 
     An exemplary embodiment of the present invention is shown in the drawings and will be explained in greater detail below. 
     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 
       In the drawings: 
         FIG. 1  is schematic view of an anesthetic vaporizer according to the invention in the switched-off state; 
         FIG. 2  is schematic view showing the anesthetic vaporizer according to  FIG. 1  with the valve device opened; 
         FIG. 3  is schematic view showing an anesthetic vaporizer in the switched-on state; 
         FIG. 4  is schematic view showing the anesthetic vaporizer according to  FIG. 3  with the valve device opened; and 
         FIG. 5  is schematic view showing an alternative valve device with a clamping device that remains open. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular,  FIG. 1  schematically shows an anesthetic vaporizer  1 , which contains an anesthetic tank  2  for liquid anesthetic  3 , a dispensing valve  4 , an adjustable dispensing gap  5 , a bypass line  6  with a bypass gap  7 , a differential pressure sensor  8 , a heater  9  for the anesthetic and an electronic control unit  10 . A valve device  11  on the top side of the anesthetic vaporizer  1  has a lower part  16  with a gas inlet  13  and with a gas outlet  14  and gas ducts  17 ,  18  and an upper part  12  with gas ducts  15 ,  19 . The upper part  12  is fastened against the lower part  16  in the form of a rotary or slide valve, so that individual gas ducts  15 ,  19  of the upper part  12  are connected to gas ducts  17 ,  18  of the lower part  16  in predetermined positions of the upper part  12 . The upper part  12  is pressed onto the lower part  16  by means of a spring  22 . 
     In the switching position shown in  FIG. 1 , the gas inlet  13  and the gas outlet  14  are connected to one another directly via the gas ducts  15 ,  17 , and the anesthetic gas is sent past the dispensing device  2 ,  4 ,  5 ,  6 ,  7 . Together with the gas ducts  18 ,  19 , the bypass line  6  now forms a closed circular pipe. The gas ducts  15 ,  17 ,  18 ,  19  cross an interface  23  between the upper part  12  and the lower part  16 . 
     If an increased pressure or pressure rise occurs within the bypass line  6  or at the differential pressure sensor  8  connected with the bypass line  6 , such a pressing force is exerted on the upper part  12  via the gas duct  19  that, as is illustrated in  FIG. 2 , the upper part  12  lifts off from the lower part  16  and the pressure can drop along arrow  24 . Identical components in  FIG. 2  are designated by the same reference numbers as in  FIG. 1 . Since the gas duct  15  is connected to the gas inlet  13  and the gas outlet  14  via the gas ducts  17 , the pressure also drops when an increased pressure or pressure rise is present in the gas duct  15 . 
       FIG. 3  illustrates the anesthetic vaporizer  1  in a second switching position in the switched-on state. The gas inlet  13  is connected with the gas outlet  14  here via the gas ducts  17 ,  18 ,  20 ,  21  and the bypass line  6 . The gas ducts  20 ,  21  in the upper part  12  are connected with the corresponding gas ducts  17 ,  18  of the lower part  16  in this switching position of the valve device  11 . If an increased pressure rise occurs within the gas ducts  20 ,  21 , a force will act at the interface  23  between the upper part  12  and the lower part  16 , and the upper part  12  is lifted off by this force from the lower part  16 , corresponding to  FIG. 4 , and excess gas can escape along arrow  24 . The limiting pressure at which the upper part  12  just lifts off can be set, for example, by selecting the rigidity of the sprig  22 . To set the closing force of the spring, an adjusting screw is provided, which is not shown specifically in  FIG. 4  and with which the pressing force of the spring  22  can be changed. 
       FIG. 5  schematically shows an alternative valve device  111 . This valve device is used on the top side of the anesthetic vaporizer  1  in a manner similar to valve device  11 . However, the valve device  111  has a clamping device  30  that remains open in the form of two tongues  27  with predetermined breaking points  28 . The tongues  27  have hook-shaped clamps  29 , with which the upper part  121  is pressed against the lower part  161 . When the pressure exceeds a predetermined limit value at the interface  231  between the upper part  121  and the lower part  161 , the predetermined breaking points  28  break and the clamps  29  release the upper part  121 . An immediate and permanent pressure release takes place. 
     While specific embodiments of the invention have been shown and 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.