GASIFICATION AND DOSAGE ARRANGEMENT

Abstract: A gasification and dosage arrangement, intended in parti­ cular for the feeding of anaesthetic gas to a fresh gas stream in an anaesthesia apparatus, comprising a source (1) of a liquid which is intended for gasificaton, a gasification chamber (6) to a mixing point for mixture with another gas, e g the said fresh gas. An arrangement in accordance with the invention is cha­ racterized in that the gasification chamber (6) is adapted to be kept at a constant pressure at a predetermined temperature which is such that the liquid fed, in the main, is directly gasified.

Description: TECHNICAL FIELD The present invention relates to a dosage and gasification arrangement, intended in particular for the feeding of anaesthetic gas to a fresh gas stream in an anaesthesia apparatus, comprising a source of gas of constant pressure, a source of a liquid which is intended for gasification, a gasification chamber and a dosage line, which is arranged to conduct the gas from the gasification chamber to a mixing point for mixture with another gas, e g the said fresh gas by means of a valve arrangement giving a defined dosage of gas per Stroke of a control valve of said valve arrangement. It will be clear, however, to those versed in the art that such an arrangement can also be used for other purposes, e g for the moistening of breathing gases in a respirator apparatus. BACKGROUND ART Various experiments have been carried out to gasify anaesthetic liquid or moistening liquid directly into the fresh gas stream. See, for example US patents 3 251 361, 4 038 980 and 4 657 008. In such systems it has proved difficult, however, to bring about a uniform and controllable dosage. Experiments also have been carried out with gasification of anaesthetic liquid in a separate gasification chamber were both gas and liquid phase existed simultaneously. Here a problem arose, though, at the filling up of new liquid. This problem is solved in a simple manner with the help of the present invention (c.f. e.g. SE-A-8403447). Reference is also being made to DE-A1-27 06 192 which is describing a device of essentially the above mentioned kind and as set out in the first part of claim 1 comprising a source of liquid which is fed to a gasification chamber. An important difference compared with the present invention is, however, that said gasification chamber is not adapted to be kept at a constant pressure at a predetermined temperature. DISCLOSURE OF INVENTION The present invention thus relates to a gasification and dosage arrangement of the type defined above which, more particularly, is characterized in that the gasification chamber is adapted to be kept at a constant pressure and, by means of a controllable heating arrangement is adapted to be maintained at such temperature that the liquid fed from the source into the gasification chamber, in the main, is directly gasified and after equilibrium has been reached no more liquid can be introduced from the source into the chamber than is apportioned in the dosage line by means of the valve arrangement arranged in the dosage line. In this manner, after equilibrium has been reached, a uniform gas mass of a constant temperature and constant pressure is obtained from which smaller quantitites readily can be apportioned into another gas, e g a fresh gas, in an anaesthesia apparatus. The said constant pressure preferably is arranged to be brought about by feeding the liquid which is to be gasified at the said pressure. This can be achieved in that the source of liquid is adapted to be maintained at this pressure by feeding a gas, e g air, under the same pressure from a source of pressure via a governor. In order to achieve the dosage, the dosage line may be provided with a time-controlled valve, the opening frequency and/or opening time of which can be varied. Alternatively the dosage line may be provided instead with a, preferably controllable, throttle valve. In practice it has been found to be appropriate to arrange the gasification chamber at a higher level than the source of liquid and connect it to the same via a riser which, starting from a point near the bottom of the source of liquid, preferably ends near the bottom of the gasification chamber. At the same time it may be suitable to let the dosage line originate from the gasification chamber at the highest point of the latter or near that point. The invention can also be applied to the dosage of liquid in that a condensation stage is inserted directly after the abovementioned dosage valve. The dosage thus takes place in gaseous state, whereupon the gas is reformed to liquid. In this way a very precise method for the dosage, especially of small quantities of liquid is achieved, something which otherwise is very difficult. BRIEF DESCRIPTION OF DRAWINGS The invention will be described in greater detail in the following with reference to the attached drawing which, by way of example, schematically shows a preferred embodiment of the same. BEST MODE OF CARRYING OUT THE INVENTION The preferred embodiment of the subject of the invention shown, by way of example, on the attached drawing is intended to be used in an anaesthesia apparatus. In the following description reference is made, therefore, to such an application, even though it will be clear to those versed in the art that the same principle can also be used for other purposes e.g., as stated above, to the dosage of liquid. On the drawing is shown a source 1 for an anaesthesia liquid 2. In practice this source may be constituted of a liquid-filled pressure-proof glass flask which is intended to be supplied with a constant pressure via a governor from a source of pressure, these items being jointly designated 3. This may be done simply by means of feeding compressed air via the line 4. The liquid 2 is made thereby to rise via the riser pipe 5 up to a gasification chamber 6 which via a schematically indicated heating arrangement 7 is adapted to be maintained at such a temperature that the liquid fed, in the main, is directly gasified. The heating is controlled in the case shown by a controller device 8 which in turn is controlled by a microprocessor or the like 9. This is indicated by the broken line 10. A broken line 11 indicates how the same microprocessor 9 can control a controller device 12 for a schematically indicated solenoid valve 13 which controls the flow in a dosage line. This dosage line 14, moreover or alternatively, may contain a throttle valve 15 which possibly may also be controllable by the microprocessor 9, as indicated by the broken line 16. The dosage line 14 terminates in a fresh gas line 17, only a small secton of which is shown. Numeral 18 finally designates a broken line which indicates that the microprocessor also may be adapted to control the combination of governor and source of gas designated 3. When it is a matter of the commonly occuring anaesthetic liquids, such as halothane, n-furan or isofuran, it has proved to be appropriate to make use of a temperature of approx. 70-80°C in the gasification chamber 6. At the same time it has proved appropriate to use a pressure of the order of magnitude of 400 cm water column, that is to say 0.4 bar. The pressure in the gasification chamber 6 hereby may not rise above 400 cm water column, since in such a case the liquid would be pressed back. Within the abovementioned temperature range the liquid gasifies directly as it enters the gasification chamber. At the same time no more liquid can be introduced that is apportioned via the dosage line 14. In a practical embodiment a constant opening duration of the solenoid valve 13, namely 60 ms, is used, the opening frequency being varied between 0.1 Hz and 10 Hz. At the same time a throttle 15 is used here which was set so that it gave a dosage of 1 ml per stroke. As a result the dosage could readily be varied between 0.1 ml and 10 ml/s. Alternatively or moreover it also would have been possible to vary the opening duration. On using a solenoid valve this would have been possible from a minimum time of approx. 20 ms up to being kept open permanently. The pressure too can be varied, of course, but is limited in practice by the sturdiness of the flasks wherein the anaesthetic gas is normally supplied in liquid form. The pressure is limited downwards by the fact that if the pressure is too low the liquid level in the vessel 1 would acquire a decisive importance for the dosage. In practice preferably a pressure between 100 and 800 cm water column is used. Naturally the invention is not limited simply to the embodiment described above, but may be varied within the scope of the following claims. For example, the invention may also be applied to the dosage of liquid. In such an imaginary application the device 15 shown schematically may constitute a condensation apparatus wherein the quantity of liquid metered in gaseous state recovers its liquid form.

Claims: A dosage and gasification arrangement, intended in particular for the feeding of anaesthetic gas to a fresh gas stream in an anaesthesia apparatus, comprising a source (3) of gas of constant pressure, a source (1) of a liquid which is intended for gasification, a gasification chamber (6) and a dosage line (14) which is arranged to conduct the gas from the gasification chamber (6) to a mixing point (17) for mixture with another gas, e g the said fresh gas and a valve arrangement (12,13,15) giving a defined dosage of gas per stroke of a control valve (13) of said valve arrangement, characterized in that the gasification chamber (6) is adapted to be kept at a constant pressure and, by means of a controllable heating arrangement (7) is adapted to be maintained (8,9,10) at such temperature that the liquid fed from the source (1) into the gasification chamber (6), in the main, is directly gasified and after equilibrium has been reached no more liquid can be introduced from the source (1) into the chamber (6) than is apportioned in the dosage line (14) by means of the valve arrangement (12,13,15) arranged in the dosage line (14). An arrangement in accordance with claim 1, characterized in that the said source (3) of gas of constant pressure is arranged for keeping said source (1) of the liquid at said constant pressure in order to feed the liquid from the source (1) to the gasification chamber (6) at the same pressure. An arrangement in accordance with claim 2, characterized in that the valve (13) provided in the dosage line (14) is time-controlled, the opening frequency and/or opening time of which can be varied. An arrangement in accordance with claim 1 or 2, characterized in that the dosage line (14) is provided with a, preferably controllable, throttle valve (15). An arrangement in accordance with anyone of the preceding claims, characterized in that the gasification chamber (6) is arranged at a higher level than the source of liquid (1) and is connected to the same via a riser (5) which, starting from a point near the bottom of the source of liquid, preferably ends near the bottom of the gasification chamber. An arrangement in accordance with claim 5, characterized in that the dosage line (14) originates from the gasification chamber (6) at its highest point or near this point. An arrangement in accordance with anyone of the preceding claims relating to the dosage of liquid, characterized in that the dosage take place in gaseous state, whereupon the gas is reformed to liquid.

Inventors: ANKARTROSS, JAN OLOV, LUNDELL, ULF GUSTAV, NYMAN, RUNE
Applicants: GAMBRO ENGSTROEM AB
Application year: 1986
Main classification: A61M16
IPC codes: B01F3, A61M16