The invention relates to an apparatus for testing of s breathing systems for divers at a chosen testing pressure, comprising a means for simulating the breathing cycle of a diver according to a desired breathing pattern, and for supply of gas to or drainage of gas from the device under test in accordance with the simulated breathing pattern. 0 in the later years, Norwegian authorities has sharpened the rules for professional diving in the North Sea with a view to improving the security. As an element in this work one has wanted to establish better routines for testing of breathing equipment which has been overhauled or modified. However, s hyperbar testing equipment which is relevant for this purpose, is cumbersome to use, and in addition it is too bulky and heavy to be suitable for work on a routine basis on board a diver support vessel. Thus, there is a need for simple and preferably mobile testing devices which may be used for, respectively, o functional testing of helmet/breathing valves and for testing of capacity/ performance of complete breathing systems installed on board diver support vessels.

Testing devices for breathing systems normally are based on a breathing simulator comprising a manikin (model head) 5 and an artificial lung. The devices preferably comprises a breathing simulator which is arranged to give a sinusoidal breathing course on standardized ventilations, preferably in the range of 15-90 liters per minute. The capacity of the system and its ability to easy breathing may be determined from pressure recordings in the "mouth portion" of the manikin.

Existing breathing simulators for divers preferably are based on the ventilation (the breathing cycle) being simulated by a hydraulic or electrically driven piston pump which is precision controlled by means of electronics. The breathing simulators are relatively heavy and not very mobile. It is therefore normal that the simulator is supplied fixedly mounted on a separate pressure chamber. The use of a piston pump within a pressure chamber entails that the effective volume of the chamber - and therefore the chamber pressure - varies in step

with the ventilation. In order to reduce these pressure variations to an acceptable level, it is necessary to use large pressure chambers, or alternatively to couple the chamber to a relatively large buffer volume. The object of the invention is to provide a testing apparatus having substantially smaller dimensions and being substantially simpler to use than existing apparatus for the topical purpose.

Another object of the invention is to provide such a testing apparatus making it possible to carry out the topical functional tests with compressed air as the single source of energy.

The above-mentioned objects are achieved by means of an apparatus of the introductorily stated type which, according to the invention, is characterized in that it comprises a gas regulating unit which is connected to a first and a second gas reservoir having respectively a higher and a lower pressure than said testing pressure, said reservoirs also communicating with the apparatus under test, and the gas regulating unit comprising a switching means which is arranged to form a flow connection alternately between the high pressure reservoir and the apparatus under test, and between the apparatus under test and the low pressure reservoir, and a simulating means utilizing the overpressure and the underpressure, respectively, to simulate the desired breathing pattern, so that oppositely directed flow courses are generated through the apparatus under test in accordance with the simulated breathing pattern.

The special thing in the principle of the testing apparatus according to the invention, is that testing of the supply side of the breathing apparatus is based on the fact that the outlet or exhaust side is activated, and vice versa. The desired breathing course or breathing pattern is achieved in that the gas regulating unit varies the opening towards two gas reservoirs having overpressure and underpressure, respectively, in relation to a manikin. Inhalation is simulated in that the gas regulating unit controls the gas quantity from the mainikin to the reservoir having a lower pressure. Inhalation is simulated in a corresponding manner in that the manikin is supplied with gas from the reservoir having overpressure.

Compared with the use of a piston simulator, the apparatus according to the invention has a substantial advantage in that no pressure variations occur in the pressure chamber during the ventilation. This means that the testing setup may be based on relatively small pressure chambers without any buffer volume. When the simulator is to be used for the testing of complete breathing systems on board diver support vessels, etc., it will be convenient to use a diving bell as a pressure chamber. This means that the easily portable simulator, in addition to the necessary monitoring equipment, only consists of the manikin and a small gas regulating unit.

In closed breathing systems for divers, the diving helmet is provided with valves controlling supply and discharge, respectively, of gas in accordance with the demand of the diver. Inhalation and exhalation may be controlled by separate valves or possibly by an integrated inhalation/exhalation valve. In addition, some breathing systems are based on the inhalation valve and/or the exhalation valve having several reduction steps. In any case, it is usual that the supply pressure to the diver lies 10-15 bars above the ambient pressure of the diver, and that the pressure in the exhaust line from the diver lies approxi¬ mately 2-2,5 bars under the ambient pressure of the diver. For the sake of simplicity, the breathing valves on the breathing helmet in the following will be illustrated as an integrated unit, hereinafter called integrated breathing valve, based on a supply pressure and an exhaust pressure respectively, as stated above.

In functional testing of a helmet/breathing valves it is a simple and efficient method to establish a test setup which is based on a fixed, simulated depth, a standard gas mixture, standard ventilations, etc. By comparing the topical test data with previously recorded results, one may, in a simple manner, unveil deviations in performance. In a convenient embodiment for this purpose, the simulator is incorporated in a small pressure tank. The simulator is calibrated for a fixed testing depth of 25 meters, with air as the breathing gas and with air as the surrounding medium. As stated above, breathing systems which are of interest in this connection, preferably are based on the fact that the pressure in the exhaust line is to lie 2-2,5 bars under

the ambient pressure of the diver. By standardizing on a simulated depth of 25 m, one may therefore test the exhaust or exhalation valve with the outlet in open connection with the surrounding atmosphere. In this embodiment, the simulator may be made portable with a total weight of ca. 40 kg, the simulator having an outer shell having a diameter of ca. 50 cm and a total height of ca. 60 cm. In principle, the simulator may be operated with compressed air as the only energy source, the capacity/ performance of the breathing valves being recorded by means of mechanical flow meters and pressure meters. Alternatively, the simulator may be provided with electronic monitoring equipment.

The invention will be further described below in connection with exemplary embodiments with reference to the drawings, wherein Figs. 1 and 2 show schematic views of the apparatus according to the invention and illustrate the gas flow directions during the inhalation and exhalation phase respectively, of a breathing cycle;

Fig. 3 shows a block diagram of a first embodiment of the gas regulating unit of the apparatus;

Fig. 4 shows a schematic view of the apparatus according to the invention; and

Fig. 5 shows a second embodiment of the gas regulating unit forming part of the apparatus of Fig. 4. in the drawings, corresponding elements are designated by similar reference numerals in the different Figures.

The schematic views in Figs. 1 and 2 show a testing apparatus according to the invention which is connected to a unit which is to be tested (also called "the unit under test"). The testing apparatus comprises a gas regulating unit which, via respective conduits or lines 2 and 3, is connected to a high pressure reservoir 4 and a low pressure reservoir 5. As suggested, the pressure of the high pressure reservoir 4 lies 10 - 15 bars above the topical testing pressure, whereas the pressure of the low pressure reservoir 5 lies 2 - 2,5 bars below the testing pressure, i.e. the pressure surrounding the unit under test. Further, the gas regulating unit 1 is connected through a line 6 to the unit 7 under test. This unit in the shown case consists of an integrated breathing valve 8 which is

arranged on the front of a diving helmet 9 and communicates with an oral/nasal mask 10 which is mounted on a manikin 11. As shown, the gas reservoirs 4 and 5 communicate with the breathing valve 8 via respective connecting lines 12 and 13. As further described below, the gas regulating unit contains a switching means controlling the flow pattern in the circuit of the apparatus during a breathing cycle. Fig. 1 illustrates the flow pattern during inhalation, whereas Fig. 2 illustrates the flow pattern during exhalation. Solid arrows indicate the flow direction for the simulated ventilation, and dashed arrows the direction of the gas flow generated by the ventilation in the circuit. Inhalation is simulated in that the gas regulating unit 1 utilizes the pressure in the exhaust line 14 to produce a sinusoidal flow course from the mask 10 through the manikin 11 to the exhaust line (Fig. 1). In a similar manner, exhalation is simulated in that the overpressure in the supply line 15 is utilized by the gas regulating unit 1 to produce a sinusoidal flow course from the supply line 15 in the opposite direction through the mainikin 11 to the mask 10 (Fig. 2). The gas regulating unit in the apparatus according to the invention may be constructed in many different manners. By using the technology of today it has been found to be relatively simple to construct an electronic/mechanic regulating unit which, with a good accuracy, can simulate a desired breathing pattern. A gas regulating unit 1 which is arranged for electronic control, is shown in Fig. 3. The unit comprises a valve means 20 which is arranged to vary the gas flow to and from the unit 7 under test (Figs. 1 and 2) in accordance with the desired breathing pattern under the control of a microprocessor 21, the microprocessor communicating with units for the supply of control data representing flow quantity and pressure. Thus, there is provided a control data unit 22 containing electronic pressure gauges sensing the pressure level in the line 6 on either side of an orifice meter 23, and producing the difference ΛP between the pressure levels. With proper design of the orifice meter 23, the pressure difference ΔP is proportional to the gas quantity flowing through the orifice meter. By means of the microprocessor 21 this is utilized to control the throughput in the valve means 21, so that the desired sinusoidal "ventilation"

through the oral/nasal mask 10 is achieved. Transition from inhalation to exhalation, and vice versa, takes places by means of a change-over or switching means in the form of a reversing valve 24 which is operated by means of the microprocessor 21, the s reversing valve alternately forming a connection between the line 6 to the manikin and the line 2 to the high pressure reservoir 4, and between the line 6 and the line 3 to the low pressure reservoir 5.

Ventilation frequency and amplitude is adjusted by o means of a unit 25 for inputting a control signal to a pressure reference means 26 which, on the basis of the testing pressure (chamber pressure) and the signal from the input unit 25, produces a reference signal corresponding to the value of the maniken pressure P desired at any time. The processor 21 compares s this reference signal to the actual value of the pressure P, whereby it delivers a control signal seing to it that a deviation from the desired flow course is immediately corrected by the valve means 20. It will be clear that the precision of the simulator is dependent on a quick data processing and an o accurately calibrated electronics. Thus, in a preferred embodi¬ ment, one may at any time establish stationary conditions with respect to the gas flow through the orifice meter 23 and compare the electronic measuring results with a precision manometer.

Another embodiment of the apparatus according to the 5 invention, which is provided with a mechanical embodiment of the gas regulating unit, is shown in Figs. 4 and 5.

In Fig. 4 the manikin 11, with associated oral/nasal mask 10, helmet 9 and breathing valve 8, is placed within a chamber 30 which is pressurized to a testing pressure of 3,5 bars. The gas supply from the high pressure reservoir 4 takes place through a reduction valve 31 the outlet pressure of which is adjusted to the recommended supply pressure to the breathing valve 8. A desired "ventilation" (breathing cycle) is generated in that the gas regulating unit 1 steers the opening to the oral/nasal mask 10 to the low pressure reservoir 5 (which in this case may be the surrounding atmosphere) through the line 14, or alternatively to the outlet from an adjustable, additional reduction valve 32 which is connected in the line 2 from the high pressure reservoir 4. This reduction valve is adapted to maintain

a very stable outlet pressure P ₀ .

The gas regulating unit 1 comprises a flow valve 33 which is connected in the line 6 between the device 7 under test and the switching means 24 (corresponding to the switching means s in the first embodiment). The valve 33 consists of a nozzle 34 and a valve body 35, wherein the valve body is shaped so that the gas flow through the nozzle increases substantially proportional to the displacement of the valve body from the closed position. The valve body 35 is moved by an operating means causing a ιo gradual opening and closing of the valve 33 in accordance with the simulated breathing pattern. The operating means comprises a piston 36 which is moved back and forth with a uniform velocity between two end positions. The piston is connected to a sinus element 37 having a shape corresponding to half a period of a is sinus curve, and which is in driving connection with the valve body 35 through a transmission means 38. In the shown embodiment, the transmission means 38 consists of a pair of cooperating levers 39, 40, wherein the movement of the levers is controlled by the sinus element 37, so that the movement of the piston

2o produces a sinusoidal flow course through the valve 33.

As shown, the piston 36 is slidably arranged in a container 41 which, at the end surfaces of the piston, communica¬ tes with respective liquid reservoirs 42, 43. The surface of one reservoir 42 is under permanent pressure influence by the topical

25 testing pressure in the chamber 30, and the surface of the other reservoir 43 is arranged to be put alternately under pressure influence by the overpressure or the underpressure by means of the switching means 24, so that the driving force for the piston 36 is constituted by the pressure difference between the liquid

30 reservoirs.

The frequency of the ventilation or breathing cycle is directly proportional to the piston velocity, a breathing cycle corresponding to a complete to-and-fro travel of the piston 36. When the piston passes an end position, a pneumatic sensor means

35 44 provides for a signal causing switching of the switching means 24 in accordance with the breathing mode. The outlet pressure P ₀ from the reduction valve 32 is finely adjusted so that the gas flow through the valve 33 is equally large (but oppositely directed) in the inhalation hand exhalation phases. This implies

that the maximum pressure drop across the shown manometer 45, which is connected across the orifice meter 23 in the line 6, is equally large, but oppositely directed, in the two breathing phases. 5 The two liquid reservoirs 42, 43, which e.g. may contain water, have for their task to provide for a "smooth" movement of the piston 36. As shown, the liquid reservoir 43 is provided with a narrowed flow passage which is adjustable by means of a suitable nozzle or valve 46, e.g. a needle valve, for o adjustment of the liquid flow, and consequently of the breathing frequency of the breathing pattern. There is also provided a means for adjustment of the tidal or breathing cycle volume. This means consists of an eccentric screw 47 which is in engagement with a displaceable block 48 wherein one end of the lever 40 is s supported. With rotation of the eccentric screw 47, the point of support of the lever is displaced, and thereby the excursion or amplitude of the movement pattern of the valve body 35 is changed.

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