There is a requirement for apparatus which can deliver an accurately mixed gas supply consisting of a mixture of two or more gases.

An accurately mixed gas mixture can be used for applications such as an atmosphere in the culture of mammalian embryos, the culture of human, animal, bacterial and plant cells, and the culture of specific cell lines or genetically engineered cells.

The gas mixture can also be used to accurately maintain the pH of organic and inorganic buffers and media used in bio-reactors for the production of polypeptides, proteins and hormones. The gas can also be used as a fuel source in chemical lasers and in industrial oxidative and fermentative processes.

The apparatus to which the present invention is directed can be used in any instance where accurate control of the mixing of two or more gases is required and where the delivery of the mixture of gases may be required to be intermittent, on demand or continuous.

It is an object of this invention therefore to provide a source of accurately mixed gases where the component gases and the concentration of each component gas is adjustable and defined by a user. The use of the gas mixture for the apparatus may be intermittent, on demand or continuous at any particular instant such that the use may be zero up to the maximum deliverable by the apparatus.

In one form therefore, although this may not necessarily be the only or broadest form, the embodiments describe gas mixing apparatus including a plurality of gas chambers with at least two of the chambers being of unequal capacities, regulation means for controlling the flow of gases from pressure supply sources to the respective gas chambers, a reservoir for storing the gases from the chambers, and means for controlling the transfer

of the gases from the chambers to the reservoir. The apparatus may have a pressure regulated gas supply line to be connected to each chamber, and an outlet line of each chamber to a mixed gas reservoir.

The pressure regulated gas supply line to each chamber may be all at the same pressure and same temperature so that according to Bernouli's theorem the volume of gas can be defined.

Preferably the outlet line of each chamber includes a non-return valve.

The non-return valve acts to prevent gas returning from the reservoir to any one of the chambers.

Each of the outlet lines may also include a variable orifice throttle valve to regulate the flow of gas in each outlet line. The use of the throttle valve proportionally slows down the gas flow from each chamber so that the time taken for each chamber to empty into the reservoir is substantially the same. This gives proportional mixing during the whole cycle of emptying the chamber. The result is that transitory concentration peaks within a single cycle are removed, giving a more accurate mixing and decreasing the amount of gas needed to prime the system.

In a preferred form of the invention, the selected volume gas chambers may have variable volumes so that a required volume of each gas may be selected. The variable volume chambers may be cylinders with pistons which can be moveable in them to change the selected volume of the gas chamber. By changing the volume of each chamber the proportions of each gas in the final mixture may be varied.

In one preferred form, inlet and outlet valves to the gas chambers may be comprised of a single three-way valve having three gas lines extending from it with one line to the three-way valve being the pressure regulated gas supply line, a second line being a combination of inlet line and the outlet line from the chamber and a third line being a line to the mixed gas reservoir. The valve or valves for each cylinder may be manually or electrically or micro-processor controlled so that gas can be let into the variable volume chamber and then released from the variable volume

chamber into the mixing chamber as required.

There may be two, three or more pressurised gas supplies to an equivalent number of variable volume chambers. A control regulator and matched regulators in a supply line from each supply line may be used preferably to ensure that the pressure of gas supplied to each of the chambers is exactly the same in each instance.

It should be noted that the apparatus according to this invention may take into account the volumes of the supply and outlet lines as part of the respective volumes of the chambers so that an accurately known volume of the chambers is used.

In a further form the invention may be said to reside in a volumetric gas mixing apparatus including a plurality of selected volume gas chambers, a pressure regulated gas supply, each chamber having a three-way valve associated with it, with three gas lines extending from the three-way valve, one line from the three-way valve extending to the pressure regulated gas supply, a second line from the three-way valve extending to the respective chamber, and a third line from the three-way valve extending to a manifold and a mixed gas line extending from the manifold to a mixed gas reservoir, each third line having a non-return valve and a variable orifice throttle valve.

In a preferred form of the invention the selected volume gas chambers may be cylinders with pistons which can be moveable in them to change the selected volume of the gas chamber.

The mixed gas reservoir may have a baffle within if adjacent the mixed gas inlet so that mixing of gases upon entry occurs.

The mixed gas reservoir may have an output line with a mixed gas pressure regulator.

The mixed gas reservoir may have a pressure relief valve.

There may be provided computer or microprocessor control so that as gas is used from the mixed gas reservoir the three way valves are opened to the pressurised gas supplies to commence a new charging cycle. When pressure has equilibrated in the respective chambers, the three-way valves

are then opened to the manifold and the mixed gas reservoir to recharge the reservoir.

This then generally describes the invention but to assist with understanding, reference will now be made to the accompanying drawings which show preferred embodiments of the invention.

FIG. 1 shows a first embodiment of a gas mixing apparatus according to the present invention; FIG. 2 shows an alternative embodiment; and FIG. 3 shows a further alternative embodiment.

Now looking more closely at FIG. 1 which shows a first embodiment of a gas mixing apparatus according to the present invention for two gases, it will be seen that the gas mixing apparatus comprises gas supply cylinders 1 and 2 for the different gases that are to be mixed. The cylinders have first pressure regulators 3 and 4 respectively. Supply lines 6 and 7 extend from the cylinders 1 and 2 and from the supply line 7, a side tap 8 extends to a pressure control regulator 10. The pressure control regulator provides a set pressure in line 11 which sets the pressure supplied by regulators 12 and 13 in supply lines 6 and 7 respectively. Hence the pressure in chamber supply lines 15 and 16 is preferably set at the same nominal pressure. Pressure regulators 12 and 13 are preferably matched so that they supply substantially the same pressure of gas regardless of variations in supply pressure in the respective lines.

A first pressure chamber 20 is provided for gas from the cylinder 1 and a second pressure chamber 22 is provided for gas from cylinder 2. The pressure chamber 20 has a piston 24 which is moveable in a cylinder 25 so that a volume in the region 26 can be accurately set preferably with the assistance of a graduated scale 27. Once valve 28 in the supply line 15 has been opened a sufficient length of time for the pressure in the region 26 to equilibrate with the supply pressure, valve 28 is closed. The piston 24 is set at a selected position and then is not moved during the filling and

emptying process.

In a similar manner in chamber 22, a volume in region 33 is set by means of piston 30 having a graduated scalpe 32 ; being placed in a selected distance into the cylinder 31. When pressure in chamber 22 is equilibrated with the supply pressure through line 16, valve 34 is closed. Once again the piston 30 is set at a selected position and then is not moved during the filling and emptying process.

When both chambers are filled to the selected pressure, valves 40 and 41 are then opened to allow gas supply through outlet lines 42 and 43 to mixing manifold 44 before passing through line 45 into storage or mixing chamber or reservoir 46. Non-return valves 47 and 48 are provided in lines 42 and 43 respectively so that gases cannot pass back into the respective chamber regions 26 and 33. A supply line 49 is provided from the storage chamber 26 to supply gas through valve 50 as required. Mixing chamber 46 has a pressure relief valve 51 and an output pressure regulator 52. By this apparatus pressurised gas of a selected composition can be supplied by variation of the amount of volume in the chambers 20 and 22.

In FIG. 2 an alternative embodiment of the invention is disclosed.

In this embodiment there are three pressurised gas supplies 60,61 and 62 supplying gas through matched regulators 63,64 and 65 to respective chambers 66,67 and 68 through three-way valves 69,70 and 71 respectively so that the pressure of gas supplied to each chamber is the same as that to the other chambers.

The pistons 66a, 67a and 68a are positioned in the respective cylinders 66,67 and 68 when the selected volume of each gas in the final mixture is chosen and are not moved in the subsequent steps.

Once the chambers 66,67 and 68 have been filled and the pressure equilibrated in each chamber with the supply pressure, three-way valves 69,70 and 71 are moved so that gas flows through the respective supply lines 88,89 and 90 to manifold 72 and into storage or mixing chamber or reservoir 73 via non-return valves 78,79 and 80. A pressure

transducer 75 in tank 73 records when gas pressure goes below a selected value and if so, micro-processor 76 sends instructions to open the respective valves 69,70 and 71 to provide further gas into the respective chambers 66,67 and 68 to replenish the storage chamber.

The operation of the apparatus according to the second embodiment of the invention in a preferred manner is as follows: Base or pure gases are supplied to the apparatus from regulated gas bottles 60,61 and 62, or in the case where air is used, a scrubbed filtered clean regulated supply may be obtained from a compressor. The delivery pressures for each of the supply gases is preferably set to the same nominal pressure, as an example only, may be 1,500kPa.

The input gases are connected to the gas mixing apparatus of the present invention by high pressure hoses. On entering the apparatus the input gases are again pressure regulated by a set of pressure matched regulators 63,64 and 65. The output pressures of these regulators must be substantially equal and may be controlled by gas pressure from a further control regulator 77. The nominal set pressure for the mass regulators, as an example only, may be 800kPa.

The input gases then pass through input solenoid operated valves 69,70 and 71 into the metering manifold. The metering manifold is a series of different sized chambers 66,67 and 68 with adjustable pistons fitted.

The pistons are fitted with gas-type 0-rings. The volumes of the respective chambers are adjusted to the ratio of gases required in the final mixture.

When the input solenoid operated valves are activated the chambers are connected to the high pressure input gases. The input solenoid operated valves are held in the activated state for sufficient time to allow for pressure equalisation with the input pressure, for instance, as discussed above, 800kPa. After this time, the input solenoid operated valves are de-activated to their default position which allows the gas in the chambers to flow out into the reservoir 73 which is at a lower pressure. The gas flowing out of each single chamber passes through a check or non-return valve 78,79 and

80 respectively and then strikes a baffle 81 in the reservoir 73. The baffle is present to cause turbulence and mixing of the in-rushing gases. The action of the input solenoid operated valves is micro-processor 76 controlled and is dependent on a feedback system from a pressure transducer 75 in the reservoir. The pressure in the reservoir is monitored. The pressure in the reservoir is maintained at an operational pressure for example only of 320kPa. When gas is used from the reservoir and the pressure decreases to say 300kPa the apparatus cycles another injection of gases into the reservoir. This will increase the pressure within the reservoir to greater than 300kPa. It is not until gas has been drawn from the reservoir and the pressure again falls to 300kPa that the apparatus will again cycle to add more gas to the reservoir. When gas is injected the pressure in the reservoir increases and reaches an equilibrium point above 300kPa. At this high equilibrium point complete exhaustion of the gases in each of the chambers is inhibited. Back mixing in the mixture in the reservoir with the pure gases in the chambers cannot occur as the check valves are fitted to prevent this.

As gas is removed from the reservoir and the pressure drops to 300kPa further pure gas exhausts from each of the chambers into the reservoir until at 300kPa the system cycles again. The process of injecting gas into the reservoir, always at the same initial pressure, ensures the maintenance of the ratio of gases by volume set by the user.

When the apparatus is powered up, sufficient cycles are performed under the control of the micro-processor to ensure that the required mixture is being delivered. During the start up cycle the output solenoid operated valve 82 is activated and this allows the mixture produced to be vented to atmosphere, or to a fume hood if the mixture is toxic. At the end of the start up cycle the output solenoid operated valve 82 is de-activated to allow the pressure within the reservoir to build up to the operating pressure. The apparatus will not cycle again until gas is removed from the reservoir.

The volume of the reservoir required is dependent on the total volume of the chambers emptying into it. Preferably the volume of the

reservoir is greater than 20 times the total volume of all the chambers emptying into it so that the accuracy of the final mixture does not decrease.

The apparatus of this embodiment of the present invention is adapted to maintain its accuracy because: (a) gases are metered by volume at a set pressure, (b) gases are mixed only at the same initial pressure, (c) check valves are used to stop back mixing of the mixture and pure gases thus removing the variability of an unknown quantity, and (d) the storage reservoir volume is preferably at least 20 times the total of all input chambers.

The input valves 28 and so forth in the embodiments of Figures 1 and 2 can form part of regulators 12,13 and so forth, as one-way valves, or they can be inserted in supply lines 6 and 7 for example.

In a similar way, the output valves can form part of one-way valves 47 and 48 or can be at the entrance to the manifold.

The pressures applied to lines 15 and 16 are preferably of similar magnitude but they can be significantly different, but that will require recalibration of the volumes of chambers 22 and 25, in order to achieve the required mix of gases.

Valves 69,70 and 71 have for convenience been referred to as three-way valves, but they could be considered to be two-way valves.

Known forms of two-way valves, would, however, not be practical.

A third embodiment of the invention is shown in FIG. 3. In this embodiment those items with the same function as those in FIG. 2 are given the same reference numeral and are described in the description for that embodiment.

In the third embodiment the respective supply lines 88,89 and 90 to manifold 72 have the non-return valves 78,79 and 80 and variable orifice throttle valves 85,86 and 87. The non-return valves act to prevent gas returning from the reservoir to any one of the chambers. The use of the throttle valves proportionally slows down the gas flow from each chamber

so that the time taken for each chamber to empty into the reservoir is substantially the same. This gives proportional mixing during the whole cycle of emptying the chamber. The result is that transitory concentration peaks within a single cycle are removed, giving a more accurate mixing and decreasing the amount of gas needed to prime the system.

The orifice diameter in the variable orifice throttle valves 85,86 and 87 may be in the range of from 125 to 725 microns but the invention is not restricted to these diameters. In general the smaller the volume of the respective chamber then the smaller the orifice diameter.

In general the reference in this specification to emptying of a chamber is not to be read as indicating that the gas is completely removed from that chamber but should be taken to indicate that the gas exits the chamber until such time as the pressure in the chamber is the same as that in the output reservoir.

Throughout this specification various indications have been given as to the scope of this invention but the invention is not limited to any one of these but may reside in two or more of these combined together. The examples are given for illustration only and not for limitation.

Throughout this specification and the claims that follow unless the context requires otherwise, the words'comprise'and'include'and variations such as'comprising'and'including'will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.