GB2202459A

GB2202459A - Gas mixing apparatus

Info

Publication number: GB2202459A
Application number: GB08706864A
Authority: GB
Inventors: Clive Stewart Cumner
Original assignee: Distillers Co Ltd
Current assignee: Distillers Co Ltd
Priority date: 1987-03-23
Filing date: 1987-03-23
Publication date: 1988-09-28
Anticipated expiration: 2007-03-23
Also published as: GB8706864D0; GB2202459B

Abstract

A gas mixing apparatus for providing a mixture of two gases, for example, carbon dioxide and nitrogen for applying top pressure to stout in kegs, in predetermined proportions and at a predetermined pressure comprises a supply line 1 for the first gas and a supply line 2 for the supply of the second gas. The first gas flows through an adjustable orifice 4 and a solenoid valve 5 to an outlet line 6. The second gas is supplied through a balanced seat regulator 9, a fixed orifice 14 and a non-return valve 15 into the line 3 where it is mixed with the first gas. The pressure in the outlet line 6 is monitored by a pressure switch 18 which controls the solenoid valve 5. <IMAGE>

Description

Gas Mixing Apparatus This invention relates to gas mixing apparatus for providing a mixture of at least two gases in predetermined proportions and at a predetermined pressure.

The apparatus is particularly intended for providing a mixture of nitrogen and carbon dioxide for the application of a top pressure to stout in kegs, because stout is nitrogenated, as well as containing carbon dioxide, to give it its creamy head. Some lighter beers are also dispensed with a mixture of nitrogen and carbon dioxide. The apparatus may, however, also be used for providing a mixture of any other two or more gases.

One form of gas mixing apparatus, which has been used to provide such a top pressure of mixed gases comprises a flow-controlling orifice for each gas and means for supplying the gases to the orifices at equal pressures. The gas from the downstream sides of the orifices is then mixed and supplied directly to the kegs.

This arrangement has proved satisfactory where quite a large number of kegs are supplied by a single mixing apparatus because the flow from the apparatus and hence through the orifices is then always sufficient to enable the orifices to meter the flows of the gases satisfactorily.

When, for example, it is required for the mixing apparatus to supply only a single keg or when for any other reason very low flows oi the mixed gas are likely to occur, the accuracy of the flows determined by the orifices tends to decrease. This happens, of course, because as the flow through the orifices tends to zero the pressure drop across the orifices also tends to zero and the metering effect on the orifices is dependent upon the pressure drop across them. It has been found that with one example of such apparatus, it is possible to obtain satisfactory mixture proportions at 3 instantaneous flow rates of down to about 0.15 m per hour, but below this flow rate, the mixture ratio is no longer at all reliable.

To overcome this inaccuracy, and to provide satisfactory mixture ratios at very low overall flow rates, according to this invention, a gas mixing apparatus for providing a mixture of at least two gases in predetermined proportions at a first predetermined pressure comprises a flow controlling orifice for each gas, means for supplying the gases to the orifices at equal second predetermined pressures, which are higher than the first predetermined pressure, an electrically operated shut-off valve in a line for the supply of the mixed gases downstream of the orifices and a pressure switch, which is sensitive to the mixed gas pressure downstream of the valve and operates to open the valve when the pressure which it senses is below the first predetermined pressure and to close the valve when the pressure rises to the first predetermined pressure.

By using this concept of supplying the two gases at a pressure which is higher, and preferably substantially higher for example about twice, the final pressure at which the mixed gas is required to be supplied, and making the supply intermittent by means of the electrically controlled valve, it is ensured that the instantaneous flow rates through the orifices whenever the valve is open are well above the minimum at which the orifices will provide accurate metering of the gas flows.

In consequence the proportions of the gases in the mixture supplied from the apparatus can be accurately maintained however low the overall long-term flow rate of the gas mixture may become. For example, when the mixture of gases is supplied to a single keg, the top pressure on the keg may decrease very slowly indeed over a period of time as stout, or indeed, other beer, is dispensed from the keg, but as soon as the pressure drops sufficiently far to cause the pressure switch to open the valve, the pressure drop across the orifices will at once become equal to the difference between the first and second predetermined pressures and this difference can be set to ensure that accurate metering ensues.

Preferably, when only two gases are to be mixed together, they are both supplied, with one gas at a higher pressure than the other, to a balanced seat regulator which accurately equalises the pressures of the two gases.

The balanced seat regulator comprises a valve with a seating and closure member which are opened and closed by a diaphragm. One gas is supplied at a higher pressure to the valve seating and the pressure of this gas on the outlet side of the seating is applied to one side of the diaphragm. A tap from a supply line of the other gas at a lower pressure supplies the other gas to the other side of the diaphragm. When the outlet pressure of the gas which flows through the seating is higher than the pressure of the other gas, the diaphragm causes the seating to be closed by the closure member and opened again when the pressure on the outlet side of the seating falls below that of the other gas. In consequence the seating is opened and closed continuously by the diaphragm to maintain the two pressures on the opposite sides of the diaphragm accurately equal to each other.

Preferably a second pressure switch, which also controls the electrically operated valve, is provided in a supply line of one of the two gases upstream of its orifice. If the supply of this gas fails, for example when a cylinder of the gas becomes exhausted, the second pressure switch closes the electrically operated valve regardless of the pressure sensed by the first pressure switch so that it is impossible for the apparatus to supply unmixed gas.

An example of an apparatus in accordance with the invention, which is specifically intended for supplying a mixture of nitrogen and carbon dioxide to a stout or other beer keg is illustrated in the accompanying drawing which is a flow diagram.

In this example, carbon dioxide is supplied through a line 1 from a gas cylinder and a pressure regulator at a pressure of 275 kPa and, nitrogen is supplied through a line 2 in a similar manner at a pressure of 345 kPa. The carbon dioxide flows through a line 3, an adjustable orifice 4 and a solenoid valve 5 to an outlet line 6 A bleed from the carbon dioxide supply passes through a line 7 to a chamber 8 of a balanced seat pressure regulator 9.

The nitrogen line 2 leads through an inlet 10 of the regulator 9 and thence through a seating 11 to a chamber 12 of the regulator Thence the nitrogen flows through a line 13 d a fixed orifice 14 and a non-return valve 15 into the carbon dioxide line 3 downstream of the metering orifice d e Thence the nitrogen flows through the outlet line 6 in admixture with the carbon dioxide.

In the pressure regulator 9, the chambers 8 and 12 are separated by a diaphragm 16 which carries the seating 11 and moves this seating relative to a closure member 17. When the carbon dioxide pressure in the chamber 8 is greater than the nitrogen pressure in the chamber 12, the diaphragm 16 is moved upwards to allow the flow of nitrogen through the seating 11 into the chamber 12 so that the nitrogen pressure in this chamber is increased. When this pressure rises to that of the carbon dioxide in the chamber 8, the seating 11 is moved back onto the closure member 17 and in this way the nitrogen pressure in the line 13 upstream of the orifice 14 is kept accurately equal to the carbon dioxide pressure in the line 3 upstream of the orifice 4.The ratio of the mass flow of carbon dioxide to nitrogen is therefore accurately controlled by the ratio of the area of the orifice 4 to that of the orifice 14 since the downstream pressures from the two orifices are the same.

In this example a mixture of gases is produced consisting of 70% nitrogen and 30% carbon dioxide.

The pressure in the outlet line 6 is monitored by a first pressure switch 18, which controls the solenoid valve 5 and is set to close the solenoid valve 5 at a pressure of 137 kPa, that is half the matched pressures of the nitrogen and carbon dioxide upstream of the orifices 14 and 4, and to open the valve 5 when the pressure in the outlet line 6 is below 137 kPa. The pressure drop below the predetermined pressure of 137 kPa at which the valve 5 is opened, can be adjusted by adjusting the pressure switch 18.

The outlet line 6 is connected to provide a top pressure to stout in a keg and when the top pressure in the keg has fallen below the pressure at which the pressure switch 18 operates to open the valve 5, there is an immediate and substantial flow through the orifices 4 and 14 brought about by the pressure drop of about 137 kPa across them and then as soon as the required outlet pressure of 137 kPa in the outlet line 6 and hence in the keg has been reached, the valve 5 is closed again.

A second pressure switch 19 is connected to the line 13 upstream of the orifice 14. If the supply pressure of the nitrogen to the orifice 14 drops below the required value, for example if the nitrogen cylinder is exhausted, and this pressure cannot incidentally be raised by a back-flow of carbon dioxide because of the non-return valve 15, the pressure switch 19 closes the valve 5 and shuts down the supply of mixed gases.

If the supply pressure of the carbon dioxide falls below the required value, the diaphragm 16 of the pressure regulator 9 will move downwards to close the seating 11 and shut off the supply of nitrogen. Again therefore the pressure switch 19 will close the valve 5.

The pressure switch 19 thus provides protection against the failure of the supply of either gas.

Although orifices are referred to throughout this specification, and this is the usual term for describing gas metering openings, the orifices may be substituted by jets or other metering openings and the term "orifices' is intended to include all such devices.

Claims

1. A gas mixing apparatus for providing a mixture of at least two gases in predetermined proportions at a first predetermined pressure, the apparatus comprising a flow controlling orifice for each gas, means for supplying the gases to the orifices at equal second predetermined pressures, which are higher than the first predetermined pressure, an electrically operated shutroff valve in a line for the supply of the mixed gases downstream of the orifices and a pressure switch, which is sensitive to the mixed gas pressure downstream of the valve and operates to open the valve when the pressure which it senses is below the first predetermined pressure and to close the valve when the pressure rises to the first predetermined pressure.

2. Apparatus according to claim 1, for supplying a mixture of only two gases, in which the means for supplying the gases to the orifices at equal second predetermined pressures comprises a balanced seat regulator for equalizing the pressures of two gases supplied to it, and means for supplying the two gases to the balanced seat regulator with one gas at a higher pressure than the other.

3. Apparatus according to claim 2, in which the balanced seat regulator comprises a valve having a seating and a closure member, which is opened and closed by a diaphragm, an inlet for the supply of the one gas at a higher pressure to the valve seating, means for applying the pressure of the one gas on the outlet side of the seating to one side of the diaphragm, a supply line for the supply of the other gas at a lower pressure and a tap from the supply line for applying the pressure of the other gas to the other side of the diaphragm.

4. Apparatus according to claim 2 or claim 3, in which a second pressure switch, which also controls the electrically operated valve, is provided in a supply line of one of the two gases upstream of its orifice, the second pressure switch being arranged to close the electrically operated valve regardless of the pressure sensed by the first pressure switch if the supply of the one of the two gases fails.

5. A gas mixing apparatus for providing a mixture of two gases in predetermined proportions at a predetermined pressure substantially as described with reference to the accompanying drawing.