Fluid Mixing

Abstract

An apparatus for mixing two or more fluids including a series of passages into each of which each fluid to be mixed can be passed at a chosen rate so that each passage can supply a chosen mixture, and valve means operable to select which of the passages is used to supply the mixture.

Description

The present invention relates to fluid mixing, and particularly to apparatus for mixing gases for medical purposes.

In order to provide a comprehensive gas supply service for respiratory purposes it is necessary to be able to provide a mixture of two different gases in which the constituent gases may be present in any one of several different ratios. It has been customary to provide such a mixture by using a gas mixing apparatus which can provide continuous variation in the composition ratio of the mixture over a considerable range. This apparatus is relatively complex, and hence, expensive.

It is an aim of the invention to provide a fluid mixing apparatus which is relatively simple in construction. Accordingly the present invention provides an apparatus for mixing two or more different fluids which is as claimed in the appended claims.

The present invention will now be described by way of example with reference to the accompanying drawing which is a schematic flow diagram of apparatus for producing an air-oxygen mixture for a lung ventilator.

Referring to the drawing, oxygen and air are passed along their respective inlet lines 1 and 3 to regulators 2 and 4 respectively at a pressure of 0.4N/mm.sup.2. These regulators are designed and fluid loaded to ensure that the oxygen and air leave their respective regulators at a constant pressure of 0.28N/mm.sup.2.

The oxygen passes from regulator 2 along the inlet line and is directed into four separate flow lines, 6, 8, 10 and 12. The air leaves the regulator 4 and is directed along the inlet line 3 into four flow lines 14, 16, 18 and 20. All the flow lines are connected to an outlet line 21 at a common outlet point 22.

Before reaching the outlet point 22, the oxygen lines 6, 8, and 10 are joined to the air lines 16, 18 and 20 respectively. Flow impedances in the form of calibrated orifices 26 are located in the flow lines 6, 8, 10, 16, 18 and 20. These orifices (or throttles) are dimensioned so that their flow impedances have such relative magnitudes as to be able to give from the pairs of flow lines 6 and 16, 8 and 18 and 10 and 20, mixtures containing 25 percent, 35 percent and 60 percent by volume of oxygen, respectively. It will be appreciated that there will be 100 percent and approximately 20 percent of oxygen in the flow lines 12 and 14 respectively because the line 12 is an oxygen line and the line 14 is an air line.

Push button on/off switches 28, 30, 32, 34 and 36 are located in the flow lines as shown in the drawing. The switches 30, 32 and 34 control the mixed pairs of flow lines 6 and 16, 8 and 18, and 10 and 20 respectively.

Non-return valves 38 are located in all the flow lines downstream of the on/off switches to prevent reversed gas flow.

The outlet line 21 leads from the outlet point 22 to the lung ventilator (not shown). An outlet regulator 40 is located in the outlet line 21. An off/on switch 42 and a calibrated orifice 44 are located in the outlet line 21 downstream of the outlet regulator 40. The bore of the orifice 44 defines the gas flow rate to the ventilator.

The operation of the apparatus is as follows:

The oxygen and air supplies are turned on, and the switch 42 is switched off. The appropriate one of the on/off switches 28 to 36 is pressed to select a gas of the required composition.

At the start of each inspiratory phase of the ventilator, the switch 42 is switched on by the flow mechanism of the ventilator. This allows the selected gas to pass through the orifice 44 to the ventilator.

At the end of each inspiratory phase, the switch 42 is switched off by the ventilator flow mechanism thereby shutting off the inspiratory gas supply to the ventilator until the start of the next inspiratory phase.

The composition of the gas being fed to the ventilator can be changed simply by pressing the appropriate one of the switches 28 to 36 so as to open the required flow line or pair of flow lines. The action of pressing one of these on/off switches automatically releases a previously pressed switch so as to close the previously opened flow line or pair of flow lines. This prevents two flow lines or pairs of flow lines from being open at the same time so as to pass a gas of incorrect composition.

In this particular apparatus, the gas is fed from the outlet regulator 40 at a pressure of 0.2N/mm.sup.2. Although non-return valves 38 are included in this described apparatus, it is to be understood that apparatus according to the invention may operate efficiently without non-return valves.

The orifices 26 and 44 may be replaced by orifices of adjustable cross-sectional area. The calibrated orifice 44 may be replaced by either a demand valve, or a fine adjustment valve which allows a preset adjustable gas flow. The fine adjustment valve may be used either with or without a flowmeter.

In a modified apparatus provision may be made for two or more of the on/off switches to remain on at the same time. This increases the number of gas composition ratios which can be selected by an operator.

Claims

I claim:

1. A gas mixing apparatus including:

a. at least two gas inlet passages for the gases to be mixed;

b. a gas pressure regulator in each inlet passage;

c. a plurality of gas mixture distribution passages;

d. a plurality of flow rate control passages, each flow rate control passage being connected between an inlet passage and a gas mixture distribution passage, and each gas mixture distribution passage being connected by flow rate control passages to both of said at least two gas inlet passages;

e. a calibrated flow impedance in each flow rate control passage, for passing gas at a chosen flow rate to the gas mixture distribution passage downstream thereof, whereby gas mixtures of different chosen compositions are able to be formed in the gas mixture distribution passages;

f. a common outlet to which all the gas mixture distribution passages are connected, and from which a gas mixture can be supplied; and

g. valve means operable to close selected gas mixture distribution passages, whereby the composition of the gas mixture supplied from the common outlet depends on which of the gas distribution passages is left open to the passage of gas therethrough.

2. Apparatus as claimed in claim 1, in which each flow impedance is in the form of an orifice.

3. Apparatus as claimed in claim 1, in which each flow impedance has associated with it a non-return valve for each of the fluids passed to it.

4. Apparatus as claimed in claim 1, in which the cross-sectional area of at least one of the orifices is adjustable.

5. Apparatus as claimed in claim 1 including a pressure regulator located in the outlet line.

6. Apparatus as claimed in claim 5, including an outlet switch in the outlet line downstream of the pressure regulator.

7. Apparatus as claimed in claim 5, including an orifice of reduced cross-sectional area downstream of the pressure regulator in the outlet line.

8. Apparatus as claimed in claim 5, including a demand valve downstream of the pressure regulator in the outlet line.